Alfalfa plants and the bacteria Sinorhizobium meliloti interact in a symbiotic relationship in which the alfalfa plant receives a usable form of nitrogen, ammonia, to use as a fertilizer, while the bacteria receive a carbon and energy source from the plant roots. During this exchange, there is formation of a root nodule, and these bacteria are implanted inside the alfalfa root cells. To convert the nitrogen by the process of nitrogen fixation for the alfalfa plant, Sinorhizobium meliloti requires a great deal of energy. To conserve the energy that it has, this bacterium performs what is known as catabolite repression. Catabolite repression is the process by which the bacterium uses the carbon source that is most energy efficient for it, and represses the genes responsible for all the other carbon sources. When observing succinate control over the production of B-galactosidase, catabolite repression was seen. (Ucker and Signer, 1978). Glucose-mediated catabolite repression and succinate-mediated catabolite repression were also observed with these bacteria, and an additive effect was observed when both were tested together, suggesting that glucose and succinate-mediated catabolite repression may occur by different mechanisms. (Jelesko and Leigh, 1994). Mutated strains 20749, 307620, 30944, and 30924 were used to identify genes responsible for glucose-mediated catabolite repression. Strains were grown in M9t media with various carbon sources (gluconate, glucose, lactose), and growth was observed by taking absorbance readings on a single-beam spectrophotometer. Growth curves constructed gave many conflicting results, and more growth experiments must be done to confirm growth of these strains on various carbon sources.
Murnin, E. R. (2017). Glucose-mediated catabolite repression in Sinorhizobium meliloti (Undergraduate honors thesis, University of Redlands). Retrieved from http://inspire.redlands.edu/cas_honors/153