Monounsaturated fatty acid biosynthesis is critical for streptococcal envelope homeostasis and stress tolerance

The genus Streptococcus contains some of the most important commensals and pathogens of the human microbiome. To obtain the fatty acids required for cell membranes, Streptococcus either produce fatty acids de novo through the fatty acid biosynthesis (fab) pathway or uptake host fatty acids through the fatty acid kinase (fak) pathway. Although both the fab and fak pathways represent potential therapeutic targets to prevent or treat infection, progress is limited because of an incomplete understanding of taxon-to-taxon variability in streptococcal lipid metabolism. Here, we examined the role of de novo monounsaturated fatty acid (MUFA) synthesis in physiology and virulence-associated traits in Streptococcus mutans, Streptococcus pyogenes, and Streptococcus pneumoniae, three major pathogens that cause disease at distinct body sites. In all three species, deletion of fabM abolished MUFA production and caused severe growth defects, decreased stress tolerance, increased antibiotic susceptibility, and defects in cell viability, morphology, and division. In S. mutans, loss of fabM also markedly reduced competence signaling and production of the mutacin IV bacteriocin. Deletion of fabM increased susceptibility to killing by human neutrophils in S. mutans and S. pneumoniae, but not S. pyogenes. Together, these findings illustrate that MUFA synthesis is broadly important for streptococcal physiology and cell membrane homeostasis, while its contribution to pathogenesis is strongly species- and context-dependent, providing leads to guide the development of novel therapeutic and/or preventative strategies.IMPORTANCEStreptococcus spp. exert profound effects on human health, with several species causing significant morbidity and mortality. Although streptococcal fatty acid biosynthesis and utilization are attractive metabolic targets for development of therapeutics, this opportunity is vexed by an incomplete understanding of taxon-to-taxon variability in lipid metabolism. In this study, the role of de novo monounsaturated fatty acid (MUFA) synthesis in physiology and virulence-associated traits was examined in Streptococcus mutans, Streptococcus pyogenes, and Streptococcus pneumoniae, three major pathogens that cause disease at distinct body sites. MUFA synthesis was important for stress and antibiotic tolerance across all three species, while its impact on virulence was species- and context-dependent. Overall, these discoveries provide leads to guide the development of novel therapeutic and/or preventative strategies.