Staphylococcus aureus Overcomes Anaerobe-Derived Short- Chain Fatty Acid Stress via FadX and the CodY Regulon

Chronic rhinosinusitis (CRS) is characterized by immune dysfunction, mucus hypersecretion, and persistent infection of the paranasal sinuses. While Staphylococcus aureus is a primary CRS pathogen, recent sequence-based surveys have found increased relative abundances of anaerobic bacteria, suggesting that S. aureus may experience altered metabolic landscapes in CRS relative to healthy airways. To test this possibility, we characterized the growth kinetics and transcriptome of S. aureus in supernatants of the abundant CRS anaerobe Fusobacterium nucleatum. While growth was initially delayed, S. aureus ultimately grew to similar levels as in the control medium. The transcriptome was significantly affected by F. nucleatum metabolites, with the agr quorum sensing system notably repressed. Conversely, expression of fadX, encoding a putative propionate coenzyme A (CoA)-transferase, was significantly increased, leading to our hypothesis that short-chain fatty acids (SCFAs) produced by F. nucleatum could mediate S. aureus growth behavior and gene expression. Supplementation with propionate and butyrate, but not acetate, recapitulated delayed growth phenotypes observed in F. nucleatum supernatants. A fadX mutant was found to be more sensitive than wild type to propionate, suggesting a role for FadX in the S. aureus SCFA stress response. Interestingly, spontaneous resistance to butyrate, but not propionate, was observed frequently. Whole-genome sequencing and targeted mutagenesis identified codY mutants as resistant to butyrate inhibition. Together, these data show that S. aureus physiology is dependent on its cocolonizing microbiota and metabolites they exchange and indicate that propionate and butyrate may act on different targets in S. aureus to suppress its growth.