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PubMedDate not supplied

[Effect of deficiency of dietary nitrogen on cellulose digestibility and nitrogen-fixing flora activity in the sibling vole Microtus rossiaemeridionalis].

The effect of food composition on nitrogen-fixing activity of the symbionts living in the digestive tract of the sibling vole Microtus rossiaemeridionalis was experimentally studied. In the control, the rodents were allowed to select any of three food mixes: protein-rich, protein-free with low cellulose content, and protein-free with high cellulose content. The voles consumed the food in a proportion corresponding to 16% of protein and about 6% of cellulose. Exclusion of the protein-rich food considerably increased cellulose consumption (up to 12%) and digestibility (from 35 to 64%). The changes in the consumed food composition were reflected in localization of nitrogenase activity in the digestive tract: the control level of nitrogen-fixing activity in the cecum was three times that in the proventriculus, while an inverse proportion was observed in the experimental groups. In all cases, the colon was the major locus of nitrogen fixation.

Animals↗

PubMed2005

[Study on AHL-like quorum signals in Mesorhizobium huakuii].

Quorum sensing is a mechanism used by single-cell bacteria to monitor their population density and control a variety of physiological functions in a cell-density-dependent manner. An ultrasensitive quorum signal acyl-homoserine lactone (AHL) detecting Agrobacterium tumefaciens strain, which strongly overproduces quorum-sensing regulator TraR and was proved to be able to detect AHLs at nano-molar concentration, was used to detect the production of AHLs in three Mesorhizobium huakuii strains. We showed that AHLs were produced in these strains with some variations. We also found that elevating of medium pH during cell growth greatly affected the stability of AHL signals. This study paved the way of further studying the relationship between quorum sensing and symbiotic nitrogen fixation of the M. huakuii strains.

4-Butyrolactone↗

PubMed1981

Nitrogenase reactivity: insight into the nitrogen-fixing process through hydrogen-inhibition and HD-forming reactions.

The dihydrogen reactions of nitrogenase are H2 evolution, H2 inhibition of N2 reduction, and HD production from H2/D2O or D2/H2O. The relationships among these dihydrogen reactions are studied to gain insight into the mechanism of N2 reduction. Detailed studies have probed (1) the formation of HD by nitrogenase as a function of partial pressures of N2, D2, and CO, (2) the formation of TOH from T2 under N2-fixing conditions, and (3) the reduction of hydrazine by nitrogenase. Experiments under T2 demonstrate that negligible tritium is incorporated into water compared to the HD produced under similar conditions. Studies of total electron flow, in the presence or absence of D2, establish a requirement of 1 mol of electrons/mol of HD formed. These findings show definitively that HD formation is not due to a simple H2O/D2 exchange mechanism. Kinetic analysis shows that HD is produced by two separate processes. In the minor process, the HD formed is proportional to the H2 evolved, electron requiring, and partially inhibited by 1% CO. In the major process, HD formation is dependent on N2 pressure, electron requiring, and completely inhibited by CO. A mechanism is proposed whereby HD from the N2-dependent process is formed from a bound, reduced dinitrogen intermediate. This mechanism is supported by studies using hydrazine as a substrate for nitrogenase and leads to the conclusion that H2 inhibition of nitrogen fixation and N2-dependent HD formation are manifestations of the same molecular process.

Ammonia↗

PubMed2003

Citrate synthase mutants of Sinorhizobium fredii USDA257 form ineffective nodules with aberrant ultrastructure.

The tricarboxylic acid (TCA) cycle plays an important role in generating the energy required by bacteroids to fix atmospheric nitrogen. Citrate synthase is the first enzyme that controls the entry of carbon into the TCA cycle. We cloned and determined the nucleotide sequence of the gltA gene that encodes citrate synthase in Sinorhizobium fredii USDA257, a symbiont of soybeans (Glycine max [L.] Merr.) and several other legumes. The deduced citrate synthase protein has a molecular weight of 48,198 and exhibits sequence similarity to citrate synthases from several bacterial species, including Sinorhizobium meliloti and Rhizobium tropici. Southern blot analysis revealed that the fast-growing S. fredii strains and Rhizobium sp. strain NGR234 contained a single copy of the gene located in the bacterial chromosome. S. fredii USDA257 gltA mutant HBK-CS1, which had no detectable citrate synthase activity, had diminished nodulation capacity and produced ineffective nodules on soybean. Light and electron microscopy observations revealed that the nodules initiated by HBK-CS1 contained very few bacteroids. The infected cells contained large vacuoles and prominent starch grains. Within the vacuoles, membrane structures that appeared to be reminiscent of disintegrating bacteroids were detected. The citrate synthase mutant had altered cell surface characteristics and produced three times more exopolysaccarides than the wild type produced. A plasmid carrying the USDA257 gltA gene, when introduced into HBK-CS1, was able to restore all of the defects mentioned above. Our results demonstrate that a functional citrate synthase gene of S. fredii USDA257 is essential for efficient soybean nodulation and nitrogen fixation.

Citrate (si)-Synthase↗

PubMed2003

Post-genomic insights into plant nodulation symbioses.

Several legume genes involved in establishing nitrogen fixation have been discovered using functional genomics; when mutated, the genes affect symbioses, and all encode receptor kinases. This provides long-awaited insights into a complex plant-bacterium interaction and heralds the possibility of extending the range of plants susceptible to nitrogen-fixing nodulation.

Genomics↗

PubMed1992

Activator-independent formation of a closed complex between sigma 54-holoenzyme and nifH and nifU promoters of Klebsiella pneumoniae.

The alternative sigma factor sigma 54 is required for transcription of nitrogen fixation genes in Klebsiella pneumoniae and other diazotrophs. The nif genes, and other E sigma 54-dependent genes whose products are necessary for a wide range of processes, are postively regulated. A unifying model that is well supported by studies on nif and other nitrogen-regulated (ntr) genes includes the central tenet that sigma 54 confers upon core RNA polymerase the ability to recognize and bind specific promoter sequences, but not the ability to isomerize to the open complex without assistance from the appropriate activator protein. Direct physical evidence for formation of an activator-independent complex between E sigma 54 and the NifA-dependent K. pneumoniae nifH and nifU promoters has, to date, been lacking. Using purified components we have now demonstrated formation of the closed complex at these promoters, indicating that it is an intermediate along the pathway to open complex formation. The closed complex was not detected when conserved features of the promoter were altered by mutation, nor was its stability increased when integration host factor protein was bound adjacent to the E sigma 54 recognition sequence.

Base Sequence↗

PubMed1998

Transcriptional and translational regulation of photosystem I and II genes in light-dark- and continuous-light-grown cultures of the unicellular cyanobacterium Cyanothece sp. strain ATCC 51142.

Cyanothece sp. strain ATCC 51142, a unicellular, diazotrophic cyanobacterium, demonstrated extensive metabolic periodicities of photosynthesis, respiration, and nitrogen fixation when grown under N2-fixing conditions. This report describes the relationship of the biosynthesis of photosynthesis genes to changes in the oligomerization state of the photosystems. Transcripts of the psbA gene family, encoding the photosystem II (PSII) reaction center protein D1, accumulated primarily during the light period, and net transcription reached a peak between 2 to 6 h in the light in light-dark (LD) growth and between 4 to 10 h in the subjective light when grown under continuous light (LL). The relative amount of the D1 protein (form 1 versus form 2) appeared to change during this diurnal cycle, along with changes in the PSII monomer/dimer ratio. D1 form 1 accumulated at approximately equal levels throughout the 24-h cycle, whereas D1 form 2 accumulated at significantly higher levels at approximately 8 to 10 h in the light or subjective light. The psbD gene, encoding the reaction center protein D2, also demonstrated differences between the two copies of this gene, with one copy transcribed more heavily around 6 to 8 h in the light. Accumulation of the PSI reaction center proteins PsaA and PsaB was maximal in the dark or subjective-dark periods, a period during which PSI was primarily in the trimeric form. We conclude that photosystem organization changes during the diurnal cycle to favor either noncyclic electron flow, which leads to O2 evolution and CO2 fixation, or cyclic electron flow, which favors ATP synthesis.

Bacterial Proteins↗

PubMed2026

Complete genome sequences of three effective nitrogen-fixing strains of Bradyrhizobium ottawaense from Canada.

We report complete genome sequences of three nitrogen-fixing Bradyrhizobium ottawaense strains isolated from soybeans in Canada. Each ~9.0 Mb genome (chromosome and plasmid) harbors predicted genes for nodulation, nitrogen fixation, N2O mitigation, phosphate solubilization, iron acquisition, phytohormone production, and stress tolerance, highlighting their potential for sustainable agriculture.

Bradyrhizobium ottawaense↗

PubMedDate not supplied

[Respiration of oligonitrophilic bacteria].

The respiration rate of 25 studied oligonitrophilous strains belonging to various genera and species of bacteria varied within wide limits depending on their taxonomy, conditions of cultivation, substrates, and other factors. No strict correlation was established between the respiration rate and the activity of nitrogen fixation. One of the typical properties of oligonitrophilous bacteria is a high rate of endogeneous respiration --50% and more of the respiration rate during assimilation of exogeneous substrates. The level of oxidative metabolism of oligonitrophilous bacteria was found to be higher on media containing bound nitrogen than on media without nitrogen.

Acetates↗

PubMed1994

The isolated catalytic domain of NIFA, a bacterial enhancer-binding protein, activates transcription in vitro: activation is inhibited by NIFL.

The NIFA protein of Klebsiella pneumoniae is required for transcription of all nif (nitrogen fixation) operons except the regulatory nifLA operon itself. NIFA activates transcription of nif operons by the alternative holoenzyme form of RNA polymerase, sigma 54-holoenzyme, in a nucleoside triphosphate (NTP)-dependent manner. NIFL antagonizes the action of NIFA in the presence of molecular oxygen or combined nitrogen. The NIFA protein of K. pneumoniae is composed of three domains: an N-terminal domain with unclear function, a central catalytic domain, and a C-terminal DNA-binding domain. We report that the isolated central domain of NIFA activates transcription in vitro and that this activation requires NTP with a hydrolyzable beta-gamma bond, as does activation by intact NIFA. Transcriptional activation by the isolated central domain has the heat lability characteristic of intact NIFA and is inhibited by NIFL. The central domain has an NTPase activity that is also heat-labile but is not inhibited by NIFL. Taken together, these results imply that NIFL interferes with contact between NIFA and sigma 54-holoenzyme.

Adenosine Triphosphatases↗

PubMed1998

Tricarboxylic acid cycle and anaplerotic enzymes in rhizobia.

Rhizobia are a diverse group of Gram-negative bacteria comprised of the genera Rhizobium, Bradyrhizobium, Mesorhizobium, Sinorhizobium and Azorhizobium. A unifying characteristic of the rhizobia is their capacity to reduce (fix) atmospheric nitrogen in symbiotic association with a compatible plant host. Symbiotic nitrogen fixation requires a substantial input of energy from the rhizobial symbiont. This review focuses on recent studies of rhizobial carbon metabolism which have demonstrated the importance of a functional tricarboxylic acid (TCA) cycle in allowing rhizobia to efficiently colonize the plant host and/or develop an effective nitrogen fixing symbiosis. Several anaplerotic pathways have also been shown to maintain TCA cycle activity under specific conditions. Biochemical and physiological characterization of carbon metabolic mutants, along with the analysis of cloned genes and their corresponding gene products, have greatly advanced our understanding of the function of enzymes such as citrate synthase, oxoglutarate dehydrogenase, pyruvate carboxylase and malic enzymes. However, much remains to be learned about the control and function of these and other key metabolic enzymes in rhizobia.

Citric Acid Cycle↗

PubMed1998

Dictyostelium discoideum fatty-acyl amidase II has deacylase activity on Rhizobium nodulation factors.

Dictyostelium discoideum (Amoebidae) secretes cell-lysing enzymes: esterases, amidases, and glycosylases, many of which degrade soil bacteria to provide a source of nutrients. Two of these enzymes, fatty-acyl amidases FAA I and FAA II, act sequentially on the N-linked long chain acyl groups of lipid A, the lipid anchor of Gram-negative bacterial lipopolysaccharide. FAA I selectively hydrolyzes the 3-hydroxymyristoyl group N-linked to the proximal glucosamine residue of de-O-acylated lipid A. Substrate specificity for FAA II is less selective, but does require prior de-N-acylation of the proximal sugar, i.e. bis-N-acylated lipid A is not a substrate. We have synthesized a 14C-labeled substrate analog for FAA II and used this in a novel assay to monitor its purification. Inhibitory studies indicate that FAA II is not a serine protease, but may have a catalytic mechanism similar to metalloprotein de-N-acetylases such as LpxC. Interestingly, rhizobial Nod factor signal oligosaccharides that induce root nodules on leguminous plants have many of the structural requirements for substrate recognition by FAA II. In vitro evidence indicates that Rhizobium fredii Nod factors are selectively de-N-acylated by purified FAA II, suggesting that the enzyme may reduce the N2-fixing efficiency of Rhizobium-legume symbioses. In contrast, N-methylated Nod factors from transgenic R. fredii carrying the rhizobial nodS gene were resistant to FAA II, suggesting a mechanism by which Nod factors may be protected from enzymatic de-N-acylation. Since FAA II and Nod factors are both secreted, and Nod factors that lack the N-acyl group are unable to induce nodules, dictyostelial FAA II may decrease the efficiency of symbiotic nitrogen fixation in the environment by reducing the available biologically active nodule inducer signal.

Amidohydrolases↗

PubMed2005

[Expression of the symbiotic nod4 pea gene against various genotypic backgrounds].

Experiments on the effect of genotypic environment on the expression of the nod4 gene, responsible for supernodulation in pea, were performed. The genotypic background was found to affect the manifestation of both major symbiosis-related traits (number of nitrogen-fixing bacterial nodules and nitrogenase activity) and productivity-related traits (stem height, seed number, and seed weight), which form the pleiotropic complex of the mutant gene. Using recurrent selection, we developed supernodulating lines significantly exceeding the original mutant line and studied them up to generations F5-F6. Of special importance is the fact that these lines showed high levels of nodulation and nitrogen fixation. The results are discussed from the viewpoint of breeding.

Genes, Plant↗

PubMed2005

[Effects of different nitrogenous compounds on growth and nodulation of Abrus cantoniensis].

OBJECTIVE: The research aimed at the effects of different nitrogenous compounds on growth and nodulation of Abrus cantoniensis. METHOD: After the seedlings of the herb were inoculated with rhizobia in potted culture, they were supplied with nutrition solutions which contained the three nitrogenous compounds, KNO3, NH4NO3, (NH4)2SO4 of different nitrogen concentration. The growth and nodulation of seedlings was determined after 70 days. RESULT: Different nitrogenous compounds were able to enhance the vegetable growth of seedlings variously. The effect of (NH4)2SO4 and NH4NO3 on growth was better than that of KNO3. Seedlings nodulation was obviously inhibited by these nitrogenous compounds. Their inhibitory effects ranked NH4NO3 > (NH4)2SO4 > KNO3. The treatments of KNO3 and the lower concentration treatments of NH4NO3 and (NH4)2 SO4 didn't inhibit the nodulation of seedlings, but the higher concentration treatment of NH4NO3 and (NH4)2SO4 severely inhibited nodulation or even made a no formation of nodule. CONCLUSION: The results showed that ammonium nitrogen the higher inhibitory ability to the nodulation of seedlings of A. cantoniensis than nitrate nitrogen. Therefore, the application of ammonium nitrogen fertilizer should be controlled in culture of the herb, which is in favor of increasing the function of biological nitrogen fixation and the quality of the medicinal materials of A. cantoniensis.

Abrus↗

PubMed2006

Spatial and temporal organization of sucrose metabolism in Lotus japonicus nitrogen-fixing nodules suggests a role for the elusive alkaline/neutral invertase.

Symbiotic nitrogen fixation (SNF) in legume nodules is a highly energy demanding process, fuelled by plant-supplied carbohydrates mainly in the form of sucrose. In this study, we have combined molecular and biochemical approaches in order to study the spatial and temporal organisation of sucrose metabolism in nitrogen-fixing nodules of the model legume Lotus japonicus, with an emphasis on the neglected role of alkaline/neutral invertase. For this purpose, a full-length cDNA clone coding for an alkaline/neutral invertase isoform, termed LjInv1, was identified in a L. japonicus mature nodule cDNA libraries. Alkaline/neutral invertase activity was also found to be the predominant invertase activity in mature nodules. Real-time reverse-transcription polymerase chain reaction analysis was used in order to study the temporal expression patterns of LjInv1 in parallel with genes encoding acid invertase and sucrose synthase (SuSy) isoforms, and enzymes involved in the subsequent hexose partitioning including hexokinase, phosphoglucomutase (PGM) and phosphoglucose isomerase (PGI). The spatial organisation of sucrose metabolism was studied by in situ localisation of LjInv1 transcripts and alkaline/neutral invertase activity, and SuSy protein during nodule development. Furthermore, the spatial organisation of hexose metabolism was investigated by histochemical localisation of hexokinase, PGM and PGI activities in mature nodules. The results considered together indicate that alkaline/neutral invertase could contribute to both the Glc-1-P and Glc-6-P pools in nodules, fuelling both biosynthetic processes and SNF. Furthermore, transcript profiling analysis revealed that genes coding for hexokinase and putative plastidic PGM and PGI isoforms are upregulated during the early stages of nodule development, while the levels of transcripts corresponding to cytosolic PGM and PGI isoforms remained similar to uninfected roots, indicating a possible role of LjInv1 in producing hexoses for starch production and other biosynthetic processes in developing nodules.

Amino Acid Sequence↗

PubMed1989

Open reading frame 5 (ORF5), encoding a ferredoxinlike protein, and nifQ are cotranscribed with nifE, nifN, nifX, and ORF4 in Rhodobacter capsulatus.

DNA sequence analysis of a 1,600-base-pair fragment located downstream of nifENX in nif region A of Rhodobacter capsulatus revealed two additional open reading frames (ORFs): ORF5, encoding a ferredoxinlike protein, and nifQ. The ferredoxinlike gene product contained two cysteine motifs, typical of ferredoxins coordinating two 4Fe-4S clusters, but the distance between these two motifs was unusual for low-molecular-weight ferredoxins. The R. capsulatus nifQ gene product shared a high degree of homology with Klebsiella pneumoniae and Azotobacter vinelandii NifQ, including a typical cysteine motif located in the C-terminal part. nifQ insertion mutants and also an ORF5-nifQ double deletion mutant showed normal diazotrophic growth only in the presence of high concentrations of molybdate. This demonstrated that the gene encoding the ferredoxinlike protein is not essential for nitrogen fixation. No NifA-activated consensus promoter could be found in the intergenic region between nifENX-ORF4 and ORF5-nifQ. Analyses of a nifQ-lacZYA fusion revealed that transcription of nifQ was initiated at a promoter in front of nifE. In contrast to other nitrogen-fixing organisms, R. capsulatus nifE, nifN, nifX, ORF4, ORF5, and nifQ were organized in one transcriptional unit.

Amino Acid Sequence↗

PubMedDate not supplied

[Effectiveness of bacterization of soy plants by active races of nodule bacteria].

Spontaneous nodule bacteria of soybean plants are absent from the Sutn-Eastern Kazakhstan soils. Therefore, bacterization of soybean plants with these bacteria is necessary for obtaining high crops of this culture. Among tested strains of soybean nodule bacteria, strain 623(a) was found to be the most effective one. The use of nitrogen with this strain stimulated the intensive formation of nodules, the growth and development of plants, the activation of physiological processes in them, and increased the yield of green mass, hay and grains as well as the content of protein in them and its yield per area unit. Mineral nitrogen added to soil at a concentration of 120 kg per hectare decreased the activity of symbiotic nitrogen fixation, increased the crop of green mass and hay, but decreased the yield of grain of soybean and other cultures sown after it in crop rotation.

Bacteria↗

PubMed1991

Arrangement of nitrogenase structural genes in an aerobic filamentous nonheterocystous cyanobacterium.

Members of the marine filamentous, nonheterocystous cyanobacterial genus Trichodesmium not only are capable of fixing nitrogen aerobically in the light but when grown under a light-dark cycle will fix nitrogen only during the light phase. In this study, we constructed a restriction map of the structural nitrogen fixation genes (nifHDK) in Trichodesmium sp. strain NIBB 1067. We found that the organization of the nif genes in Trichodesmium sp. strain NIBB 1067 is contiguous, as found in other nonheterocystous cyanobacteria and in heterocysts. Furthermore, the nif gene arrangement was identical when the cultures were grown with combined nitrogen or under nitrogen-fixing conditions. Therefore, no gene rearrangements occur, such as those that occur during the development of heterocysts in heterocystous species.

Blotting, Southern↗