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leukotriene b4 omega-oxidation by human polymorphonuclear leukocytes is inhibited by pyocyanin, a phenazine derivative produced by pseudomonas aeruginosa.human polymorphonuclear leukocytes (pmnl) metabolize the potent chemotaxin leukotriene b4 (ltb4) by omega-oxidation to 20-hydroxyl-ltb4 and 20-carboxy-ltb4. the ability of unstimulated human pmnl to metabolize exogenous ltb4 was found to be inhibited by pyocyanin, a phenazine derivative produced by pseudomonas aeruginosa, in a dose-dependent manner. 1-hydroxyphenazine (1-ohp), a metabolite of pyocyanin, was not inhibitory under identical conditions. the initial enzymic step in the conversion of ...19921316878
hyperreiterated dna regions are conserved among bradyrhizobium japonicum serocluster 123 strains.we have identified and cloned two dna regions which are highly reiterated in bradyrhizobium japonicum serocluster 123 strains. while one of the reiterated dna regions, pfr2503, is closely linked to the b. japonicum common and genotype-specific nodulation genes in strain usda 424, the other, pmap9, is located next to a tn5 insertion site in a host-range extension mutant of b. japonicum usda 438. the dna cloned in pfr2503 and pmap9 are reiterated 18 to 21 times, respectively, in the genomes of b. ...19921622264
cloning and characterization of a rhizobium meliloti homolog of the escherichia coli cell division gene ftsz.the ftsz gene is essential for initiation of cell division in escherichia coli and bacillus subtilis. to begin our studies of division arrest during differentiation of rhizobium meliloti bacteroids, we isolated a r. meliloti ftsz homolog, ftszrm. degenerate primers directed towards a conserved region of ftsz were used to amplify a segment of r. meliloti dna by polymerase chain reaction, and the product of this reaction was then used to isolate positive clones from a bacteriophage library. the dn ...19911653222
specific oligosaccharide form of the rhizobium meliloti exopolysaccharide promotes nodule invasion in alfalfa.rhizobium meliloti strain su47 produces both high molecular weight (hmw) and low molecular weight (lmw) forms of an acidic exopolysaccharide, succinoglycan. genetic studies have shown that succinoglycan is required for alfalfa root nodule invasion. we found that lmw succinoglycan, when applied exogenously to alfalfa roots, restored nodule invasion to exoa, exob, exof, and exoh mutants. nodule initiation signals were not involved, since lmw succinoglycan from r. meliloti nodd1d2d3 and noda mutant ...19921608972
the ntra gene of agrobacterium tumefaciens: identification, cloning, and phenotype of a site-directed mutant.a 3.6-kb ecori fragment containing the ntra gene of agrobacterium tumefaciens was cloned by using the homologous ntra gene of rhizobium meliloti as a probe. construction of an ntra mutant of a. tumefaciens by site-directed insertional mutagenesis demonstrated the requirement of the ntra gene for nitrate utilization and c4-dicarboxylate transport but not for vir gene expression or tumorigenesis.19921556090
ndvf, a novel locus located on megaplasmid prmesu47b (pexo) of rhizobium meliloti, is required for normal nodule development.rhizobium meliloti strains carrying either of two overlapping deletions (delta 5408 and delta f114) of the megaplasmid prmesu47b form nodules on alfalfa which fail to fix n2 (fix-). strains carrying these deletions also fail to fluoresce on media containing calcofluor, indicating a defect in synthesis of the acidic exopolysaccharide (exo-) of r. meliloti. we have isolated cosmid clones (pth21 and pth22) which complement the fix- but not the exo- phenotype of the strains carrying the delta 5408 a ...19911648074
role of divalent cations in the subunit associations of complex flagella from rhizobium meliloti.rhizobium meliloti, a symbiotic, nitrogen-fixing soil bacterium with complex flagella, as well as other members of the family rhizobiaceae, rapidly lost motility when suspended in buffers lacking divalent cations but retained good motility in buffers containing calcium, magnesium, barium, or strontium. loss of motility was associated with loss of flagella from the cells. analysis of flagella by sedimentation, gel electrophoresis, and electron microscopy revealed that removal of divalent cations ...19921597412
use of repetitive (repetitive extragenic palindromic and enterobacterial repetitive intergeneric consensus) sequences and the polymerase chain reaction to fingerprint the genomes of rhizobium meliloti isolates and other soil bacteria.the distribution of dispersed repetitive dna (repetitive extragenic palindromic [rep] and enterobacterial repetitive intergenic consensus [eric]) sequences in the genomes of a number of gram-negative soil bacteria was examined by using conserved primers corresponding to rep and eric sequences and the polymerase chain reaction (pcr). the patterns of the resulting pcr products were analyzed on agarose gels and found to be highly specific for each strain. the rep and eric pcr patterns of a series o ...19921637156
the fixl protein of rhizobium meliloti can be separated into a heme-binding oxygen-sensing domain and a functional c-terminal kinase domain.transcription of nitrogen fixation (nif and fix) genes in rhizobium meliloti is induced by a decrease in oxygen concentration. the products of two genes, fixl and fixj, are responsible for sensing and transmitting the low-oxygen signal. the proteins encoded by fixl and fixj (fixl and fixj, respectively) are homologous to a family of bacterial proteins that transduce environmental signals through a common phosphotransfer mechanism [david, m., daveran, m., batut, j., dedieu, a., domergue, o., ghai ...19921584762
mutational analysis of the rhizobium meliloti nifa promoter.the nifa gene of rhizobium meliloti, the bacterial endosymbiont of alfalfa, is a regulatory nitrogen fixation gene required for the induction of several key nif and fix genes. transcription of nifa is strongly induced in planta and under microaerobic conditions ex planta. induction of nifa, in turn, is positively controlled by the fixl and fixj genes of r. meliloti, the sensor and regulator, respectively, of a two-component system responsible for oxygen sensing by this bacterium. this system is ...19921597427
exogenous suppression of the symbiotic deficiencies of rhizobium meliloti exo mutants.the acidic exopolysaccharide (eps i) produced by rhizobium meliloti during symbiosis with medicago sativa has been shown to be required for the proper development of nitrogen-fixing nodules. cloned dna from the exo region of r. meliloti is shown to stimulate production of the low-molecular-weight form of this exopolysaccharide, and in this report we show that the symbiotic deficiencies of two exo mutants of r. meliloti, the exoa and exoh mutants, can be rescued by the addition of this low-molecu ...19921577707
genetic structure of natural populations of the nitrogen-fixing bacterium rhizobium meliloti.the genetic structure of populations of the symbiotic nitrogen-fixing soil bacterium rhizobium meliloti was examined by analysis of electrophoretically demonstrable allelic variation in 14 metabolic, presumably chromosomal, enzyme genes. a total of 232 strains were examined, most of which were isolated from southwest asia, where there is an unsurpassed number of indigenous host species for r. meliloti. the collection consisted of 115 isolates recovered from annual species of medicago in syria, t ...19901689982
characterization of a fixlj-regulated bradyrhizobium japonicum gene sharing similarity with the escherichia coli fnr and rhizobium meliloti fixk genes.we describe the cloning, sequencing, regulation, and mutational analysis of a bradyrhizobium japonicum fixk-like gene whose product belongs to the family of fnr-crp-related regulatory proteins. the predicted 237-amino-acid fixk protein was found to share between 28 and 38% sequence identity with the escherichia coli fnr protein, other bacterial fnr-like proteins (fnrn, anr, and hlyx), and two rhizobial fixk proteins. the b. japonicum fixk-like gene, when expressed from a lac promoter, could func ...19921551834
yeast flavohemoglobin is an ancient protein related to globins and a reductase family.the hemoglobin of yeast is a two-domain protein with both heme and flavin prosthetic groups. the nucleotide sequences of the cdna and genomic dna encoding the protein from saccharomyces cerevisiae show that introns are absent and that both domains are homologous with a flavoheme protein from escherichia coli. the heme domains are also homologous with those of o2-binding heme proteins from several other distantly related bacteria, plants, and animals; all appear to be members of the same globin s ...19921594608
rhizobium meliloti genes involved in sulfate activation: the two copies of nodpq and a new locus, saa.the nitrogen-fixing symbiont rhizobium meliloti establishes nodules on leguminous host plants. nodulation (nod) genes used for this process are located in a cluster on the psym-a megaplasmid of r. meliloti. these genes include nodp and nodq (here termed nodpq), which encode atp sulfurylase and aps kinase, enzymes that catalyze the conversion of atp and so(4)2- into the activated sulfate form 3'-phosphoadenosine 5'-phosphosulfate (paps), an intermediate in cysteine synthesis. in rhizobium, paps i ...19921459442
molecular cloning of higher-plant 3-oxoacyl-(acyl carrier protein) reductase. sequence identities with the nodg-gene product of the nitrogen-fixing soil bacterium rhizobium meliloti.cdna clones encoding the fatty-acid- biosynthetic enzyme nadph-linked 3-oxoacyl-(acyl carrier protein) (acp) reductase were isolated from a brassica napus (rape) developing seed library and from an arabidopsis thaliana (thale cress) leaf library. the n-terminal end of the coding region shows features typical of a stromal-targeting plastid-transit peptide. the deduced amino acid sequences have 41% and 55% identity respectively with the nodg-gene product of rhizobium meliloti, one of the host-spec ...19921575676
rhizobium meliloti elicits transient expression of the early nodulin gene enod12 in the differentiating root epidermis of transgenic alfalfa.to study the molecular responses of the host legume during early stages of the symbiotic interaction with rhizobium, we have cloned and characterized the infection-related early nodulin gene mtenod12 from medicago truncatula. in situ hybridization experiments have shown that, within the indeterminate medicago nodule, transcription of the mtenod12 gene begins in cell layers of meristematic origin that lie ahead of the infection zone, suggesting that these cells are undergoing preparation for bact ...19921446169
a region of the broad-host-range plasmid rk2 causes stable in planta inheritance of plasmids in rhizobium meliloti cells isolated from alfalfa root nodules.we demonstrate for the first time that the broad-host-range stabilization loci from plasmid rk2 cause total retention of plasmids in cells of rhizobium meliloti during symbiosis with alfalfa. two derivatives of plasmid rk2, prk290 and a 7.3-kb mini-rk2 plasmid, were stabilized in r. meliloti cells isolated from root nodules by the insertion of a 3.2-kb dna fragment or a smaller 0.8-kb dna fragment derived from the rk2 stabilization region.19921429472
rhizobium nodm and nodn genes are common nod genes: nodm encodes functions for efficiency of nod signal production and bacteroid maturation.earlier, we showed that rhizobium meliloti nodm codes for glucosamine synthase and that nodm and nodn mutants produce strongly reduced root hair deformation activity and display delayed nodulation of medicago sativa (baev et al., mol. gen. genet. 228:113-124, 1991). here, we demonstrate that nodm and nodn genes from rhizobium leguminosarum biovar viciae restore the root hair deformation activity of exudates of the corresponding r. meliloti mutant strains. partial restoration of the nodulation ph ...19921447128
regulation of rhizobium meliloti exo genes in free-living cells and in planta examined by using tnphoa fusions.the exo loci of rhizobium meliloti are necessary for the production of an acidic exopolysaccharide, eps i, that is needed for alfalfa nodule invasion by strain rm1021. we have isolated and characterized alkaline phosphatase fusions made with tnphoa in several exo loci of r. meliloti and used these fusions to examine the subcellular localization of exo gene products and the regulation of exo genes in free-living cells and in planta. in the course of this work, we isolated a new exo locus, exot. w ...19911846141
structure and expression of a cyanobacterial ilvc gene encoding acetohydroxyacid isomeroreductase.acetohydroxyacid isomeroreductase (ahair) is the shared second enzyme in the biosynthetic pathways leading to isoleucine and valine. ahair is encoded by the ilvc gene in bacteria. a 1,544-bp fragment of genomic dna containing the ilvc gene was cloned from the cyanobacterium synechocystis sp. strain pcc 6803, and the complete nucleotide sequence was determined. the identity of the gene was established by comparison of the nucleotide and derived peptide sequences with those of other ilvc genes. th ...19921459938
a rhizobium meliloti lipopolysaccharide mutant altered in competitiveness for nodulation of alfalfa.a transposon tn5-induced mutant of rhizobium meliloti rm2011, designated rm6963, showed a rough colony morphology on rich and minimal media and an altered lipopolysaccharide (lps). major differences from the wild-type lps were observed in (i) hexose and 2-keto-3-deoxyoctonate elution profiles of crude phenol extracts chromatographed in sepharose cl-4b, (ii) silver-stained sodium dodecyl sulfate (sds)-polyacrylamide gel electrophoresis patterns of crude and purified lps fractions, and (iii) immun ...19921325969
cloning and mutagenesis of the rhizobium meliloti isocitrate dehydrogenase gene.the gene encoding rhizobium meliloti isocitrate dehydrogenase (icd) was cloned by complementation of an escherichia coli icd mutant with an r. meliloti genomic library constructed in puc18. the complementing dna was located on a 4.4-kb bamhi fragment. it encoded an icd that had the same mobility as r. meliloti icd in nondenaturing polyacrylamide gels. in western immunoblot analysis, antibodies raised against this protein reacted with r. meliloti icd but not with e. coli icd. the complementing dn ...19921320616
rhizobium meliloti mutants unable to synthesize anthranilate display a novel symbiotic phenotype.analyses of rhizobium meliloti trp auxotrophs suggest that anthranilate biosynthesis by the r. meliloti trpe(g) gene product is necessary during nodule development for establishment of an effective symbiosis. trpe(g) mutants, as well as mutants blocked earlier along this pathway in aromatic amino acid biosynthesis, form nodules on alfalfa that have novel defects. in contrast, r. meliloti trp mutants blocked later in the tryptophan-biosynthetic pathway form normal, pink, nitrogen-fixing nodules. ...19921320610
isolation and characterization of rhizobitoxine mutants of bradyrhizobium japonicum.to explore the role of rhizobitoxine in bradyrhizobium-legume symbiosis, 11 rhizobitoxine mutants of b. japonicum usda61 were isolated on the basis of their inability to synthesize the toxin in culture. each mutant is prototrophic and symbiotically effective on soybean, cowpea, siratro, and glycine soja. the rhizobitoxine mutants differ in their chlorosis phenotypes and rhizobitoxine production in planta. as expected, one group of mutant fail to make toxin in planta, resulting in the absence of ...19921317377
a directional, high-frequency chromosomal mobilization system for genetic mapping of rhizobium meliloti.a system for mapping of the rhizobium meliloti chromosome that utilizes transposon tn5-mob, which carries the mobilization site of incp plasmid rp4 (r. simon, mol. gen. genet. 196:413-420, 1984), was developed. insertions of tn5-mob that were located at particular sites on the r. meliloti chromosome were isolated and served as origins of high-frequency chromosomal transfer when incp tra functions were provided in trans. this approach is, in principle, applicable to any gram-negative bacterium in ...19921309521
phylogenetic position of rhizobium sp. strain or 191, a symbiont of both medicago sativa and phaseolus vulgaris, based on partial sequences of the 16s rrna and nifh genes.phenotypic and dna sequence comparisons are presented for eight rhizobium isolates that were cultured from field-grown alfalfa (medicago sativa l.) in oregon. these isolates were previously shown to nodulate both alfalfa and common bean (phaseolus vulgaris (l.) savi.). the objective of the present study was to determine their phylogenetic relationships to the normal symbionts of these plants, rhizobium meliloti and rhizobium leguminosarum biovar phaseoli, respectively. phenotypically, the oregon ...19921377901
discovery of a rhizobial rna that is essential for symbiotic root nodule development.all of the azorhizobium, bradyrhizobium, and rhizobium genes known to be involved in the development of nitrogen-fixing legume root nodules are genes that code for proteins. here we report the first exception to this rule: the sra gene; it was discovered during the genetic analysis of a bradyrhizobium japonicum tn5 mutant (strain 259) which had a severe deficiency in colonizing soybean nodules. a dna region as small as 0.56 kb cloned from the parental wild type restored a wild-type phenotype in ...19911717438
distribution of an l-isoaspartyl protein methyltransferase in eubacteria.a protein carboxyl methyltransferase (ec 2.1.1.77) that recognizes age-damaged proteins for potential repair or degradation reactions has been found in all vertebrate tissues and cells examined to date. this enzyme catalyzes the transfer of methyl groups from s-adenosylmethionine to the carboxyl groups of d-aspartyl or l-isoaspartyl residues that are formed spontaneously from normal l-aspartyl and l-asparaginyl residues. a similar methyltransferase has been found in two bacterial species, escher ...19921729230
the exor gene of rhizobium meliloti affects rna levels of other exo genes but lacks homology to known transcriptional regulators.rhizobium meliloti strains mutant in the exor gene overproduce an exopolysaccharide called succinoglycan or eps i. protein fusions to several different exo genes required for eps i biosynthesis are expressed at a higher level in an exor strain than in a wild-type strain, showing that the overproduction of eps i in exor strains results at least in part from increased gene expression. this regulation is important to nodulation, since exor mutants fail to invade alfalfa nodules unless secondary sup ...19911711027
rhizobium meliloti produces a family of sulfated lipooligosaccharides exhibiting different degrees of plant host specificity.we have shown that a rhizobium meliloti strain overexpressing nodulation genes excreted high amounts of a family of n-acylated and 6-o-sulfated n-acetyl-beta-1,4-d-glucosamine penta-, tetra-, and trisaccharide nod factors. either a c(16:2) or a c(16:3) acyl chain is attached to the nonreducing end subunit, whereas the sulfate group is bound to the reducing glucosamine. one of the tetrasaccharides is identical to the previously described nodrm-1 factor. the two pentasaccharides as well as nodrm-1 ...19921729688
a self-transmissible, narrow-host-range endogenous plasmid of rhodobacter sphaeroides 2.4.1: physical structure, incompatibility determinants, origin of replication, and transfer functions.rhodobacter sphaeroides 2.4.1 naturally harbors five cryptic endogenous plasmids (c. s. fornari, m. watkins, and s. kaplan, plasmid 11:39-47, 1984). the smallest plasmid (prs241e), with a molecular size of 42 kb, was observed to be a self-transmissible plasmid which can transfer only to certain strains of r. sphaeroides. transfer frequencies can be as high as 10(-2) to 10(-3) per donor under optimal mating conditions in liquid media in the absence of oxygen. prs241e, designated the s factor, was ...19921735707
aerobic inactivation of rhizobium meliloti nifa in escherichia coli is mediated by lon and two newly identified genes, snob and snoc.the rhizobium meliloti nifa protein is an oxygen-sensitive transcriptional regulator of nitrogen fixation genes. regulation of nifa activity by oxygen occurs at the transcriptional level through fixlj and at the posttranslational level through the sensitivity of nifa to oxygen. we have previously reported that the nifa protein is sensitive to oxygen in escherichia coli as well as in r. meliloti. to investigate whether the posttranslational regulation of nifa is dependent on host factors conserve ...19911846139
the genomes of the family rhizobiaceae: size, stability, and rarely cutting restriction endonucleases.the lack of high-resolution genetic or physical maps for the family rhizobiaceae limits our understanding of this agronomically important bacterial family. on the basis of statistical analyses of dna sequences of the rhizobiaceae and direct evaluation by pulsed-field agarose gel electrophoresis (pfe), five restriction endonucleases with at-rich target sites were identified as the most rarely cutting: asei (5'-attaat-3'), drai (5'-tttaaa-3'), spei (5'-actagt-3'), sspi (5'-aataat-3'), and xbai (5' ...19911846148
the central domain of rhizobium leguminosarum dctd functions independently to activate transcription.sigma 54-dependent transcriptional activators such as escherichia coli ntrc, rhizobium meliloti nifa, and rhizobium leguminosarum dctd share similar central and carboxy-terminal domains but differ in the structure and function of their amino-terminal domains. we have deleted the amino-terminal and carboxy-terminal domains of r. leguminosarum dctd and have demonstrated that the central domain of dctd, like that of nifa, is transcriptionally competent.19921735730
the product of the rhizobium meliloti ilvc gene is required for isoleucine and valine synthesis and nodulation of alfalfa.tn5-induced mutants of rhizobium meliloti that require the amino acids isoleucine and valine for growth on minimal medium were studied. in one mutant, 1028, the defect is associated with an inability to induce nodules on alfalfa. the tn5 mutation in 1028 is located in a chromosomal 5.5-kb ecori fragment. complementation analysis with cloned dna indicated that 2.0 kb of dna from the 5.5-kb ecori fragment restored the wild-type phenotype in the ilv- nod- mutant. this region was further characteriz ...19911744032
aerobic growth and respiration of a delta-aminolevulinic acid synthase (hema) mutant of bradyrhizobium japonicum.oxygen-dependent growth of the bradyrhizobium japonicum hema mutant mlg1 (m.l. guerinot and b.k. chelm, proc. natl. acad. sci. usa 83:1837-1841, 1986) was demonstrated in cultured cells in the absence of exogenous delta-aminolevulinic acid (ala), but growth of analogous mutants of rhizobium meliloti or of escherichia coli was not observed unless ala was added to the yeast extract-containing media. no heme could be detected in extracts of strain mlg1 cells as measured by the absorption or by the ...19911846857
isolation and characterization of insertion sequence elements from gram-negative bacteria by using new broad-host-range, positive selection vectors.on the basis of an rsf1010-derived broad-host-range vector, three different systems which enable positive detection and isolation of insertion sequence (is) elements from gram-negative bacteria were constructed. vectors psup104-phes, psup104-rpsl, and psup104-sac were used successfully in a number of rhizobium strains and in xanthomonas campestris. more than 20 different is elements were isolated and characterized. the 16 is elements from rhizobium meliloti were further used to characterize vari ...19911847366
identification and nucleotide sequence of rhizobium meliloti insertion sequence isrm3: similarity between the putative transposase encoded by isrm3 and those encoded by staphylococcus aureus is256 and thiobacillus ferrooxidans ist2.the insertion sequence isrm3 was discovered simultaneously in different rhizobium meliloti strains by probing southern blots of total cellular dna with 32p-labeled pta2. this plasmid is indigenous to strain iz450 and fortuitously contained four copies of isrm3. by using an internal ecori fragment as a specific probe (prwrm31), homology to isrm3 was subsequently detected in over 90% of r. meliloti strains tested from different geographical locations around the world. the frequency of stable nonle ...19911849509
hypoosmotic adaptation in rhizobium meliloti requires beta-(1----2)-glucan.beta-(1----2)-glucan, an unusual cyclic oligosaccharide, can be isolated from the periplasm of bacteria belonging to the family rhizobiaceae. data presented here suggest that the periplasmic beta-(1----2)-glucan of rhizobium meliloti plays a major role in osmotic adaptation. first, growth of r. meliloti in a low-osmolarity medium causes a large accumulation of periplasmic beta-(1----2)-glucan. second, mutations in the ndv genes, which prevent this accumulation of beta-(1----2)-glucan, reduce cel ...19901689716
in vitro activity of the nitrogen fixation regulatory protein fixj from rhizobium meliloti.cell extracts of an escherichia coli strain that overproduces the regulatory protein fixj from rhizobium meliloti promoted transcription of fixk, a known fixj-dependent gene, in a coupled transcription-translation assay. activation by fixj was dependent on the sigma 70 holoenzyme form of rna polymerase.19911885556
analysis of a 1600-kilobase rhizobium meliloti megaplasmid using defined deletions generated in vivo.a series of 120-600 kilobase deletions with defined endpoints were made in the 1600-kilobase rhizobium meliloti megaplasmid prmesu47b, by homologous recombination between the is50 elements of transposon insertions. utilizing is 50-mediated homologous recombination we also made defined reductions in deletion size and combined adjacent deletions. deletion structure was confirmed by phage transduction and southern hybridization analysis. collectively these deletions span 1400 kilobases of prmesu47b ...19911849856
mutations that affect activity of the rhizobium meliloti trpe(g) promoter in rhizobium meliloti and escherichia coli.the cloned rhizobium meliloti trpe(g) gene is not expressed in escherichia coli. oligonucleotide-directed mutagenesis was used to introduce base substitution mutations in the promoter region of this gene. three separate mutations that increased homology of the putative -10 region of this promoter with the e. coli -10 promoter consensus sequence by 1 bp converted this promoter to an active promoter in e. coli. a deletion extending to position -43 from the 5' side had a minor effect on transcripti ...19911885552
rhodobacter sphaeroides rdxa, a homolog of rhizobium meliloti fixg, encodes a membrane protein which may bind cytoplasmic [4fe-4s] clusters.in the photosynthetic bacterium rhodobacter sphaeroides, a chromosomal gene, rdxa, which encodes a 52-kda protein, was found to be homologous to fixg, the first gene of a rhizobium meliloti nitrogen fixation operon on the psym plasmid (d. kahn, m. david, o. domergue, m.-l. daveran, j. ghai, p. r. hirsch, and j. batut, j. bacteriol. 171:929-939, 1989). the deduced amino acid sequences of rdxa and fixg are 53% identical and 73% similar; sequence analyses suggested that each has five transmembrane ...19921400197
the exod gene of rhizobium meliloti encodes a novel function needed for alfalfa nodule invasion.during the symbiotic interaction between alfalfa and the nitrogen-fixing bacterium rhizobium meliloti, the bacterium induces the formation of nodules on the plant roots and then invades these nodules. among the bacterial genes required for nodule invasion are the exo genes, involved in production of an extracellular polysaccharide, and the ndv genes, needed for production of a periplasmic cyclic glucan. mutations in the exod gene result in altered exopolysaccharide production and in a nodule inv ...19911987158
visualization of bacterial flagella by video-enhanced light microscopy.we have imaged individual flagellar filaments of escherichia coli, a motile streptococcus sp., and rhizobium meliloti by video-enhanced differential interference-contrast microscopy (nomarski dic) and computer-based image processing. this approach has advantages over existing methods in that filaments on living cells can be seen over their entire lengths.19911987174
occurrence of lipid a variants with 27-hydroxyoctacosanoic acid in lipopolysaccharides from members of the family rhizobiaceae.lipopolysaccharides (lpss) isolated from several strains of rhizobium, bradyrhizobium, agrobacterium, and azorhizobium were screened for the presence of 27-hydroxyoctacosanoic acid. the lpss from all strains, with the exception of azorhizobium caulinodans, contained various amounts of this long-chain hydroxy fatty acid in the lipid a fractions. analysis of the lipid a sugars revealed three types of backbones: those containing glucosamine (as found in rhizobium meliloti and rhizobium fredii), tho ...19912007543
the virc and vird operons of the agrobacterium ti plasmid are regulated by the ros chromosomal gene: analysis of the cloned ros gene.the ros chromosomal gene is present in octopine and nopaline strains of agrobacterium tumefaciens as well as in rhizobium meliloti. this gene encodes a 15.5-kda protein that specifically represses the virc and vird operons in the virulence region of the ti plasmid. the ros gene was cloned from a genomic bank by electroporation and complementation in agrobacterium cells. reporter fusion to the ros gene indicates that the level of transcription is controlled in part by autoregulation. a consensus ...19912013576
biosynthesis and excretion of cyclic glucans by rhizobium meliloti 1021.cyclic beta-1,2-glucans produced by agrobacterium and rhizobium species play an important role in the interaction of these bacteria with plant hosts. in this study, we show that (i) the neutral cyclic glucans are the biosynthetic precursors of anionic cyclic glucans; (ii) the conversion of neutral to anionic glucans is much more rapid and more extensive in exponentially growing cultures than in cultures in the stationary phase, although the latter synthesize large amounts of glucan; and (iii) th ...19912019565
bradyrhizobium japonicum has two differentially regulated, functional homologs of the sigma 54 gene (rpon).recognition of -24/-12-type promoters by rna polymerase requires a special sigma factor, sigma 54 (rpon ntra glnf). in the nitrogen-fixing soybean symbiont bradyrhizobium japonicum, two functional, highly conserved rpon genes (rpon1 and rpon2) were identified and sequenced. the two predicted b. japonicum rpon protein sequences were 87% identical, and both showed different levels of homology to the rpon proteins of other bacteria. downstream of rpon2 (but not of rpon1), two additional open readin ...19911991712
aspartate aminotransferase activity is required for aspartate catabolism and symbiotic nitrogen fixation in rhizobium meliloti.a mutant of rhizobium meliloti, 4r3, which is unable to grow on aspartate has been isolated. the defect is specific to aspartate utilization, since 4r3 is not an auxotroph and grows as well as its parent strain on other carbon and nitrogen sources. the defect was correlated with an inability to fix nitrogen within nodules formed on alfalfa. transport of aspartate into the mutant cells was found to be normal. analysis of enzymes involved in aspartate catabolism showed a significantly lower level ...19912019560
genetic and physical analysis of the nodd3 region of rhizobium meliloti.the nodulation (nod) genes of the symbiont rhizobium meliloti are transcriptionally controlled by protein activators in the nodd gene family. while nodd1 and nodd2 act in concert with small molecular weight inducers provided by the host legume plant, nodd3 is an inducer-independent activator of the nod promoters. we determined the sequence of the nodd3 gene, confirmed the expression of a 35 kda protein in vitro, and determined the insertion points of five tn5 insertions in the region of the nodd ...19912017373
genetic analysis of the attenuator of the rhizobium meliloti trpe(g) gene.it was previously reported that transcription of the rhizobium meliloti trpe(g) gene starts at the adenine residue of the aug codon of the leader peptide coding sequence (trpl), suggesting that translation of the trpl sequence starts without the shine-dalgarno sequence. we constructed mutations replacing the aug codon of the trpl sequence with aag or acg. these mutations reduced the expression of a trpl'-'lacz fusion gene to 0.1 and 0.2% of the wild-type level, respectively, indicating that the ...19912045362
early recognition in the rhizobium meliloti-alfalfa symbiosis: root exudate factor stimulates root adsorption of homologous rhizobia.adsorption of rhizobium meliloti to alfalfa roots before their infection and nodule formation shows the specificity of the symbiotic association (g. caetano-anollés and g. favelukes, appl. environ. microbiol. 52:377-382, 1986). the time course of specific adsorption of r. meliloti (10(3) to 10(4) cells per ml) to roots shows an initial lag period of 3 h, suggesting that either or both symbionts must become conditioned for the adsorption process. preincubation of r. meliloti l5-30 for 3 h with di ...19912045369
mutations in the two flagellin genes of rhizobium meliloti.the previously cloned dna fragment which complements the behavioral defects of the che-1 and che-3 mutations of rhizobium meliloti codes for two nearly identical (93%) flagellin genes. a wild-type copy of one of the two genes (flaa) but not the other (flab) can complement the mutations. the behavior and flagellar morphology of newly isolated strains carrying insertion and deletion mutations or various combinations of these mutations demonstrated that either gene product alone can form functional ...19912050631
heterologous exopolysaccharide production in rhizobium sp. strain ngr234 and consequences for nodule development.rhizobium sp. strain ngr234 produces large amounts of acidic exopolysaccharide. mutants that fail to synthesize this exopolysaccharide are also unable to nodulate the host plant leucaena leucocephala. a hybrid strain of rhizobium sp. strain ngr234 containing exo genes from rhizobium meliloti was constructed. the background genetics and nod genes of rhizobium sp. strain ngr234 are retained, but the cluster of genes involved in exopolysaccharide biosynthesis was deleted. these exo genes were repla ...19912022612
analysis of rhizobium meliloti nodulation mutant wl131: novel insertion sequence isrm3 in nodg and altered nodh protein product.nodulation (nod) genes are required for invasion of legumes by rhizobium bacteria. mutant wl131 is a derivative of 102f51 that has a severe nod- phenotype on alfalfa. upon examination of the extended dna region containing host-specific nodulation genes nodfeg and nodh, we found that the nodg gene of wl131 bears a novel insertion sequence, isrm3. complementation studies implied, however, that the phenotype on alfalfa correlated with the nodh locus. we found that nodh in wl131 encodes an altered g ...19911850728
lpsz, a lipopolysaccharide gene involved in symbiosis of rhizobium meliloti.lpsz+ is an allele that allows exo (exopolysaccharide-deficient) mutants of rhizobium meliloti to invade nodules by modifying rhizobial lipopolysaccharide. we have cloned and sequenced the lpsz gene. the predicted lpsz protein has a molecular weight of 48,589 and is probably localized in the cytoplasm. a beta-glucuronidase fusion in the lpsz gene indicates that lpsz is not regulated by oxygen or nitrogen.19912022621
rhizobium meliloti exog and exoj mutations affect the exox-exoy system for modulation of exopolysaccharide production.r. meliloti rm1021 normally produces an acidic calcofluor-binding exopolysaccharide, called succinoglycan or eps i, which is required for successful nodulation of alfalfa by this strain. at least 13 loci affecting production of eps i were previously mapped to a cluster on the second of two symbiotic megaplasmids in rm1021, prmesu47b. a putative regulatory region was originally defined by the exog and exoj mutations. exog and exoj mutants produced less exopolysaccharide than wild-type strains and ...19912050634
genetic analysis of a region of the rhizobium meliloti psym plasmid specifying catabolism of trigonelline, a secondary metabolite present in legumes.genes controlling the catabolism of trigonelline, a secondary metabolite that is often present in legumes, are located on the psym megaplasmid of rhizobium meliloti. to investigate the role of bacterial trigonelline catabolism in the rhizobium-legume symbiosis, we identified and characterized the r. meliloti rcr2011 genetic loci (trc) controlling trigonelline catabolism. tn5-b20 mutagenesis showed that the trc region is a continuous dna segment of 9 kb located 4 kb downstream of the nifab and fd ...19911850402
rhizobium meliloti and rhizobium leguminosarum dctd gene products bind to tandem sites in an activation sequence located upstream of sigma 54-dependent dcta promoters.free-living rhizobia transport external c4-dicarboxylates to use as sole carbon sources, and uptake of these compounds is essential for nitrogen fixation by rhizobial bacteroids. in both rhizobium leguminosarum and rhizobium meliloti, the genes dctb and dctd are believed to form an ntrb/ntrc-like two-component system which regulates the synthesis of a c4-dicarboxylate transport protein encoded by dcta. here we confirm the identity of sigma 54-dependent promoters previously hypothesized for the r ...19902193923
induction of the alka gene of escherichia coli in gram-negative bacteria.a broad-host-range plasmid containing a fusion of the alka and lacz genes of escherichia coli was introduced into various aerobic and facultative gram-negative bacteria--33 species belonging to 19 genera--to study the induction of expression of the alka gene by alkylating agents. the bacteria included species of the families enterobacteriaceae, pseudomonadaceae, rhizobiaceae, vibrionaceae, neisseriaceae, rhodospirillaceae, and azotobacteraceae. results obtained show that all bacteria tested, exc ...19911938974
induction of the second exopolysaccharide (epsb) in rhizobium meliloti su47 by low phosphate concentrations.in previous work, rhizobium meliloti su47 produced its alternative exopolysaccharide (epsb [also called eps ii]) only in strains that were genetically altered to activate epsb synthesis. here we report that epsb synthesis is not entirely cryptic but occurred under conditions of limiting phosphate. this was shown in several different exo mutants that are blocked in the synthesis of the normal exopolysaccharide, succinoglycan. in addition, epsb biosynthetic gene expression was markedly increased b ...19911938929
detection of alternative nitrogenases in aerobic gram-negative nitrogen-fixing bacteria.strains of aerobic, microaerobic, nonsymbiotic, and symbiotic dinitrogen-fixing bacteria were screened for the presence of alternative nitrogenase (n2ase) genes by dna hybridization between genomic dna and dna encoding structural genes for components 1 of three different enzymes. a nifdk gene probe was used as a control to test for the presence of the commonly occurring mo-fe n2ase, a vnfdgk gene probe was used to show the presence of v-fe n2ase, and an anfdgk probe was used to detect fe n2ase. ...19911987127
electrophoretic separation of the three rhizobium meliloti replicons.the megaplasmids and the chromosome from the bacterium rhizobium meliloti 1021 were separated in preparative quantities by using transverse alternating-field gel electrophoresis. the genetic content of each electrophoretically separated band was determined by southern hybridization with replicon-specific probes and by comparison with agrobacterium tumefaciens transconjugants harboring either psym-a or psym-b megaplasmids. pulsed-field gel electrophoresis analyses of paci (5'-ttaattaa-3') and swa ...19911860826
thymidylate synthase gene from lactococcus lactis as a genetic marker: an alternative to antibiotic resistance genes.the potential of the thymidylate synthase thya gene cloned from lactococcus lactis subsp. lactis as a possible alternative selectable marker gene to antibiotic resistance markers has been examined. the thya mutation is a recessive lethal one; thya mutants cannot survive in environments containing low amounts of thymidine or thymine (such as luria-bertani medium) unless complemented by the thya gene. the cloned thya gene was strongly expressed in l. lactis subsp. lactis, escherichia coli, rhizobi ...19902117883
rhizobium meliloti adenylate cyclase is related to eucaryotic adenylate and guanylate cyclases.a gene from rhizobium meliloti coding for an adenylate cyclase was sequenced, and the deduced protein sequence was compared with those of other known adenylate cyclases. no similarity could be detected with the procaryotic counterparts. however, striking similarity was found with the catalytic region of saccharomyces cerevisiae adenylate cyclase, the cytoplasmic domains of bovine adenylate cyclase, and two mammalian guanylate cyclases. the gene was fused to the enteric beta-galactosidase, and th ...19901970565
the bacillus subtilis sigl gene encodes an equivalent of sigma 54 from gram-negative bacteria.the levanase operon in bacillus subtilis is expressed from a -12, -24 promoter and transcription is stimulated by the regulator levr, which contains a domain homologous with the central domain of the nifa and ntrc family of regulators. we isolated mutants defective in the expression of the levanase operon. these strains contain mutations that define a gene, called sigl, located between cysb and sacb on the genetic map. the sigl gene was cloned and sequenced. it encodes a polypeptide containing 4 ...19911924373
expression of two rhizobium meliloti flagellin genes and their contribution to the complex filament structure.the complex flagellar filaments of rhizobium meliloti are composed of two related (87% identical) flagellins that are encoded by closely linked, separately transcribed genes, flaa and flab (e. pleier and r. schmitt, j. bacteriol. 171:1467-1475, 1989). to elucidate the role of the subunits, a and b, in assembling the complex filament, the wild-type alleles were replaced with defective ones containing a 2,249-bp deletion (accompanied by substitution of a kanamycin resistance cartridge), which elim ...19912002009
rhizobium meliloti fix l is an oxygen sensor and regulates r. meliloti nifa and fixk genes differently in escherichia coli.in rhizobium meliloti, nif and fix genes, involved in nitrogen fixation during symbiosis with alfalfa, are under the control of two transcriptional regulators encoded by nifa and fixk. expression of nifa and fixk is under the control of fixl/j, a two-component regulatory system. we showed, using escherichia coli as a heterologous host, that fixl/j controls nifa and fixk expression in response to microaerobiosis. furthermore, expression of the sensor gene fixl and of the activator gene fixj under ...19902115865
the symbiotic defect of rhizobium meliloti exopolysaccharide mutants is suppressed by lpsz+, a gene involved in lipopolysaccharide biosynthesis.exo mutants of rhizobium meliloti su47, which fail to secrete acidic extracellular polysaccharide (eps), induce fix- nodules on alfalfa. however, mutants of r. meliloti rm41 carrying the same exo lesions induce normal fix+ nodules. we show that such induction is due to a gene from strain rm41, which we call lpsz+, that is missing in strain su47. lpsz+ does not restore eps production but instead alters the composition and structure of lipopolysaccharide. in both su47 and rm41, either lpsz+ or exo ...19902158975
sequence of the pseudomonas aeruginosa trpi activator gene and relatedness of trpi to other procaryotic regulatory genes.in pseudomonas aeruginosa, the trpi gene product regulates the expression of the trpba gene pair encoding tryptophan synthase. trpi and trpba are transcribed divergently. the trpi dna sequence and deduced amino acid sequence were determined. the trpi start codon was found to be 103 base pairs from that of trpb. trpi encodes a 293-residue protein and the size of the trpi gene product, measured on sodium dodecyl sulfatepolyacrylamide gels, was close to that calculated from the amino acid sequence. ...19892492495
genetic map of rhizobium meliloti megaplasmid prmesu47b.a circular linkage map of the rhizobium meliloti megaplasmid prmesu47b was constructed. the map consists of transposon insertions carrying alternating antibiotic resistance markers linked by phi m12 transduction. data from conjugation experiments utilizing donor strains carrying tn5-orit insertions in the megaplasmid supported the proposed genetic map. in addition, the positions of previously identified fix, exopolysaccharide synthetic, thiamine synthetic, and c4-dicarboxylate transport loci on ...19902158971
isolation and characterization of the constitutive acyl carrier protein from rhizobium meliloti.rhizobium species produce an inducible acyl carrier protein (acp), encoded by the nodf gene, that somehow functions in an exchange of cell signals between bacteria and specific plant hosts, leading to nodulation of plant roots and symbiotic nitrogen fixation, as well as a constitutive acp needed for the synthesis of essential cell lipids. the periplasmic cyclic glucans of rhizobium spp. are also involved in specific rhizobium-plant interaction. these glucans are strongly similar to the periplasm ...19902144277
rhizobium meliloti lipopolysaccharide and exopolysaccharide can have the same function in the plant-bacterium interaction.a fix region of rhizobium meliloti 41 involved both in symbiotic nodule development and in the adsorption of bacteriophage 16-3 was delimited by directed tn5 mutagenesis. mutations in this dna region were assigned to four complementation units and were mapped close to the pyr-2 and pyr-29 chromosomal markers. phage inactivation studies with bacterial cell envelope preparations and crude lipopolysaccharides (lps) as well as preliminary characterization of lps in the mutants indicated that these g ...19902168384
cloning, characterization, and complementation of lesions causing acid sensitivity in tn5-induced mutants of rhizobium meliloti wsm419.four tn5-induced mutants of rhizobium meliloti wsm419 were unable to grow or maintain intracellular ph at an external ph of 5.6. restriction analysis of dna fragments carrying tn5 and flanking sequences cloned from these mutants indicated that all four cloned mutations are unique and that the two strains (tg1-6 and tg1-11) carry tn5 insertions which are within 4.4 kilobases of each other on a single ecori fragment. southern analysis of total mutant dna indicated a single copy of tn5 in each muta ...19902168374
two genes that regulate exopolysaccharide production in rhizobium meliloti.we describe a new rhizobium meliloti gene, exox, that regulates the synthesis of the exopolysaccharide, succinoglycan, exox resembled the psi gene of r. leguminosarum bv. phaseoli and the exox gene of rhizobium sp. strain ngr234 in its ability to inhibit exopolysaccharide synthesis when present in multiple copies, exox did not appear to regulate the expression of exop. the effect of exox was counterbalanced by another r. meliloti gene, exof. exof is equivalent to rhizobium sp. strain ngr234 exoy ...19902118508
identification of a caulobacter basal body structural gene and a cis-acting site required for activation of transcription.the genes that encode the components and regulatory proteins of the caulobacter crescentus flagellum are transcribed at specific times in the cell cycle. one of these genes, flbn, is required early in the flagellar assembly process. the flbn gene was cloned and sequenced, and the time of transcription activation was determined. the derived amino acid sequence indicates that fibn encodes a 25-kilodalton protein with a cleavable leader peptide. the flbn-encoded protein has 30.8% identity with the ...19902211524
rhizobium meliloti fixghi sequence predicts involvement of a specific cation pump in symbiotic nitrogen fixation.we present genetic and structural analyses of a fix operon conserved among rhizobia, fixghi from rhizobium meliloti. the nucleotide sequence of the operon suggests it may contain a fourth gene, fixs. adjacent open reading frames of this operon showed an overlap between tga stop codons and atg start codons in the form of an atga motif suggestive of translational coupling. all four predicted gene products contained probable transmembrane sequences. fixg contained two cysteine clusters typical of i ...19892536685
functional and evolutionary relatedness of genes for exopolysaccharide synthesis in rhizobium meliloti and rhizobium sp. strain ngr234.rhizobium meliloti su47 and rhizobium sp. strain ngr234 produce distinct exopolysaccharides that have some similarities in structure. r. meliloti has a narrow host range, whereas rhizobium strain ngr234 has a very broad host range. in cross-species complementation and hybridization experiments, we found that several of the genes required for the production of the two polysaccharides were functionally interchangeable and similar in evolutionary origin. ngr234 exoc and exoy corresponded to r. meli ...19902203745
complementation of escherichia coli sigma 54 (ntra)-dependent formate hydrogenlyase activity by a cloned thiobacillus ferrooxidans ntra gene.the ntra gene of thiobacillus ferrooxidans was cloned by complementation of an escherichia coli ntra mutant that was unable to produce gas via the sigma 54 (ntra)-dependent formate hydrogenlyase pathway. analysis of the dna sequence showed that the t. ferrooxidans ntra gene coded for a protein of 475 amino acids (calculated mr, 52,972). the t. ferrooxidans ntra protein had 49, 44, 33, and 18% amino acid similarity with the ntra proteins of klebsiella pneumoniae, azotobacter vinelandii, rhizobium ...19902198257
the rhizobium meliloti trpe(g) gene is regulated by attenuation, and its product, anthranilate synthase, is regulated by feedback inhibition.in rhizobium meliloti, the genes involved in biosynthesis of the amino acid tryptophan are found at three separate chromosomal locations. of the three gene clusters, trpe(g), trpdc, and trpfba, only the trpe(g) gene is regulated by the end product of the pathway, tryptophan. we found that trpe(g) mrna contains a leader transcript that terminates at a stem-loop structure in a putative transcription attenuator. the level of this leader transcript was constant regardless of the amount of tryptophan ...19902111807
cytokine induction by lipopolysaccharide (lps) corresponds to lethal toxicity and is inhibited by nontoxic rhodobacter capsulatus lps.many pathological effects of gram-negative bacteria are produced by their cell wall-derived lipopolysaccharides (lpss). differing pathogenicity of gram-negative lpss, however, may depend on their capacities to induce cytokines. thus, we studied the lethal toxicity of four nonenterobacterial lpss and compared it with their capacity to induce mononuclear cell (mnc)-derived interleukin-1 (il-1), interleukin-6 (il-6), and tumor necrosis factor (tnf). unstimulated mnc did not release these cytokines. ...19902228245
rhizobium meliloti chromosomal loci required for suppression of exopolysaccharide mutations by lipopolysaccharide.mutants of alfalfa symbiont rhizobium meliloti su47 that fail to make extracellular polysaccharide (exo mutants) induce the formation of nodules that are devoid of bacteria and consequently do not fix nitrogen. this fix- phenotype can be suppressed by an r. meliloti rm41 gene that affects lipopolysaccharide structure. here we describe mutations preventing suppression that map at two new chromosomal loci, lpsy and lpsx, present in both strains. two other lps mutations isolated previously from su4 ...19902228976
3-oxoacyl-(acyl-carrier protein) reductase from avocado (persea americana) fruit mesocarp.the nadph-linked 3-oxoacyl-(acyl-carrier protein) (acp) reductase (ec 1.1.1.100), also known as 'beta-ketoacyl-acp reductase', has been purified from the mesocarp of mature avocado pears (persea americana). the enzyme is inactivated by low ionic strength and low temperature. on sds/page under reducing conditions, purified 3-oxoacyl-acp reductase migrated as a single polypeptide giving a molecular mass of 28 kda. gel-filtration chromatography gave an apparent native molecular mass of 130 kda, sug ...19902244875
expression of the agrobacterium tumefaciens chvb virulence region in azospirillum spp.inner membranes of azospirillum brasilense incubated with udp-glucose were unable to synthesize beta-(1-2) glucan and lacked the 235-kilodalton intermediate protein known to be involved in the synthesis of beta-(1-2) glucan in agrobacterium tumefaciens and rhizobium meliloti. inner membranes of a. brasilense strains carrying a cosmid containing the chromosomal virulence genes chva and chvb of agrobacterium tumefaciens formed beta-(1-2) glucan in vitro and synthesized the 235-kilodalton intermedi ...19902332404
correlation between ultrastructural differentiation of bacteroids and nitrogen fixation in alfalfa nodules.bacteroid differentiation was examined in developing and mature alfalfa nodules elicited by wild-type or fix- mutant strains of rhizobium meliloti. ultrastructural studies of wild-type nodules distinguished five steps in bacteroid differentiation (types 1 to 5), each being restricted to a well-defined histological region of the nodule. correlative studies between nodule development, bacteroid differentiation, and acetylene reduction showed that nitrogenase activity was always associated with the ...19902376562
osmotic regulation of beta(1-2) glucan synthesis in members of the family rhizobiaceae.high osmolarity in the culture medium of growing agrobacterium tumefaciens strongly inhibited the accumulation of cellular beta(1-2) glucan. however, the enzymatic system required for the synthesis of this polysaccharide from udp-glucose was not repressed by high osmolarity. mutants of a. tumefaciens and rhizobium meliloti affected in beta(1-2) glucan synthesis were unable to grow normally in low-osmolarity media.19902376569
symbiotic pseudorevertants of rhizobium meliloti ndv mutants.nodule development (ndv) mutants of rhizobium meliloti cannot invade alfalfa to establish a nitrogen-fixing symbiosis and instead induce the formation of small, white, unoccupied nodules on alfalfa roots. such mutants also fail to produce the unusual cyclic oligosaccharide beta-(1----2)-glucan and show defects in several aspects of vegetative growth and function. here we show that ndv mutants are severely reduced, although not totally deficient, in the ability to attach to and initiate infection ...19902307652
the nifa gene of rhizobium meliloti is oxygen regulated.experiments using plasmid-borne gene fusions and direct rna measurements have revealed that expression from the nifa gene is induced in rhizobium meliloti when the external oxygen concentration is reduced to microaerobic levels. induction occurs in the absence of alfalfa and in the presence of fixed nitrogen and does not require ntrc. the production of functional nifa gene product (nifa) can be demonstrated by its ability to activate the nitrogenase promoter p1. aerobic induction of nifa can als ...19872439489
biochemical characterization of avirulent exoc mutants of agrobacterium tumefaciens.the synthesis of periplasmic beta(1-2)glucan is required for crown gall tumor formation by agrobacterium tumefaciens and for effective nodulation of alfalfa by rhizobium meliloti. the exoc (psca) gene is required for this synthesis by both bacteria as well as for the synthesis of capsular polysaccharide and normal lipopolysaccharide. we tested the possibility that the pleiotropic exoc phenotype is due to a defect in the synthesis of an intermediate common to several polysaccharide biosynthetic p ...19902307661
rhizobium meliloti suhr suppresses the phenotype of an escherichia coli rna polymerase sigma 32 mutant.sigma 32, the product of the escherichia coli rpoh locus, is an alternative rna polymerase sigma factor utilized to express heat shock genes upon a sudden rise in temperature. e. coli k165 [rpoh165(am) supc(ts)] is temperature sensitive for growth and does not induce heat shock protein synthesis. we have isolated a locus from rhizobium meliloti called suhr that allows e. coli k165 to grow at high temperature and induce heat shock protein synthesis. r. meliloti suhr mutants were viable and symbio ...19902113906
transcription patterns of rhizobium meliloti symbiotic plasmid psym: identification of nifa-independent fix genes.we performed a systematic survey of transcription of a large region of the rhizobium meliloti symbiotic plasmid psym. this led to the discovery of two new sequences induced during symbiosis. the first sequence was linked to the known nitrogen fixation (nif-fix) gene cluster, and its expression depended on the nifa gene product. the second sequence was a novel fix locus (m.-h. renalier, j. batut, j. ghai, b. terzaghi, m. gherardi, m. david, a.-m. garnerone, j. vasse, g. truchet, t. huguet, and p. ...19872437100
two host-inducible genes of rhizobium fredii and characterization of the inducing compound.random transcription fusions with mu d1(kan lac) generated three mutants in rhizobium fredii (strain usda 201) which showed induction of beta-galactosidase when grown in root exudate of the host plants glycine max, phaseolus vulgaris, and vigna ungliculata. two genes were isolated from a library of total plasmid dna of one of the mutants, 3f1. these genes, present in tandem on a 4.2-kilobase hindiii fragment, appear in one copy each on the symbiotic plasmid and do not hybridize to the rhizobium ...19882447061
two genes that regulate exopolysaccharide production in rhizobium sp. strain ngr234: dna sequences and resultant phenotypes.two closely linked genes involved in the regulation of exopolysaccharide (eps) production in rhizobium sp. strain ngr234, exox and exoy, were sequenced, and their corresponding phenotypes were investigated. inhibition of eps synthesis occurred in wild-type strains when extra copies of exox were introduced, but only when exoy had been deleted or mutated or was present at a lower copy number. normal eps synthesis occurred in rhizobium sp. when both exox and exoy were introduced on the same replico ...19902152899
implication of nifa in regulation of genes located on a rhizobium meliloti cryptic plasmid that affect nodulation efficiency.we examined the contribution of a cryptic plasmid, prmegr4b, to the nodulation of medicago sativa by strain gr4 of rhizobium meliloti. a 905-base-pair psti dna fragment in prmegr4b was found to hybridize dna of the r. meliloti fixa promoter region as a probe. sequence analysis of the psti fragment showed a 206-base-pair region displaying high homology with the dna upstream of the rna start points of the p1 and p2 symbiotic promoters. putative nif promoter consensus sequences were conserved in th ...19892546913
symbiotic properties of rhizobia containing a flavonoid-independent hybrid nodd product.a hybrid nodd gene consisting of 75% of the nodd1 gene of rhizobium meliloti at the 5' end and 27% of the nodd gene of rhizobium trifolii at the 3' end activates the six tested inducible nod promoters of rhizobium leguminosarum, r. trifolii, or r. meliloti to maximal levels, even in the absence of flavonoids. in strains containing such a constitutive activating nodd gene, transcription of nod genes started at the same site as in flavonoid-induced strains containing a wild-type nodd gene. in cont ...19892544568
identification and sequence analysis of the rhizobium meliloti dcta gene encoding the c4-dicarboxylate carrier.transposon tn5-induced c4-dicarboxylate transport mutants of rhizobium meliloti 2011 which could be complemented by cosmid prmsc121 were subdivided into two classes. class i mutants (rms37 and rms938) were defective in symbiotic c4-dicarboxylate transport and in nitrogen fixation. they were mutated in the structural gene dcta, which codes for the c4-dicarboxylate carrier. class ii mutants (rms11, rms16, rms17, rms24, and rms31) expressed reduced activity in symbiotic c4-dicarboxylate transport a ...19892551890
rhizobium meliloti anthranilate synthase gene: cloning, sequence, and expression in escherichia coli.we determined the dna sequence of the rhizobium meliloti gene encoding anthranilate synthase, the first enzyme of the tryptophan pathway. sequences similar to those seen for the two subunits of the enzyme as found in all other procaryotic species studied are present in a single open reading frame of 729 codons. this apparent gene fusion joins the c terminus of the large subunit (trpe) to the n terminus of the small subunit (trpg) through a short connecting segment. we designate the fused gene tr ...19892656657
aromatic aminotransferase activity and indoleacetic acid production in rhizobium meliloti.bacterial indoleacetic acid (iaa) production, which has been proposed to play a role in the rhizobium-legume symbiosis, is a poorly understood process. previous data have suggested that iaa biosynthesis in rhizobium meliloti can occur through an indolepyruvate intermediate derived from tryptophan by an aminotransferase activity. to further examine this biosynthetic pathway, the aromatic aminotransferase (aat) activity of rhizobium meliloti 102f34 (f34) was characterized. at least four proteins w ...19892551887
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