1,721,301 research outputs found
Il controllo biologico della qualità degli inoculi per la batterizzazione delle leguminose.
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A critical role for aniA in energy-carbon flux and symbiotic nitrogen fixation in Sinorhizobium meliloti
No full textDuring free-living reproductive growth, Sinorhizobium meliloti accumulates poly-#-hydroxybutyrate (PHB) and glycogen, and produces and excretes exopolysaccharides and #-1,2-glucan. In previous investigations, PHB-minus mutants of S. meliloti 41 were obtained and studied; and the genes for PHB biosynthesis, phaAB and phaC, were described. In this work, the role of an open reading frame (orf) upstream of phaAB is studied. This orf is designated aniA because the gene was found to be expressed during anaerobic growth. Under low oxygen conditions, glycogen decreases and the production of extracellular polymeric substances (EPS) is partially repressed. When the aniA mutant is incubated under oxygen-limiting conditions, the only significant change observed is an overproduction of EPS. Subsequent in planta tests showed that although the mutant strain produced abundant nodules, only very low acetylene-reduction activity was detected, indicating that nitrogen fixation was not adequately supported by endogenous substrates
Inoculi per la batterizzazione dei semi: controllo della qualità e standards produttivi.
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Role of aniA in the regulation of Polyhydroxyalkanoate synthesis in Sinorhizobium meliloti
No full textSinorhizobium meliloti is a nitrogen-fixing soil bacterium that can accumulate poly-3-hydroxybutyrate (PHB), poly-3(hydroxybutyrate-co-hydroxyvalerate), glycogen and produce considerable amounts of exopolysaccharides . PHB in rhizobia and other bacteria is thought to serve as a carbon and/or energy reserve to be utilized under suboptimal growth conditions. To control the production and accumulation of these different polymers a fine regulation must be operating, possibly involving a group of genes. Recently, we studied a gene referred to as aniA (1). The occurrence of AniA orthologs (described in some cases as PhaR) and organization of the respective genes were described in detail in at least 29 different bacteria (Ref. ??). Based on sequence similarity and on the presence of a DNA-binding domain we have proposed that AniA functions in S. meliloti as a transcriptional regulator (1). The product of the aniA ortholog PhaR of P. denitrificans has been shown to bind to the intergenic region phaC-phaP and to repress the in vivo expression of the granule-associated phasin PhaP (2). Recently, similar results were shown in R. eutropha (3, 4). Other putative ortholog includes a steroid-inducible gene (stdC) in Comamonas testosteroni (5). An aniA-defective mutant of S. meliloti produced larger amounts of exopolysaccharides (EPS), especially after induction under low oxygen concentration, were expression of aniA is induced. This mutant accumulates less PHB and glycogen than the parental strain under conditions of polymer production (Ref. 1??).
In this study we present new data regarding physiological and genetic characterization of aniA in S. meliloti. Recently, aniA was studied in Rhizobium etli and was also shown to have a role in polymer accumulation in addition to control of global protein expression (6). We found that aniA of S. meliloti is involved in carbon/energy regulation under normal growth conditions, but especially under low oxygen conditions it seems to modulate polymer production in rhizobia. Since an efficient control of carbon/energy flux is one of the requisites to increase PHB production, we studied the role of aniA in EPS synthesis by transferring an aniA::Km mutation to different S. meliloti strains carrying exp-lacZ and exo-lacZ fusions. -galactosidase activities were assayed in the double mutants and compared to the wild-type background. The results indicated that aniA regulates some exp and exo genes. The type of EPS produced by aniA-negative mutant and the parental strain was also analyzed. Finally, the role of aniA in the regulation of PHB accumulation in S. meliloti was studied and the related results will be presented
Poly-3-hydroxybutyrate has an important role for the survival of Rhizobium tropici under starvation
No full textAccumulation of poly-3-hydroxybutyrate P(3HB) granules serves to sustain the survival of bacterial cells under conditions of nutrient shortage. P(3HB) is produced by many Rhizobium, Sinorhizobium, Bradyrhizobium and Azorhizobium species in free-living and in symbiotic state. However, the physiol. role for this polymer has not been entirely clarified. A stable P(3HB)-minus mutant of Rhizobium tropici was obtained by inactivation of the phaC gene and characterized. Nodule-inducing ability on bean plants and ARA of the mutant strain did not differ from those of the parental strain. However, P(3HB)-minus mutant showed higher accumulation of glycogen as compared to the parental strain. Persistence studies were performed and survival differences in carbon-free liquid microcosms were observed between the two strains
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