The role of GpsB in cell morphogenesis ofStaphylococcus aureus

Abstract

AbstractFor decades, cells of the gram-positive bacterial pathogenStaphylococcus aureuswere thought to lack a dedicated elongation machinery. However,S. aureuscells were recently shown to elongate before division, in a process that requires a SEDS (Shape Elongation Division and Sporulation) / PBP (Penicillin Binding Protein) pair for peptidoglycan synthesis, consisting of the glycosyltransferase RodA and the transpeptidase PBP3. In ovococci and rod-shaped bacteria the elongation machinery, known as elongasome, is composed of various proteins besides a dedicated SEDS/PBP pair. To identify proteins involved in the elongation ofS. aureus, we screened the Nebraska Transposon Mutant Library, which contains transposon mutants in virtually all non-essential staphylococcal genes, for mutants with modified cell shape. We confirmed the roles of RodA/PBP3 inS. aureuselongation and identified GpsB, SsaA, and RodZ as additional proteins involved in this process. ThegpsBmutant showed the strongest phenotype, mediated by the partial delocalization from the division septum of PBP2, the only bifunctional PBP inS. aureus, with both glycosyltransferase and transpeptidase activity, and of the PBP4 transpeptidase. Increased levels of these PBPs at the cell periphery result in higher levels of peptidoglycan insertion throughout the entire cell, overriding the RodA/PBP3-mediated peptidoglycan synthesis at the outer edge of the septum, which leads to cell elongation. As a consequence, in the absence of GpsB,S. aureuscells become more spherical.