Functional characterization of the glxR deletion mutant of Corynebacterium glutamicum ATCC 13032: involvement of GlxR in acetate metabolism and carbon catabolite repression

Recently, a cyclic AMP receptor protein homologue, GlxR, was reported to bind to the upstream regions of several genes involved in the regulation of diverse physiological processes in Corynebacterium glutamicum. However, the function of GlxR has not yet been explored in C. glutamicum in vivo using a glxR deletion mutant. Therefore, this study examines the role of GlxR as a repressor in glyoxylate bypass and carbon catabolite repression (CCR) using a deletion mutant. The disruption of glxR resulted in a severe growth defect, but growth was restored by complementation with the glxR and crp genes from C. glutamicum and Streptomyces coelicolor, respectively. The production of isocitrate lyase (ICL) and malate synthase (MS) was significantly increased in the glxR mutant. The specific activities of both enzymes were increased in the glxR mutant, regardless of the carbon source. In accordance, the promoter activities of ICL and MS using lacZ fusion were derepressed in the glxR mutant. In addition, the glxR mutant exhibited derepression of the gluA gene for glutamate uptake in the presence of glucose, thereby relieving CCR by glucose. These results indicate that GlxR plays an important role in CCR as well as in acetate metabolism.