Identification of a system that allows a Rhizobium tropici dctA mutant to grow on succinate, but not on other C4-dicarboxylates

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Abstract:

A defined insertion mutant of a gene encoding a homolog of the rhizobial C4-dicarboxylate permease (dctA) was constructed in Rhizobium tropici strain CIAT899. This mutant (GA1) was unable to grow on fumarate or malate; however, in contrast with other rhizobial dctA mutants, it retained a limited ability to grow on succinate with ammonia as a nitrogen source. Our results suggest the presence of a novel succinate-specific transport system in R. tropici. Biochemical characterization indicated that this alternative transport system in GA1 is active and dependent on an energized membrane. It was also induced by succinate and aspartate, and was repressed by glucose and glycerol. Bean plants inoculated with GA1 showed a reduced nitrogen-fixing ability, achieving only 29% of the acetylene reduction activity determined in CIAT899 strain nodules, 33 days after inoculation. Also, bean plants inoculated with GA1 had reduced shoot dry weight compared with plants inoculated with the wild-type strain.Key words: succinate transport, Rhizobium tropici, C4-dicarboxylate uptake.

Un mutant insertionnel défini pour un gène codant pour un homologue de la C4-dicarboxylate perméase des rhizobia (dctA) a été construit dans la souche CIAT899 de Rhizobium tropici. Ce mutant (GA1) était incapable de croître sur du fumarate ou du malate; cependant, contrairement aux autres mutants rhizobiens dctA, il a conservé une faculté limitée à croître sur du succinate en présence d'ammoniac comme source d'azote. Nos résultats indiquent la présence d'un nouveau système de transport spécifique au succinate dans R. tropici. La caractérisation biochimique a indiqué que ce système de transport alternatif dans GA1 est actif et dépendant d'une membrane activée. Il était également induit par le succinate, l'aspartate et réprimé par le glucose et le glycérol. Les plants de haricots inoculés avec GA1 ont montré une habileté réduite à fixer l'azote, atteignant seulement 29 % de l'activité de réduction de l'acétylène telle que déterminée dans les nodules de la souche CIAT899, 33 jours après inoculation. De plus, les plants de haricots inoculés avec GA1 avaient un poids sec de pousse inférieur comparativement aux plants inoculés avec la souche de type sauvage.Mots clés : transport du succinate, Rhizobium tropici, incorporation du C4-dicarboxylate.[Traduit par la Rédaction]

Keywords: C4-dicarboxylate uptake; Rhizobium tropici; incorporation du C4-dicarboxylate; succinate transport; transport du succinate

Document Type: Research Article

Publication date: June 1, 2001

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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