| Abstract | The ClpXP protease functions as a global regulator of many bacterial proteins. It is comprised ofClpX, a regulatory ATPase that recognizes and unfolds proteins, and ClpP, which forms the proteolytic core. ClpX and/or ClpP have been linked to virulence in several pathogens including Bacillus anthracis. While ClpXP is important for survival within the host, it is unclear the mechanism by which it is doing so. We have found that B. anthracis deficient in ClpX (Delta-ClpX) is more susceptible to antimicrobial agents thatinteract with the cell wall such as penicillin, daptomycin and cathelicidin antimicrobial peptides but not non-cell wall active agents. Microarray analysis also revealed thatexpression of the lrgAB operon is substantially decreased in DeltaClpX and this was confirmed by QPCR.LrgA andLrgB act as negative regulators of autolysis and loss of these increases susceptibility of Staphylococcus aureus to penicillin. We hypothesize that the decreased expression of lrgA/B in our ClpX mutant leads to increased autolytic activityand a corresponding increase in susceptibility to cell wall-targeting antibiotics. We compared the rate of cell lysis and the activity of autolytic enzymes between wild-type and ClpX B.anthracis. We found no detectable difference in enzyme activity, but we did observe a small increase in autolytic activity in ClpX. We also found that S. aureusdeficient in LrgA/B is more susceptible to daptomycin. Thus, LrgA/B appears to be involved in resistance to antibiotics besides just penicillin. Therefore, the decrease inlrgAB expression in ClpX might contribute to the increase in antibiotic susceptibility seen in the ClpX mutant. However, furtherwork is still needed to determine whether there is a direct connection between loss of ClpX, decreased LrgA/B and increased antibiotic susceptibility. |
