Sinorhizobium meliloti forms a symbiosis with Medicago species of legumes. Within the legume root nodules, S. meliloti differentiates into a bacteroid, which fixes atmospheric nitrogen into ammonia for the legume. The legume produces hundreds of nodule-specific cysteine-rich (NCR) peptides, which mediate bacteroid differentiation. The S. meliloti BacA protein was the first bacterial factor identified to be essential for bacteroid development. BacA sensitises S. meliloti to certain antimicrobial peptides and influences the modification of the bacterial lipopolysaccharide (LPS) with a very-long-chain fatty acid (VLCFA). Therefore, it is thought that either the peptide uptake function or the role of BacA in LPS VLCFA decoration could be essential for survival of S. meliloti within the legume. In this PhD project, a role for BacA in the response of S. meliloti towards NCR peptides was investigated. It was determined that BacA protects S. meliloti from NCR-induced cell death. Furthermore, it was found that the structure and composition of the LPS plays a key role in the response of S. meliloti to NCR peptides. It was also shown that the peptide uptake function of BacA was conserved among different rhizobia. The role and biosynthesis of the LPS VLCFA in bacteroid development was also explored. It was determined that the acyltransferase but not the acyl-carrier-protein, was essential for the biosynthesis of VLCFA modified LPS in planta. Six genes, located in a gene cluster were proposed to be involved in the LPS VLCFA biosynthesis in rhizobia and my research found that this was the case. The outcome of this research has provided important insights into the mechanism of prolonged bacterial-host infections and the biosynthesis of unusual lipids.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:553800 |
| Date | January 2011 |
| Creators | Haag, Andreas F. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=183674 |
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