Publications

evidence for a regulatory link of nitrogen fixation and photosynthesis in rhodobacter capsulatus via hvra.	a rhodobacter capsulatus reporter strain, carrying a constitutively expressed nifa gene and a nifh-lacz gene fusion, was used for random transposon tn5 mutagenesis to search for genes required for the ntrc-independent ammonium repression of nifa activity. a mutation in hvra, which is known to be involved in low-light activation of the photosynthetic apparatus, released both ammonium and oxygen control of nifh expression in this reporter strain, demonstrating a regulatory link of nitrogen fixatio ...	1998	9537402
self-transmissible mercury resistance plasmids with gene-mobilizing capacity in soil bacterial populations: influence of wheat roots and mercury addition.	a set of mercury resistance plasmids was obtained from wheat rhizosphere soil amended or not amended with mercuric chloride via exogenous plasmid isolation by using pseudomonas fluorescens r2f, pseudomonas putida uwc1, and enterobacter cloacae be1 as recipient strains. the isolation frequencies were highest from soil amended with high levels of mercury, and the isolation frequencies from unamended soil were low. with p. putida uwc1 as the recipient, the isolation frequency was significantly enha ...	1998	9546155
targeted mutants of cochliobolus carbonum lacking the two major extracellular polygalacturonases.	the filamentous fungus cochliobolus carbonum produces endo-alpha 1,4-polygalacturonase (endopg), exo-alpha 1,4-polygalacturonase (exopg), and pectin methylesterase when grown in culture on pectin. residual activity in a pgn1 mutant (lacking endopg) was due to exopg activity, and the responsible protein has now been purified. after chemical deglycosylation, the molecular mass of the purified protein decreased from greater than 60 to 45 kda. the gene that encodes exopg, pgx1, was isolated with pcr ...	1998	9546185
the rhizobium etli fixl protein differs in structure from other known fixl proteins.	the central heme-binding domain in the fixl proteins of sinorhizobium meliloti, bradyrhizobium japonicum, rhizobium leguminosarum biovar viciae and azorhizobium caulinodans, is highly conserved. the similarity with the corresponding domain in the rhizobium etli fixl protein is considerably less. this observation prompted us to analyze the heme-binding capacities of the r. etli fixl protein. the r. etli fixl gene was overexpressed in escherichia coli. in the presence of s. meliloti fixj, the over ...	1998	9563844
decreased symbiotic effectiveness of rhizobium leguminosarum strains carrying plasmid rp4.	the presence of derivatives of the broad host range plasmid rp4 in strains of rhizobium leguminosarum biovar viciae severely inhibited nitrogen fixation by these strains in nodules on cultivars of pea (pisum sativum). the strains formed small white nodules. yield and total nitrogen values were comparable with those obtained for plants inoculated with a non-nodulating mutant. strains carrying the same derivatives gave rise to nitrogen fixing nodules when inoculated on cultivars of lentils (lens c ...	1998	9570119
a transposable partitioning locus used to stabilize plasmid-borne hydrogen oxidation and trifolitoxin production genes in a sinorhizobium strain.	improved nitrogen-fixing inoculum strains for leguminous crops must be able to effectively compete with indigenous strains for nodulation, enhance legume productivity compared to the productivity obtained with indigenous strains, and maintain stable expression of any added genes in the absence of selection pressure. we constructed a transposable element containing the tfx region for expression of increased nodulation competitiveness and the par locus for plasmid stability. the transposon was ins ...	1998	9572932
regulation of lipid synthesis in bradyrhizobium japonicum: low oxygen concentrations trigger phosphatidylinositol biosynthesis.	lowering oxygen tension in free-living bradyrhizobium japonicum resulted in a dramatic switch of membrane chemistry in which phosphatidylcholine, the predominant lipid in aerated cultures, was no longer synthesized and phosphatidylethanolamine became the major lipid. besides this change, phosphatidylinositol, a typical plant lipid rarely found in bacteria, was also synthesized.	1998	9572982
(methyl)ammonium transport in the nitrogen-fixing bacterium azospirillum brasilense.	an ammonium transporter of azospirillum brasilense was characterized. in contrast to most previously reported putative prokaryotic nh4+ transporter genes, a. brasilense amtb is not part of an operon with glnb or glnz which, in a. brasilense, encode nitrogen regulatory proteins pii and pz, respectively. sequence analysis predicts the presence of 12 transmembrane domains in the deduced amtb protein and classifies amtb as an integral membrane protein. nitrogen regulates the transcription of the amt ...	1998	9573149
roles of dcta and dctb in signal detection by the dicarboxylic acid transport system of rhizobium leguminosarum.	the dcta gene, coding for the dicarboxylate transport protein, has an inducible promoter dependent on activation by the two-component sensor-regulator pair dctb and dctd. lacz fusion analysis indicates that there is a single promoter for dctb and dctd. the dcta promoter is also induced by nitrogen limitation, an effect that requires dctb-dctd and ntrc. dctb alone is able to detect dicarboxylates in the absence of dcta and initiate transcription via dctd. however, dcta modifies signal detection b ...	1998	9573150
unconventional genomic organization in the alpha subgroup of the proteobacteria.	pulsed-field gel electrophoresis was used to analyze the genomic organization of 16 bacteria belonging or related to the family rhizobiaceae of the alpha subgroup of the class proteobacteria. the number and sizes of replicons were determined by separating nondigested dna. hybridization of an rrn gene probe was used to distinguish between chromosomes and plasmids. members of the genus agrobacterium all possess two chromosomes, and each biovar has a specific genome size. as previously demonstrated ...	1998	9573163
mutational analysis of the phosphate-binding loop of rhizobium meliloti dctd, a sigma54-dependent activator.	the phosphate-binding loop of sigma54-dependent activators is thought to participate in atp binding and/or hydrolysis. alanine substitutions at positions 3, 4, 6, 7, and 8 of this motif in rhizobium meliloti dctd disrupted transcriptional activation and atp hydrolysis. interestingly, substitution of alanine at position 7 also affected dna binding.	1998	9573172
identification, cloning and initial characterisation of feupq in brucella suis: a new sub-family of two-component regulatory systems.	to cause disease, brucella species have to adapt to a range of different environments. environmental sensing and adaptive responses in bacteria often involve the concerted action of a two-component regulatory system, consisting of sensor and response regulator components. amplification and sequence analysis of response regulators from brucella species identified a response regulator sequence with 96% similarity to rhizobium leguminosarum feup. in r. leguminosarum, the feupq two-component system ...	1998	9595675
pseudomonas aeruginosa lasr transcription correlates with the transcription of lasa, lasb, and toxa in chronic lung infections associated with cystic fibrosis.	the role of pseudomonas aeruginosa quorum-sensing systems in the lung infections associated with cystic fibrosis (cf) has not been examined. the purpose of this study was to determine if genes regulated by the lasr-lasi quorum-sensing system were coordinately regulated by the p. aeruginosa populations during the lung infections associated with cf. we also wanted to ascertain if there was a relationship between the expression of lasr, a transcriptional regulator, and some p. aeruginosa virulence ...	1998	9596711
genotypic characterization of bradyrhizobium strains nodulating endemic woody legumes of the canary islands by pcr-restriction fragment length polymorphism analysis of genes encoding 16s rrna (16s rdna) and 16s-23s rdna intergenic spacers, repetitive extragenic palindromic pcr genomic fingerprinting, and partial 16s rdna sequencing.	we present a phylogenetic analysis of nine strains of symbiotic nitrogen-fixing bacteria isolated from nodules of tagasaste (chamaecytisus proliferus) and other endemic woody legumes of the canary islands, spain. these and several reference strains were characterized genotypically at different levels of taxonomic resolution by computer-assisted analysis of 16s ribosomal dna (rdna) pcr-restriction fragment length polymorphisms (pcr-rflps), 16s-23s rdna intergenic spacer (igs) rflps, and repetitiv ...	1998	9603820
genes essential for nod factor production and nodulation are located on a symbiotic amplicon (amprtrcfn299pc60) in rhizobium tropici.	amplifiable dna regions (amplicons) have been identified in the genome of rhizobium etli. here we report the isolation and molecular characterization of a symbiotic amplicon of rhizobium tropici. to search for symbiotic amplicons, a cartridge containing a kanamycin resistance marker that responds to gene dosage and conditional origins of replication and transfer was inserted in the nodulation region of the symbiotic plasmid (psym) of r. tropici cfn299. derivatives harboring amplifications were s ...	1998	9603874
nonnative proteins induce expression of the bacillus subtilis circe regulon.	the chaperone-encoding groesl and dnak operons constitute the circe regulon of bacillus subtilis. both operons are under negative control of the repressor protein hrca, which interacts with the circe operator and whose activity is modulated by the groesl chaperone machine. in this report, we demonstrate that induction of the circe regulon can also be accomplished by ethanol stress and puromycin. introduction of the hrca gene and a transcriptional fusion under the control of the circe operator in ...	1998	9603878
a tn7-like transposon is present in the glmus region of the obligately chemoautolithotrophic bacterium thiobacillus ferrooxidans.	the region downstream of the thiobacillus ferrooxidans atcc 33020 atp operon was examined, and the genes encoding n-acetylglucosamine-1-uridyltransferase (glmu) and glucosamine synthetase (glms) were found. this atpefhagdc-glmus gene order is identical to that of escherichia coli. the t. ferrooxidans glms gene was shown to complement e. coli glms mutants for growth on minimal medium lacking glucosamine. a tn7-like transposon, tn5468, was found inserted into the region immediately downstream of t ...	1998	9603897
the bradyrhizobium japonicum noed gene: a negatively acting, genotype-specific nodulation gene for soybean.	bradyrhizobium japonicum strain usda 110 is restricted for nodulation by soybean genotype pi 417566. we previously reported the identification of a usda 110 tn5 mutant, strain d4.2-5, that had the ability to overcome nodulation restriction conditioned by pi 417566 (s. m. lohrke, j. h. orf, e. martínez-romero, and m. j. sadowsky, appl. environ. microbiol. 61:2378-2383, 1995). in this study, we report the cloning and characterization of the negatively acting dna region mutated in strain d4.2-5 tha ...	1998	9612946
acylation of escherichia coli hemolysin: a unique protein lipidation mechanism underlying toxin function.	the pore-forming hemolysin (hlya) of escherichia coli represents a unique class of bacterial toxins that require a posttranslational modification for activity. the inactive protoxin pro-hlya is activated intracellularly by amide linkage of fatty acids to two internal lysine residues 126 amino acids apart, directed by the cosynthesized hlyc protein with acyl carrier protein as the fatty acid donor. this action distinguishes hlyc from all bacterial acyltransferases such as the lipid a, lux-specifi ...	1998	9618444
the caulobacter crescentus paracrystalline s-layer protein is secreted by an abc transporter (type i) secretion apparatus.	caulobacter crescentus is a gram-negative bacterium that produces a two-dimensional crystalline array on its surface composed of a single 98-kda protein, rsaa. secretion of rsaa to the cell surface relies on an uncleaved c-terminal secretion signal. in this report, we identify two genes encoding components of the rsaa secretion apparatus. these components are part of a type i secretion system involving an abc transporter protein. these genes, lying immediately 3' of rsaa, were found by screening ...	1998	9620954
transcriptional regulation of alcaligenes eutrophus hydrogenase genes.	alcaligenes eutrophus h16 produces a soluble hydrogenase (sh) and a membrane-bound hydrogenase (mbh) which catalyze the oxidation of h2, supplying the organism with energy for autotrophic growth. the promoters of the structural genes for the sh and the mbh, psh and pmbh, respectively, were identified by means of the primer extension technique. both promoters were active in vivo under hydrogenase-derepressing conditions but directed only low levels of transcription under condition which repressed ...	1998	9620971
cloning, sequencing, and characterization of the reca gene from rhodopseudomonas viridis and construction of a reca strain.	a recombination-deficient strain of the phototrophic bacterium rhodopseudomonas viridis was constructed for the homologous expression of modified photosynthetic reaction center genes. the r. viridis reca gene was cloned and subsequently deleted from the r. viridis genome. the cloned r. viridis reca gene shows high identity to known reca genes and was able to complement the rec- phenotype of a rhizobium meliloti reca strain. the constructed r. viridis reca strain showed the general rec- phenotype ...	1998	9620976
the fixk2 protein is involved in regulation of symbiotic hydrogenase expression in bradyrhizobium japonicum.	the roles of the nitrogen fixation regulatory proteins nifa, fixk1, and fixk2 in the symbiotic regulation of hydrogenase structural gene expression in bradyrhizobium japonicum have been investigated. bacteroids from fixj and fixk2 mutants have little or no hydrogenase activity, and extracts from these mutant bacteroids contain no hydrogenase protein. bacteroids from a fixk1 mutant exhibit wild-type levels of hydrogenase activity. in beta-galactosidase transcriptional assays with nifa and fixk2 e ...	1998	9620982
release of flavonoids by the soybean cultivars mccall and peking and their perception as signals by the nitrogen-fixing symbiont sinorhizobium fredii	sinorhizobium fredii strain usda191 forms n-fixing nodules on the soybean (glycine max l. merr.) cultivars (cvs) mccall and peking, but s. fredii strain usda257 nodulates only cv peking. we wondered whether specificity in this system is conditioned by the release of unique flavonoid signals from one of the cultivars or by differential perception of signals by the strains. we isolated flavonoids and used nodc and nolx, which are nod-box-dependent and -independent nod genes, respectively, to deter ...	1998	9625713
desensitization of the perception system for chitin fragments in tomato cells	suspension-cultured tomato (lycopersicon esculentum) cells react to stimulation by chitin fragments with a rapid, transient alkalinization of the growth medium, but behave refractory to a second treatment with the same stimulus (g. felix, m. regenass, t. boller [1993] plant j 4: 307-316). we analyzed this phenomenon and found that chitin fragments caused desensitization in a time- and concentration-dependent manner. partially desensitized cells exhibited a clear shift toward lower sensitivity of ...	1998	9625717
a negative regulator mediates quorum-sensing control of exopolysaccharide production in pantoea stewartii subsp. stewartii.	classical quorum-sensing (autoinduction) regulation, as exemplified by the lux system of vibrio fischeri, requires n-acyl homoserine lactone (ahl) signals to stimulate cognate transcriptional activators for the cell density-dependent expression of specific target gene systems. for pantoea stewartii subsp. stewartii, a bacterial pathogen of sweet corn and maize, the extracellular polysaccharide (eps) stewartan is a major virulence factor, and its production is controlled by quorum sensing in a po ...	1998	9636211
trifolitoxin production increases nodulation competitiveness of rhizobium etli ce3 under agricultural conditions.	a major barrier to the use of nitrogen-fixing inoculum strains for the enhancement of legume productivity is the inability of commercially available strains to compete with indigenous rhizobia for nodule formation. despite extensive research on nodulation competitiveness, there are no examples of field efficacy studies of strains that have been genetically improved for nodulation competitiveness. we have shown previously that production of the peptide antibiotic trifolitoxin (tfx) by rhizobium e ...	1998	9647840
effect of insertion site and metabolic load on the environmental fitness of a genetically modified pseudomonas fluorescens isolate.	an isolate of pseudomonas fluorescens (sbw25) was modified with different marker genes (laczy, aph-1, and xyle). these marker genes were inserted singly or in combination into two separate (1 mbp apart) and presumably nonessential sites (-6- and ee) on the chromosome of sbw25. this allowed the production of a range of genetically modified sbw25 variants that differed with respect to insertion site of the marker genes and metabolic burden. the environmental fitness of the different sbw25 variants ...	1998	9647841
synthesis of the unique trisaccharide repeating unit, isolated from lipopolysaccharides rhizobium leguminosarum bv. trifolii 24, and its analogue.	the synthesis of trisaccharide: 6-d-alpha-l-talp(1-->2)-alpha-l-rhap(1-->5)-dha, and its analogue: 6-d-alpha-l-talp(1-->2)-beta-l-rhaf(1-->5)dha is described. in the first step a disaccharide, composed of 6-d-l-talp and l-rhap was obtained. this, in turn, was converted to the corresponding 1-trichloroacetimidate and coupled with dha alcohol to afford the required trisaccharide. its analogue was achieved by the conversion of the above disaccharide to the glycosyl bromide, involving the rhamnopyra ...	1998	9648246
activity of the yeast mnn1 alpha-1,3-mannosyltransferase requires a motif conserved in many other families of glycosyltransferases.	a wide diversity of biological molecules are modified by the addition of sugar residues, and a large number of glycosyltransferases have been identified that are responsible for these reactions. despite catalyzing closely related reactions, many of these transferases show little apparent sequence homology. by comparing two apparently unrelated families of yeast golgi mannosyltransferases, a short motif containing two aspartate residues was observed that was conserved in both groups of proteins. ...	1998	9653120
differential regulation of rhizobium etli rpon2 gene expression during symbiosis and free-living growth.	the rhizobium etli rpon1 gene, encoding the alternative sigma factor sigma54 (rpon), was recently characterized and shown to be involved in the assimilation of several nitrogen and carbon sources during free-living aerobic growth (j. michiels, t. van soom, i. d'hooghe, b. dombrecht, t. benhassine, p. de wilde, and j. vanderleyden, j. bacteriol. 180:1729-1740, 1998). we identified a second rpon gene copy in r. etli, rpon2, encoding a 54.0-kda protein which displays 59% amino acid identity with th ...	1998	9658006
rpos (sigma-s) controls expression of rsma, a global regulator of secondary metabolites, harpin, and extracellular proteins in erwinia carotovora.	rpos (sigma-s or sigma-38) controls a large array of genes that are expressed during stationary phase and under various stress conditions in escherichia coli and other bacteria. we document here that plant pathogenic and epiphytic erwinia species, such as e. amylovora; e. carotovora subsp. atroseptica, betavasculorum, and carotovora; e. chrysanthemi; e. herbicola; e. rhapontici; and e. stewartii, possess rpos genes and produce the alternate sigma factor. we show that rpos transcription in e. car ...	1998	9658007
contribution of outer membrane efflux protein oprm to antibiotic resistance in pseudomonas aeruginosa independent of mexab.	a pseudomonas aeruginosa strain carrying an insertion of an omega hg interposon in the mexb gene (mexb::omega hg; strain k879) produced markedly reduced but still detectable levels of oprm, the product of the third gene of the mexab-oprm multidrug efflux operon. by using a lacz transcriptional fusion vector, promoter activity likely responsible for oprm expression in the mexb::omega hg mutant was identified upstream of oprm. introduction of the oprm gene, but not the mexab genes, into a p. aerug ...	1998	9661004
the regulated outer membrane protein omp21 from comamonas acidovorans is identified as a member of a new family of eight-stranded beta-sheet proteins by its sequence and properties.	omp21, a minor outer membrane protein of the soil bacterium comamonas acidovorans, was purified from a spontaneous mutant lacking a surface layer and long-chain lipopolysaccharide. omp21 synthesis is enhanced by oxygen depletion, and the protein has a variable electrophoretic mobility in sodium dodecyl sulfate-polyacrylamide gel electrophoresis due to its heat-modifiable behavior. the structural gene omp21 encodes a precursor of 204 amino acids with a putative signal peptide of 21 amino acids. m ...	1998	9683466
expression of the fixr-nifa operon in bradyrhizobium japonicum depends on a new response regulator, regr.	many nitrogen fixation-associated genes in the soybean symbiont bradyrhizobium japonicum are regulated by the transcriptional activator nifa, whose activity is inhibited by aerobiosis. nifa is encoded in the fixr-nifa operon, which is expressed at a low level under aerobic conditions and induced approximately fivefold under low-oxygen tension. this induction depends on a -24/-12-type promoter (fixrp1) that is recognized by the sigma54 rna polymerase and activated by nifa. low-level aerobic expre ...	1998	9683482
construction and physiological analysis of a xanthomonas mutant to examine the role of the oxyr gene in oxidant-induced protection against peroxide killing.	we constructed and characterized a xanthomonas campestris pv. phaseoli oxyr mutant. the mutant was hypersensitive to h2o2 and menadione killing and had reduced aerobic plating efficiency. the oxidants' induction of the catalase and ahpc genes was also abolished in the mutant. analysis of the adaptive responses showed that hydrogen peroxide-induced protection against hydrogen peroxide was lost, while menadione-induced protection against hydrogen peroxide was retained in the oxyr mutant. these res ...	1998	9683499
a hu-like protein binds to specific sites within nod promoters of rhizobium leguminosarum.	nodulation genes (nod) of rhizobia are essential for establishment of its symbiosis with specific legume hosts and are usually located on the sym(biosis) megaplasmid. in this work we identified a new sym plasmid independent protein in rhizobium leguminosarum, px, by its ability to bind to nod promoters and induce dna bending. depending upon its concentrations relative to dna templates, px could either stimulate or inhibit in vitro transcription of the major regulatory nodulation gene nodd. this ...	1998	9685414
characterization of the mexc-mexd-oprj multidrug efflux system in deltamexa-mexb-oprm mutants of pseudomonas aeruginosa.	expression of the multidrug efflux system mexc-mexd-oprj in nfxb mutants of pseudomonas aeruginosa contributes to resistance to fluoroquinolones and the "fourth-generation" cephems (cefpirome and cefozopran), but not to most beta-lactams, including the ordinary cephems (ceftazidime and cefoperazone). nfxb mutants also express a second multidrug efflux system, mexa-mexb-oprm, due to incomplete transcriptional repression of this operon by the mexr gene product. to characterize the contribution of ...	1998	9687387
gene transfer by transduction in the marine environment.	to determine the potential for bacteriophage-mediated gene transfer in the marine environment, we established transduction systems by using marine phage host isolates. plasmid pqsr50, which contains transposon tn5 and encodes kanamycin and streptomycin resistance, was used in plasmid transduction assays. both marine bacterial isolates and concentrated natural bacterial communities were used as recipients in transduction studies. transductants were detected by a gene probe complementary to the ne ...	1998	9687430
isolation of broad-host-range replicons from marine sediment bacteria.	naturally occurring plasmids isolated from heterotrophic bacterial isolates originating from coastal california marine sediments were characterized by analyzing their incompatibility and replication properties. previously, we reported on the lack of dna homology between plasmids from the culturable bacterial population of marine sediments and the replicon probes specific for a number of well-characterized incompatibility and replication groups (p. a. sobecky, t. j. mincer, m. c. chang, and d. r. ...	1998	9687436
acetoacetyl coenzyme a reductase and polyhydroxybutyrate synthesis in rhizobium (cicer) sp. strain cc 1192	biochemical controls that regulate the biosynthesis of poly-3-hydroxybutyrate (phb) were investigated in rhizobium (cicer) sp. strain cc 1192. this species is of interest for studying phb synthesis because the polymer accumulates to a large extent in free-living cells but not in bacteroids during nitrogen-fixing symbiosis with chickpea (cicer arietinum l.) plants. evidence is presented that indicates that cc 1192 cells retain the enzymic capacity to synthesize phb when they differentiate from th ...	1998	9687441
mspg3, a medicago sativa polygalacturonase gene expressed during the alfalfa-rhizobium meliloti interaction.	polygalacturonase (pg) is one of the most important enzymes associated with plant cell wall degradation. it has been proposed to participate in the early steps of the rhizobium-legume interaction. we have identified two classes of cdna fragments corresponding to two classes of pg genes in the medicago genome. one of this class, represented by e2 in m. truncatula and pl1 in m. sativa, seems to be related to previously characterized plant pg genes expressed in pollen. we have isolated the genomic ...	1998	9689142
rhizobium leguminosarum contains a group of genes that appear to code for methyl-accepting chemotaxis proteins.	methyl-accepting chemotaxis proteins (mcps) play important roles in the chemotactic response of many bacteria. oligonucleotide primers designed to amplify the conserved signalling domain of mcps by pcr were used to identify potential mcp-encoding genes in rhizobium leguminosarum. using a pcr-derived probe created from these primers a genomic library of r. leguminosarum vf39sm was screened; at least five putative mcp-encoding genes (termed mcpb to mcpf) were identified and isolated from the libra ...	1998	9695927
a silent abc transporter isolated from streptomyces rochei f20 induces multidrug resistance.	in the search for heterologous activators for actinorhodin production in streptomyces lividans, 3.4 kb of dna from streptomyces rochei f20 (a streptothricin producer) were characterized. subcloning experiments showed that the minimal dna fragment required for activation was 0.4 kb in size. the activation is mediated by increasing the levels of transcription of the actii-orf4 gene. sequencing of the minimal activating fragment did not reveal any clues about its mechanism; nevertheless, it was sho ...	1998	9696745
the succinyl and acetyl modifications of succinoglycan influence susceptibility of succinoglycan to cleavage by the rhizobium meliloti glycanases exok and exsh.	in rhizobium meliloti (sinorhizobium meliloti) cultures, the endo-1, 3-1,4-beta-glycanases exok and exsh depolymerize nascent high-molecular-weight (hmw) succinoglycan to yield low-molecular-weight (lmw) succinoglycan. we report here that the succinyl and acetyl modifications of succinoglycan influence the susceptibility of succinoglycan to cleavage by these glycanases. it was previously shown that exoh mutants, which are blocked in the succinylation of succinoglycan, exhibit a defect in the pro ...	1998	9696768
phosphate assimilation in rhizobium (sinorhizobium) meliloti: identification of a pit-like gene.	rhizobium meliloti mutants defective in the phocdet-encoded phosphate transport system form root nodules on alfalfa plants that fail to fix nitrogen (fix-). we have previously reported that two classes of second-site mutations can suppress the fix- phenotype of phocdet mutants to fix+. here we show that one of these suppressor loci (sfx1) contains two genes, orfa and pit, which appear to form an operon transcribed in the order orfa-pit. the pit protein is homologous to various phosphate transpor ...	1998	9696772
expressed sequence tags from a root-hair-enriched medicago truncatula cdna library	the root hair is a specialized cell type involved in water and nutrient uptake in plants. in legumes the root hair is also the primary site of recognition and infection by symbiotic nitrogen-fixing rhizobium bacteria. we have studied the root hairs of medicago truncatula, which is emerging as an increasingly important model legume for studies of symbiotic nodulation. however, only 27 genes from m. truncatula were represented in genbank/embl as of october, 1997. we report here the construction of ...	1998	9701588
a cluster of genes involved in polysaccharide biosynthesis from enterococcus faecalis og1rf.	our previous work identified a cosmid clone containing a 43-kb insert from enterococcus faecalis og1rf that produced a nonprotein antigen in escherichia coli. in the present work, we studied this clone in detail. periodate treatment of lysates of the clone confirmed that the antigen was carbohydrate in nature. analysis of dna sequences and transposon insertion mutants suggested that the insert contained a multicistronic gene cluster. database comparison showed that the cluster contained genes si ...	1998	9712783
monitoring genetically modified rhizobia in field soils using the polymerase chain reaction.	monitoring genetically modified (gm) bacterial inoculants after field release using conventional culture methods can be difficult. an alternative is the detection of marker genes in dna extracted directly from soil, using specific oligonucleotide primers with the polymerase chain reaction (pcr). the pcr was used to monitor survival of two gm rhizobium leguminosarum bv. viciae inoculants after release in the field at rothamsted. one strain, rsm2004, is marked by insertion of transposon tn5; the s ...	1998	9717287
molecular cloning and characterization of cgs, the brucella abortus cyclic beta(1-2) glucan synthetase gene: genetic complementation of rhizobium meliloti ndvb and agrobacterium tumefaciens chvb mutants.	the animal pathogen brucella abortus contains a gene, cgs, that complemented a rhizobium meliloti nodule development (ndvb) mutant and an agrobacterium tumefaciens chromosomal virulence (chvb) mutant. the complemented strains recovered the synthesis of cyclic beta(1-2) glucan, motility, virulence in a. tumefaciens, and nitrogen fixation in r. meliloti; all traits were strictly associated with the presence of an active cyclic beta(1-2) glucan synthetase protein in the membranes. nucleotide sequen ...	1998	9721274
three cdg operons control cellular turnover of cyclic di-gmp in acetobacter xylinum: genetic organization and occurrence of conserved domains in isoenzymes.	cyclic di-gmp (c-di-gmp) is the specific nucleotide regulator of beta-1,4-glucan (cellulose) synthase in acetobacter xylinum. the enzymes controlling turnover of c-di-gmp are diguanylate cyclase (dgc), which catalyzes its formation, and phosphodiesterase a (pdea), which catalyzes its degradation. following biochemical purification of dgc and pdea, genes encoding isoforms of these enzymes have been isolated and found to be located on three distinct yet highly homologous operons for cyclic diguany ...	1998	9721278
cloning and identification of conjugative transfer origins in the rhizobium meliloti genome.	a simple approach was used to identify rhizobium meliloti dna regions with the ability to convert a nontransmissible vector into a mobilizable plasmid, i.e., to contain origins of conjugative transfer (orit, mob). reca-defective r. meliloti merodiploid populations, where each individual contained a hybrid cosmid from an r. meliloti gr4 gene library, were used as donors en masse in conjugation with another r. meliloti recipient strain, selecting transconjugants for vector-encoded antibiotic resis ...	1998	9721299
expression of glnb and a glnb-like gene (glnk) in a ribulose bisphosphate carboxylase/oxygenase-deficient mutant of rhodobacter sphaeroides.	in a ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco)-deficient mutant of rhodobacter sphaeroides, strain 16phc, nitrogenase activity was derepressed in the presence of ammonia under photoheterotrophic growth conditions. previous studies also showed that reintroduction of a functional rubisco and calvin-benson-bassham (cbb) pathway suppressed the deregulation of nitrogenase synthesis in this strain. in this study, the derepression of nitrogenase synthesis in the presence of ammonia in s ...	1998	9721307
prevalence of the rhizobium etli-like allele in genes coding for 16s rrna among the indigenous rhizobial populations found associated with wild beans from the southern andes in argentina.	a collection of rhizobial isolates from nodules of wild beans, phaseolus vulgaris var. aborigineus, found growing in virgin lands in 17 geographically separate sites in northwest argentina was characterized on the basis of host range, growth, hybridization to a nifh probe, analysis of genes coding for 16s rrna (16s rdna), dna fingerprinting, and plasmid profiles. nodules in field-collected wild bean plants were largely dominated by rhizobia carrying the 16s rdna allele of rhizobium etli. a simil ...	1998	9726909
bacillus thuringiensis and its pesticidal crystal proteins.	during the past decade the pesticidal bacterium bacillus thuringiensis has been the subject of intensive research. these efforts have yielded considerable data about the complex relationships between the structure, mechanism of action, and genetics of the organism's pesticidal crystal proteins, and a coherent picture of these relationships is beginning to emerge. other studies have focused on the ecological role of the b. thuringiensis crystal proteins, their performance in agricultural and othe ...	1998	9729609
probing the role of cysteine residues in glucosamine-1-phosphate acetyltransferase activity of the bifunctional glmu protein from escherichia coli: site-directed mutagenesis and characterization of the mutant enzymes.	the glucosamine-1-phosphate acetyltransferase activity but not the uridyltransferase activity of the bifunctional glmu enzyme from escherichia coli was lost when glmu was stored in the absence of beta-mercaptoethanol or incubated with thiol-specific reagents. the enzyme was protected from inactivation in the presence of its substrate acetyl coenzyme a (acetyl-coa), suggesting the presence of an essential cysteine residue in or near the active site of the acetyltransferase domain. to ascertain th ...	1998	9733680
characterization of a novel acyl carrier protein, rkpf, encoded by an operon involved in capsular polysaccharide biosynthesis in sinorhizobium meliloti.	rhizobial capsular polysaccharides (rkps) play an important role in the development of a nitrogen-fixing symbiosis with the plant host and in sinorhizobium meliloti ak631 functional rkpabcdef genes are required for the production of rkps. after cloning the rkpf gene, we overexpressed and purified the derived protein product (rkpf) in escherichia coli. like acyl carrier protein (acp), the rkpf protein can be labeled in vivo with radioactive beta-alanine added to the growth medium. if homogeneous ...	1998	9733701
heterologous expression of the desulfovibrio gigas [nife] hydrogenase in desulfovibrio fructosovorans mr400.	the ability of desulfovibrio fructosovorans mr400 deltahynabc to express the heterologous cloned [nife] hydrogenase of desulfovibrio gigas was investigated. the [nife] hydrogenase operon from d. gigas, hynabcd, was cloned, sequenced, and introduced into d. fructosovorans mr400. a portion of the recombinant heterologous [nife] hydrogenase was totally matured, exhibiting catalytic and spectroscopic properties identical to those of the native d. gigas protein. a chimeric operon containing hynab fro ...	1998	9733707
rhizobium huautlense sp. nov., a symbiont of sesbania herbacea that has a close phylogenetic relationship with rhizobium galegae.	the nitrogen-fixing rhizobial symbionts of sesbania herbacea growing in the nature reserve at the sierra de huautla, mexico, were isolated and characterized. all 104 isolates together with the type strain for rhizobium galegae, hambi 540t, had similar 16s rrna genes as revealed by pcr-rflp analysis. similarity in the sequences of the 16s rrna genes placed the isolates on a phylogenetic branch shared with r. galegae. among 66 randomly selected isolates, three closely related electrophoretic alloe ...	1998	9734023
presence of a gene encoding choline sulfatase in sinorhizobium meliloti bet operon: choline-o-sulfate is metabolized into glycine betaine.	glycine betaine is a potent osmoprotectant accumulated by sinorhizobium meliloti to cope with osmotic stress. the biosynthesis of glycine betaine from choline is encoded by an operon of four genes, beticba, as determined by sequence and mutant analysis. the beti and betc genes are separated by an intergenic region containing a 130-bp mosaic element that also is present between the betb and beta genes. in addition to the genes encoding a presumed regulatory protein (beti), the betaine aldehyde de ...	1998	9736747
determination of plasmid-encoded functions in rhizobium leguminosarum biovar trifolii using proteome analysis of plasmid-cured derivatives.	we have used proteome analysis of derivatives of r. leguminosarum biovar trifolii strain anu843, cured of indigenous plasmids by a direct selection system, to investigate plasmid-encoded functions. under the conditions used, the plasmid-encoded gene products contributed to only a small proportion of the 2000 proteins visualised in the two-dimensional (2-d) protein map of strain anu843. the level of synthesis of thirty-nine proteins was affected after curing of either plasmid a, c or e. the diffe ...	1998	9740057
an arginine residue (arg101), which is conserved in many groel homologues, is required for interactions between the two heptameric rings.	homologous recombination was used to construct a series of hybrid chaperonin genes, containing various lengths of escherichia coli groel replaced by the equivalent region from the homologous cpn60-1 gene of rhizobium leguminosarum. analysis of proteins produced by these hybrids showed that many of them formed structures with properties consistent with their being single heptameric rings under some conditions, as opposed to the double ring form in which both the groel and the cpn60-1 proteins are ...	1998	9743627
sucrose is a nonaccumulated osmoprotectant in sinorhizobium meliloti.	intracellular accumulation of sucrose in response to lowered water activity seems to occur only in photosynthetic organisms. here we demonstrate, for the first time, the potent ability of this common sugar, supplied exogenously, to reduce growth inhibition of sinorhizobium meliloti cells in media of inhibitory osmolarity. independently of the nature of the growth substrates and the osmotic agent, sucrose appears particularly efficient in promoting the recovery of cytoplasmic volume after plasmol ...	1998	9748435
poly-beta-hydroxybutyrate turnover in azorhizobium caulinodans is required for growth and affects nifa expression.	azorhizobium caulinodans is able to fix nitrogen in the free-living state and in symbiosis with the tropical legume sesbania rostrata. the bacteria accumulate poly-beta-hydroxybutyrate (phb) under both conditions. the structural gene for phb synthase, phbc, was inactivated by insertion of an interposon. the mutant strains obtained were devoid of phb, impaired in their growth properties, totally devoid of nitrogenase activity ex planta (nif-), and affected in nucleotide pools and induced fix- nod ...	1998	9748438
succinoglycan is required for initiation and elongation of infection threads during nodulation of alfalfa by rhizobium meliloti.	rhizobium meliloti rm1021 must be able to synthesize succinoglycan in order to invade successfully the nodules which it elicits on alfalfa and to establish an effective nitrogen-fixing symbiosis. using r. meliloti cells that express green fluorescent protein (gfp), we have examined the nature of the symbiotic deficiency of exo mutants that are defective or altered in succinoglycan production. our observations indicate that an exoy mutant, which does not produce succinoglycan, is symbiotically de ...	1998	9748453
bradyrhizobium japonicum fixk2, a crucial distributor in the fixlj-dependent regulatory cascade for control of genes inducible by low oxygen levels.	bradyrhizobium japonicum possesses a second fixk-like gene, fixk2, in addition to the previously identified fixk1 gene. the expression of both genes depends in a hierarchical fashion on the low-oxygen-responsive two-component regulatory system fixlj, whereby fixj first activates fixk2, whose product then activates fixk1. while the target genes for control by fixk1 are unknown, there is evidence for activation of the fixnoqp, fixghis, and rpon1 genes and some heme biosynthesis and nitrate respira ...	1998	9748464
identification of multiple sigma54-dependent transcriptional activators in vibrio cholerae.	in the pathogenic bacterium vibrio cholerae, the alternate sigma factor sigma54 is required for expression of multiple sets of genes, including an unidentified gene(s) necessary for enhanced colonization within the host. to identify sigma54-dependent transcriptional activators involved in colonization, pcr was performed with v. cholerae chromosomal dna and degenerate primers, revealing six novel and distinct coding sequences with homology to sigma54-dependent activators. one sequence had high ho ...	1998	9748465
cloning and overexpression of glycosyltransferases that generate the lipopolysaccharide core of rhizobium leguminosarum.	the lipopolysaccharide (lps) core of the gram-negative bacterium rhizobium leguminosarum is more amenable to enzymatic study than that of escherichia coli because much of it is synthesized from readily available sugar nucleotides. the inner portion of the r. leguminosarum core contains mannose, galactose, and three 3-deoxy-d-manno-octulosonate (kdo) residues, arranged in the order: lipid a-(kdo)2-man-gal-kdo-[o antigen]. a mannosyltransferase that uses gdp-mannose and the conserved precursor kdo ...	1998	9756877
the cytochrome c maturation operon is involved in manganese oxidation in pseudomonas putida gb-1.	a pseudomonas putida strain, strain gb-1, oxidizes mn2+ to mn oxide in the early stationary growth phase. it also secretes a siderophore (identified as pyoverdine) when it is subjected to iron limitation. after transposon (tn5) mutagenesis several classes of mutants with differences in mn2+ oxidation and/or secretion of the mn2+-oxidizing activity were identified. preliminary analysis of the tn5 insertion site in one of the nonoxidizing mutants suggested that a multicopper oxidase-related enzyme ...	1998	9758767
colonization of wheat roots by an exopolysaccharide-producing pantoea agglomerans strain and its effect on rhizosphere soil aggregation	the effect of bacterial secretion of an exopolysaccharide (eps) on rhizosphere soil physical properties was investigated by inoculating strain nas206, which was isolated from the rhizosphere of wheat (triticum durum l.) growing in a moroccan vertisol and was identified as pantoea aglomerans. phenotypic identification of this strain with the biotype-100 system was confirmed by amplified ribosomal dna restriction analysis. after inoculation of wheat seedlings with strain nas206, colonization incre ...	1998	9758793
comparison of paenibacillus azotofixans strains isolated from rhizoplane, rhizosphere, and non-root-associated soil from maize planted in two different brazilian soils	paenibacillus azotofixans is a nitrogen-fixing bacterium often found in soil and in the rhizospheres of different grasses. in this study, two brazilian clay soils were planted with cross-hybrid maize (br-201) and four stages of plant growth were analyzed to characterize the p. azotofixans populations present in the rhizoplanes, rhizospheres, and non-root-associated soils (herein called nonrhizospheres). a total of 106 strains were isolated and identified as p. azotofixans with an api 50ch kit, b ...	1998	9758811
a new genetic locus in sinorhizobium meliloti is involved in stachydrine utilization	stachydrine, a betaine released by germinating alfalfa seeds, functions as an inducer of nodulation genes, a catabolite, and an osmoprotectant in sinorhizobium meliloti. two stachydrine-inducible genes were found in s. meliloti 1021 by mutation with a tn5-luxab promoter probe. both mutant strains (s10 and s11) formed effective alfalfa root nodules, but neither grew on stachydrine as the sole carbon and nitrogen source. when grown in the absence or presence of salt stress, s10 and s11 took up [14 ...	1998	9758825
molecular diversity of rhizobia occurring on native shrubby legumes in southeastern australia	the structure of rhizobial communities nodulating native shrubby legumes in open eucalypt forest of southeastern australia was investigated by a molecular approach. twenty-one genomic species were characterized by small-subunit ribosomal dna pcr-restriction fragment length polymorphism and phylogenetic analyses, among 745 rhizobial strains isolated from nodules sampled on 32 different legume host species at 12 sites. among these rhizobial genomic species, 16 belonged to the bradyrhizobium subgro ...	1998	9758831
conserved structural regions involved in the catalytic mechanism of escherichia coli k-12 waao (rfai).	escherichia coli k-12 waao (formerly known as rfai) is a nonprocessive alpha-1,3 glucosyltransferase, involved in the synthesis of the r core of lipopolysaccharide. by comparing the amino acid sequence of waao with those of 11 homologous alpha-glycosyltransferases, four strictly conserved regions, i, ii, iii, and iv, were identified. since functionally related transferases are predicted to have a similar architecture in the catalytic sites, it is assumed that these four regions are directly invo ...	1998	9765561
analogs of the autoinducer 3-oxooctanoyl-homoserine lactone strongly inhibit activity of the trar protein of agrobacterium tumefaciens.	the trar and trai proteins of agrobacterium tumefaciens mediate cell-density-dependent expression of the ti plasmid tra regulon. trai synthesizes the autoinducer pheromone n-(3-oxooctanoyl)-l-homoserine lactone (3-oxo-c8-hsl), while trar is an 3-oxo-c8-hsl-responsive transcriptional activator. we have compared the abilities of 3-oxo-c8-hsl and 32 related compounds to activate expression of a trar-regulated promoter. in a strain that expresses wild-type levels of trar, only 3-oxo-c8-hsl was stron ...	1998	9765571
fumarate regulation of gene expression in escherichia coli by the dcusr (dcusr genes) two-component regulatory system.	in escherichia coli the genes encoding the anaerobic fumarate respiratory system are transcriptionally regulated by c4-dicarboxylates. the regulation is effected by a two-component regulatory system, dcusr, consisting of a sensory histidine kinase (dcus) and a response regulator (dcur). dcus and dcur are encoded by the dcusr genes (previously yjdhg) at 93.7 min on the calculated e. coli map. inactivation of the dcur and dcus genes caused the loss of c4-dicarboxylate-stimulated synthesis of fumar ...	1998	9765574
novel rkp gene clusters of sinorhizobium meliloti involved in capsular polysaccharide production and invasion of the symbiotic nodule: the rkpk gene encodes a udp-glucose dehydrogenase.	the production of exopolysaccharide (eps) was shown to be required for the infection process by rhizobia that induce the formation of indeterminate nodules on the roots of leguminous host plants. in sinorhizobium meliloti (also known as rhizobium meliloti) rm41, a capsular polysaccharide (kps) analogous to the group ii k antigens of escherichia coli can replace eps during symbiotic nodule development and serve as an attachment site for the strain-specific bacteriophage phi16-3. the rkpa to -j ge ...	1998	9765575
different phenotypic classes of sinorhizobium meliloti mutants defective in synthesis of k antigen.	for sinorhizobium meliloti (also known as rhizobium meliloti) ak631 to establish effective symbiosis with alfalfa, it must be able to synthesize a symbiotically active form of its k antigen, a capsular polysaccharide containing a kdo (3-deoxy-d-manno-octulosonic acid) derivative. previously isolated mutants defective in the synthesis of k antigen are resistant to bacteriophage phi16-3. by screening ca. 100,000 tn5-mutagenized r. meliloti bacteria for resistance to bacteriophage phi16-3, we isola ...	1998	9765576
a stomatin-like protein encoded by the slp gene of rhizobium etli is required for nodulation competitiveness on the common bean.	rhizobium etli strain tal182 is a competitive strain for effective nodulation of beans. from this strain, a novel gene was isolated, slp, which is 669 bp in size and required for nodulation competition on the common bean. the slp knockout mutant of tal182 is defective in nodulation competition, shows reduced growth in the presence of 200 mm nacl, kcl or licl and is complemented by the cloned slp gene. the deduced amino acid sequence of slp shows 66-72% similarity to stomatin proteins of homo sap ...	1998	9782511
a cytochrome cbb3 (cytochrome c) terminal oxidase in azospirillum brasilense sp7 supports microaerobic growth.	spectral analysis indicated the presence of a cytochrome cbb3 oxidase under microaerobic conditions in azospirillum brasilense sp7 cells. the corresponding genes (cytnoqp) were isolated by using pcr. these genes are organized in an operon, preceded by a putative anaerobox. the phenotype of an a. brasilense cytn mutant was analyzed. under aerobic conditions, the specific growth rate during exponential phase (mu(e)) of the a. brasilense cytn mutant was comparable to the wild-type specific growth r ...	1998	9791120
alpha-galactoside uptake in rhizobium meliloti: isolation and characterization of agpa, a gene encoding a periplasmic binding protein required for melibiose and raffinose utilization.	rhizobium meliloti can occupy at least two distinct ecological niches; it is found in the soil as a free-living saprophyte, and it also lives as a nitrogen-fixing intracellular symbiont in root nodules of alfalfa and related legumes. one approach to understanding how r. meliloti alters its physiology in order to become an integral part of a developing nodule is to identify and characterize genes that are differentially expressed by bacteria living inside nodules. we used a screen to identify gen ...	1998	9791127
physiological diversity of the rhizosphere diazotroph assemblages of selected salt marsh grasses.	rhizosphere diazotroph assemblages of salt marsh grasses are thought to be influenced by host plant species and by a number of porewater geochemical parameters. several geochemical variables can adversely affect plant productivity and spatial distributions, resulting in strong zonation of plant species and growth forms. this geochemically induced stress may also influence the species compositions and distributions of rhizosphere diazotroph assemblages, but little is currently known about these o ...	1998	9797277
a model for the catabolism of rhizopine in rhizobium leguminosarum involves a ferredoxin oxygenase complex and the inositol degradative pathway.	rhizopines are nodule-specific compounds that confer an intraspecies competitive nodulation advantage to strains that can catabolize them. the rhizopine (3-o-methyl-scyllo-inosamine, 3-o-msi) catabolic moc gene cluster moccabrde(f) in rhizobium leguminosarum bv. viciae strain 1a is located on the sym plasmid. moccabr are homologous to the moccabr gene products from sinorhizobium meliloti. mocd and moce contain motifs corresponding to a tol-like oxygenase and a [2fe-2s] rieske-like ferredoxin, re ...	1998	9805393
molecular characterization of psscde genes of rhizobium leguminosarum bv. trifolii strain ta1: pssd mutant is affected in exopolysaccharide synthesis and endocytosis of bacteria.	we have identified the three genes psscde in rhizobium leguminosarum bv. trifolii ta1. even though they were almost identical to earlier identified psscde genes of r. leguminosarum, they differed in gene lengths and gene overlaps. the predicted gene products of psscde genes shared significant homology to prokaryotic glycosyl transferases involved in exopolysaccharide synthesis. the tn5 insertion in pssd created the nonmucoid mutant that induced non-nitrogen-fixing nodules. the microscopic analys ...	1998	9805402
identification and characterization of the fis operon in enteric bacteria.	the small dna binding protein fis is involved in several different biological processes in escherichia coli. it has been shown to stimulate dna inversion reactions mediated by the hin family of recombinases, stimulate integration and excision of phage lambda genome, regulate the transcription of several different genes including those of stable rna operons, and regulate the initiation of dna replication at oric. fis has also been isolated from salmonella typhimurium, and the genomic sequence of ...	1998	9811652
three replicons of rhizobium sp. strain ngr234 harbor symbiotic gene sequences.	rhizobium sp. strain ngr234 contains three replicons: the symbiotic plasmid or pngr234a, a megaplasmid (pngr234b), and the chromosome. symbiotic gene sequences not present in pngr234a were analyzed by hybridization. dna sequences homologous to the genes fixljknopqghis were found on the chromosome, while sequences homologous to nodpq and exobdflk were found on pngr234b.	1998	9811668
a pii-like protein in arabidopsis: putative role in nitrogen sensing.	pii is a protein allosteric effector in escherichia coli and other bacteria that indirectly regulates glutamine synthetase at the transcriptional and post-translational levels in response to nitrogen availability. data supporting the notion that plants have a nitrogen regulatory system(s) includes previous studies showing that the levels of mrna for plant nitrogen assimilatory genes such as glutamine synthetase (gln) and asparagine synthetase (asn) are modulated by carbon and organic nitrogen me ...	1998	9811909
genetic complementation of rhizobial nod mutants with frankia dna: artifact or reality?	two divergent reports have been published on the genetic complementation of rhizobial nod mutants using frankia dna. in 1991 putative frankia cosmid library clones were reported to restore normal nodulation properties to rhizobium leguminosarum biovar viciae nodd::tn5, but no supporting sequence data were published. in 1992 a second group reported a failure to find any evidence of functional complementation of various rhizobial nod mutants by frankia dna (noda, nodb and nodc). complementation te ...	1998	9829835
mutational analysis of the rhizobium etli reca operator.	based upon our earlier studies (a. tapias, a. r. fernández de henestrosa, and j. barbé, j. bacteriol. 179:1573-1579, 1997) we hypothesized that the regulatory sequence of the rhizobium etli reca gene was ttgn11caa. however, further detailed analysis of the r. etli reca operator described in the present work suggests that it may in fact be gaacn7gtac. this new conclusion is based upon pcr mutagenesis analysis carried out in the r. etli reca operator, which indicates that the gaac and gtac submoti ...	1998	9829943
detecting linkage disequilibrium in bacterial populations.	the distribution of the number of pairwise differences calculated from comparisons between n haploid genomes has frequently been used as a starting point for testing the hypothesis of linkage equilibrium. for this purpose the variance of the pairwise differences, vd, is used as a test statistic to evaluate the null hypothesis that all loci are in linkage equilibrium. the problem is to determine the critical value of the distribution of vd. this critical value can be estimated either by monte car ...	1998	9832514
is the fur gene of rhizobium leguminosarum essential?	using primers corresponding to conserved regions of the bacterial regulatory gene fur, a homologue of this gene from the genome of rhizobium leguminosarum biovar viciae, the nitrogen-fixing symbiont of peas, was isolated and sequenced. the fur gene is normally expressed constitutively, independent of the presence of fe in the medium, but in one rhizobium strain it was transcribed at a low level. attempts to isolate a fur knockout mutant failed, suggesting that the gene is essential for free-livi ...	1998	9835040
effect of canavanine from alfalfa seeds on the population biology of bacillus cereus	bacillus cereus uw85 suppresses diseases of alfalfa seedlings, although alfalfa seed exudate inhibits the growth of uw85 in culture (j. l. milner, s. j. raffel, b. j. lethbridge, and j. handelsman, appl. microbiol. biotechnol. 43:685-691, 1995). in this study, we determined the chemical basis for and biological role of the inhibitory activity. all of the alfalfa germ plasm tested included seeds that released inhibitory material. we purified the inhibitory material from one alfalfa cultivar and i ...	1998	9835549
a new approach to utilize pcr-single-strand-conformation polymorphism for 16s rrna gene-based microbial community analysis.	single-strand-conformation polymorphism (sscp) of dna, a method widely used in mutation analysis, was adapted to the analysis and differentiation of cultivated pure-culture soil microorganisms and noncultivated rhizosphere microbial communities. a fragment (approximately 400 bp) of the bacterial 16s rrna gene (v-4 and v-5 regions) was amplified by pcr with universal primers, with one primer phosphorylated at the 5' end. the phosphorylated strands of the pcr products were selectively digested wit ...	1998	9835576
genetic diversity and phylogeny of rhizobia that nodulate acacia spp. in morocco assessed by analysis of rrna genes	forty rhizobia nodulating four acacia species (a. gummifera, a. raddiana, a. cyanophylla, and a. horrida) were isolated from different sites in morocco. these rhizobia were compared by analyzing both the 16s rrna gene (rdna) and the 16s-23s rrna spacer by pcr with restriction fragment length polymorphism (rflp) analysis. analysis of the length of 16s-23s spacer showed a considerable diversity within these microsymbionts, but rflp analysis of the amplified spacer revealed no additional heterogene ...	1998	9835582
sinorhizobium fredii and sinorhizobium meliloti produce structurally conserved lipopolysaccharides and strain-specific k antigens.	lipopolysaccharides (lps) and capsular polysaccharides (k antigens) may influence the interaction of rhizobia with their specific hosts; therefore, we conducted a comparative analysis of sinorhizobium fredii and sinorhizobium meliloti, which are genetically related, yet symbiotically distinct, nitrogen-fixing microsymbionts of legumes. we found that both species typically produce strain-specific k antigens that consist of 3-deoxy-d-manno-2-octulosonic acid (kdo), or other 1-carboxy-2-keto-3-deox ...	1998	9835585
effects of bacterial antibiotic production on rhizosphere microbial communities from a culture-independent perspective	the effects of antibiotic production on rhizosphere microbial communities of field-grown phaseolus vulgaris were assessed by using ribosomal intergenic spacer analysis. inoculum strains of rhizobium etli ce3 differing only in trifolitoxin production were used. trifolitoxin production dramatically reduced the diversity of trifolitoxin-sensitive members of the alpha subdivision of the class proteobacteria with little apparent effect on most microbes.	1998	9835600
stability of the agrobacterium tumefaciens virb10 protein is modulated by growth temperature and periplasmic osmoadaption.	export of oncogenic t-dna from the phytopathogen agrobacterium tumefaciens is mediated by the products of the virb operon. it has recently been reported (k. j. fullner and e. w. nester, j. bacteriol. 178:1498-1504, 1996) that dna transfer does not occur at elevated temperatures; these observations correlate well with much earlier studies on the temperature sensitivity of crown gall tumor development on plants. in testing the hypothesis that this loss of dna movement reflects a defect in assembly ...	1998	9852004
feasibility of using prokaryote biosensors to assess acute toxicity of polycyclic aromatic hydrocarbons.	the aim of this study was to assess the acute toxicity of polycyclic aromatic hydrocarbons using lux-marked bacterial biosensors. standard solutions of phenanthrene, pyrene and benzo[a]pyrene were produced using 50 mm hydroxpropyl-beta-cyclodextrin solution which contained each respective polycyclic aromatic hydrocarbon at 6.25 times the aqueous solubility limit of the compound. the polycyclic aromatic hydrocarbon solutions were incubated with each of the biosensors for 280 min and the biolumine ...	1998	9868766
rhizobium leguminosarum bv. viciae hypa gene is specifically expressed in pea (pisum sativum) bacteroids and required for hydrogenase activity and processing.	rhizobium leguminosarum bv. viciae strain upm791 induces in symbiosis with peas the synthesis of a nickel-containing hydrogenase which recycles the hydrogen evolved by nitrogenase. the genes required for synthesis of this hydrogenase, hupslcdefghijkhypabfcdex, are clustered in the symbiotic plasmid. analysis of a hypa-deficient mutant showed that hypa is essential for symbiotic hydrogenase activity and required for correct processing of the hydrogenase large subunit. unlike other microoxically i ...	1998	9868773
jasmonic acid stimulates the expression of nod genes in rhizobium.	jasmonates and salicylic acid are considered to be signal molecules that induce a variety of plant genes involved in wound or defence response, as well as affecting nos promoter activity. in this paper we examined whether these chemicals could also affect nod genes from isogenic rhizobia strains. isogenic strains contain the rhizobium leguminosarum noda promoter fused to the lacz gene of escherichia coli and differ only in the source of the regulatory nodd gene. naringenin, jasmonic acid and met ...	1998	9869421