Carotenogenesis of Staphylococcus aureus: New insights and impact on membrane biophysical properties

Staphyloxanthin (STX) is a saccharolipid derived from a carotenoid in Staphylococcus aureus involved in oxidative-stress tolerance and antimicrobial peptide resistance. STX influences the biophysical properties of the bacterial membrane and has been associated to the formation of lipid domains in the regulation of methicillin-resistance. In this work, a targeted metabolomics and biophysical characterization study was carried out to investigate the biosynthetic pathways of carotenoids, and their impact on the membrane biophysical properties. Five different S. aureus strains were investigated, including three wild-type strains containing the crtM gene related to STX biosynthesis, a crtM-deletion mutant, and a crtMN plasmid-complemented variant. LC-DAD-MS/MS analysis of extracts allowed the identification of 34 metabolites related to carotenogenesis in S. aureus at different growth phases (8, 24 and 48 h), showing the progression of these metabolites as the bacteria advances into the stationary phase. For the first time, 22 members of a large family of carotenoids were identified, including STX and STX-homologues, as well as Dehydro-STX and Dehydro-STX-homologues. Moreover, thermotropic behavior of the CH₂ stretch of lipid acyl chains in live cells by FTIR, show that the presence of STX increases acyl chain order at the bacterial growth temperature. Indeed, the cooperative melting event of the bacterial membrane, which occurs around 15 °C in the native strains, shifts with increased carotenoid content. These results show the diversity biosynthetic of carotenoids in S. aureus, and their influence on membrane biophysical properties.