Heterologous Production of Polyketides inStreptomyces coelicolorandEscherichia coli

This chapter reviews the development of heterologous polyketide production systems in Streptomyces coelicolor and Escherichia coli, providing specific examples of polyketides produced in these hosts to illustrate the utility of the approach. The first section covers S. coelicolor, an actinomycete that produces a number of polyketides, most notably the blue pigment actinorhodin. The success with S. coelicolor provided motivation to develop heterologous production systems in E. coli and Saccharomyces cerevisiae, user-friendly organisms for which advanced molecular biology tools and fermentation systems are available. In the second section, the development of an E. coli production system is described. Standard Streptomyces transformation methods are employed to introduce expression plasmids into S. coelicolor CH999, a strain that contains a chromosomal deletion of the actinorhodin gene cluster encoding the activities required for the synthesis of the aromatic polyketide actinorhodin. The epothilones are mixed polyketides/nonribosomal peptides that have microtubule-stabilizing activities similar to those of the taxanes but are active against Taxol-resistant tumors. Many polyketides, including epothilone and certain analogs of 6-deoxyerythronolide B (6Deb), are produced at low levels in the S. coelicolor heterologous production system. The availability of heterologous E. coli production systems, together with recent advances in synthetic biology, has accelerated studies of polyketide synthase (PKS) modularity and specificity. With further refinement of the connectivity rules, it is anticipated that virtually any polyketide can be produced in E. coli by coexpression of a suitable set of synthetic PKS modules.