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Requirement of a plasmid-encoded catalase for survival of Rhizobium etli CFN42 in a polyphenol-rich environment.

ABSTRACT: Nitrogen-fixing bacteria collectively called rhizobia are adapted to live in polyphenol-rich environments. The mechanisms that allow these bacteria to overcome toxic concentrations of plant polyphenols have not been clearly elucidated. We used a crude extract of polyphenols released from the seed coat of the black bean to simulate a polyphenol-rich environment and analyze the response of the bean-nodulating strain Rhizobium etli CFN42. Our results showed that the viability of the wild type as well as that of derivative strains cured of plasmids p42a, p42b, p42c, and p42d or lacking 200 kb of plasmid p42e was not affected in this environment. In contrast, survival of the mutant lacking plasmid p42f was severely diminished. Complementation analysis revealed that the katG gene located on this plasmid, encoding the only catalase present in this bacterium, restored full resistance to testa polyphenols. Our results indicate that oxidation of polyphenols due to interaction with bacterial cells results in the production of a high quantity of H(2)O(2), whose removal by the katG-encoded catalase plays a key role for cell survival in a polyphenol-rich environment.

SUBMITTER: Garcia-de Los Santos A

PROVIDER: S-EPMC2293148 | biostudies-literature | 2008 Apr

REPOSITORIES: biostudies-literature

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Requirement of a plasmid-encoded catalase for survival of Rhizobium etli CFN42 in a polyphenol-rich environment.

García-de Los Santos Alejandro A López Erika E Cubillas Ciro A CA Noel K Dale KD Brom Susana S Romero David D

Applied and environmental microbiology 20080229 8

Nitrogen-fixing bacteria collectively called rhizobia are adapted to live in polyphenol-rich environments. The mechanisms that allow these bacteria to overcome toxic concentrations of plant polyphenols have not been clearly elucidated. We used a crude extract of polyphenols released from the seed coat of the black bean to simulate a polyphenol-rich environment and analyze the response of the bean-nodulating strain Rhizobium etli CFN42. Our results showed that the viability of the wild type as we ...[more]

PMID: 18310436

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Project description:Conjugative transfer is one of the mechanisms allowing diversification and evolution of bacteria. Rhizobium etli CFN42 is a bacterial strain whose habitat is the rhizosphere and is able to form nodules as a result of the nitrogen-fixing symbiotic relationship it may establish with the roots of Phaseolus vulgaris. R. etli CFN42 contains one chromosome and six large plasmids (pRet42a - pRet42f). Most of the genetic information involved in the establishment of the symbiosis is localized on plasmid pRet42d, named as the symbiotic plasmid (pSym). This plasmid is able to perform conjugation, using pSym encoded transfer genes controlled by the RctA/RctB system. Another plasmid of CFN42, pRet42a, has been shown to perform conjugative transfer not only in vitro, but also on the surface of roots and inside nodules, using other rhizobia as recipients. In addition to the rhizobia involved in the formation of nodules, these structures have been shown to contain endophytic bacteria from different genera and species. In this work, we have explored the conjugative transfer of the pSym (pRet42d) from R. etli CFN42 to endophytic bacteria as putative recipients, using as donor a CFN42 derivative labeled with GFP in the pRet42d and RFP in the chromosome. We were able to isolate some transconjugants, which inherit the GFP, but not the RFP marker. Some of them were identified, analyzed and evaluated for their ability to nodulate. We found transconjugants from genera such as Stenotrophomonas, Achromobacter, and Bacillus, among others. Although all the transconjugants carried the GFP marker, and nod, fix, and nif genes from pRet42d, not all were able to nodulate. Ultrastructure microscopy analysis showed some differences in the structure of the nodules of one of the transconjugants. A replicon of the size of pRet42d (371 Kb) could not be visualized in the transconjugants, suggesting that the pSym or a segment of the plasmid is integrated in the chromosome of the recipients. These findings strengthen the proposal that nodules constitute a propitious environment for exchange of genetic information among bacteria, in addition to their function as structures where nitrogen fixation and assimilation takes place.

Project description:BackgroundA traditional concept in bacterial genetics states that housekeeping genes, those involved in basic metabolic functions needed for maintenance of the cell, are encoded in the chromosome, whereas genes required for dealing with challenging environmental conditions are located in plasmids. Exceptions to this rule have emerged from genomic sequence data of bacteria with multipartite genomes. The genome sequence of R. etli CFN42 predicts the presence of panC and panB genes clustered together on the 642 kb plasmid p42f and a second copy of panB on plasmid p42e. They encode putative pantothenate biosynthesis enzymes (pantoate-β-alanine ligase and 3-methyl-2-oxobutanoate hydroxymethyltransferase, respectively). Due to their ubiquitous distribution and relevance in the central metabolism of the cell, these genes are considered part of the core genome; thus, their occurrence in a plasmid is noteworthy. In this study we investigate the contribution of these genes to pantothenate biosynthesis, examine whether their presence in plasmids is a prevalent characteristic of the Rhizobiales with multipartite genomes, and assess the possibility that the panCB genes may have reached plasmids by horizontal gene transfer.ResultsAnalysis of mutants confirmed that the panC and panB genes located on plasmid p42f are indispensable for the synthesis of pantothenate. A screening of the location of panCB genes among members of the Rhizobiales showed that only R. etli and R. leguminosarum strains carry panCB genes in plasmids. The panCB phylogeny attested a common origin for chromosomal and plasmid-borne panCB sequences, suggesting that the R. etli and R. leguminosarum panCB genes are orthologs rather than xenologs. The panCB genes could not totally restore the ability of a strain cured of plasmid p42f to grow in minimal medium.ConclusionsThis study shows experimental evidence that core panCB genes located in plasmids of R. etli and R. leguminosarum are indispensable for the synthesis of pantothenate. The unusual presence of panCB genes in plasmids of Rhizobiales may be due to an intragenomic transfer from chromosome to plasmid. Plasmid p42f encodes other functions required for growth in minimal medium. Our results support the hypothesis of cooperation among different replicons for basic cellular functions in multipartite rhizobia genomes.

Project description:UnlabelledBacteria play important roles in mineral weathering, soil formation, and element cycling. However, little is known about the interaction between silicate minerals and rhizobia. In this study, Rhizobium yantingense H66 (a novel mineral-weathering rhizobium) and Rhizobium etli CFN42 were compared with respect to potash feldspar weathering, mineral surface adsorption, and metabolic activity during the mineral weathering process. Strain H66 showed significantly higher Si, Al, and K mobilization from the mineral and higher ratios of cell numbers on the mineral surface to total cell numbers than strain CFN42. Although the two strains produced gluconic acid, strain H66 also produced acetic, malic, and succinic acids during mineral weathering in low- and high-glucose media. Notably, higher Si, Al, and K releases, higher ratios of cell numbers on the mineral surface to total cell numbers, and a higher production of organic acids by strain H66 were observed in the low-glucose medium than in the high-glucose medium. Scanning electron microscope analyses of the mineral surfaces and redundancy analysis showed stronger positive correlations between the mineral surface cell adsorption and mineral weathering, indicated by the dissolved Al and K concentrations. The results showed that the two rhizobia behaved differently with respect to mineral weathering. The results suggested that Rhizobium yantingense H66 promoted potash feldspar weathering through increased adsorption of cells to the mineral surface and through differences in glucose metabolism at low and high nutrient concentrations, especially at low nutrient concentrations.ImportanceThis study reported the potash feldspar weathering, the cell adsorption capacity of the mineral surfaces, and the metabolic differences between the novel mineral-weathering Rhizobium yantingense H66 and Rhizobium etli CFN42 under different nutritional conditions. The results showed that Rhizobium yantingense H66 had a greater ability to weather the mineral in low- and high-glucose media, especially in the low-glucose medium. Furthermore, Rhizobium yantingense H66 promoted mineral weathering through the increased adsorption of cells to the mineral surface and through increased organic acid production. Our results allow us to better comprehend the roles of different rhizobia in silicate mineral weathering, element cycling, and soil formation in various soil environments, providing more insight into the geomicrobial contributions of rhizobia to these processes.

Dataset Information

Requirement of a plasmid-encoded catalase for survival of Rhizobium etli CFN42 in a polyphenol-rich environment.

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Requirement of a plasmid-encoded catalase for survival of Rhizobium etli CFN42 in a polyphenol-rich environment.

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