Recombinant polyketide synthesis in Streptomyces: Engineering of improved host strains

Efficient polyketide synthesis derived from plasmid-borne heterologous Stre ptomyces polyketide synthase (PKS) gene clusters necessitates a suitable ho st strain. Well-characterized laboratory strains such as Streptomyces coeli color or Streptomyces lividans and their frequently used derivatives carry endogenous genes for the synthesis of actinorhodin (among other PKS genes), which might interfere with the efficient production of extrachromosomally encoded PKS proteins and the quantitative analysis of their secreted polyke tide products. To circumvent this problem, a frequently used S. coelicolor derivative, designated CH999, was engineered to lack most of the actinorhod in gene cluster. However, this strain can only be transformed with methyl-f ree DNA. Additionally, unlike its otherwise isogenic parent CH1, CH999 exhi bits low transformation efficiencies. Here, we report the construction of t wo S. lividans host strains, K4-114 and K4-155. With respect to the actinor hodin gene cluster, both are genotypically identical to CH999; however, bot h can be transformed at considerably higher frequencies and also with methy lated DNA. Upon transformation with the appropriate expression vector, CH99 9, K4-114 and K4-155 all produce the erythromycin precursor 6-deoxyerythron olide B(6-dEB) equally well.