Date of Award


Degree Name

Master of Science


Biological Sciences

First Advisor

Dr. Silvia Rossbach

Second Advisor

Dr. Karim Essani

Third Advisor

Dr. John Geiser

Access Setting

Masters Thesis-Campus Only


Sinorhizobium meliloti, a beneficial soil bacterium, is known for participating in a symbiotic relationship with legume plants and fixing atmospheric nitrogen within specialized organs callednodules. Mutations in genes responsible for the biosynthesis ofamino acids such as methionine have been reported to affect the ability ofthese mutants to either form nodules or fix nitrogen. Methionine biosynthesis has been studied in depth in bacterialstrains such as Escherichia coli and even other rhizobial strains, however no such studies have been reported in S. meliloti strains 1021 or 2011.

Mutant strains with mutations in putative methionine biosynthesis genes were tested for methionine auxotrophy and the metA, metZ, metH and metF mutants were found to be methionine auxotrophs. In addition, it was attempted to unifythe genetic background ofthe mutations using S. meliloti strain2011 and to characterize the phenotype of the methionine auxotrophic mutants in regards to their nitrogen fixing symbiosis with Medicago sativa(alfalfa).

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