The Antimicrobial Role of Candidate Biosynthetic Gene Clusters from Actinomyces Strains within the Oral Human Microbiome

Abstract

The oral community is an essential part of the human microbiome controlled by both aerotolerant and anaerobic commensal bacteria including the Streptococci and Actinomyces genera. Recent studies have shown the antimicrobial role of commensals through production of antibiotic metabolites that can inhibit bacterial growth within the human microbiome. These secondary metabolites are produced through biosynthetic pathways regulated by biosynthetic gene clusters (BGCs), which have become a key genomic tool in identifying candidate gene clusters to test for antibiotic bioactivity. Two BGCs – a phenazine-like cluster and a thiopeptide-like cluster – from different Actinomyces spp. were identified using an antiSMASH similarity analysis against known homologous antimicrobial gene clusters. We hypothesized that these BGCs each produce secondary metabolites that can inhibit both pathogenic and commensal growth within the oral community. We endogenously cultured BGCs within their Actinomyces strains to assess the cell extracts using 1) bioassays against a panel of oral indicator pathogens and commensals to test for antimicrobial activity, and 2) liquid chromatography-mass spectrometry (LC-MS) to analyze extract composition for phenazine-like and thiopeptide-like molecules. The bioassays have shown potential bioactivity at lower extract concentractions, but heterologous expression of the phenazine BGC in E. coli BL-21 has shown little evidence of phenazine in comparative LC-MS analyses. Further experimentation into endogenous Actinomyces LC-MS analysis and the heterologous expression of the thiopeptide candidate BGC could help to determine the importance of Actinomyces abundance in the human microbiome for potentially limiting both pathogenic and commensal growth within the oral community.