B-276. Contribution of the Bacillus anthracis lrgAB Operon to Stationary Phase Survival, Murein Hydrolase Activity and Sporulation

L. Chandramohan, J. S. Ahn, K. W. Bayles;
Univ. of Nebraska Med. Ctr., OMAHA, NE.

Previous studies of Staphylococcus aureus have demonstrated that the cid and lrg operons regulate antibiotic tolerance, cell death and lysis. Based on the effects of cid and lrg mutations on murein hydrolase activity and on similarities to the holin family of proteins it was proposed that the gene products of cidA and lrgA function similar to effector and inhibitor holins, respectively. Expression of the S. aureus lrg operon is regulated by the LytSR two-component regulatory system, whereas the cid operon is regulated by the product of the cidR gene, a LysR-type transcriptional regulator. It has been proposed that the cid and lrg gene products serve as molecular control elements of cell death and lysis during biofilm development. The ubiquitous distribution of cid and lrg homologues in several bacterial species including Bacillus anthracis suggests that these genes play a ubiquitous role in the control of cell death and lysis in bacteria. Similar to the S. aureus lrgAB mutant, a B. anthracis lrgAB mutant exhibited increased murein hydrolase activity compared to the parental strain. However, sodium azide-induced autolysis of mid-exponential phase cells was reduced in the lrgAB mutant compared to the parental strain. Interestingly, unlike the S. aureus lrgAB mutation, which had no impact on cell death in stationary phase, a B. anthracis lrgAB mutant displayed dramatically decreased stationary phase survival relative to the parental strain. Furthermore, a quantitative analysis of sporulation efficiency revealed that the lrgAB mutant formed fewer spores compared to the parental strain. Similar to S. aureus, agents known to dissipate the proton motive force (gramicidin and CCCP) induced B. anthracis lrgAB expression in a lytSR-dependent manner. Taken together, the results of this study demonstrate that the B. anthracis lrgAB operon plays an important role in the control of cell death and lysis in this organism but that its effects on these processes are distinct from that observed in S. aureus.