Mis-localization of PBPs in Staphylococcus aureus gdpP mutant contributes to β-lactam resistance and surface protein cross-wall trafficking

Mutations in gdpP are frequently associated with β-lactam resistance in Staphylococcus aureus. GdpP is a phosphodiesterase that degrades the second messenger c-di-AMP, which plays a key role in osmoregulation and antibiotic resistance in many Gram-positive bacteria. However, the mechanisms of β-lactam resistance remain unknown. We show here that deletion of gdpP disrupted penicillin-binding proteins (PBPs)-mediated deposition of YSIRK+ surface protein SpA to septal peptidoglycan (cross-wall). In contrast to their septal localization in WT staphylococcal cells, all four PBPs (PBP1-4) were drastically mis-localized as distinct single foci in ΔgdpP. The mis-localization of PBPs is attributed to c-di-AMP accumulation as overexpression of c-di-AMP synthetase dacA phenocopied ΔgdpP. In addition, ΔgdpP exhibited severe cell cycle retardation deficient in cell division initiation. The aberrant foci formation of PBPs altered the spatial distribution of cell wall synthesis but did not affect the overall cell wall cross-linking. The foci formation of PBPs correlated with β-lactam resistance: the foci gradually decreased with increased concentrations of penicillin. We concluded that the aberrant spatial distribution of PBPs and the cell division defects of ΔgdpP contribute to β-lactam resistance and YSIRK+ protein cross-wall trafficking.