Acid stress response of Staphylococcus xylosus elicits changes in the proteome and cellular membrane

Aims: Coagulase negative Staphylococcus xylosus strains are used as starter organisms for sausage fermentation. As those strains have to cope with low pH-values during fermentation, the aim of this study was to identify the acid adaptation mechanisms of S. xylosus TMW 2.1523 previously isolated from salami. Methods and Results: A comparative proteomic study between two different acid tolerant mutants was performed. Therefore, both S. xylosus mutants were grown pH-static under acid stress (pH 5.1) and reference conditions (pH 7.0). Proteomic data were supported by metabolite and cell membrane lipids analyses. S. xylosus acid stress adaptation is mainly characterized by a metabolic change towards neutral metabolites, enhanced urease activity, reduced ATP consumption, an increase in membrane fluidity and changes of the membrane thickness. Conclusion: This study corroborates mechanisms as previously described for other Gram-positive bacteria. Additionally, the adjustment of membrane structure and composition in S. xylosus TMW 2.1523 play a prominent role in its acid adaptation. Significance and Impact of the Study: This study demonstrates for the first time changes of the membrane lipid composition due to acid stress adaptation in staphylococci.