Heterologous Expression of a Type II Polyketide Synthase from Blautia wexlerae, a Human Intestinal Commensal

Abstract

Efforts to characterize the human microbiome have produced a trove of sequenced genomes from commensal bacteria. Genome mining allows exploration for bacterial secondary metabolites through identification of the biosynthetic gene clusters which are required to synthesize them. These secondary metabolites are likely to mediate many of the important microbe-microbe and microbe-host interactions which affect human health and disease. Type II polyketides are among these secondary metabolites, and include highly bioactive compounds like antibiotics and cancer drugs. A type II polyketide synthase biosynthetic gene cluster has been found in Blautia wexlerae, a commensal bacterium from the human gut. This thesis reports on the investigation of this gene cluster through partial heterologous expression in Bacillus subtilis. The partial heterologous expression of this gene cluster in B. subtilis results in the production of a dark color, which likely indicates the biosynthesis of aromatic, polyketide-type compounds. LC-MS and HPLC are used to analyze chemical extracts of the heterologous expression system to attempt to identify the compounds being produced. Several compounds are identified, and these leads will help guide further efforts to purify, characterize, and test the products of this gene cluster. This is the first successful heterologous expression of a type II polyketide synthase from an anaerobic bacterium and from a human symbiont, and a step towards identifying the first type II polyketide produced endogenously in the human microbiome.