Characterization and identification of environmental stress tolerance mechanisms in Sinorhizobium meliloti
| dc.contributor.author | Hawkins, Justin P. | |
| dc.contributor.examiningcommittee | Court, Deborah (Microbiology) Brassinga, Ann Karen (Microbiology) Belmonte, Mark (Biological Sciences) Long, Sharon R. (Biology, Stanford University) | en_US |
| dc.contributor.supervisor | Oresnik, Ivan (Microbiology) | en_US |
| dc.date.accessioned | 2018-01-17T19:34:21Z | |
| dc.date.available | 2018-01-17T19:34:21Z | |
| dc.date.issued | 2017 | |
| dc.degree.discipline | Microbiology | en_US |
| dc.degree.level | Doctor of Philosophy (Ph.D.) | en_US |
| dc.description.abstract | The process of biological nitrogen fixation by rhizobial inoculum provides an environmental beneficial alternative to nitrogen acquisition compared to artificial fertilizers. Sinorhizobium meliloti is a gram-negative α-proteobacteria which can fix nitrogen when in a symbiotic relationship with its legume hosts Medicago sativa and Medicago truncatula. The ability of rhizobium to carry out this process however is dependent on rhizobium being able to thrive in the diverse conditions present in both soil and during symbiosis. This thesis describes the use of bacterial genetics to characterize how metabolism and the production of polysaccharides affect the survival of strains under salt and acidic pH stress. The gene SMc00722 was characterized and shown to be integral for tolerance of high magnesium concentrations, though was not necessary for symbiotic establishment. The production of low molecular weight succinoglycan was shown be directly involved tolerating acidic pH, and directly influences the ability of the strain to compete for nodule occupancy. The gene tkt2 was characterized as being the primary transketolase involved in the non-oxidative pentose phosphate pathway. The activity of this protein was shown to directly influence the production of succinoglycan, and tolerate acidic pH. Mutants in this gene were also shown to be impaired in biological nitrogen fixation, and the rate of nodule formation. Overall, these results are consistent with they hypothesis that mechanisms used by rhizobia to tolerate diverse environmental conditions directly interact with the symbiotic process. These data may lead to further understanding of the complex signaling process between rhizobia and legumes, and an understand of how rhizobial inoculums could be applied in more diverse soil conditions. | en_US |
| dc.description.note | February 2018 | en_US |
| dc.identifier.uri | http://hdl.handle.net/1993/32851 | |
| dc.language.iso | eng | en_US |
| dc.rights | open access | en_US |
| dc.subject | Sinorhizobium | en_US |
| dc.subject | Exopolysaccharides | en_US |
| dc.subject | Metabolism | en_US |
| dc.title | Characterization and identification of environmental stress tolerance mechanisms in Sinorhizobium meliloti | en_US |
| dc.type | doctoral thesis | en_US |