RiPP Discovery and Regulation in Streptococcus thermophilus

Abstract

Mounting bacterial resistance to antibiotics over the past two decades has imperiled their therapeutic efficacy. Since the majority of antibiotics currently used are derived from bacterial secondary metabolites, the discovery of new secondary metabolites may lead to the development of new, effective antibiotics. Ribosomally synthesized and post-translationally modified peptides (RiPPs) have recently emerged as a prominent class of secondary metabolites in bacteria, though RiPP diversity and regulation are not yet well understood. To these ends, I focus here on the str and kgr RiPP biosynthetic gene clusters (BGCs), which are both thought be regulated by specific short hydrophobic peptide (SHP) signaling, in the unstudied bacterium Streptococcus thermophilus JIM 8232. First, I show that S. thermophilus JIM 8232 produces the known secondary metabolite streptide and the cognate str SHP. It appears that the str SHP turns on streptide production towards mid-log growth phase. Second, targeted metabolomics suggests that the kgr BGC may not be expressed under normal growth conditions. Third, I report a tentative interaction between the kgr and str biosynthetic loci in S. thermophilus JIM 8232. Finally, I demonstrate progress towards identifying the RiPP that the kgr BGC encodes. Taken together, this work presents the first experimental characterization of RiPPs in S. thermophilus JIM 8232 and may provide a framework for leveraging SHP signaling for future secondary metabolite discovery in this strain.