The Cell Wall Polymer Lipoteichoic Acid Becomes Nonessential in Staphylococcus aureus Cells Lacking the ClpX Chaperone

Lipoteichoic acid (LTA) is an important cell wall component of Gram-positive bacteria and a promising target for the development of vaccines and antimicrobial compounds against Staphylococcus aureus. Here we demonstrate that mutations in the conditionally essential ltaS (LTA synthase) gene arise spontaneously in an S. aureus mutant lacking the ClpX chaperone. A wide variety of ltaS mutations were selected, and among these, a substantial portion resulted in premature stop codons and other changes predicted to abolish LtaS synthesis. Consistent with this assumption, the clpX ltaS double mutants did not produce LTA, and genetic analyses confirmed that LTA becomes nonessential in the absence of the ClpX chaperone. In fact, inactivation of ltaS alleviated the severe growth defect conferred by the clpX deletion. Microscopic analyses showed that the absence of ClpX partly alleviates the septum placement defects of an LTA-depleted strain, while other phenotypes typical of LTA-negative S. aureus mutants, including increased cell size and decreased autolytic activity, are retained. In conclusion, our results indicate that LTA has an essential role in septum placement that can be bypassed by inactivating the ClpX chaperone. IMPORTANCE Lipoteichoic acid is an essential component of the Staphylococcus aureus cell envelope and an attractive target for the development of vaccines and antimicrobials directed against antibiotic-resistant Gram-positive bacteria such as methicillin-resistant S. aureus and vancomycin-resistant enterococci. In this study, we showed that the lipoteichoic acid polymer is essential for growth of S. aureus only as long as the ClpX chaperone is present in the cell. Our results indicate that lipoteichoic acid and ClpX play opposite roles in a pathway that controls two key cell division processes in S. aureus, namely, septum formation and autolytic activity. The discovery of a novel functional connection in the genetic network that controls cell division in S. aureus may expand the repertoire of possible strategies to identify compounds or compound combinations that kill antibiotic-resistant S. aureus.