Thesis
C4-dicarboxylate uptake and metabolism in free-living Mesorhizobium ciceri CC1192
Honours, Murdoch University
2024
Abstract
Rhizobia are free-living soil bacteria capable of infecting legume root nodules, within which they fix atmospheric N2 into ammonia, supplying this source of symbiotically fixed N2 to the host plant. While free-living rhizobia can metabolise a wide range of organic carbon sources, N2 fixation inside nodules is fuelled exclusively by the supply of the C4-dicarboxylates fumarate, malate and succinate from the host plant to rhizobia. The dctABD system, encoding the DctA transporter and the DctBD two-component regulator system, facilitates free-living and symbiotic dicarboxylate uptake, with some strains harbouring secondary systems that can mediate dicarboxylate supply in the absence of dctA. Mesorhizobium ciceri CC1192, which nodulates Cicer arietinum (chickpea), harbours three dctA genes, with dctA1 chromosomally encoded, and dctA2 and dctA3 located on the 419-kb mobile symbiosis Integrative and Conjugative Element (ICEMcSym1192). Although each dctA has been individually mutated, their phenotypes and the possibility of synergistic interactions between the genes is yet to be investigated. Therefore, vectors for markerless deletion of all three genes were constructed and double and triple dctA mutants were subsequently isolated. Free-living growth of all dctA1 mutants was abolished on C4-dicarboxylates, while growth of dctA2 and dctA3 mutants was unaffected. Complementation of dctA1 in mutant strains by plasmid-encoded wild-type dctA1 did not restore free-living growth on C4-dicarboxylates to wild-type levels, but did generate possible suppressor mutants. Therefore, DctA1 is likely essential for free-living growth on C4-dicarboxylates in CC1192. Further work will investigate alternative approaches to restore dctA1 function and characterise the symbiotic phenotype of the mutants generated in this study.
Details
- Title
- C4-dicarboxylate uptake and metabolism in free-living Mesorhizobium ciceri CC1192
- Authors/Creators
- Cristina Arcodia Burriolo
- Contributors
- Jason Terpolilli (Supervisor) - Murdoch University, Centre for Sustainable Farming SystemsGraham O'Hara (Supervisor) - Murdoch University, Centre for Sustainable Farming SystemsYvette Hill (Supervisor) - Murdoch University, Centre for Sustainable Farming Systems
- Awarding Institution
- Murdoch University; Honours
- Identifiers
- 991005721270307891
- Murdoch Affiliation
- Centre for Sustainable Farming Systems
- Resource Type
- Thesis
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