Increased c-di-AMP levels allow Staphylococcus aureus growth in the absence of lipoteichoic acid

The cell wall polymer lipoteichoic acid (LTA) is crucial for normal growth of many Gram-positive bacteria. Inactivation of LtaS, the enzyme responsible for LTA synthesis in Staphylococcus aureus can be achieved but only under high-osmolarity conditions. In this work, LTA-deficient S. aureus suppressor strains that regained the ability to grow almost normally in the absence of LTA were characterized. Using a whole genome sequencing approach compensatory mutations were identified and revealed that mutations within gdpP (GGDEF domain protein containing phosphodiesterase) allow laboratory and clinical isolates of S. aureus to grow in the absence of LTA. GdpP has phosphodiesterase activity in vitro and uses c-di-AMP as a substrate. We further demonstrate that GdpP also functions in vivo as c-di-AMP-specific phosphodiesterase, as intracellular c-di-AMP levels increase drastically upon its deletion. We quantify for the first time c-di-AMP levels in the cytoplasm of a bacterium and characterize S. aureus proteins involved in its synthesis and degradation. Furthermore, our findings suggest a link between this novel secondary messenger and cell wall properties in Gram-positive bacteria.