Glucose-mediated Catabolite Repression in Sinorhizobium meliloti
Authors:
Bryan S. Artmann, Shane Bradner, Meghan E. KingMentor:
Daniel B. Wacks, Professor of Chemistry, University of RedlandsSinorhizobium meliloti develops a mutualistic symbiotic relationship with alfalfa plants. The plant provides a variety of carbon sources to S. meliloti, while the bacteria induce the formation of nitrogen-fixing nodules on the plant roots, in which the bacteria convert atmospheric nitrogen to usable ammonia. During the process of nodulation, S. meliloti encounters a variety of carbon sources. The bacteria utilize catabolite repression, the process of repressing the use of one carbon source in the presence of a preferred carbon source, to efficiently control metabolism. Our group has chosen to study glucose-mediated catabolite repression in S. meliloti. We wanted to determine the extent to which glucose must be metabolized to exert catabolite repression. Following up preliminary results from 2011 (Bradner, S. 19th Annual Southern California Conference on Undergraduate Research) we studied carbon sources entering the Entner-Doudoroff pathway at different points to see which exerted catabolite repression. The bacteria were grown on minimal medium plus lactose, and lactose plus one of the following carbon sources: glucose, succinate, fructose, galactose, gluconate, sucrose or maltose. ß-galactosidase assays were then performed to determine ß-galactosidase activity of cells grown on lactose versus cells grown on lactose plus the second carbon source to determine if catabolite repression was exerted. We found that fructose and gluconate, but not galactose, caused catabolite repression. This suggests that either 6-phosphogluconate or 2-dehydro-3-deoxyphosphogluconate serves as a signal for glucose-mediated catabolite repression. Further work will involve investigating mutants blocked at different points in the Entner-Doudoroff pathway to confirm which intermediates are responsible for catabolite repression. (All authors contributed equally to this work.)