Sinorhizobium meliloti strain 1021 bioS and bdhA gene transcriptions are both affected by biotin available in defined medium

Hofmann, Kai

doi:10.1016/s0378-1097(99)00565-0

Cited by 7 publications

(11 citation statements)

References 10 publications

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“…3). This marked drop in cellular biotin content, as measured by 14 C, was observed in both Rm1021-B3 and Rm1021-B6 relative to the parent Rm1021 cells.…”

Section: Downloaded Frommentioning

confidence: 82%

“…Whether biotin is essential or simply stimulatory for rhizobial growth has been long debated (36)(37)(38), but clearly, cell densities of Rm1021 and many other rhizobia under biotin-limiting conditions are increased greatly by small amounts of biotin (8). Growing S. meliloti serially under biotin-limited conditions produces several physiological and metabolic changes, including the accumulation of polyhydroxybutyrate and a significant reduction in cell size (8,14). Biotin-dependent enzymes such as pyruvate carboxylase are also affected under biotin-limited conditions, and several tricarboxylic acid cycle auxiliary enzymes show decreased activities (4,5).…”

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confidence: 99%

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Functional Analysis of Sinorhizobium meliloti Genes Involved in Biotin Synthesis and Transport

Entcheva

Phillips

Streit

2002

Appl Environ Microbiol

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External biotin greatly stimulates bacterial growth and alfalfa root colonization by Sinorhizobium meliloti strain 1021. Several genes involved in responses to plant-derived biotin have been identified in this bacterium, but no genes required for biotin transport are known, and not all loci required for biotin synthesis have been assigned. Searches of the S. meliloti genome database in combination with complementation tests of Escherichia coli biotin auxotrophs indicate that biotin synthesis probably is limited in S. meliloti 1021 by the poor functioning or complete absence of several key genes. Although several open reading frames with significant similarities to genes required for synthesis of biotin in gram-positive and gram-negative bacteria were found, only bioB, bioF, and bioH were demonstrably functional in complementation tests with known E. coli mutants. No sequence or complementation evidence was found for bioA, bioC, bioD, or bioZ. In contrast to other microorganisms, the S. meliloti bioB and bioF genes are not localized in a biotin synthesis operon, but bioB is cotranscribed with two genes coding for ABC transporter-like proteins, designated here bioM and bioN. Mutations in bioM and bioN eliminated growth on alfalfa roots and reduced bacterial capacity to maintain normal intracellular levels of biotin. Taken together, these data suggest that S. meliloti normally grows on exogenous biotin using bioM and bioN to conserve biotin assimilated from external sources.Microorganisms from the gram-negative genera Rhizobium, Sinorhizobium, Bradyrhizobium, Mesorhizobium, and Azorhizobium, collectively termed rhizobia, are well known for their capacity to establish N 2 -fixing symbioses with legume plants (2). Although the molecular basis of rhizobial N 2 reduction is defined (17) and a foundation has been constructed for understanding other bacterial genes expressed in the plant (25), our knowledge of how rhizobia grow on plant roots is less complete. Good growth of S. meliloti strain 1021 (Rm1021) on alfalfa roots requires external biotin (33), often supplied by plant roots (27), which regulates a gene, bioS, that helps S. meliloti compete under such conditions (13, 34). Whether biotin is essential or simply stimulatory for rhizobial growth has been long debated (36-38), but clearly, cell densities of Rm1021 and many other rhizobia under biotin-limiting conditions are increased greatly by small amounts of biotin (8). Growing S. meliloti serially under biotin-limited conditions produces several physiological and metabolic changes, including the accumulation of polyhydroxybutyrate and a significant reduction in cell size (8,14). Biotin-dependent enzymes such as pyruvate carboxylase are also affected under biotin-limited conditions, and several tricarboxylic acid cycle auxiliary enzymes show decreased activities (4, 5).Biotin is formed in bacteria by a well-defined pathway ( Fig. 1) (6,7,15,16,23,26). Many microorganisms, including Mesorhizobium loti, have biotin synthesis genes organized in operons (1,18,19,21,2...

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“…3). This marked drop in cellular biotin content, as measured by 14 C, was observed in both Rm1021-B3 and Rm1021-B6 relative to the parent Rm1021 cells.…”

Section: Downloaded Frommentioning

confidence: 82%

mentioning

confidence: 99%

Functional Analysis of Sinorhizobium meliloti Genes Involved in Biotin Synthesis and Transport

Entcheva

Phillips

Streit

2002

Appl Environ Microbiol

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“…Macromolecular metabolism. When an imbalance between carbon and nitrogen, phosphorus, or biotin occurs, many rhizobia sequester the excess carbon as polyhydroxybutyrate (13,25,45). Proteins involved in the degradation of polyhydroxybutyrate, BdhA (poly-3-hydroxybutyrate-dehydrogenase) and PhaZ (poly-3-hydroxybutyrate-depolymerase), were found.…”

Section: Resultsmentioning

confidence: 99%

An Evolutionary Hot Spot: the pNGR234 b Replicon of Rhizobium sp. Strain NGR234

et al. 2004

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Rhizobium sp. strain NGR234 has an exceptionally broad host range and is able to nodulate more than 112 genera of legumes. Since the overall organization of the NGR234 genome is strikingly similar to that of the narrow-host-range symbiont Rhizobium meliloti strain 1021 (also known as Sinorhizobium meliloti), the obvious question is why are the spectra of hosts so different? Study of the early symbiotic genes of both bacteria (carried by the SymA plasmids) did not provide obvious answers. Yet, both rhizobia also possess second megaplasmids that bear, among many other genes, those that are involved in the synthesis of extracellular polysaccharides (EPSs). EPSs are involved in fine-tuning symbiotic interactions and thus may help answer the broad-versus narrow-host-range question. Accordingly, we sequenced two fragments (total, 594 kb) that encode 575 open reading frames (ORFs). Comparisons revealed 19 conserved gene clusters with high similarity to R. meliloti, suggesting that a minimum of 28% (158 ORFs) of the genetic information may have been acquired from a common ancestor. The largest conserved cluster carried the exo and exs genes and contained 31 ORFs. In addition, nine highly conserved regions with high similarity to Agrobacterium tumefaciens C58, Bradyrhizobium japonicum USDA110, and Mesorhizobium loti strain MAFF303099, as well as two conserved clusters that are highly homologous to similar regions in the plant pathogen Erwinia carotovora, were identified. Altogether, these findings suggest that >40% of the pNGR234b genes are not strain specific and were probably acquired from a wide variety of other microbes. The presence of 26 ORFs coding for transposases and site-specific integrases supports this contention. Surprisingly, several genes involved in the degradation of aromatic carbon sources and genes coding for a type IV pilus were also found.The Proteobacteria contain many bacterial species that associate with plants either as symbionts or pathogens. Complete sequencing of the genomes of several of these microbes, including Agrobacterium tumefaciens (20, 49), Bradyrhizobium japonicum (28), Mesorhizobium loti (27), and Rhizobium (Sinorhizobium) meliloti (18), has made comparative genome analyses possible. Rhizobium sp. strain NGR234 belongs to the ␣-proteobacteria and is able to establish nitrogen-fixing symbiosis with many different legumes. Despite extensive study, the molecular mechanisms behind this broad host range are not fully apparent (6). Although R. meliloti has a very limited host range (5), it is phylogenetically close to NGR234 and the organization of both genomes is similar (14a, 31a). In both cases, the genome comprises three replicons (14a). Most symbiotic genes are carried on SymA plasmids of 0.54 Mb in strain NGR234 (17) and 1.35 Mb in R. meliloti (1). Both bacteria also possess a second group of plasmids, the so-called exo-or megaplasmids (pSymB). pNGR234b is estimated to be 2.2 Mb (31a), and the size of R. meliloti is 1.68 Mb (14). Chromosomes in both bacteria are about the same size ...

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“…Lane A, HSL extracts derived from biotin-starved cells; lane B, HSL from cells which were growing in the presence of 40 nM biotin. and metabolic changes, including the accumulation of poly-3-hydroxybutyrate and a significant reduction in cell size (6,10). Biotin-dependent enzymes such as pyruvate carboxylase also are affected under biotin-limiting conditions, and several tricarboxylic acid cycle auxiliary enzymes show decreased activities (3,4).…”

Section: Discussionmentioning

confidence: 99%

“…Whether biotin is essential or simply stimulatory for rhizobial growth has long been debated, but clearly, cell densities of strain Rm1021 and many other rhizobia under biotin-limiting conditions are increased greatly by small amounts of biotin (6,27,31), and biotin biosynthesis appears to be limited because several key genes are nonfunctional or absent (7). Growing S. meliloti serially under biotin-limiting conditions produces several physiological and metabolic changes, including the accumulation of poly-3-hydroxybutyrate and a significant reduction in cell size (10). In addition, biotin-dependent enzymes such as pyruvate carboxylase are affected under biotin-limiting conditions, and several tricarboxylic acid cycle auxiliary enzymes show decreased activities (3)(4)(5).…”

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confidence: 99%

Biotin Limitation in Sinorhizobium meliloti Strain 1021 Alters Transcription and Translation

Heinz

Streit

2003

Appl Environ Microbiol

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Sinorhizobium meliloti strain 1021 bioS and bdhA gene transcriptions are both affected by biotin available in defined medium

Cited by 7 publications

References 10 publications

Functional Analysis of Sinorhizobium meliloti Genes Involved in Biotin Synthesis and Transport

Functional Analysis of Sinorhizobium meliloti Genes Involved in Biotin Synthesis and Transport

An Evolutionary Hot Spot: the pNGR234 b Replicon of Rhizobium sp. Strain NGR234

Biotin Limitation in Sinorhizobium meliloti Strain 1021 Alters Transcription and Translation

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