| 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 ... | 1989 | 2544568 |
| 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 ... | 1989 | 2546913 |
| 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 ... | 1989 | 2551890 |
| rhizobium meliloti 1021 has three differentially regulated loci involved in glutamine biosynthesis, none of which is essential for symbiotic nitrogen fixation. | we have cloned and characterized three distinct rhizobium meliloti loci involved in glutamine biosynthesis (glna, glnii, and glnt). the glna locus shares dna homology with the glna gene of klebsiella pneumoniae, encodes a 55,000-dalton monomer subunit of the heat-stable glutamine synthetase (gs) protein (gsi), and complemented an escherichia coli glna mutation. the glnii locus shares dna homology with the glnii gene of bradyrhizobium japonicum and encodes a 36,000-dalton monomer subunit of the h ... | 1989 | 2563998 |
| isolation, characterization, and complementation of rhizobium meliloti 104a14 mutants that lack glutamine synthetase ii activity. | the glutamine synthetase (gs)-glutamate synthase pathway is the primary route used by members of the family rhizobiaceae to assimilate ammonia. two forms of glutamine synthetase, gsi and gsii, are found in rhizobium and bradyrhizobium species. these are encoded by the glna and glnii genes, respectively. starting with a rhizobium meliloti glna mutant as the parent strain, we isolated mutants unable to grow on minimal medium with ammonia as the sole nitrogen source. for two auxotrophs that lacked ... | 1989 | 2570058 |
| regulation of glutamine synthetase ii activity in rhizobium meliloti 104a14. | most rhizobia contain two glutamine synthetase (gs) enzymes: gsi, encoded by glna, and gsii, encoded by glnii. we have found that wsu414, a rhizobium meliloti 104a14 glutamine auxotroph derived from a glna parental strain, is an ntra mutant. the r. meliloti glnii promoter region contains dna sequences similar to those found in front of other genes that require ntra for their transcription. no gsii was found in the glna ntra mutant, and when a translational fusion of glnii to the escherichia coli ... | 1989 | 2570059 |
| rhizobium meliloti regulatory gene fixj activates transcription of r. meliloti nifa and fixk genes in escherichia coli. | when present in escherichia coli on the multicopy expression vector puc19, a rhizobium meliloti regulatory gene, fixj, belonging to a two-component regulatory system, activated the expression of two r. meliloti symbiotic genes, nifa and fixk. primer extension by reverse transcription showed that fixj stimulates nifa expression in e. coli by activating pnifa. | 1989 | 2646295 |
| cloning and sequencing of the gltx gene, encoding the glutamyl-trna synthetase of rhizobium meliloti a2. | the gltx gene, coding for the glutamyl-trna synthetase of rhizobium meliloti a2, was cloned by using as probe a synthetic oligonucleotide corresponding to the amino acid sequence of a segment of the glutamyl-trna synthetase. the codons chosen for this 42-mer were those most frequently used in a set of r. meliloti genes. dna sequence analysis revealed an open reading frame of 484 codons, encoding a polypeptide of mr 54,166 containing the amino acid sequences of an nh2-terminal and various interna ... | 1989 | 2661539 |
| fixk, a gene homologous with fnr and crp from escherichia coli, regulates nitrogen fixation genes both positively and negatively in rhizobium meliloti. | nitrogen fixation genes are shown to undergo a complex positive and negative regulation in rhizobium meliloti. activation of fixn by fixlj is shown to require a third regulatory gene, fixk. as fixk is activated by fixlj, we propose a cascade model for fixn regulation such that fixlj activates fixn via fixk. in addition fixk negatively regulates expression of the nif-specific activator nifa as well as its own expression by autoregulation. thus nifa and fixk are subject to a mixed regulation, posi ... | 1989 | 2663474 |
| gene transfer system for rhodopseudomonas viridis. | a gene transfer system for rhodopseudomonas viridis was established which uses conjugation with escherichia coli s17-i as the donor and mobilizable plasmids as vectors. initially, plasmids of the incompatibility group p1 (prk290 and prk404) were used. the more effective shuttle vectors between e. coli and r. viridis, pkv1 and pkvs1, were derived from plasmid pbr322 and showed the highest conjugation frequency (10(-2] thus far demonstrated in purple bacteria. it was also demonstrated that rhizobi ... | 1989 | 2666398 |
| identification of a gene linked to rhizobium meliloti ntra whose product is homologous to a family to atp-binding proteins. | the ntra gene of rhizobium meliloti has recently been identified and shown to be required for a diverse set of metabolic functions (c. w. ronson, b. t. nixon, l. m. albright, and f. m. ausubel, j. bacteriol. 169:2424-2431, 1987). as a result of sequencing the ntra gene and its flanking regions from r. meliloti, we identified an open reading frame directly upstream of ntra, orf1, whose predicted product is homologous to a superfamily of atp-binding proteins involved in transport, cell division, n ... | 1989 | 2703463 |
| a second exopolysaccharide of rhizobium meliloti strain su47 that can function in root nodule invasion. | rhizobium meliloti strain su47 produces the calcofluor-binding exopolysaccharide, succinoglycan, that is required for alfalfa root nodule invasion. strains derived from r. meliloti su47 secreted an acidic exopolysaccharide, epsb, that replaced succinoglycan in nodule invasion. epsb, which has not formerly been identified among the rhizobiaceae, consisted of the repeating unit 4,6-o-(1-carboxyethylidene)-alpha-d-galp1----3(x-o-ac)-beta-d-g lcp1----3. epsb synthesis occurred either in strains cont ... | 1989 | 2717610 |
| a family of activator genes regulates expression of rhizobium meliloti nodulation genes. | nodulation (nod) gene expression in rhizobium meliloti requires plant inducers and the activating protein product of the nodd gene. we have examined three genes in r. meliloti which have nodd activity and sequence homology. these three nodd genes are designated nodd1, nodd2 and nodd3, and have distinctive properties. the nodd1 gene product activates expression of the nodabc operon, as measured by a nodc-lacz fusion or by transcript analysis, in the presence of crude seed or plant wash or the ind ... | 1989 | 2731734 |
| lipopolysaccharide mutants of rhizobium meliloti are not defective in symbiosis. | mutants of rhizobium meliloti selected primarily for bacteriophage resistance fall into 13 groups. mutants in the four best-characterized groups (class a, lpsb, lpsc, and class d), which map to the rhizobial chromosome, appear to affect lipopolysaccharide (lps) as judged by the reactivity with monoclonal antibodies and behavior on sodium dodecyl sulfate-polyacrylamide gels of extracted lps. mutations in all 13 groups, in an otherwise wild-type genetic background, are fix+ on alfalfa. this sugges ... | 1989 | 2738026 |
| immunogold localization of the nodc and noda proteins of rhizobium meliloti. | monospecific, polyclonal antibodies to the nodc and noda gene products of rhizobium meliloti were used in combination with immunogold labeling and transmission electron microscopy to localize the nodc and noda proteins in cultures of r. meliloti. both nodc and noda were detected in the cytoplasm and cell envelope in thin sections of free-living rhizobia treated with luteolin, a known inducer of nod gene expression; however, only nodc was detected on cell surfaces when immunolabeling was performe ... | 1989 | 2768184 |
| an osmoregulated dipeptide in stressed rhizobium meliloti. | one common mechanism of cellular adaptation to osmotic stress is the accumulation of organic solutes in the cytosol. we have used natural-abundance 13c nuclear magnetic resonance to identify all organic solutes that accumulate to significant levels in rhizobium meliloti. our studies led to the discovery of a new dipeptide, n-acetylglutaminylglutamine amide (naggn), which is accumulated during osmotic stress. only rarely have peptides been shown to function in bacteria, and furthermore, this is t ... | 1989 | 2768187 |
| conservation between coding and regulatory elements of rhizobium meliloti and rhizobium leguminosarum dct genes. | complementation of rhizobium leguminosarum dct mutants with a cosmid bank yielded rhizobium meliloti homologs of the dcta, dctb, and dctd genes. the genes dctb and dctd are thought to form a two-component system which responds to the presence of c4-dicarboxylates to regulate expression of a transport protein encoded by dcta. dna sequence analysis showed that dct coding and intergenic regions, including putative binding sites for the dctd protein and sigma 54-rna polymerase, were highly conserved ... | 1989 | 2793824 |
| dna footprint analysis of the transcriptional activator proteins nodd1 and nodd3 on inducible nod gene promoters. | the rhizobium meliloti nodd1 and nodd3 gene products (nodd1 and nodd3) are members of the lysr-nodd gene regulator family. they are functionally distinct in that nodd1 transcriptionally activates other nod genes in the presence of a flavonoid inducer such as luteolin, while nodd3 is capable of activating nod gene expression at high levels in the absence of inducer. nodd1 and nodd3 are dna-binding proteins which interact with dna sequences situated upstream of the transcription initiation sites o ... | 1989 | 2793828 |
| genetic and physical analyses of group e exo- mutants of rhizobium meliloti. | mutants of rhizobium meliloti which are deficient in exopolysaccharide synthesis have been classified into six different genetic groups (a through f) (j. a. leigh, e. r. signer, and g. c. walker, proc. natl. acad. sci. usa 82:6231-6235, 1985). using physical and genetic techniques, we have demonstrated that the group e exo- mutants carry deletions in the exoa-exob region of the megaplasmid prmesu47b. we have constructed strains carrying defined deletions which remove up to 200 kilobases of prmes ... | 1988 | 2826404 |
| virulence genes, borders, and overdrive generate single-stranded t-dna molecules from the a6 ti plasmid of agrobacterium tumefaciens. | agrobacterium tumefaciens transfers the t-dna portion of its ti plasmid to the nuclear genome of plant cells. upon cocultivation of a. tumefaciens a348 with regenerating tobacco leaf protoplasts, six distinct single-stranded t-dna molecules (t strands) were generated in addition to double-stranded t-dna border cleavages which we have previously reported (k. veluthambi, r.k. jayaswal, and s.b. gelvin, proc. natl. acad. sci. usa 84:1881-1885, 1987). the t region of an octopine-type ti plasmid has ... | 1988 | 2832367 |
| mutants of rhizobium meliloti defective in succinate metabolism. | we characterized mutants of rhizobium meliloti su47 that were unable to grow on succinate as the carbon source. the mutants fell into five groups based on complementation of the succinate mutations by individual recombinant plasmids isolated from a r. meliloti clone bank. enzyme analysis showed that mutants in the following groups lacked the indicated common enzyme activities: group ii, enolase (eno); group iii, phosphoenolpyruvate carboxykinase (pck); group iv, glyceraldehyde-3-phosphate dehydr ... | 1988 | 2841284 |
| genetic analysis of a cluster of genes required for synthesis of the calcofluor-binding exopolysaccharide of rhizobium meliloti. | rhizobium meliloti produces an acidic, calcofluor-binding exopolysaccharide which plays a role in nodulation of alfalfa plants by this bacterium. we constructed and mapped 102 transposon insertions in a 48-kilobase (kb) region previously shown to contain several exo genes. mutations affecting production of the calcofluor-binding exopolysaccharide were clustered in a 22-kb region and fell into 12 complementation groups. strains carrying mutations in seven of the complementation groups (exoa, exob ... | 1988 | 2842306 |
| rhizobium meliloti mutants that overproduce the r. meliloti acidic calcofluor-binding exopolysaccharide. | the acidic calcofluor-binding exopolysaccharide of rhizobium meliloti rm1021 plays one or more critical roles in nodule invasion and possibly in nodule development. two loci, exor and exos, that affect the regulation of synthesis of this exopolysaccharide were identified by screening for derivatives of strain rm1021 that formed mucoid colonies that fluoresced extremely brightly under uv light when grown on medium containing calcofluor. the exopolysaccharide produced in large quantities by the ex ... | 1988 | 2842307 |
| symbiotic loci of rhizobium meliloti identified by random tnphoa mutagenesis. | we have developed a system for using tnphoa (tnphoa is tn5 is50l::phoa), which generates fusions to alkaline phosphatase (c. manoil and j. beckwith, proc. natl. acad. sci. usa 82:8129-8133, 1985), in rhizobium meliloti. active fusions expressing alkaline phosphatase can arise only when this transposon inserts in genes encoding secreted or membrane-spanning proteins. by confining our screening to 1,250 tnphoa-generated mutants of r. meliloti that expressed alkaline phosphatase, we efficiently ide ... | 1988 | 2842308 |
| bacterial-type ferredoxin genes in the nitrogen fixation regions of the cyanobacterium anabaena sp. strain pcc 7120 and rhizobium meliloti. | the nucleotide sequence of a region located downstream of the nifb gene, both in the cyanobacterium anabaena sp. strain pcc 7120 and in rhizobium meliloti, has been determined. this region contains a gene (fdxn) whose predicted polypeptide product strongly resembles typical bacterial ferredoxins. cyanobacteria have not previously been shown to contain bacterial-type ferredoxins. the presence of this gene suggests that nitrogen-fixing cyanobacteria have at least four distinct ferredoxins. | 1988 | 2842320 |
| interference between rhizobium meliloti and rhizobium trifolii nodulation genes: genetic basis of r. meliloti dominance. | transfer of an incp plasmid carrying the rhizobium meliloti nodfe, nodg, and nodh genes to rhizobium trifolii enabled r. trifolii to nodulate alfalfa (medicago sativa), the normal host of r. meliloti. using transposon tn5-linked mutations and in vitro-constructed deletions of the r. meliloti nodfe, nodg, and nodh genes, we showed that r. meliloti nodh was required for r. trifolii to elicit both root hair curling and nodule initiation on alfalfa and that nodh, nodfe, and nodg were required for r. ... | 1988 | 2848012 |
| synthesis of an opine-like compound, a rhizopine, in alfalfa nodules is symbiotically regulated. | we show that the promoter of the mos locus, which encodes genes required for the synthesis of a nodule-specific, opine-like compound, a rhizopine, in alfalfa nodules is regulated by the symbiotic nitrogen-fixation regulatory gene nifa. the 5'-regulatory region and amino-terminal end of the first open reading frame of the mos locus are highly homologous to the 5'-regulatory region and amino-terminal portion of the rhizobium meliloti nifh gene. the coordinate regulation of mos and nif genes sugges ... | 1988 | 2848255 |
| identification and characterization of the rhizobium meliloti ntrc gene: r. meliloti has separate regulatory pathways for activation of nitrogen fixation genes in free-living and symbiotic cells. | we show here that rhizobium meliloti, the nitrogen-fixing endosymbiont of alfalfa (medicago sativa), has a regulatory gene that is structurally homologous to previously characterized ntrc genes in enteric bacteria. dna sequence analysis showed that r. meliloti ntrc is homologous to previously sequenced ntrc genes from klebsiella pneumoniae and bradyrhizobium sp. (parasponia) and that an ntrb-like gene is situated directly upstream from r. meliloti ntrc. similar to its counterparts in k. pneumoni ... | 1987 | 2881918 |
| characterization of three choline transport activities in rhizobium meliloti: modulation by choline and osmotic stress. | choline has both a nutritional and osmoregulatory role in rhizobium meliloti (t. bernard, j. a. pocard, b. perroud, and d. le rudulier, arch. microbiol. 143:359-364, 1986). in view of this fact, choline transport was studied in r. meliloti 102f34 to determine how the rate of choline uptake is modulated. the effects of the cultural conditions on the kinetics of transport are presented. a high-affinity activity and a low-affinity activity were found in cells grown in minimal medium. the addition o ... | 1989 | 2914855 |
| identification and sequence analysis of two related flagellin genes in rhizobium meliloti. | the genomic region that codes for the flagellin subunits of the complex flagellar filaments of rhizobium meliloti was cloned and sequenced. two structural genes, flaa and flab, that encode 395- and 396-amino-acid polypeptides, respectively, were identified. these exhibit 87% sequence identity. the amino acid sequences of tryptic peptides suggest that both of these subunit proteins are represented in the flagellar filaments. the n-terminal methionine was absent from the mature flagellin subunits. ... | 1989 | 2921241 |
| a plasmid of rhizobium meliloti 41 encodes catabolism of two compounds from root exudate of calystegium sepium. | our objectives were to identify substances produced by plant roots that might act as nutritional mediators of specific plant-bacterium relationships and to delineate the bacterial genes responsible for catabolizing these substances. we discovered new compounds, which we call calystegins, that have the characteristics of nutritional mediators. they were detected in only 3 of 105 species of higher plants examined: calystegia sepium, convolvulus arvensis (both of the convolvulaceae family), and atr ... | 1988 | 2981046 |
| physical and genetic map of a rhizobium meliloti nodulation gene region and nucleotide sequence of nodc. | infection of alfalfa by the soil bacterium rhizobium meliloti proceeds by deformation of root hairs and bacterial invasion of host tissue by way of an infection thread. we studied an 8.7-kilobase (kb) segment of the r. meliloti megaplasmid, which contains genes required for infection. site-directed tn5 mutagenesis was used to examine this fragment for nodulation genes. a total of 81 r. meliloti strains with mapped tn5 insertions in the 8.7-kb fragment were evaluated for nodulation phenotype on a ... | 1985 | 2985535 |
| nitrogen fixation specific regulatory genes of klebsiella pneumoniae and rhizobium meliloti share homology with the general nitrogen regulatory gene ntrc of k. pneumoniae. | we have determined the complete nucleotide sequences of three functionally related nitrogen assimilation regulatory genes from klebsiella pneumoniae and rhizobium meliloti. these genes are: 1) the k. pneumoniae general nitrogen assimilation regulatory gene ntrc (formerly called glng), 2) the k. pneumoniae nif-specific regulatory gene nifa, and 3) an r. meliloti nif-specific regulatory gene that appears to be functionally analogous to the k. pneumoniae nifa gene. in addition to the dna sequence d ... | 1985 | 2989799 |
| evidence for plasmid- and chromosome-borne multiple nif genes in rhizobium fredii. | rhizobium fredii is a fast-growing rhizobium isolated from the primitive chinese soybean cultivar peking and from the wild soybean glycine soja. this rhizobium harbors nif genes on 150- to 200-megadalton plasmids. by passage on acridine orange plates, we obtained a mutant of r. fredii usda 206 cured of the 197-megadalton plasmid (usda 206c) which carries both nif and nod genes. this strain, however, has retained its symbiotic effectiveness. probing ecori digests of wild-type and cured plasmid dn ... | 1985 | 2992376 |
| catabolite repression and role of cyclic amp in co2 fixation and h2 metabolism in rhizobium spp. | co2 fixation in rhizobium meliloti was repressed by a variety of organic carbon sources. cellular cyclic amp levels were similar in repressed and nonrepressed cultures. exogenous cyclic amp or additional copies of the adenyl cyclase gene in cells experiencing repression failed to affect the rates of co2 fixation. however, in r. japonicum catabolite repression of h2 utilization was partially circumvented by the presence of the r. meliloti adenyl cyclase gene. | 1985 | 2993243 |
| analysis of the 5' regulatory region of the gene for delta-aminolevulinic acid synthetase of rhizobium meliloti. | transcriptional regulation of the delta-aminolevulinic acid synthetase gene of rhizobium meliloti was investigated under conditions of normal vegetative growth and during symbiosis with the legume host alfalfa. s1 nuclease mapping and dna sequence analysis indicated that transcription originates from two sites separated by 238 base pairs. a deletion analysis of the putative promoter regions p1 and p2, corresponding to the proximal and distal rna start sites, was carried out with bal-31 nuclease. ... | 1985 | 2994020 |
| cryptic plasmid and rifampin resistance in rhizobium meliloti influencing nodulation competitiveness. | an assessment was made of the relative contributions of a spontaneous mutation to rifampin resistance and a cryptic plasmid, pta2, to competitive nodulation of medicago sativa by a strain of rhizobium meliloti. this was facilitated by use of rifampin-resistant derivatives of this strain in which pta2 was originally present, cured, or reintroduced. both curing of pta2 and spontaneous mutation to rifampin resistance significantly influenced nodulating competitiveness, but the effect of rifampin re ... | 1985 | 2995316 |
| rhizobium meliloti nodulation genes: identification of noddabc gene products, purification of noda protein, and expression of noda in rhizobium meliloti. | a set of conserved, or common, bacterial nodulation (nod) loci is required for host plant infection by rhizobium meliloti and other rhizobium species. four such genes, noddabc, have been indicated in r. meliloti 1021 by genetic analysis and dna sequencing. an essential step toward understanding the function of these genes is to characterize their protein products. we used in vitro and maxicell escherichia coli expression systems, together with gel electrophoresis and autoradiography, to detect p ... | 1985 | 2997121 |
| measurement of the proton motive force in rhizobium meliloti with the escherichia coli lacy gene product. | an escherichia coli lac operon constitutive for lacy was subcloned into the ecori site of a wide-host-range plasmid of the q incompatibility group, and the resulting recombinant plasmid was introduced into tn5-generated lac- mutants of rhizobium meliloti. the r. meliloti transconjugants accumulated lactose about 1,000-fold, equivalent to a proton motive force of -170 to -180 mv, not significantly different from the values calculated from the distributions of weak acids and lipophilic cations. | 1985 | 2997139 |
| isolation and characterization of the dna region encoding nodulation functions in bradyrhizobium japonicum. | the dna region encoding early nodulation functions of bradyrhizobium japonicum 3i1b110 (i110) was isolated by its homology to the functionally similar region from rhizobium meliloti. isolation of a number of overlapping recombinant clones from this region allowed the construction of a restriction map of the region. the identified nodulation region of b. japonicum shows homology exclusively to those regions of r. meliloti and rhizobium leguminosarum dna known to encode early nodulation functions. ... | 1985 | 2999080 |
| characterization of three genomic loci encoding rhizobium sp. strain ors571 n2 fixation genes. | sixty-five independent, n2 fixation-defective (nif-) vector insertion (vi) mutants were selected, cloned, and mapped to the ors571 genome. the recombinant nif::vi plasmids obtained in this way were used as dna hybridization probes to isolate homologous phages from a genomic library of ors571 constructed in lambda embl3. genomic maps were drawn for three ors571 nif gene loci. forty-five nif::vi mutants in genomic nif locus 1 defined two gene clusters separated by 8 kilobase pairs (kb) of dna. in ... | 1986 | 3001035 |
| sequence and domain relationships of ntrc and nifa from klebsiella pneumoniae: homologies to other regulatory proteins. | we have determined the nucleotide sequences of two genes from klebsiella pneumoniae, nifa, the nif-specific activator of transcription and ntrc, the bifunctional regulatory protein involved in 'nitrogen control'. these sequences differ significantly from those previously published. in particular, nifa extends 40 codons beyond the stop codon reported earlier. this extension encodes a putative dna-binding domain strongly homologous to the rhizobium meliloti nifa protein and to some extent to the n ... | 1986 | 3011408 |
| nucleotide sequence of rhizobium meliloti rcr2011 genes involved in host specificity of nodulation. | a 6 kb dna segment of the r. meliloti 2011 psym megaplasmid, which contains genes controlling host specificity of root hair infection and of nodulation, was cloned and sequenced. the dna sequence analysis, in conjunction with previous genetic data, allowed identification of four nod genes designated as e, f, g and h. nodh is divergently transcribed with respect to nodfe and nodg. a conserved nucleotide sequence was found around 200 bp upstream of the translation start of nodf, nodh and noda. thi ... | 1986 | 3020515 |
| biosynthesis and degradation of nodule-specific rhizobium loti compounds in lotus nodules. | two nodule-specific rhizobium loti compounds were identified in lotus tenuis and lotus pedunculatus nodules induced by strain nzp2037. one, a silver nitrate-positive cation called rhizolotine, has been characterized as the riboside of a novel alpha-hydroxyimino acid containing a 1,4,5,6-tetrahydropyrimidine ring (g. j. shaw, r. d. wilson, g. a. lane, l. d. kennedy, d. b. scott, and g. j. gainsford, j. chem. soc. chem. commun., p. 180-181, 1986), and the other, yellow-1, stains yellow with ninhyd ... | 1987 | 3025173 |
| conservation of structure and location of rhizobium meliloti and klebsiella pneumoniae nifb genes. | using transposon tn5-mediated mutagenesis, an essential rhizobium meliloti nitrogen fixation (nif) gene was identified and located directly downstream of the regulatory gene nifa. maxicell and dna sequence analysis demonstrated that the new gene is transcribed in the same direction as nifa and codes for a 54-kilodalton protein. in klebsiella pneumoniae, the nifbq operon is located directly downstream of a gene which is structurally and functionally homologous to the r. meliloti nifa gene. the dn ... | 1987 | 3029020 |
| genetic and structural analysis of the rhizobium meliloti fixa, fixb, fixc, and fixx genes. | the fixa, fixb, fixc, and fixx genes of rhizobium meliloti 1021 constitute an operon and are required for nitrogen fixation in alfalfa nodules. dna homologous to the r. meliloti fixabc genes is present in all other rhizobium and bradyrhizobium species examined, but fixabc-homologous sequences were found in only one free-living diazotroph, azotobacter vinelandii. to determine whether the fixabcx genes share sequence homology with any of the 17 klebsiella pneumoniae nif genes, we determined the en ... | 1987 | 3029021 |
| rhizobium meliloti ntra (rpon) gene is required for diverse metabolic functions. | we report the identification and cloning of an ntra-like (glnf rpon) gene of rhizobium meliloti and show that the r. meliloti ntra product (ntra) is required for c4-dicarboxylate transport as well as for nitrate assimilation and symbiotic nitrogen fixation. dna sequence analysis showed that r. meliloti ntra is 38% homologous with klebsiella pneumoniae ntra. subcloning and complementation analysis suggested that the r. meliloti ntra promoter lies within 125 base pairs of the initiation codon and ... | 1987 | 3034856 |
| high-frequency transformation of rhizobium meliloti. | transformation of r factor rp4 and its derivative prk290 from escherichia coli to rhizobium meliloti is reported. the efficiency of transformation was in the range of 10(-5) per viable cell. in addition, chromosomal dna prepared from one r. meliloti strain resistant to streptomycin was transferred to the isoleucine-valine-requiring mutant susceptible to streptomycin. | 1988 | 3056925 |
| the dna-binding domain of the transcriptional activator protein nifa resides in its carboxy terminus, recognises the upstream activator sequences of nif promoters and can be separated from the positive control function of nifa. | the positive control protein nifa activates transcription of nitrogen fixation promoters in klebsiella pneumoniae. nifa is believed to bind to specific sites, the upstream activator sequences (uas's), of the nif promoters which it activates. we have now shown by mutation of the carboxy terminus of nifa that this is the dna-binding domain and that the dna-binding and positive activator functions of nifa can be separated. mutational analysis of the nifh uas and in vivo methylation protection analy ... | 1988 | 3062575 |
| phosphoglycerol substituents present on the cyclic beta-1,2-glucans of rhizobium meliloti 1021 are derived from phosphatidylglycerol. | the synthesis of periplasmic cyclic beta-1,2-glucans is a property unique to species of the family rhizobiaceae. for this reason, it is generally believed that these molecules may play an important role in the plant infection process. in the present study, we determined that the cyclic beta-1,2-glucans produced by rhizobium meliloti 1021 were predominantly anionic in character and contained both phosphoglycerol and succinic acid substituents. in addition, we demonstrated that phosphatidylglycero ... | 1988 | 3170478 |
| isolation and characterization of azospirillum brasilense loci that correct rhizobium meliloti exob and exoc mutations. | the occurrence in azospirillum brasilense of genes that code for exopolysaccharide (eps) synthesis was investigated through complementation studies of rhizobium meliloti exo- mutants. these mutants are deficient in the synthesis of the major acidic eps of rhizobium species and form empty, non-nitrogen-fixing root nodules on alfalfa (j. a. leigh, e. r. signer, and g. c. walker, proc. natl. acad. sci. usa 82:6231-6235, 1985). we demonstrated that the exoc mutation of r. meliloti could be corrected ... | 1988 | 3182731 |
| osmotic control of glycine betaine biosynthesis and degradation in rhizobium meliloti. | intracellular accumulation of glycine betaine has been shown to confer an enhanced level of osmotic stress tolerance in rhizobium meliloti. in this study, we used a physiological approach to investigate the mechanism by which glycine betaine is accumulated in osmotically stressed r. meliloti. results from growth experiments, 14c labeling of intermediates, and enzyme activity assays are presented. the results provide evidence for the pathway of biosynthesis and degradation of glycine betaine and ... | 1988 | 3290197 |
| rhizobium meliloti nifn (fixf) gene is part of an operon regulated by a nifa-dependent promoter and codes for a polypeptide homologous to the nifk gene product. | an essential gene for symbiotic nitrogen fixation (fixf) is located near the common nodulation region of rhizobium meliloti. a dna fragment carrying fixf was characterized by hybridization with klebsiella pneumoniae nif dna and by nucleotide sequence analysis. the fixf gene was found to be related to k. pneumoniae nifn and was therefore renamed as the r. meliloti nifn gene. upstream of the nifn coding region a second open reading frame was identified coding for a putative polypeptide of 110 amin ... | 1987 | 3316182 |
| all nod genes of rhizobium meliloti are involved in alfalfa nodulation by exo mutants. | nodulation of alfalfa by exob mutants of rhizobium meliloti occurred without root hair curling or infection thread formation. nod exob double mutants had the same nodulation deficiency as single nod mutants. therefore, all the known nod genes are involved in nodule induction by exob mutants, which apparently occurs via intercellular invasion. | 1988 | 3338972 |
| essential and non-essential domains in the bradyrhizobium japonicum nifa protein: identification of indispensable cysteine residues potentially involved in redox reactivity and/or metal binding. | the amino acid sequence of the bradyrhizobium japonicum nitrogen fixation regulatory protein nifa, as derived from the nucleotide sequence of the nifa gene, was aligned to the corresponding protein sequences from klebsiella pneumoniae, rhizobium meliloti and rhizobium leguminosarum biovar viciae. high conservation was found in the central domain and in the cooh-terminal, putative dna binding domain, whereas very little homology was present within the first 250 amino acids from the nh2-terminus. ... | 1988 | 3357773 |
| chemotaxis of rhizobium meliloti to the plant flavone luteolin requires functional nodulation genes. | luteolin is a phenolic compound from plants that acts as a potent and specific inducer of nodabc gene expression in rhizobium meliloti. we have found that r. meliloti rcr2011 exhibits positive chemotaxis towards luteolin. a maximum chemotactic response was observed at 10(-8) m. two closely related flavonoids, naringenin and apigenin, were not chemoattractants. the presence of naringenin but not apigenin abolished chemotaxis of r. meliloti towards luteolin. a large deletion in the nif-nod region ... | 1988 | 3384804 |
| physiology of behavioral mutants of rhizobium meliloti: evidence for a dual chemotaxis pathway. | wild-type and nonchemotactic mutant strains of rhizobium meliloti were tested for attraction to localized sites on alfalfa roots and for attraction to numerous small molecules, including sugars, amino acids, and two fractions derived from alfalfa root extracts. four strains (carrying mutations che-6, che-11, che-12, and che-26) lost all responses and were classified as generally nonchemotactic mutants. one strain (carrying mutation che-7) lost responses to a group of structurally unrelated amino ... | 1988 | 3384809 |
| characterization of polysaccharides of rhizobium meliloti exo mutants that form ineffective nodules. | mutants of rhizobium meliloti su47 with defects in the production of the calcofluor-binding expolysaccharide succinoglycan failed to gain entry into alfalfa root nodules. in order to define better the polysaccharide phenotypes of these exo mutants, we analyzed the periplasmic oligosaccharide cyclic (1-2)-beta-d-glucan and lipopolysaccharide (lps) in representative mutants. the exoc mutant lacked the glucan and had abnormal lps which appeared to lack a substantial portion of the o side chain. the ... | 1988 | 3403505 |
| dicarboxylic acid transport in bradyrhizobium japonicum: use of rhizobium meliloti dct gene(s) to enhance nitrogen fixation. | a recombinant plasmid encoding rhizobium meliloti sequences involved in dicarboxylic acid transport (plasmid prk290:4:46) (e. bolton, b. higgisson, a. harrington, and f. o'gara, arch. microbiol. 144:142-146, 1986) was used to study the relationship between dicarboxylic acid transport and nitrogen fixation in bradyrhizobium japonicum. the expression of the dct sequences on plasmid prk290:4:46 in b. japonicum cj1 resulted in increased growth rates in media containing dicarboxylic acids as the sole ... | 1988 | 3422072 |
| laboratory and clinical evaluation of isolation media for campylobacter jejuni. | six selective isolation media were evaluated for their ability to support the growth of campylobacter jejuni. colony counts of 70 isolated strains of c. jejuni and recovery studies on these strains in simulated positive feces samples demonstrated that bolton and hutchinson' charcoal, cefoperazone, deoxycholate agar and karmali's charcoal-based selective medium produced the highest recovery rates with the greatest suppression of other fecal flora. c. jejuni colonies were more easily recognized on ... | 1987 | 3429621 |
| rhizobium meliloti has three functional copies of the nodd symbiotic regulatory gene. | we have identified two rhizobium meliloti genes (nodd2 and nodd3) that are highly homologous and closely linked to the regulatory gene nodd (nodd1). r. meliloti strains containing mutations in the three nodd genes in all possible combinations were constructed and their nodulation phenotypes were assayed on medicago sativa (alfalfa) and melilotus alba (sweet clover). a triple nodd1-nodd2-nodd3 mutant exhibited a nod- phenotype on alfalfa and sweet clover, indicating that nodd is an essential nodu ... | 1987 | 3479806 |
| common loci for agrobacterium tumefaciens and rhizobium meliloti exopolysaccharide synthesis and their roles in plant interactions. | mutants of rhizobium meliloti have been isolated which are deficient in exopolysaccharide (eps) production and effective nodulation of alfalfa (j. a. leigh, e. r. signer, and g. c. walker, proc. natl. acad. sci. usa 82:6231-6235, 1985). we isolated approximately 100 analogous eps-deficient (exo) mutants of the closely related plant pathogen agrobacterium tumefaciens, including strains whose eps deficiencies were specifically complemented by each of five cloned r. meliloti exo loci. we also clone ... | 1987 | 3571162 |
| a new symbiotic cluster on the psym megaplasmid of rhizobium meliloti 2011 carries a functional fix gene repeat and a nod locus. | a 290-kilobase (kb) region of the rhizobium meliloti 2011 psym megaplasmid, which contains nodulation genes (nod) as well as genes involved in nitrogen fixation (nif and fix), was shown to carry at least six sequences repeated elsewhere in the genome. one of these reiterated sequences, about 5 kb in size, had previously been identified as part of a cluster of fix genes located 220 kb downstream of the nifhdk promoter. deletion of the reiterated part of this fix cluster does not alter the symbiot ... | 1987 | 3571166 |
| a locus encoding host range is linked to the common nodulation genes of bradyrhizobium japonicum. | by using cloned rhizobium meliloti, rhizobium leguminosarum, and rhizobium sp. strain mpik3030 nodulation (nod) genes as hybridization probes, homologous regions were detected in the slow-growing soybean symbiont bradyrhizobium japonicum usda 110. these regions were found to cluster within a 25-kilobase (kb) region. specific nod probes from r. meliloti were used to identify noda-, nodb-, nodc-, and nodd-like sequences clustered on two adjacent hindiii restriction fragments of 3.9 and 5.6 kb. a 7 ... | 1987 | 3584066 |
| expression of rhizobium meliloti nod genes in rhizobium and agrobacterium backgrounds. | rhizobium meliloti nod genes are required for the infection of alfalfa. induction of the nodc gene depends on a chemical signal from alfalfa and on nodd gene expression. by using a nodc-lacz fusion, we have shown that the induction of the r. meliloti nodc gene and the expression of nodd occur at almost normal levels in other rhizobium backgrounds and in agrobacterium tumefaciens, but not in escherichia coli. xanthomonas campestris, or pseudomonas savastanoi. our results suggest that bacterial ge ... | 1987 | 3597319 |
| rhizobium meliloti swims by unidirectional, intermittent rotation of right-handed flagellar helices. | the 5 to 10 peritrichously inserted complex flagella of rhizobium meliloti mvii-1 were found to form right-handed flagellar bundles. bacteria swam at speeds up to 60 microns/s, their random three-dimensional walk consisting of straight runs and quick directional changes (turns) without the vigorous angular motion (tumbling) seen in swimming escherichia coli cells. observations of r. meliloti cells tethered by a single flagellar filament revealed that flagellar rotation was exclusively clockwise, ... | 1987 | 3597320 |
| agrobacterium tumefaciens virulence locus psca is related to the rhizobium meliloti exoc locus. | agrobacterium tumefaciens and rhizobium meliloti carry related genetic loci which have important roles in virulence and symbiosis. previously, it was shown that two virulence loci of a. tumefaciens, chva and chvb, are related to two r. meliloti symbiosis loci, ndva and ndvb, respectively (t. dylan, l. ielpi, s. stanfield, l. kashyap, c. douglas, m. yanofsky, e. nester, d. r. helinski, and g. ditta, proc. natl. acad. sci. usa 83:4403-4407, 1986). here we show that these two phytobacteria possess ... | 1987 | 3680180 |
| galactose metabolism in rhizobium meliloti l5-30. | data from previous studies of rhizobium meliloti mutants have been consistent with the catabolism of hexoses via the entner-doudoroff pathway. however, galactose metabolism was not impaired in those mutants. we show here by enzymatic assay and by identification of a galactose mutant lacking 2-keto-3-deoxy-6-phosphogalactonate aldolase that the de ley-doudoroff pathway is used for galactose metabolism. mutants in this pathway have not been previously reported for any organism. | 1986 | 3745118 |
| two gene clusters of rhizobium meliloti code for early essential nodulation functions and a third influences nodulation efficiency. | a plafr1 cosmid clone (ppp346) carrying the nodulation region of the symbiotic plasmid prme41b was isolated from a gene library of rhizobium meliloti 41 by direct complementation of a nod- deletion mutant of r. meliloti. agrobacterium tumefaciens and rhizobium species containing ppp346 were able to form ineffective nodules on alfalfa. the 24-kilobase insert in ppp346 carries both the common nodulation genes and genes involved in host specificity of nodulation. it was shown that these two regions ... | 1986 | 3745124 |
| biosynthesis of a galactose-and galacturonic acid-containing polysaccharide in rhizobium meliloti. | previous work showed that two different strains derived from a culture of rhizobium meliloti 102f51 differed with respect to phage specificity, agglutinability by alfalfa seed lectin, and synthesis of a galactose-containing polysaccharide (r. a. ugalde, h. handelsman, and w. j. brill, j. bacteriol. 166:148-154, 1986). inner membranes from the more competitive strain incorporated galactose from udp-galactose when a thermostable factor was present. this factor has now been identified as udp-galact ... | 1986 | 3759905 |
| a rhizobium meliloti mutant that forms ineffective pseudonodules in alfalfa produces exopolysaccharide but fails to form beta-(1----2) glucan. | a mutant of rhizobium meliloti that elicited the formation of inactive nodules in alfalfa was found not to form beta-(1----2) glucan in vivo or in vitro. it was nonmotile because it lacks flagella. the 235-kilodalton protein which acts as an intermediate in beta-(1----2) glucan synthesis was undetectable in the mutant. these properties of the mutant are common to those of chvb mutants of agrobacterium tumefaciens. exopolysaccharide formation by the r. meliloti mutant was about double that by the ... | 1987 | 3804979 |
| exopolysaccharide-deficient mutants of rhizobium meliloti that form ineffective nodules. | by screening with the fluorescent stain calcofluor, we have isolated 26 independent transposon tn5 insertion mutants of rhizobium meliloti that are deficient in the production of a known extracellular polysaccharide (exo-). the mutants belonged to six distinct genetic groups based on the ability of their exo- phenotype to be complemented by different recombinant plasmids from a r. meliloti clone bank. with few exceptions, all of the mutants formed ineffective (non-nitrogen-fixing) nodules on alf ... | 1985 | 3862129 |
| characterization of a rhizobium meliloti fixation gene (fixf) located near the common nodulation region. | rhizobium meliloti 2011 dna from prmsl26, a plasmid which is known to carry genes involved in the early stages of nodulation, was used to construct tn5 mutations by site-directed tn5 mutagenesis. tn5 mutations located within an 8.7 kilobase ecori fragment defined two adjacent loci encoding functions for nodulation (nod) and symbiotic n2 fixation (fix). we investigated the organization and regulation of the fix locus and the characteristics of alfalfa nodules induced by these fix- mutants. by mon ... | 1985 | 3900039 |
| induction of rhizobium meliloti nodc expression by plant exudate requires nodd. | the soil bacterium rhizobium meliloti invades and establishes a symbiosis with host plants such as alfalfa. bacterial nodulation (nod) genes are required for this invasion, but their mechanism of action and the timing of their expression are not known. we have used translational lacz fusions to monitor expression of nodd and nodc, which are located in the cluster of four nod genes on the r. meliloti megaplasmid (psym). nodd is expressed at comparable levels by broth-grown bacterial cells and by ... | 1985 | 3931078 |
| enzymes of the beta-ketoadipate pathway are inducible in rhizobium and agrobacterium spp. and constitutive in bradyrhizobium spp. | protocatechuate is a universal growth substrate for members of the family rhizobiaceae, and these bacteria utilize the aromatic compound via the beta-ketoadipate pathway. this report describes transcriptional controls exercised by different subgroups of the rhizobiaceae over five enzymes that catalyze consecutive reactions in the pathway: protocatechuate oxygenase (ec 1.13.11.3), beta-carboxy-cis,cis-muconate lactonizing enzyme (ec 5.5.1.2), gamma-carboxymuconolactone decarboxylase (ec 4.1.1.44) ... | 1986 | 3941043 |
| nodules are induced on alfalfa roots by agrobacterium tumefaciens and rhizobium trifolii containing small segments of the rhizobium meliloti nodulation region. | regions of the rhizobium meliloti nodulation genes from the symbiotic plasmid were transferred to agrobacterium tumefaciens and rhizobium trifolii by conjugation. the a. tumefaciens and r. trifolii transconjugants were unable to elicit curling of alfalfa root hairs, but were able to induce nodule development at a low frequency. these were judged to be genuine nodules on the basis of cytological and developmental criteria. like genuine alfalfa nodules, the nodules were initiated from divisions of ... | 1985 | 3968028 |
| purification and subunit characterization of rhizobium meliloti rna polymerase. | the rna polymerase of the symbiotic, nitrogen-fixing bacterium rhizobium meliloti was purified, and its subunit composition was determined. the cells were disrupted in the presence of protease inhibitors, and holoenzyme fractions were purified by fractionation by using deae-cellulose and dna-agarose chromatography. the core polymerase was purified by additional chromatography on phosphocellulose. the subunit structure is beta prime (155,000 molecular weight), beta (151,000), alpha (43,000), and ... | 1985 | 3988706 |
| legume agglutinins that bind to rhizobium meliloti. | a protein found in seeds and roots of alfalfa (medicago sativa) was implicated in the specificity of the infection process, based on its binding to the symbiont rhizobium meliloti. we found an agglutinin with similar properties in seeds and roots of sweet clover (melilotis alba). the sweet clover differed from alfalfa in nodulation by a mutant strain of r. meliloti, but the agglutinins were indistinguishable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, rhizobium agglutination, a ... | 1985 | 3988714 |
| erwinia herbicola isolates from alfalfa plants may play a role in nodulation of alfalfa by rhizobium meliloti. | erwinia herbicola was isolated from roots of plants derived from surface-sterilized seeds of all alfalfa varieties that were tested. some of these e. herbicola strains affected nodulation by certain strains of rhizobium meliloti. in previously published work we presented the isolation of slow-and fast-nodulating variants from a single culture of r. meliloti 102f51. in the absence of e. herbicola, the slow-nodulating variant induced the formation of nodules on alfalfa as rapidly as the faster-nod ... | 1985 | 4004214 |
| conservation of symbiotic nitrogen fixation gene sequences in rhizobium japonicum and bradyrhizobium japonicum. | southern hybridization with nif (nitrogen fixation) and nod (nodulation) dna probes from rhizobium meliloti against intact plasmid dna of rhizobium japonicum and bradyrhizobium japonicum strains indicated that both nif and nod sequences are on plasmid dna in most r. japonicum strains. an exception is found with r. japonicum strain usda194 and all b. japonicum strains where nif and nod sequences are on the chromosome. in r. japonicum strains, with the exception of strain usda205, both nif and nod ... | 1985 | 4008441 |
| regions of broad-host-range plasmid rk2 involved in replication and stable maintenance in nine species of gram-negative bacteria. | the replication and maintenance properties of the broad-host-range plasmid rk2 and its derivatives were examined in nine gram-negative bacterial species. two regions of rk2, the origin of replication (oriv) and a segment that encodes for a replication protein (trfa delta kild, designated trfa*), are sufficient for replication in all nine species tested. however, stable maintenance of this minimal replicon (less than 0.3% loss per generation under nonselection conditions) is observed only in esch ... | 1985 | 4044529 |
| identification of a rhizobium meliloti psym2011 region controlling the host specificity of root hair curling and nodulation. | in rhizobium meliloti 2011 nodulation genes (nod) required to nodulate specifically alfalfa are located on a psym megaplasmid. nod- derivatives carrying large psym deletions were isolated. by complementation of these strains with in vivo- and in vitro-constructed episomes containing psym of sequences and introduction of these episomes into agrobacterium tumefaciens, we show (i) that from a region of psym of about 360 kilobases, genes required for specific alfalfa nodulation are clustered in a dn ... | 1985 | 4066612 |
| physical organization of the bradyrhizobium japonicum nitrogenase gene region. | in bradyrhizobium japonicum usda 110 the three genes that encode the nitrogenase enzyme complex are separated into two transcription units, nifh and nifdk. we have physically mapped a 33-kilobase-pair region of the b. japonicum genome that contains both nifh and nifdk. the nifdk operon is located transcriptionally upstream from nifh, and all three genes are transcribed in the same direction. within the 20-kilobase-pair region that separates the promoters for these two transcription units, we hav ... | 1984 | 6090394 |
| reiteration of genes involved in symbiotic nitrogen fixation by fast-growing rhizobium japonicum. | by using cloned rhizobium meliloti nodulation (nod) genes and nitrogen fixation (nif) genes, we found that the genes for both nodulation and nitrogen fixation were on a plasmid present in fast-growing rhizobium japonicum strains. two ecori restriction fragments from a plasmid of fast-growing r. japonicum hybridized with nif structural genes of r. meliloti, and three ecori restriction fragments hybridized with the nod clone of r. meliloti. cross-hybridization between the hybridizing fragments rev ... | 1984 | 6094491 |
| ammonium assimilation in rhizobium meliloti. | we have characterized a mutant of rhizobium meliloti strain 2011 which cannot use ammonium as a nitrogen source. this mutant, rtm2620, was found to have significantly altered glutamate synthase activity. both the mutant and the wild-type strains had glutamate dehydrogenase activity, which, although stimulated in the presence of glutamate and ammonium, was apparently insufficient to allow ammonium assimmilation. we conclude that the glutamine synthetase-glutamate synthase pathway may be the norma ... | 1980 | 6106011 |
| succinate dehydrogenase mutant of rhizobium meliloti. | a succinate dehydrogenase mutant strain of rhizobium meliloti was isolated after nitrosoguanidine mutagenesis. it failed to grow on succinate, glutamate, acetate, pyruvate, or arabinose but grew on glucose, sucrose, fructose, and other carbohydrates. the mutant strain showed delayed nodulation of lucerne plants, and the nodules were white and ineffective. a spontaneous revertant strain of normal growth phenotype induced red and effective nodules. | 1982 | 6125502 |
| rhizobium meliloti mutants altered in ammonium utilization. | derivatives of rhizobium meliloti 2011 required trace amounts of glutamate to use ammonium as the nitrogen source for growth, although they could use serine as the sole nitrogen source. specific activities of ammonium assimilatory enzymes were similar to those in strain rm2011. the mutants were deficient in nitrogen fixation. | 1982 | 6125503 |
| promoters regulated by the glng (ntrc) and nifa gene products share a heptameric consensus sequence in the -15 region. | we have determined the nucleotide sequences of the klebsiella pneumoniae nifl (regulation of n2 fixation genes) and the escherichia coli glna (glutamine synthetase) promoters. we compared these sequences with the published sequences of three other promoters that, like the nifl and glna promoters, are activated by the general nitrogen regulators glnf (ntra) and glng (ntrc). the three promoters are the argtr (arginine transport) and dhua (histidine transport) promoters of salmonella typhimurium an ... | 1983 | 6133280 |
| molecular characterization of tn5-induced symbiotic (fix-) mutants of rhizobium meliloti. | to investigate the expression of specific symbiotic genes during the development of nitrogen-fixing root nodules, we conducted a systematic analysis of nodule-specific proteins and rnas produced after the inoculation of alfalfa roots with a series of rhizobium meliloti mutants generated by site-directed transposon tn5 mutagenesis. the mutagenized region of the rhizobium genome covered approximately 10 kilobases and included the region encoding the nitrogenase polypeptides. all mutant strains tha ... | 1983 | 6196347 |
| biochemical characterization of a fructokinase mutant of rhizobium meliloti. | a double mutant strain (ur3) of rhizobium meliloti l5-30 was isolated from a phosphoglucose isomerase mutant (ur1) on the basis of its resistance to fructose inhibition when grown on fructose-rich medium. ur3 lacked both phosphoglucose isomerase and fructokinase activity. a mutant strain (ur4) lacking only the fructokinase activity was derived from ur3; it grew on the same carbon sources as the parent strain, but not on fructose, mannitol, or sorbitol. a spontaneous revertant (ur5) of normal gro ... | 1980 | 6252186 |
| physical and genetic characterization of symbiotic and auxotrophic mutants of rhizobium meliloti induced by transposon tn5 mutagenesis. | we have physically and genetically characterized 20 symbiotic and 20 auxotrophic mutants of rhizobium meliloti, the nitrogen-fixing symbiont of alfalfa (medicago sativa), isolated by transposon tn5 mutagenesis. a "suicide plasmid" mutagenesis procedure was used to generate tn-5-induced mutants, and both auxotrophic and symbiotic mutants were found at a frequency of 0.3% among strains containing random tn5 insertions. two classes of symbiotic mutants were isolated: 4 of the 20 formed no nodules ... | 1982 | 6274841 |
| transformation of rhizobium meliloti 41 with plasmid dna. | plasmid pgv1106, a derivative of the wide-host-range plasmid s-a of the w incompatibility group, was introduced into rhizobium meliloti 41 by plasmid-mediated mobilization to overcome the restriction of foreign dna. the mobilized plasmid pkk2 differed from the original pgv1106 by an extra piece of dna of 1.3 kilobase pairs which supposedly originated from pjb3ji used for mobilization. if pkk2 was isolated from r. meliloti 41, it could be successfully reintroduced by transformation. the transform ... | 1982 | 6279558 |
| transport and catabolism of d-mannose in rhizobium meliloti. | rhizobium meliloti l5-30 grows on d-mannose as the sole carbon source. the catabolic pathway of d-mannose was characterized. the following activities were present: mannose transport system, mannokinase, and mannosephosphate isomerase. several mannose-negative mutants were selected; they were classified into three functional groups: group i, mannokinase and mannosephosphate isomerase defective: group ii, mannokinase defective; and group iii, mannosephosphate isomerase defective. mannose uptake wa ... | 1982 | 6286588 |
| localization of symbiotic mutations in rhizobium meliloti. | a total of 5 nod- and 57 fix- symbiotic mutants of rhizobium meliloti strain 41 have been isolated after either nitrosoguanidine or tn5 transposition mutagenesis. chromosomal locations of mutations in 1 nod- and 11 fix- derivatives were ascertained by transferring the chromosome (mobilized by plasmid r68.45), in eight fragments, into symbiotically effective recipients and testing the recombinants for symbiotic phenotype. alternatively, the kanamycin resistance marker of tn5 was mapped. in five m ... | 1983 | 6296048 |
| isolation and characterization of the reca gene of rhizobium meliloti. | interspecific complementation of an escherichia coli reca mutant with plasmids containing a gene bank of rhizobium meliloti dna was used to identify a clone which contains the reca gene of r. meliloti. the r. meliloti reca protein can function in recombination and in response to dna damage when expressed in an e. coli reca host, and hybridization studies have shown that dna sequence homology exists between the reca gene of e. coli and that of r. meliloti. the isolated r. meliloti reca dna was us ... | 1983 | 6305915 |
| activation of klebsiella pneumoniae and rhizobium meliloti nitrogenase promoters by gln (ntr) regulatory proteins. | we have studied the expression, in different escherichia coli gln (ntr) mutants, of fusions (constructed in vitro) of the nifhdk (nitrogenase) promoters from klebsiella pneumoniae and rhizobium meliloti to e. coli lacz. derepression of the k. pneumoniae nifh::lacz fusion requires the glnf (ntra) gene product in addition to the k. pneumoniae nifa gene product, indicating that regulation of the k. pneumoniae nif genes is more closely integrated with the overall nitrogen control system than previou ... | 1983 | 6306658 |
| suicide plasmid vehicles for insertion mutagenesis in rhizobium meliloti and related bacteria. | we describe the construction and use of a set of plasmid vectors of the transposons tn1, tn5, and tn9 that are suicidal in rhizobium species and therefore suitable for mutagenesis with these three transposons. the vectors are composed of the p15a replicon which functions in escherichia coli but not in rhizobium species and a region encoding the n type of bacterial conjugation system which is very efficient in matings between e. coli and rhizobium species. the usefulness of the vectors has been m ... | 1983 | 6315684 |
| rhizobium japonicum nitrogenase fe protein gene (nifh). | a 12.1-kilobase psti fragment from rhizobium japonicum, which contains homology to both the klebsiella pneumoniae and the rhizobium meliloti nifh genes, was cloned into vector phe3 . the nifh -homologous region was localized on the restriction enzyme cleavage map by southern blot hybridization experiments. dna fragments overlapping the r. japonicum nifh gene were subcloned into plasmid vectors to allow the expression of this region in escherichia coli minicells. the nifh gene product (the polype ... | 1984 | 6327620 |
| conjugal transfer of bacterial chromosomes mediated by the rk2 plasmid transfer origin cloned into transposon tn5. | we report here a novel system for the conjugal transfer of bacterial chromosomes which utilizes the transfer origin (orit) of plasmid rk2 cloned into transposon tn5. tn5 with orit was inserted by transposition into the chromosomes of escherichia coli and rhizobium meliloti. the orit sequence then served as the origin of high-frequency chromosome transfer when a helper rk2 plasmid was present in the same cell. the broad host range features of rk2 make this system of oriented chromosome mobilizati ... | 1984 | 6090433 |
| rhizobium meliloti nodulation genes allow agrobacterium tumefaciens and escherichia coli to form pseudonodules on alfalfa. | regions of the rhizobium meliloti symbiotic plasmid (20 to 40 kilobase pairs long) containing nodulation (nod) genes were transferred to agrobacterium tumefaciens or escherichia coli by conjugation. the a. tumefaciens and e. coli transconjugants elicited root hair curling and the formation of ineffective pseudonodules on inoculated alfalfa plants. a tumefaciens elicited pseudonodules formed at a variable frequency, ranging from 15 to 45%, irrespective of the presence of the ti plasmid. these pse ... | 1984 | 6327629 |