ABC transport is inactivated by the PTS(Ntr) under potassium limitation in Rhizobium leguminosarum 3841.

PTS(Ntr) is a regulatory phosphotransferase system in many bacteria. Mutation of the PTS(Ntr) enzymes causes pleiotropic growth phenotypes, dry colony morphology and a posttranslational inactivation of ABC transporters in Rhizobium leguminosarum 3841. The PTS(Ntr) proteins EI(Ntr) and 2 copies of EIIA(Ntr) have been described previously.

Soil factors exhibit greater influence than bacterial inoculation on alfalfa growth and nitrogen fixation.

In order to study the effects of soil factors and bacterial inoculation on alfalfa (Medicago sativa), plants were inoculated with Ensifer meliloti L33 and Azospirillum brasilense Sp7 in pot experiments using two different soils separately as well as in a mixture. One soil was contaminated with chemical waste products; the other was an arable soil. Soil factors, including the availability of macro- and micronutrients as well as carbon and nitrogen contents, were found to exhibit a much greater influence on the growth of alfalfa than any of the inoculations.

Direct amplification of rhizobial nodC sequences from soil total DNA and comparison to nodC diversity of root nodule isolates.

A group-specific primer set was developed using nodC as a target gene for the amplification of rhizobial sequence diversity from nodule isolates and total soil DNA preparations. The primer set was tested on 209 nodule isolates, recovered from six different trap plant species which were grown in two soil samples collected from a chickpea and a wheat field site in India. We also amplified and cloned PCR products from total DNA isolated from the same soil samples.

The degradation of alpha-quaternary nonylphenol isomers by Sphingomonas sp. strain TTNP3 involves a type II ipso-substitution mechanism.

The degradation of radiolabeled 4(3',5'-dimethyl-3'-heptyl)-phenol [nonylphenol (NP)] was tested with resting cells of Sphingomonas sp. strain TTNP3. Concomitantly to the degradation of NP, a metabolite identified as hydroquinone transiently accumulated and short-chain organic acids were then produced at the expense of hydroquinone.

The C-terminal receiver domain of the Rhizobium leguminosarum bv. viciae FixL protein is required for free-living microaerobic induction of the fnrN promoter.

The Rhizobium leguminosarum bv. viciae VF39 FixL protein belongs to a distinct group of hybrid regulatory sensor proteins that bear a covalently linked C-terminal receiver domain. FixL has an unorthodox histidine kinase domain, which is shared with many other hybrid regulators.

Regulation of L-alanine dehydrogenase in Rhizobium leguminosarum bv. viciae and its role in pea nodules.

Alanine dehydrogenase (AldA) is the principal enzyme with which pea bacteroids synthesize alanine de novo. In free-living culture, AldA activity is induced by carboxylic acids (succinate, malate, and pyruvate), although the best inducer is alanine. Measurement of the intracellular concentration of alanine showed that AldA contributes to net alanine synthesis in laboratory cultures.

Developmental downregulation of rhizobial genes as a function of symbiosome differentiation in symbiotic root nodules of Pisum sativum.

•  The expression of nodA and dctA genes of Rhizobium leguminosarum bv. viciae has been studied in mutant nodules of pea (Pisum sativum L.), blocked at the following developmental stages: infection thread development inside the nodule (Itn); infection droplet differentiation (Idd); bacteroid differentiation after endocytosis (Bad); and nodule persistence (Nop).

Genetic dissection of the initiation of the infection process and nodule tissue development in the Rhizobium-pea (Pisum sativum L.) symbiosis.

Twelve non-nodulating pea (Pisum sativum L.) mutants were studied to identify the blocks in nodule tissue development. In nine, the reason for the lack of infection thread (IT) development was studied; this had been characterized previously in the other three mutants.

The Rhizobium leguminosarum bv. viciae VF39 gamma-aminobutyrate (GABA) aminotransferase gene (gabT) is induced by GABA and highly expressed in bacteroids.

A Rhizobium leguminosarum bv. viciae VF39 gene (gabT) encoding a gamma-aminobutyrate (GABA) aminotransferase was identified, cloned and characterized. This gene is thought to be involved in GABA metabolism via the GABA shunt pathway, a theoretical bypass of the 2-oxoglutarate dehydrogenase complex.

Characterisation of Phaseolus symbionts isolated from Mediterranean soils and analysis of genetic factors related to pH tolerance.

The ultimate objective of PhIMED, in which two European (Germany, Italy) and two Mediterranean (Morocco, Egypt) countries collaborate, is to improve the cultivation of French bean (Phaseolus vulgaris) under arid and semi-arid conditions by analysing and enhancing stress tolerance of the nitrogen fixing rhizobial microsymbionts. Rhizobial strains nodulating P. vulgaris (RP strains) isolated from areas in Morocco frequently subjected to drought were analysed for their salt and pH tolerance and their phylogenetic relationship.

Genetic diversity of indigenous Rhizobium leguminosarum bv. viciae isolates nodulating two different host plants during soil restoration with alfalfa.

A total of 360 Rhizobium leguminosarum bv. viciae strains was isolated from three brown-coal mining restoration fields of different age and plant cover (without and in the first and second year of alfalfa, Medicago sativa, cultivation) using two host species (Vicia hirsuta and Pisum sativum) as capture plants. The strains were genetically typed by restriction fragment length polymorphism analysis of polymerase chain reaction (PCR)-generated 16S-23S ribosomal DNA intergenic spacer regions (IGS-RFLP) and characterized by plasmid profiles and RFLP analysis of amplified nodABC genes.

Effect of mutations in Pisum sativum L. genes blocking different stages of nodule development on the expression of late symbiotic genes in Rhizobium leguminosarum bv. viciae.

In this report, the expression of late symbiotic genes (fnrN, fixN, and nifA) of Rhizobium leguminosarum bv. viciae was studied in nodules of mutant pea lines blocked at four successive stages of nodule development. Bacterial gene expression was analyzed in situ with transcriptional gusA reporter gene fusions.

Symbiotic plasmid rearrangement in Rhizobium leguminosarum bv. viciae VF39SM.

A rearrangement between the symbiotic plasmid (pRleVF39d) and a nonsymbiotic plasmid (pRleVF39b) in Rhizobium leguminosarum bv. viciae VF39 was observed. The rearranged derivative showed the same plasmid profile as its parent strain, but hybridization to nod, fix, and nif genes indicated that most of the symbiotic genes were now present on a plasmid corresponding in size to pRleVF39b instead of pRleVF39d.

The Rhizobium leguminosarum bv. viciae glnD gene, encoding a uridylyltransferase/uridylyl-removing enzyme, is expressed in the root nodule but is not essential for nitrogen fixation.

A Rhizobium leguminosarum bv. viciae VF39 gene (glnD) encoding the uridylyltransferase/uridylyl-removing enzyme, which constitutes the sensory component of the nitrogen regulation (ntr) system, was identified, cloned and characterized. The deduced amino acid sequence contains the conserved active site motif of the nucleotidyltransferase superfamily and is highly homologous to the glnD gene products of other bacterial species.

Unusual structure of the tonB-exb DNA region of Xanthomonas campestris pv. campestris: tonB, exbB, and exbD1 are essential for ferric iron uptake, but exbD2 is not.

The nucleotide sequence of a 3.6-kb HindIII-SmaI DNA fragment of Xanthomonas campestris pv. campestris revealed four open reading frames which, based on sequence homologies, were designated tonB, exbB, exbD1, and exbD2.

Functional and regulatory analysis of the two copies of the fixNOQP operon of Rhizobium leguminosarum strain VF39.

DNA corresponding to two copies of the Rhizobium leguminosarum bv. viciae strain VF39 fixNOQP operon coding for a putative symbiotic terminal oxidase of the heme-copper oxidase superfamily was cloned, sequenced, and genetically analyzed. The first copy is located upstream of the fixK-fixL region on plasmid pRleVF39c, whereas the second copy resides on the nodulation plasmid pRleVF39d.

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.

A homolog of the Rhizobium meliloti nitrogen fixation gene fixN is involved in the production of a microaerobically induced oxidase activity in the phytopathogenic bacterium Agrobacterium tumefaciens.

Hybridization analysis using the Rhizobium meliloti nitrogen fixation gene fixN as a probe revealed the presence of a homologous DNA region in the phytopathogenic bacterium Agrobacterium tumefaciens. Hybridization signals were also detected with total DNAs of Rhizobium leguminosarum bv. phaseoli, Rhodobacter capsulatus and Escherichia coli, but not those of Xanthomonas campestris pv.

Structure of the unusual trisaccharide lipopolysaccharide component produced by a symbiotically defective mutant of Rhizobium leguminosarum biovar viciae.

The structure of an unusual trisaccharide component isolated from the lipopolysaccharide (LPS) of a Tn5 mutant of Rhizobium leguminosarum biovar viciae VF39 which is defective in infection of its host plant has been elucidated. This mutant also appears to be defective in the synthesis of a tetrasaccharide component normally synthesized by the wild-type organism. The three glycosyl components are galactose, mannose, and 3-deoxy-D-manno-2-octulosonic acid (Kdo).

A 4.6 kb DNA region of Rhizobium meliloti involved in determining urease and hydrogenase activities carries the structural genes for urease (ureA, ureB, ureC) interrupted by other open reading frames.

A 4.6 kb DNA region of the Rhizobium meliloti strain AK631 was found to contain seven open reading frames (ORFs), all oriented in the same direction. The putative gene products of four of these ORFs were highly homologous to UreA, UreB and UreC of Klebsiella aerogenes, Proteus mirabilis, Proteus vulgaris and Canavalia ensiformis.

A 3.9-kb DNA region of Xanthomonas campestris pv. campestris that is necessary for lipopolysaccharide production encodes a set of enzymes involved in the synthesis of dTDP-rhamnose.

By mutational analysis it was found that a 3.9-kb SmaI-XhoII DNA fragment of Xanthomonas campestris pv. campestris is involved in lipopolysaccharide (LPS) biosynthesis.

Saturation mutagenesis in Escherichia coli of a cloned Xanthomonas campestris DNA fragment with the lux transposon Tn4431 using the delivery plasmid pDS1, thermosensitive in replication.

A system allowing transposon mutagenesis of cloned DNA fragments in Escherichia coli with Tn4431, which carries the promotorless luciferase (lux) operon of Vibrio fischeri, has been developed. The transposon delivery plasmid, pDS1, based on an IncF replicon, is thermosensitive in replication and mobilizable to many Gram-negative bacteria. We used pDS1 for Tn4431-saturation mutagenesis of a 10-kb DNA fragment of Xanthomonas campestris pv.

The Rhizobium leguminosarum FnrN protein is functionally similar to Escherichia coli Fnr and promotes heterologous oxygen-dependent activation of transcription.

An open reading frame from Rhizobium leguminosarum bv. viciae strain VF39, previously identified and found to be similar to Escherichia coli fnr and Rhizobium meliloti fixK (orf240, thereafter called fnrN), was further analysed. Analysis of the expression of an fnrN-lacZ transcriptional fusion revealed that fnrN is preferentially expressed under oxygen limitation.

Characterization of structural defects in the lipopolysaccharides of symbiotically impaired Rhizobium leguminosarum biovar viciae VF-39 mutants.

The lipopolysaccharides (LPS) of a wild type strain of Rhizobium leguminosarum biovar viciae (strain VF-39) and two symbiotically defective Tn5 mutants (VF-39-32 and VF-39-86) have been studied. The LPS of the mutants reflected impaired synthesis of the O-antigen. In the LPS of one mutant, the core tetrasaccharide was lacking and in that of the other it was truncated to a disaccharide containing mannose and 3-deoxy-D-manno-oct-2-ulosonic acid (KdO).

Characterization of recA genes and recA mutants of Rhizobium meliloti and Rhizobium leguminosarum biovar viciae.

DNA fragments carrying the recA genes of Rhizobium meliloti and Rhizobium leguminosarum biovar viciae were isolated by complementing a UV-sensitive recA- Escherichia coli strain. Sequence analysis revealed that the coding region of the R. meliloti recA gene consists of 1044 bp coding for 348 amino acids whereas the coding region of the R.