Carbon Source-Mediated Catabolite Repression

Catabolite repression is a regulatory mechanism by which the cell (i) coordinates metabolism of carbon a n d energy sources to maximize efficiency and (ii) regulates other metabolic processes as well. The objective of this review is to examine what is known about the molecular mechanisms by which catabolite repression operates in gram-positive bacteria, especially Bacillus subtilis. In this chapter, the author uses the term catabolite repression to refer specifically to carbon source-mediated regulation and not to regulation by nitrogen or other nutrient sources. The phenomenon of catabolite repression has been best characterized in Escherichia coli. The chapter briefly reviews the basic mechanism by which E. coli accomplishes the type of global regulation. Catabolite repression in E. coli is interference with a positive regulatory mechanism in which the catabolite repressor protein (CRP or CAP) in complex with the cyclic nucleotide cyclic AMP (cAMP) binds to a specific site in the promoter region of catabolite repression-sensitive genes or operons. In the three genera of gram-positive bacteria (S. aureus, Streptomyces spp, and B. subtilis), the molecular mechanism by which catabolite repression functions appears to be fundamentally different from that in E. coli. To date, few studies have been directed at elucidating the molecular mechanism by which carbon source-mediated catabolite repression operates. The mechanism by which B. subtilis monitors its environment for the presence of readily metabolized carbohydrates and translates that information into regulatory signals is unknown.