A HOMOLOG OF CCPA MEDIATES CATABOLITE CONTROL IN LISTERIA-MONOCYTOGENES BUT NOT CARBON SOURCE REGULATION OF VIRULENCE GENES

Readily utilizable sugars down-regulate virulence gene expression in L isteria monocytogenes, which has led to the proposal that this regulat ion may be an aspect of global catabolite regulation (CR), We recently demonstrated that the metabolic enzyme alpha-glucosidase is under CR in L. monocytogenes. Here, we report the cloning and characterization from L, monocytogenes of an apparent ortholog of ccpA, which encodes a n important mediator of CR in several low-G+C-content gram-positive ba cteria. L. monocytogenes ccpA (ccpA(Lm)) is predicted to encode a 335- amino-acid protein with nearly 65% identity to the gene product of Bac illus subtilis ccpA (ccpA(Bs)), Southern blot analysis with a probe de rived from ccpA(Lm) revealed a single strongly hybridizing band and al so a second band of much lower intensity, suggesting that there may be other closely related sequences in the L. monocytogenes chromosome, a s is the case in B, subtilis. Disruption of ccpA(Lm) resulted in the i nability of the mutant to grow on glucose-containing minimal medium or increase its growth rate in the presence of preferred sugars, and it completely eliminated CR of alpha-glucosidase activity in liquid mediu m. However, alpha-glucosidase activity was only partially relieved fro m CR on solid medium. These results suggest that ccpA is an important element of carbon source regulation in L, monocytogenes. Nevertheless, utilizable sugars still down-regulate the expression of hly, which en codes the virulence factor hemolysin, in a ccpA(Lm) mutant, indicating that CcpA is not involved in carbon source regulation of virulence ge nes.