Using Mutants to Explore Glucose-Mediated Catabolite Repression in Sinorhizobium meliloti and Assessing the Differences Between Chemical and Biofertilizers

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Mutants, glucose, sinorhizobium meliloti, biofertilizers


Agricultural Education | Environmental Chemistry | Environmental Monitoring | Soil Science


SInorhizobium meliloti, S. meliloti, is a bacterium capable of establishing symbiotic relationship with legumes. Through this symbiotic relationship, the bacteria fix nitrogen and provide this essential nutrient to the plant and ultimately, to the soil. Catabolite repression is the mechanism that allows the bacteria to grow more efficiently on the more catabolizable carbon source first, while repressing the synthesis of enzymes efficient growth, the bacteria ar able to metabolize the carbon sources and more successfully drive the conversaion of N2 to NH3 which can then be used by the plant. Although a great deal of research has been dedicated to this mechanism, little is known regarding the role of glucose in the catabolite repression of the enzyme B-galactosidase in S. meliloti. In order to determine the machinery of glucose-mediated catabolite repression, twenty two mutants believed to be unable to perform glucose mediated-catabolite repression were assayed, and their levels of B-galactosidase activity were measured. All mutants maintained catabolite repression as was demonstrated by repressed B-galactosidase levels. In the initial screening process, three mutants were identified as unable to grow on glucose while a fourth mutant was observed to behave like one of the proposed glucose minus mutants. The glucose minus mutants had similar B-galactosidase activity as the other mutants but clearly had some disruption in glucose metabolism. To determine what the glucose minus mutants were able to grow on, if not glucose, mutants 307620, 20749, 207119 and 107219 were grown on various carbon sources including sucrose, fructose, lactose, succinate, and galactose. Because S. meliloti primarily utilizes the Entner-Doudoroff pathway (as well as the TCA and De Ley-Duodoroff pathways) to metabolize various carbon sources, enzymes of this pathway were investigated as potential sources of disrupted glucose metabolism.

The overall goal of this study was to more thoroughly understand glucose metabolism in S. meliloti via the investigation of its metabolic pathways to eventually better understand how catabolite repression is exerted by S. meliloti, and how far glucose must be metabolized to exert catabolite repression.

Department 1 Awarding Honors Status

Biochemistry and Molecular Biology

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