Identification of a Polyketide Synthase Involved in Sorbicillin Biosynthesis by Penicillium chrysogenum

Secondary metabolism in Penicillium chrysogenum was intensively subjected to classical strain improvement (CSI), the resulting industrial strains producing high levels of beta-lactams. During this process, the production of yellow pigments, including sorbicillinoids, was eliminated as part of a strategy to enable the rapid purification of beta-lactams. Here we report the identification of the polyketide synthase (PKS) gene essential for sorbicillinoid biosynthesis in P. chrysogenum. We demonstrate that the production of polyketide precursors like sorbicillinol and dihydrosorbicillinol as well as their derivatives bisorbicillinoids requires the function of a highly reducing PKS encoded by the gene Pc21g05080 (pks13). This gene belongs to the cluster that was mutated and transcriptionally silenced during the strain improvement program. Using an improved beta-lactam-producing strain, repair of the mutation in pks13 led to the restoration of sorbicillinoid production. This now enables genetic studies on the mechanism of sorbicillinoid biosynthesis in P. chrysogenum and opens new perspectives for pathway engineering.