Publications

TitleAbstractYear
Filter
PMID
Filter
transcriptional analysis of the fix abcxorf1 region of azorhizobium caulinodans suggests post-transcriptional processing of the fix abcxorf1 mrna.we report here the transcriptional analysis of the fixabcxorf1 region of azorhizobium caulinodans. this led to the identification of a 0.9 kb transcript covering fixx and orf1, which was synthesized only under conditions of nitrogen fixation. the 5' end of this transcript was mapped by primer extension and s1 nuclease protection analyses and shown to be located 70 +/- 1 nucleotides upstream of the fixx start codon. by means of transcriptional fixx- and orf1-lacz fusions, it was shown that fixx a ...19921281516
the early nodulin gene srenod2 from sesbania rostrata is inducible by cytokinin.the structure and expression of the early nodulin gene enod2 from the stem-nodulated tropical legume sesbania rostrata (srenod2) was examined. genomic clones carrying the single srenod2locus were isolated and the dna sequence of the gene was determined. the srenod2 gene was found to lack introns and to encode a protein consisting primarily of a 55-fold repeat of short proline-rich oligopeptides. a putative signal sequence, which may be responsible for targeting of the enod2 protein to the cell w ...19921303791
phylogeny of fast-growing soybean-nodulating rhizobia support synonymy of sinorhizobium and rhizobium and assignment to rhizobium fredii.we determined the sequences for a 260-base segment amplified by the polymerase chain reaction (corresponding to positions 44 to 337 in the escherichia coli 16s rrna sequence) from seven strains of fast-growing soybean-nodulating rhizobia (including the type strains of rhizobium fredii chemovar fredii, rhizobium fredii chemovar siensis, sinorhizobium fredii, and sinorhizobium xinjiangensis) and broad-host-range rhizobium sp. strain ngr 234. these sequences were compared with the corresponding pre ...19921371066
broad host range and promoter selection vectors for bacteria that interact with plants.a plasmid vector, pgv910, and a derived cosmid, prg930, have been constructed. both contain the cole1 and pvs1 origins of replication and are stably maintained in escherichia coli, agrobacterium tumefaciens, and azorhizobium caulinodans ors571. they are compatible with commonly used incp cloning vectors, although pvs1 was classified as an incp plasmid, unable to replicate in e. coli (y. itoh, j.m. watson, d. haas, and t. leisinger, plasmid 11:206-220, 1984). promoter selection vectors were deriv ...19921421510
structural and functional analysis of two different nodd genes in bradyrhizobium japonicum usda110.bradyrhizobium japonicum has two closely linked homologs of the nodulation regulatory gene, nodd; these homologs are located upstream of and in divergent orientation to the nodyabcsuij gene cluster. we report here the nucleotide sequence and mutational analyses of both nodd copies. the predicted nodd1 and nodd2 proteins shared 62% identical amino acid residues at corresponding positions and exhibited different degrees of homology with nodd proteins of other bradyrhizobium, azorhizobium, and rhiz ...19921421512
signaling and host range variation in nodulation.rhizobium, bradyrhizobium, and azorhizobium strains, collectively referred to as rhizobia, elicit on their leguminous hosts, in a specific manner, the formation of nodules in which they fix nitrogen. rhizobial nod genes, which determine host specificity, infection, and nodulation, are involved in the exchange of low molecular weight signal molecules between the plant and the bacteria as follows. transcription of the nod operons is under the control of nodd regulatory proteins, which are specific ...19921444265
elucidation of the complete azorhizobium nicotinate catabolism pathway.a complete pathway for azorhizobium caulinodans nicotinate catabolism has been determined from mutant phenotype analyses, isolation of metabolic intermediates, and structural studies. nicotinate serves as a respiratory electron donor to o2 via a membrane-bound hydroxylase and a specific c-type cytochrome oxidase. the resulting oxidized product, 6-hydroxynicotinate, is next reduced to 1,4,5,6-tetrahydro-6-oxonicotinate. hydrolytic ring breakage follows, with release of pyridine n as ammonium. dec ...19921447145
identification of a new inducible nodulation gene in azorhizobium caulinodans.the narrow host range bacterial strain azorhizobium caulinodans ors571 induces the formation of nitrogen-fixing nodules on the root and stem of the tropical legume sesbania rostrata. here, a new flavonoid-inducible locus of ors571 is described, locus 4. the locus was identified and isolated via the occurrence of particular sequences, the gamma and delta elements. these elements are reiterated in the ors571 genome, linked to symbiotic loci. sequencing of locus 4 showed the presence of an open rea ...19921472718
the rhizobium, bradyrhizobium, and azorhizobium nodc proteins are homologous to yeast chitin synthases.the nodabc genes of rhizobia are essential for the synthesis of lipo-oligosaccharidic (n-acylated chitin oligomers) nodulation signals. nodc gene products from rhizobium, bradyrhizobium, and azorhizobium exhibit extensive homology with chitin synthases, suggesting that the nodc proteins are involved in the synthesis of the chitin oligomer backbone by catalyzing the beta-1,4-linkage between n-acetyl-d-glucosamine residues.19921472721
conserved motifs in a divergent nod box of azorhizobium caulinodans ors571 reveal a common structure in promoters regulated by lysr-type proteins.nodulation of leguminous plants by rhizobium, bradyrhizobium, and azorhizobium spp. is dependent on the induction by the plant host of different bacterial nodulation (nod) loci. the transcription of these nod loci is activated in the presence of plant-produced flavonoids upon binding of the nodd protein--a lysr-type activator--to specific sequences present in the nod promoters. originally, a 47-base-pair (bp) region called the nod box was shown to be the target sequence for binding of nodd. from ...19921542656
systematic sequencing of the escherichia coli genome: analysis of the 0-2.4 min region.a contiguous 111,402-nucleotide sequence corresponding to the 0 to 2.4 min region of the e. coli chromosome was determined as a first step to complete structural analysis of the genome. the resulting sequence was used to predict open reading frames and to search for sequence similarity against the pir protein database. a number of novel genes were found whose predicted protein sequences showed significant homology with known proteins from various organisms, including several clusters of genes si ...19921630901
characterization of a novel azorhizobium caulinodans ors571 two-component regulatory system, ntry/ntrx, involved in nitrogen fixation and metabolism.azorhizobium caulinodans ors571 nifa regulation is partially mediated by the nitrogen regulatory gene ntrc. however, the residual nifa expression in ntrc mutant strains is still modulated by the cellular nitrogen and oxygen status. a second ntrc-homologous region, linked to ntrc, was identified and characterized by site-directed insertion mutagenesis and dna sequencing. tn5 insertions in this region cause pleiotropic defects in nitrogen metabolism and affect free-living as well as symbiotic nitr ...19911661370
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
regulation of nitrogen fixation in azorhizobium caulinodans: identification of a fixk-like gene, a positive regulator of nifa.the nucleotide sequence of a 1 kb fragment upstream of azorhizobium caulinodans fixl was established. an open reading frame of 744 bp was identified as a fixk homologue. a kanamycin cartridge was inserted into the cloned fixk-like gene and recombined into the host genome. the resulting mutant was nif-fix-, suggesting that fixk was required for nitrogen fixation both in symbiotic conditions and in the free-living state. using a pfixk-lacz fusion, the fixlj products were shown to control the expre ...19911766374
sequence and structural organization of a nif a-like gene and part of a nifb-like gene of herbaspirillum seropedicae strain z78.the deduced amino acid sequence derived from the sequence of a fragment of dna from the free-living diazotroph herbaspirillum seropedicae was aligned to the homologous protein sequences encoded by the nifa genes from azorhizobium caulinodans, rhizobium leguminosarum, rhizobium meliloti and klebsiella pneumoniae. high similarity was found in the central domain and in the c-terminal region. the h. seropedicae putative nifa sequence was also found to contain an interdomain linker similar to that co ...19911840608
nucleotide sequence of the fixabc region of azorhizobium caulinodans ors571: similarity of the fixb product with eukaryotic flavoproteins, characterization of fixx, and identification of nifw.the nucleotide sequence of a 4.1 kb dna fragment containing the fixabc region of azorhizobium caulinodans was established. the three gene products were very similar to the corresponding polypeptides of rhizobium meliloti. the c-terminal domains of both fixb products displayed a high degree of similarity with the alpha-subunits of rat and human electron transfer flavoproteins, suggesting a role for the fixb protein in a redox reaction. two open reading frames (orf) were found downstream of fixc. ...19911850088
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
novel organization of the common nodulation genes in rhizobium leguminosarum bv. phaseoli strains.nodulation by rhizobium, bradyrhizobium, and azorhizobium species in the roots of legumes and nonlegumes requires the proper expression of plant genes and of both common and specific bacterial nodulation genes. the common nodabc genes form an operon or are physically mapped together in all species studied thus far. rhizobium leguminosarum bv. phaseoli strains are classified in two groups. the type i group has reiterated nifhdk genes and a narrow host range of nodulation. the type ii group has a ...19911991718
cloning of azorhizobium caulinodans nicotinate catabolism genes and characterization of their importance in n2 fixation.twenty azorhizobium caulinodans vector insertion (vi) mutants unable to catabolize nicotinate (nic- phenotype) were identified and directly cloned as pvi plasmids. these pvi plasmids were used as dna hybridization probes to isolate homologous wild-type sequences. from subsequent physical mapping experiments, the nic::vi mutants defined four distinct loci. two, possibly three, of these loci are physically linked. a. caulinodans nic loci ii and iii encode the structural genes for nicotinate catabo ...19912002004
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
involvement of fixlj in the regulation of nitrogen fixation in azorhizobium caulinodans.a gene bank of azorhizobium caulinodans dna constructed in the bacteriophage lambda gem11 was screened with rhizobium meliloti fixl and fixj genes as probes. one positive recombinant phage, ors lambda l, was isolated. the nucleotide sequence of a 3.7 kb fragment was established. two open reading frames of 1512bp and 613bp were identified as fixl and fixj. kanamycin cartridges were inserted into the cloned fixl and fixj genes and recombined into the host genome. the resulting mutants were nif- fi ...19912046550
identification and characterization of a functional nodd gene in azorhizobium caulinodans ors571.azorhizobium caulinodans ors571, a bacterium capable of nodulating roots and stems of the tropical legume sesbania rostrata, has been shown to have no nodd-like gene located immediately upstream from its common nodabc locus. a clone carrying a functional nodd gene of strain ors571 has now been isolated from a plafr1 gene library by screening for naringenin-induced expression of the common nod genes in an agrobacterium background. tn5 mutagenesis of the cloned insert dna delimited the inducing ac ...19902158977
common nodabc genes in nod locus 1 of azorhizobium caulinodans: nucleotide sequence and plant-inducible expression.azorhizobium caulinodans strain ors571 induces nitrogen-fixing nodules on roots and stem-located root primordia of sesbania rostrata. two essential nod loci have been previously identified in the bacterial genome, one of which (nod locus 1) shows weak homology with the common nodc gene of rhizobium meliloti. here we present the nucleotide sequence of this region and show that it contains three contiguous open reading frames (orfa, orfb and orfc) that are related to the nodabc genes of rhizobium ...19892615763
the azorhizobium caulinodans nitrogen-fixation regulatory gene, nifa, is controlled by the cellular nitrogen and oxygen status.the nucleotide sequence of the azorhizobium caulinodans ors571 nifa locus was determined and the deduced nifa amino acid sequence compared with that of nifa from other nitrogen-fixing species. highly conserved domains, including helix-turn-helix and atp-binding motifs, and specific conserved residues, such as a cluster of cysteines, were identified. the nifa 5' upstream region was found to contain dna sequence motifs highly homologous to promoter elements involved in nifa/ntr-mediated control an ...19892664425
identification of dna regions homologous to nitrogen fixation genes nife, nifus and fixabc in azospirillum brasilense sp7.a 30 kb dna region from azospirillum brasilense sp7, containing the nitrogenase structural genes (nifhdk), has been cloned. the presence of nif genes, in the 20 kb located next to nifhdk, was explored by tn5 mutagenesis after subcloning various restriction fragments in the broad-host-range suicide vehicle psup202. over 25 mutations due to tn5 random insertions were obtained in the 20 kb and each recombined into the genome of strain sp7. four new nif loci were identified, located at about 4, 9, 1 ...19892695597
identification of cyclic intermediates in azorhizobium caulinodans nicotinate catabolism.in wild-type azorhizobium caulinodans ors571, nicotinate served both as anabolic substrate for nad+ production and as catabolic substrate for use as the n source. catabolic enzyme activities were greatest from cultures grown with nicotinate as the n source and least when cultures were grown with ammonium as the n source. vector insertion mutants unable to catabolize nicotinate (nic::vi mutants) still required micromolar quantities of this compound for growth. therefore, a. caulinodans wild type ...19892722754
characterization of the azorhizobium sesbaniae ors571 genomic locus encoding nadph-glutamate synthase.sixteen independent azorhizobium sesbaniae ors571 vector insertion (vi) mutants defective in ammonium assimilation (asm-) were selected; genomic dna sequences flanking the insertion endpoints were cloned directly. resulting recombinant plasmids were used to identify, by hybridization, corresponding wild-type dna sequences from an a. sesbaniae lambda embl3 genomic library (lambda asm phages). all 16 asm- vi mutants physically mapped to a single genomic locus. plasmid subclones of recombinant phag ...19882830230
mini-mulac transposons with broad-host-range origins of conjugal transfer and replication designed for gene regulation studies in rhizobiaceae.novel mini-mu derivatives were constructed, carrying a truncated laczya operon fused to the terminal 117 bp of the mu s-end, for the isolation of translational lac fusions by mini-mu-mediated insertion mutagenesis. different selectable markers (chloramphenicol resistance; gentamycin resistance) were introduced to allow selection for mini-mu insertions in different replicons and bacterial strains. a mini-mulac derivative carrying the site for conjugal transfer of plasmid rp4 (orit) and the origin ...19882838383
the azorhizobium caulinodans nifa gene: identification of upstream-activating sequences including a new element, the 'anaerobox'.from nucleotide sequencing analyses, the a. caulinodans nifa gene seems to be under dual control by the ntr (in response to available n) and fnr (in response to available o2) transcriptional activation/repression systems. because it fixes n2 in two contexts, the ntr system might regulate a. caulinodans nif gene expression ex planta, while the fnr system might similarly regulate in planta. as nifa upstream-activating elements, we have identified: (i) a gpnifa binding site allowing autogenous nifa ...19883186446
characterization of the fixabc region of azorhizobium caulinodans ors571 and identification of a new nitrogen fixation gene.the fast growing strain, azorhizobium caulinodans ors571, isolated from stem nodules of the tropical legume sesbania rostrata, can grow in the free-living state at the expense of molecular nitrogen. five point mutants impaired in nitrogen fixation in the free-living state have been complemented by a plasmid containing the cloned fix-abc region of strain ors571. genetic analysis of the mutants showed that one was impaired in fixc, one in fixa and the three others in a new gene, located upstream f ...19883216855
the fix escherichia coli region contains four genes related to carnitine metabolism.anaerobic carnitine metabolism in escherichia coli was recently shown to involve six genes organized in the cai operon and located at the first minute on the chromosome. the dna sequence lying at the 5' end of the cai locus was further investigated. it contains four open reading frames organized as an operon. in vivo overexpression of this dna region revealed four polypeptides with apparent molecular masses of 27, 33, 45 and 6 kda. these proteins displayed significant amino acid sequence homolog ...19957473063
biosynthesis of azorhizobium caulinodans nod factors. study of the activity of the nodabcs proteins by expression of the genes in escherichia coli.by in vitro and in vivo studies with escherichia coli expressing different combinations of the nodabcs genes of azorhizobium caulinodans, nod factor intermediates were identified and their structures determined using mass spectrometry. substrate-product relationships were studied by time course experiments, and the nod factor biosynthetic pathway was partially resolved. e. coli strains, harboring noda and/or nodb, did not produce nod metabolites, whereas the strain expressing nodc produced chito ...19957493950
nods is an s-adenosyl-l-methionine-dependent methyltransferase that methylates chitooligosaccharides deacetylated at the non-reducing end.in response to phenolic compounds exuded by the host plant, symbiotic rhizobium bacteria produce signal molecules (nod factors), consisting of lipochitooligosaccharides with strain-specific substitutions. in azorhizobium caulinodans strain ors571 these modifications are an o-arabinosyl group, an o-carbamoyl group, and an n-methyl group. several lines of evidence indicate that the nods gene located in the nodabcsuij operon is implicated in the methylation of nod factors. previously we have shown ...19957494487
an azorhizobium caulinodans ors571 locus involved in lipopolysaccharide production and nodule formation on sesbania rostrata stems and roots.azorhizobium caulinodans ors571 is able to nodulate roots and stems of the tropical legume sesbania rostrata. an ors571 tn5 insertion mutant, strain ors571-x15, had a rough colony morphology, was nonmotile, and showed clumping behavior on various media. when this pleiotropic mutant was inoculated on roots or stems of the host, no nodules developed (nod-). compared with the wild type, strain ors571-x15 produced lipopolysaccharides (lps) with an altered ladder pattern on sodium dodecyl sulfate-pol ...19947506708
photosynthetic symbionts of aeschynomene spp. form a cluster with bradyrhizobia on the basis of fatty acid and rrna analyses.the relationship between photosynthetic rhizobia that nodulate 10 aeschynomene species (aeschynomene afraspera, aeschynomene denticulata, aeschynomene evenia, aeschynomene indica, aeschynomene nilotica, aeschynomene pratensis, aeschynomene rudis, aeschynomene scabra, aeschynomene schimperi, and aeschynomene sensitiva) and reference strains of the genera bradyrhizobium, rhizobium, and azorhizobium was investigated by analyzing cellular fatty acid methyl esters (fame) and 16s rrna sequences. the m ...19947520731
genetic and phenetic analyses of bradyrhizobium strains nodulating peanut (arachis hypogaea l.) roots.seventeen bradyrhizobium sp. strains and one azorhizobium strain were compared on the basis of five genetic and phenetic features: (i) partial sequence analyses of the 16s rrna gene (rdna), (ii) randomly amplified dna polymorphisms (rapd) using three oligonucleotide primers, (iii) total cellular protein profiles, (iv) utilization of 21 aliphatic and 22 aromatic substrates, and (v) intrinsic resistances to seven antibiotics. partial 16s rdna analysis revealed the presence of only two rdna homolog ...19957538280
cloning of an azorhizobium caulinodans endoglucanase gene and analysis of its role in symbiosis.azorhizobium caulinodans ors571, a symbiont of the tropical leguminous plant sesbania rostrata, showed low, constitutive levels of endoglucanase (egl) activity. a clone carrying the gene responsible for this phenotype was isolated via introduction of a genomic library into the wild-type strain and screening for transconjugants with enhanced egl activity. by subcloning and expression in escherichia coli, the egl phenotype was allocated to a 3-kb ecori-bamhi fragment. however, sequence analysis sh ...19957574641
the nodd locus from azorhizobium caulinodans is flanked by two repetitive elements.the sequence surrounding the azorhizobium caulinodans (ac) regulatory nodd gene was analyzed. upstream from nodd and in the opposite orientation, two small open reading frames were identified (orf1 and orf2). the dna sequence corresponding to orf1, termed epsilon 1, is similar to a part of the insertion element is51 from pseudomonas savastanoi. immediately downstream from nodd, a repeated element, delta 1, has been described [goethals et al., mol. plant-microbe interact. 5 (1992) 405-411]. the e ...19957590297
effect of an ntrbc mutation on the posttranslational regulation of nitrogenase activity in rhodospirillum rubrum.homologs of ntrb and ntrc genes from rhodospirillum rubrum were cloned and sequenced. a mutant lacking ntrbc was constructed, and this mutant has normal nitrogenase activity under nif-derepressing conditions, indicating that ntrbc are not necessary for the expression of the nif genes in r. rubrum. however, the post-translational regulation of nitrogenase activity by adp-ribosylation in response to nh4+ was partially abolished in this mutant. more surprisingly, the regulation of nitrogenase activ ...19957665521
the rhizobium-plant symbiosis.rhizobium, bradyrhizobium, and azorhizobium species are able to elicit the formation of unique structures, called nodules, on the roots or stems of the leguminous host. in these nodules, the rhizobia convert atmospheric n2 into ammonia for the plant. to establish this symbiosis, signals are produced early in the interaction between plant and rhizobia and they elicit discrete responses by the two symbiotic partners. first, transcription of the bacterial nodulation (nod) genes is under control of ...19957708010
the molecular basis of the host specificity of the rhizobium bacteria.the interaction between soil bacteria belonging to the genera rhizobium, bradyrhizobium and azorhizobium and leguminous plants results in the induction of a new plant organ, the root nodule. after invading these root nodules via infection threads the bacteria start to fix atmospheric nitrogen into ammonia which is beneficial for the host plant. this symbiotic interaction is highly host-specific in that each rhizobial strain is able to associate with only a limited number of host plant species. t ...19947718036
bradyrhizobium japonicum nodulation genetics.studies of the genetics of nodulation by bradyrhizobium japonicum have revealed many similar features with rhizobium and azorhizobium species, but also apparent differences. the regulation of nod gene expression in b. japonicum is complex, involving the interplay of the positive regulator, nodd1, as well as a repressor, no1a. a unique feature of b. japonicum is the involvement of a two-component regulatory system, nodv and nodw, in the control of nod gene expression. it is not clear why b. japon ...19957737469
the fnr family of transcriptional regulators.homologues of the transcriptional regulator fnr from escherichia coli have been identified in a variety of taxonomically diverse bacterial species. despite being structurally very similar, members of the fnr family have disparate regulatory roles. those from shewanella putrefaciens, pseudomonas aeruginosa, pseudomonas stutzeri and rhodopseudomonas palustris are functionally similar to fnr in that they regulate anaerobic respiration or carbon metabolism. four rhizobial proteins (from rhizobium me ...19947747934
nicotinate catabolism is dispensable and nicotinate anabolism is crucial in azorhizobium caulinodans growing in batch culture and chemostat culture on n2 as the n source.when azorhizobium caulinodans was grown in chemostat cultures with n2 as the n source at a constant dilution rate of 0.1 h-1 in media with a constant concentration (50 mm) of succinate and variable concentrations (1.5 to 585 microm) of nicotinate, neither the growth yield on succinate, the specific rate of o2 consumption, nor the specific rate of co2 production showed linear regression with the concentration of nicotinate. moreover, for transient continuous cultures in which the nicotinate conce ...19957798152
structure and transcription of genes within the beta-hbd-adh1 region of clostridium acetobutylicum p262.the 1.2-kb dna fragment upstream of the linked beta-hbd (3-hydroxybutyryl-coa dehydrogenase) and adh1 (nadph-dependent alcohol dehydrogenase) genes from clostridium acetobutylicum p262 was sequenced. the upstream region contained an open reading frame (orfb) which was found to have 44% amino acid identity to the fixb gene products of rhizobium and azorhizobium. the beta-hbd and orfb genes were expressed during the acidogenic and solventogenic phases. the beta-hbd gene was transcribed on a single ...19957875566
dna sequence of a gene in escherichia coli encoding a putative tripartite transcription factor with receiver, atpase and dna binding domains.we have sequenced downstream of the last previously sequenced gene of the glucitol operon (gutabdmrq) in e. coli and have found that gutq is the last gene of this operon. downstream of the gutq gene is found a palindromic unit (pu or rep sequence), followed by a large open reading frame of 1515 (or possibly 1590) bps transcribed in the direction opposite to that of the gut operon. this open reading frame encodes a protein of 504 (or possibly 529) amino acids with a tripartite structure. the n-te ...19947894055
[the endotoxins of gram-negative bacteria: their structure and biological role].main attention in the paper is paid to the study of lipid a, a component possessing endotoxic activity. lipids a containing glucosamine disaccharide (representatives of enterobacteriaceae family), and variants of lipid a differing from the toxic one either in the structure of carbohydrate core or in the spectrum of fatty acids are considered. they are either phototrophic, nodulating (bradyrhyzobium species) or soil species (nitrobacter and thiobacillus) bacteria. lipid a from lipopolysaccharides ...19947952230
nucleotide sequence of the rhizobium etli nods gene.the complete nucleotide sequence of the nods gene from the bean-nodulating rhizobium etli, presumably encoding a methyltransferase, was determined. a phylogenetic analysis of five different nods proteins from three genera of gram- soil bacteria, azorhizobium, bradyrhizobium and rhizobium, was performed.19947959055
genetic regulation of nitrogen fixation in rhizobia.this review presents a comparison between the complex genetic regulatory networks that control nitrogen fixation in three representative rhizobial species, rhizobium meliloti, bradyrhizobium japonicum, and azorhizobium caulinodans. transcription of nitrogen fixation genes (nif and fix genes) in these bacteria is induced primarily by low-oxygen conditions. low-oxygen sensing and transmission of this signal to the level of nif and fix gene expression involve at least five regulatory proteins, fixl ...19947968919
root nodulation of sesbania rostrata.the tropical legume sesbania rostrata can be nodulated by azorhizobium caulinodans on both its stem and its root system. here we investigate in detail the process of root nodulation and show that nodules develop exclusively at the base of secondary roots. intercellular infection leads to the formation of infection pockets, which then give rise to infection threads. concomitantly with infection, cortical cells of the secondary roots dedifferentiate, forming a meristem which has an "open-basket" c ...19948106317
identification of nodulation genes (nod locus 5) from azorhizobium caulinodans ors571.an 800 bp acci-pucii dna containing promoter region of nodabc (p1) from a. caulinodans ors571 was cloned and used as a hybridization probe against the chromosome dna, which led to the identification of another 8.4-kb ecori fragment showing homology to p1. a corresponding clone of 8.4-kb dna was isolated from a plafi gene bank (prg90). the restriction enzyme analysis and dna-dna hybridization of 8.4-kb dna indicated the p1 homology was located in the 450-bp smai-sphi region (p2 region). omega ins ...19938136031
the nodc protein of azorhizobium caulinodans is an n-acetylglucosaminyltransferase.nod factors are signal molecules produced by azorhizobium, bradyrhizobium, and rhizobium species that trigger nodule formation in leguminous host plants. the backbone of nod factors consists of a beta-1,4-n-acetylglucosamine oligosaccharide from which the n-acetyl group at the nonreducing end is replaced by a fatty acid. the nodabc gene products are necessary for backbone biosynthesis. by incubation of cell extracts from azorhizobium caulinodans with radioactive uridine diphosphate-n-acetylgluco ...19948146173
functional analysis of the fixnoqp region of azorhizobium caulinodans.the deduced amino acid sequences of four open reading frames identified upstream of the fixghi region in azorhizobium caulinodans are very similar to the putative terminal oxidase complex coded by the fixnoqp operons from rhizobium meliloti and bradyrhizobium japonicum. the expression of the a. caulinodans fixnoqp genes, which was maximal under microaerobiosis, was positively regulated by fixk and independent of nifa. in contrast to the fix- phenotype of b. japonicum and r. meliloti fixn mutants ...19948169204
the expression of nifa in azorhizobium caulinodans requires a gene product homologous to escherichia coli hf-i, an rna-binding protein involved in the replication of phage q beta rna.we report the characterization of a mutant of azorhizobium caulinodans, isolated after ethyl methanesulfonate mutagenesis. this nod+ nif- fix- mutant is unable to synthesize 10 of 15 polypeptides normally induced under conditions of nitrogen fixation. by using lacz fusions it was shown that nifa and nifa-regulated genes were not expressed in this strain. the mutation was complemented by a constitutively expressed nifa gene or by a 1.1-kb dna fragment from the wild-type strain, whose nucleotide s ...19948197116
proposal for rejection of agrobacterium tumefaciens and revised descriptions for the genus agrobacterium and for agrobacterium radiobacter and agrobacterium rhizogenes.the 16s rrna sequences of seven representative agrobacterium strains, eight representative rhizobium strains, and the type strains of azorhizobium caulinodans and bradyrhizobium japonicum were determined. these strains included the type strains of agrobacterium tumefaciens, agrobacterium rhizogenes, agrobacterium radiobacter, agrobacterium vitis, agrobacterium rubi, rhizobium fredii, rhizobium galegae, rhizobium huakuii, rhizobium leguminosarum, rhizobium loti, rhizobium meliloti, and rhizobium ...19938240952
in situ determination of the reduction levels of cytochromes b and c in growing bacteria: a case study with n2-fixing azorhizobium caulinodans.the determination of the in situ reduction levels of cytochromes b and c in growing bacteria is achieved by coupling a chemostat with a dual wavelength spectrophotometer. visible light absorption spectra of cytochromes present in bacterial cells actively growing in a chemostat at a specific growth rate of 0.1 h-1 are recorded. this is accomplished by transporting the emitted light from the spectrophotometer via glass fibers to one side of the chemostat vessel and detecting the transmitted light ...19938250218
interaction of a rhizobial dna-binding protein with the promoter region of a plant leghemoglobin gene.a nucleotide sequence was identified approximately 650 bp upstream of the sesbania rostrata leghemoglobin gene srglb3 start codon, which interacts specifically with a proteinaceous dna-binding factor found in nodule extracts but not in extracts from leaves or roots. the binding site for this factor was delimited using footprinting techniques. the dna-binding activity of this factor was found to be heat stable, dependent on divalent cations, and derived from the (infecting) azorhizobium caulinoda ...19938278541
role of the fixghi region of azorhizobium caulinodans in free-living and symbiotic nitrogen fixation.a 19-kb dna region containing genes sharing homology with rhizobium meliloti fixnoqp and fixghi was isolated from a genomic library of azorhizobium caulinodans. identity of fixg was confirmed by partial nucleotide sequencing. mutant strains in the fixghi region were constructed by deletion or tn5 insertions. in contrast with the situation in r. meliloti, the mutants still displayed a significant nitrogenase activity in symbiosis.19938282187
azorhizobium caulinodans respires with at least four terminal oxidases.in culture, azorhizobium caulinodans used at least four terminal oxidases, cytochrome aa3 (cytaa3), cytd, cyto, and a second a-type cytochrome, which together mediated general, respiratory electron (e-) transport to o2. to genetically dissect physiological roles for these various terminal oxidases, corresponding azorhizobium apocytochrome genes were cloned, and three cytaa3 mutants, a cytd mutant, and a cytaa3, cytd double mutant were constructed by reverse genetics. these cytochrome oxidase mut ...19948300541
enzyme polymorphism of azorhizobium strains and other stem- and root-nodulating bacteria isolated from sesbania rostrata.relationships between bacterial groups nodulating sesbania rostrata were evaluated through examination of electrophoretic polymorphism of esterases and metabolic enzymes. the following conclusions were drawn: (i) the differentiation of two genomic species within azorhizobium strains and a group of non-identified strains (probably rhizobium) was strongly supported by enzyme electrophoresis; (ii) esterases were more electrophoretically polymorphic than metabolic enzymes, since 35 and 11 electropho ...19938327783
characterization of the ntrbc genes of azospirillum brasilense sp7: their involvement in the regulation of nitrogenase synthesis and activity.a 7.1 kb ecori fragment from azospirillum brasilense, that hybridized with a probe carrying the ntrbc genes from bradyrhizobium japonicum, was cloned. the nucleotide sequence of a 3.8 kb subfragment was established. this led to the identification of two open reading frames, encoding polypeptides of 401 and 481 amino acids, that were similar to ntrb and ntrc, respectively. a broad host range plasmid containing the putative azospirillum ntrc gene was shown to restore nitrogen fixation under free-l ...19938355653
cloning and sequence of the rhizobium leguminosarum biovar phaseoli fixa gene.we report the identification and cloning of rhizobium leguminosarum biovar phaseoli fixabcx homologous genes and the complete nucleotide sequence of the fixa gene. the corresponding gene product is highly homologous to the rhizobium meliloti and azorhizobium caulinodans fixa proteins. putative ntra- and nifa-binding sites are identified in the fixa promoter region.19938369342
identification of nodsuij genes in nod locus 1 of azorhizobium caulinodans: evidence that nods encodes a methyltransferase involved in nod factor modification.the azorhizobium caulinodans strain ors571 nodulation genes nodsuij were located downstream from nodabc. complementation data and transcriptional analysis suggest that nodabcsuij form a single operon. mutants with tn5 insertions in the genes nods, nodu, and nodj were delayed in nodulation of sesbania rostrata roots and stems. the nods amino acid sequences of ors571, bradyrhizobium japonicum, and rhizobium sp. strain ngr234, contain a consensus with similarity to s-adenosylmethionine (sam)-utiliz ...19938412659
three unusual modifications, a d-arabinosyl, an n-methyl, and a carbamoyl group, are present on the nod factors of azorhizobium caulinodans strain ors571.azorhizobium caulinodans strain ors571 is a symbiont of the tropical legume sesbania rostrata. upon nod gene induction with naringenin, strain ors571 secretes into the culture medium nod factors that morphologically change the host plant--in particular, deformed root hairs (hai/had) and meristematic foci are formed at the basis of lateral roots. the latter infrequently develop further into nodule-like structures. the azorhizobial nod factors are chitin tetramers or pentamers, n-acylated at the n ...19938434016
azorhizobium caulinodans nitrogen fixation (nif/fix) gene regulation: mutagenesis of the nifa -24/-12 promoter element, characterization of a ntra(rpon) gene, and derivation of a model.using site-directed mutagenesis, mutations were introduced in the -24/-12 promoter element of the azorhizobium caulinodans nifa gene, and chimeric nifa-lacz reporter gene fusions were constructed. single base-pair mutations in the conserved -25 or -13 g residues were found to reduce or abolish nifa promoter activity, respectively, demonstrating that the -24/-12 promoter element is important for nifa gene expression and suggesting the involvement of a sigma 54 (ntra/rpon)-type transcription facto ...19938471796
phylogenetic analysis of rhizobia and agrobacteria based on 16s rrna gene sequences.the phylogenetic relationships of members of the genera rhizobium, agrobacterium, bradyrhizobium, and azorhizobium were studied by direct sequencing of their amplified 16s rrna genes. comparative analysis of the sequence data confirmed that the genera bradyrhizobium and azorhizobium belong to distinct phylogenetic lineages. the genera rhizobium and agrobacterium were found to be phylogenetically heterogeneous, and several subgroupings in which rhizobium and agrobacterium species were intermixed ...19938494742
identification of a nifw-like gene in azospirillum brasilense.a small orf, 5' upstream of the fixabc operon in azospirillum brasilense sp7, has been identified. sequence comparison shows significant homology to the azotobacter vinelandii and azorhizobium caulinodans nifw gene.19938504172
cdna cloning and mitochondrial import of the beta-subunit of the human electron-transfer flavoprotein.we have isolated a cdna clone which encodes the entire beta-subunit of human electron-transferring flavoprotein (etf) by screening an expression library from human liver using polyclonal antibodies against porcine etf. this cdna encodes a protein of 255 amino-acid residues with a predicted molecular mass of 27,877 da which shows a high degree of similarity with partial amino-acid sequences obtained from both rat liver and paracoccus denitrificans beta-etf. northern-blot analysis shows that the h ...19938504797
interactive regulation of azorhizobium nifa transcription via overlapping promoters.the azorhizobium nifa promoter (pnifa) is positively regulated by two physiological signal transduction pathways, ntrbc, which signals anabolic n status, and fixljk, which signals prevailing o2 status. yet, pnifa response (gene product per unit time) to these two activating signals together is more than twice that of the summed, individual signals. in the absence of nifa, a negative pnifa autoregulator, the fully induced pnifa response is more than 10-fold greater than that of summed, individual ...19958522530
structural and functional analysis of the fixlj genes of rhizobium leguminosarum biovar phaseoli cnpaf512.the fixlj genes of rhizobium leguminosarum biovar phaseoli cnpaf512 were identified by dna hybridization of a genomic library with an internal fragment of the rhizobium meliloti fixj gene. the nucleotide sequence was determined and the corresponding amino acid sequence was aligned with the amino acid sequences of the fixl proteins of r. meliloti, bradyrhizobium japonicum and azorhizobium caulinodans. while the fixj protein and the carboxy-terminal part of the fixl protein are highly homologous t ...19958552028
a new root-nodulating symbiont of the tropical legume sesbania, rhizobium sp. sin-1, is closely related to r. galegae, a species that nodulates temperate legumes.rhizobium sp. sin-1, isolated in india from root nodules on the tropical legume sesbania aculeata, also induces nitrogen-fixing nodules on roots of s. macrocarpa, s. speciosa, s. procumbens, s. punicea, s. rostrata, and vigna unguiculata. unlike azorhizobium caulinodans, sin-1 does not induce stem nodules on s. rostrata. the nodules induced by sin-1 develop exclusively at the bases of secondary roots. electron microscopic studies of mature nodule sections revealed rhizobia within intercellular s ...19958593950
isolation of monoclonal antibodies reacting with the core component of lipopolysaccharide from rhizobium leguminosarum strain 3841 and mutant derivatives.monoclonal antibodies reacting with the core oligosaccharide or lipid a component of rhizobium lipopolysaccharide (lps) could be useful for the elucidation of the structure and biosynthesis of this group of macromolecules. mutant derivatives of rhizobium leguminosarum 3841 with lps structures lacking the major o-antigen moiety were used as immunogens, and eight antibodies were selected for further study. all the antibodies reacted with the fast-migrating species known as lps-2 following gel elec ...19968631658
use of differential display to identify novel sesbania rostrata genes enhanced by azorhizobium caulinodans infection.upon infection of the tropical legume sesbania rostrata with azorhizobium caulinodans ors571, nodules are formed on the roots as well as on the stems. stem nodules appear at multiple predetermined sites consisting of dormant root primordia, which are positioned in vertical rows along the stem of the plant. we used the differential display method to isolate and characterize three cdna clones (differential display; didi-2, didi-13, and didi-20), corresponding to genes whose expression is enhanced ...19958664492
a region of a sym plasmid of rhizobium leguminosarum biovar phaseoli has similarity to prokaryotic insertion sequences and to eukaryotic integrases.near the nod and nif genes of the sym plasmid prp2ji of rhizobium leguminosarum biovar phaseoli are three open reading frames whose deduced polypeptide products have similarities to those of genes in bacterial insertion sequences. the similarity of one of these orfs was significantly greater to that of the integrase region of pol proteins of eukaryotic retroviruses and transposable elements in animals and plants than it was to the transposases of prokaryotic insertion sequences. in the noncoding ...19968700965
role of nodl and nodj in lipo-chitooligosaccharide secretion in azorhizobium caulinodans and escherichia coli.lipo-chitooligosaccharide (lco) nod factors are produced and secreted by rhizobia and trigger nodule development in leguminous host plants. the products of the bacterial nodlj genes are related to transporters of capsular polysaccharides and were proposed to be involved in lco transport. we have studied nodlj of azorhizobium caulinodans ors571 by analysis of cell-associated and secreted radioactively labelled nod factors in wild-type ors571, a nodj mutant and a complemented strain. secretion was ...19968809752
yst gene expression in yersinia enterocolitica is positively regulated by a chromosomal region that is highly homologous to escherichia coli host factor 1 gene (hfq).yersinia enterocolitica produces heat-stable enterotoxin (y-st) as one of its virulence factors. the yst gene, however, frequently and spontaneously becomes inactive (silent) during storage, which is accompanied by concurrent changes in some biological properties such as colony morphology, growth rate, carbon fermentation and ornithine decarboxylase activity. northern blot analysis revealed that the level of mrna for yst was repressed. to investigate the regulatory region, we transformed a yst-s ...19958825090
self-transmissible nif plasmid (pea9) of enterobacter agglomerans 339: molecular cloning and evidence for the existence of similar nif clusters on dissimilar plasmids in enterobacter strains.a cosmid library was generated to the 200-kb self-transmissible nif plasmid pea9 isolated from enterobacter agglomerans 339. the cosmid clone identified to contain the complete nif cluster was used to determine the nif gene organization and the physical map. the restriction pattern and nif gene organization of this nif cluster showed remarkable similarities to the nif cluster identified on the 110-kb plasmid pea3 of enterobacter agglomerans 333. nucleotide sequence of several randomly selected r ...19958825375
azorhizobium caulinodans uses both cytochrome bd (quinol) and cytochrome cbb3 (cytochrome c) terminal oxidases for symbiotic n2 fixation.azorhizobium caulinodans employs both cytochrome bd (cytbd; quinol oxidase) and cytcbb3 (cytc oxidase) as terminal oxidases in environments with very low o2 concentrations. to investigate physiological roles of these two terminal oxidases both in microaerobic culture and in symbiosis, knockout mutants were constructed. as evidenced by visible absorbance spectra taken from mutant bacteria carrying perfect gene replacements, both the cytbd- and cytcbb3- mutations were null alleles. in aerobic cult ...19968830696
rhizobium leguminosarum bv. viciae contains a second fnr/fixk-like gene and an unusual fixl homologue.genes of rhizobium leguminosarum bv. viciae vf39 coding for the regulatory elements nifa, fixl and fixk were isolated, sequenced and genetically analysed. the fixk-fixl region is located upstream of the fixnoqp operon on the non-nodulation plasmid prlevf39c. the deduced amino acid sequence of fixl revealed an unusual structure in that it contains a receiver module (homologous to the n-terminal domain of response regulators) fused to its transmitter domain. an oxygen-sensing haem-binding domain, ...19968858582
fucosylation and arabinosylation of nod factors in azorhizobium caulinodans: involvement of nolk, nodz as well as noec and/or downstream genes.the dna region downstream of the nodabcsuij operon of azorhizobium caulinodans was further characterized and two new genes, nodz and noec were identified in the same operon. the a. caulinodans wild-type strain produces a population of nod factors that, at the reducing end, are either unmodified or carry a d-arabinosyl and/or an l-fucosyl branch. nod factors produced by tn5-insertion mutants in nodz, noec, and the separate nolk locus, were analysed by thin-layer chromatography and mass spectromet ...19968858594
the genetic and biochemical basis for nodulation of legumes by rhizobia.soil bacteria of the genera azorhizobium, bradyrhizobium, and rhizobium are collectively termed rhizobia. they share the ability to penetrate legume roots and elicit morphological responses that lead to the appearance of nodules. bacteria within these symbiotic structures fix atmosphere nitrogen and thus are of immense ecological and agricultural significance. although modern genetic analysis of rhizobia began less than 20 years ago, dozens of nodulation genes have now been identified, some in m ...19968935908
expression of cell cycle genes during sesbania rostrata stem nodule development.upon infection of sesbania rostrata with azorhizobium caulinodans, nodules are formed on roots and stems. stem nodules develop from abundantly distributed dormant root primordia. to acquire more insight into the meristem organization during stem nodule development, the expression patterns of a mitotic b1-type cyclin gene (sesro; cycb1;1), a cyclin-dependent kinase gene (cdc-2-1sr), and a histone h4 gene (h4-1sr) of s. rostrata were followed by in situ hybridization. cdc2-1sr transcripts were fou ...19979100377
xanthobacter tagetidis sp. nov., an organism associated with tagetes species and able to grow on substituted thiophenes.members of the marigold genus of flowering plants (the genus tagetes), which synthesize and accumulate thiophene compounds in their roots, were investigated as potential sources of bacteria able to degrade substituted thiophenes. batch and continuous enrichment cultures inoculated with compost from root balls of tagetes patula and tagetes erecta reproducibly produced the same predominant type of bacterium when they were supplied with thiophene-2-carboxylate (t2c) or thiophene-2-acetate (t2a) as ...19979103627
bacterial nodulation protein nodz is a chitin oligosaccharide fucosyltransferase which can also recognize related substrates of animal origin.the nodz gene, which is present in various soil bacteria such as bradyrhizobium japonicum, azorhizobium caulinodans, and rhizobium loti, is involved in the addition of a fucosyl residue to the reducing n-acetylglucosamine residue of lipochitin oligosaccharide (lco) signal molecules. using an escherichia coli strain that produces large quantities of the nodz protein of b. japonicum, we have purified the nodz protein to homogeneity. the purified nodz protein appears to be active in an in vitro tra ...19979113990
characterization of azorhizobium caulinodans glnb and glna genes: involvement of the p(ii) protein in symbiotic nitrogen fixation.the nucleotide sequence and transcriptional organization of azorhizobium caulinodans ors571 glna, the structural gene for glutamine synthetase (gs), and glnb, the structural gene for the p(ii) protein, have been determined. glnb and glna are organized as a single operon transcribed from the same start site, under conditions of both nitrogen limitation and nitrogen excess. this start site may be used by two different promoters since the expression of a glnb-lacz fusion was high in the presence of ...19979171403
germination, growth, and nodulation of sesbania rostrata grown in pb/zn mine tailings/ this study examined the possibility of growth, nodulation, and nitrogen accumulation of sesbania rostrata in pure and amended pb/zn tailings. about 90% of seeds of s. rostrata germinated in pure pb/zn tailings, which contained high concentrations of pb, zn, cu, and cd. although seedling growth suffered from the adverse environment of pb/zn tailings, they became established on tailings stands, in the greenhouse, as well as on the actual tailings dam, and completed their life cycle in 4 months. ...19979175548
the nodulation gene nolk of azorhizobium caulinodans is involved in the formation of gdp-fucose from gdp-mannose.the nolk gene of azorhizobium caulinodans is essential for the incorporation of a fucosyl group in nod factors. a nad(p)-binding site is present in the nolk amino acid sequence and the gene is homologous to escherichia coli genes, presumably involved in gdp-fucose synthesis. protein extracts of a. caulinodans, overexpressing nolk, have an enzyme activity that synthesizes gdp-fucose from gdp-mannose. nolk most probably encodes a 4-reductase performing the last step in gdp-fucose synthesis. wild-t ...19979202168
specific flavonoids promote intercellular root colonization of arabidopsis thaliana by azorhizobium caulinodans ors571.the ability of azorhizobium caulinodans ors571 and other diazotrophic bacteria to internally colonize roots of arabidopsis thaliana has been studied. strains tagged with lacz or gusa reporter genes were used, and the principal colonization sites were found to be the points of emergence of lateral roots, lateral root cracks (lrcs). high frequencies of colonization were found; 63 to 100% of plants were colonized by ors571, and 100% of plants were colonized by herbaspirillum seropedicae. after lrcs ...19979204562
nod factors of azorhizobium caulinodans strain ors571 can be glycosylated with an arabinosyl group, a fucosyl group, or both.in addition to the previously described arabinosylated nod factors, azorhizobium caulinodans can also produce fucosylated nod factors and nod factors that are both arabinosylated and fucosylated. the presence of a plasmid carrying extra copies of a subset of nod genes as well as bacterial growth conditions influence the relative proportion of carbamoylated, fucosylated, and arabinosylated nod factors. by using a root hair formation assay, we demonstrate that the nod factor glycosylations are imp ...19979204572
differential regulation by the homologous response regulators narl and narp of escherichia coli k-12 depends on dna binding site arrangement.the narl and narp proteins are homologous response regulators of escherichia coli that control the expression of several operons in response to nitrate and nitrite. a consensus heptameric narl dna-binding sequence has been identified, and previous observations suggest that the narp protein has a similar sequence specificity. however, some operons are regulated by narl alone, whereas others are controlled by both narl and narp. in this study, dnase i footprinting experiments with the fdng, nirb a ...19979302020
characterization of two plasmid-borne lps beta loci of rhizobium etli required for lipopolysaccharide synthesis and for optimal interaction with plants.in rhizobium etli cfn42, both the symbiotic plasmid (pd) and plasmid b (pb) are required for effective bean nodulation. this is due to the presence on pb of a region (lps beta) involved in lipopolysaccharide (lps) biosynthesis. we report here the genetic array and functional features of this plasmid-borne region. the sequence analysis of a 3,595-bp fragment revealed the presence of a transcriptional unit integrated by two open reading frames (lps beta 1 and lps beta 2) essential for lps biosynth ...19979304861
the azotobacter vinelandii alg8 and alg44 genes are essential for alginate synthesis and can be transcribed from an algd-independent promoter.a 2.8-kb dna region, located immediately downstream of algd, contains the a. vinelandii alg8 and alg44 genes, whose sequences are highly homologous to those of the corresponding pseudomonas aeruginosa genes. these genes occur on a transcript that does not include algd, and are transcribed from a promoter different from that transcribing algd; this is the fourth promoter described within the alginate biosynthetic gene cluster. alg8 and alg44 mutants were constructed and shown to be completely imp ...19979358065
effect of combined nitrogen on the expression of nitrate reductase and nitrite reductase in azorhizobium caulinodans.in aerobically grown azorhizobium caulinodans strain irbg 46, in vivo expression of nitrate reductase (nr) and nitrite reductase (nir) requires the presence of either nitrate or nitrite. on the contrary mere microaerobic conditions are sufficient for the expression of nr and nir, however, addition of nitrate to the growth medium enhanced the activities of the enzymes. optimum concentration of nitrate for maximum expression of nr and nir activities was different in aerobic and microaerobic condit ...19979475063
effect of nitrate on nitrogen fixation and nitrate assimilation in azorhizobium-sesbania rostrata symbiotic system.root nodule formation was inhibited by 30% and 50% respectively at low concentration of 1 mm and 2 mm nitrate, while stem nodule formation was enhanced by 50% only at 1 mm nitrate. the nodule specific nitrogenase activity decreased with the increasing concentration of nitrate. at 1 mm nitrate nitrogenase activity per plant stem nodule was not affected, but it was less than 50% in the root nodules as compared to control. increasing concentration of nitrate increased in vivo activity of nitrate re ...19979475064
periplasmic nitrate-reducing system of the phototrophic bacterium rhodobacter sphaeroides dsm 158: transcriptional and mutational analysis of the napkefdabc gene cluster.the phototrophic bacterium rhodobacter sphaeroides dsm 158 is able to reduce nitrate to nitrite by means of a periplasmic nitrate reductase which is induced by nitrate and is not repressed by ammonium or oxygen. recently, a 6.8 kb psti dna fragment carrying the napabc genes coding for this periplasmic nitrate-reducing system was cloned [reyes, roldán, klipp, castillo and moreno-vivián (1996) mol. microbiol. 19, 1307-1318]. further sequence and genetic analyses of the dna region upstream from the ...19989560320
the rhizobium etli fixl protein differs in structure from other known fixl proteins.the central heme-binding domain in the fixl proteins of sinorhizobium meliloti, bradyrhizobium japonicum, rhizobium leguminosarum biovar viciae and azorhizobium caulinodans, is highly conserved. the similarity with the corresponding domain in the rhizobium etli fixl protein is considerably less. this observation prompted us to analyze the heme-binding capacities of the r. etli fixl protein. the r. etli fixl gene was overexpressed in escherichia coli. in the presence of s. meliloti fixj, the over ...19989563844
expression of rhizobium meliloti symbiotic promoters in azorhizobium caulinodans.plasmids containing rhizobium meliloti symbiotic promoters p1 (promoter of nifhdk) and p2 (promoter of fixabcx) when mobilized into the cells of azorhizobium caulinodans strain irbg 46 showed strong expression of these promoters under free-living microaerobic as well as symbiotic conditions. under free-living conditions microaerobiosis (3% or less o2) was found to be sufficient to activate these promoters; expression being higher at 1% than at 3% o2 concentration. under symbiotic conditions the ...19979567770
the symbiotic interaction between azorhizobium caulinodans and sesbania rostrata molecular cross-talk in a beneficial plant-bacterium interaction. 19989594646
patterns of enod40 gene expression in stem-borne nodules of sesbania rostrata.at the base of adventitious root primordia, located on the stem of the tropical legume sesbania rostrata, nitrogen-fixing nodules are formed upon inoculation with the microsymbiont azorhizobium caulinodans. this pattern of nodule development presents features of indeterminate and determinate nodules in early and later stages, respectively. a s. rostrata cdna clone homologous to early nodulin enod40 genes was isolated from a cdna library of developing stem nodules. srenod40-1 contained the conser ...19989620265
the control of azorhizobium caulinodans nifa expression by oxygen, ammonia and by the hf-i-like protein, nrfa.the control of azorhizobium caulinodans nifa expression in response to oxygen and ammonia involves fixlj, fixk, ntrbc, ntrxy and the hf-i-like protein nrfa. the regulation is thus complex and possibly involves post-transcriptional regulation by nrfa. the coding region of nifa was determined using a translational lacz fusion and by site-directed mutagenesis to identify which of four in frame aug codons was used. the major nifa protein is translated from the second aug codon and is predicted to co ...19989632262
Displaying items 1 - 100 of 257