Plants are unable to utilize the N2 form found in the soil environment. Bacteria known as rhizobia are capable of fixing this nitrogen into a form useable by the plant and initiate a symbiotic relationship in the legume root. One species of rhizobia, Sinorhizobium meliloti, has been thoroughly investigated in terms of its biochemical properties. Our research focuses on the concept of catabolite repression, a mechanism in which a preferred carbon source catabolized for growth represses the genes responsible for catabolizing a different carbon source such as lactose, as seen in Escherichia coli. S. meliloti displays succinate-mediated catabolite repression and glucose-mediated catabolite repression. Much research has focused on the mechanisms involved in succinate-mediated catabolite repression, while only a handful of these mechanisms are understood regarding glucose. Fructose may be an important entryway into the Entner-Doudoroff pathway with regards to glucose-mediated catabolite repression. This research seeks to answer the question of how far fructose must be metabolized in order to cause catabolite repression; is it in fact the process of phosphorylation or the formation of a metabolite such as 6-phosphogluconate that is necessary? In order to investigate this phenomenon, S. meliloti was subjected to Tn5 mutagenesis and was screened in order to find a mutant that showed fructose-inhibited growth. This bacterium was also subjected to ampicillin enrichment, as another technique used to obtain a mutant that is unable to grow on fructose. These techniques led to a fructose growth mutant, SmCT2141. Catabolite repression was assessed based on the growth of the bacteria on media plates containing X-Gal, lactose and fructose, while quantitative analyses were performed via the measurement of β-Gal (the enzyme responsible for initial catabolization of lactose).
Timmerman, C. (2015). Fructose Mediated Catabolite Repression in Sinorhizobium meliloti (Undergraduate honors thesis, University of Redlands). Retrieved from http://inspire.redlands.edu/cas_honors/109