Effect of increased dosage of the ML-236B (compactin) biosynthetic gene cluster on ML-236B production in Penicillium citrinum

The gene cluster responsible for ML-236B (compactin) biosynthesis has recently been characterized from P. citrinum No. 41520. Here, we describe how the ML-236B-producing strain was improved using a cosmid-mediated recombination technique. The introduction of the cosmid pML48, which contains seven of the nine ML-236B biosynthetic genes, into P. citrinum No. 41520 resulted in transformants which produced increased amounts of ML-236B. Southern analysis showed that pML48 had been incorporated by a homologous recombination event, and all high producers possessed two copies of each of the seven genes, mlcA-mlcF and mlcR, suggesting that increased dosage of the biosynthetic gene cluster was responsible for the enhanced production of ML-236B. On the other hand, various kinds of mutants with decreased titers of ML-236B were also obtained. Characterization of one such mutant, designated as T48.28, which was more sensitive to ML-236B than the parental strain, suggested that one of the ML-236B biosynthetic genes, mlcD, which encodes a putative HMG-CoA reductase, was involved in conferring resistance to ML-236B.