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Alfalfa and Sinorhizobium meliloti interact in a symbiotic relationship where the legume receives ammonia as fertilizer, while the bacterium receives carbon sources from the alfalfa roots. This exchange involves the formation of a root nodule and the bacteria are implanted inside the legume root cells. s. meliloti requires large amounts of energy for the production of ammonia through a nitrogen fixation reaction. As a means to conserve energy the bacterium uses the most efficient carbon source. Catabolite repression was seen in succinate control over the production of ß-galactosidase, required for the metabolism for lactose. The additive effect of glucose to this repression suggested that glucose also has control over lactose metabolism (Jelesko and Leigh, 1994). Mutated S. meliloti strains 10727, 107222,107317, 107111, and 107316 were used to identify genes responsible for glucose-mediated control of ß-galactosidase. The best growth conditions determined were to use Luria-Bertani medium with calcium and magnesium, LBCM, for a two day period with a 27 hour induction period in M9 lactose 0.4% or M9 glucose 0.4% + lactose 0.4% media. Using UV/vis spectroscopy the cleavage of ONPG by ß-galactosidase indicates the concentration of ß-galactosidase in the cells. Comparison between cells induced with glucose to those without produces a percent expression of ß-galactosidase, which is around 100% for cells not under catabolite repression. Strains 10727, 107222, and 107317 could have mutations in genes contributing to glucose-mediated catabolite repression in S. meliloti.