Impact of velvet complex on transcriptome and penicillin G production in glucose-limited chemostat cultures of a β-lactam high-producing Penicillium chrysogenum strain.

The multicomponent global regulator Velvet complex has been identified as a key regulator of secondary metabolite production in Aspergillus and Penicillium species. Previous work indicated a massive impact of PcvelA and PclaeA deletions on penicillin production in prolonged batch cultures of P. chrysogenum, as well as substantial changes in transcriptome. The present study investigated the impact of these mutations on product formation and genome-wide transcript profiles under glucose-limited aerobic conditions, relevant for industrial production of β-lactams. Predicted amino acid sequences of PcVelA and PcLaeA in this strain were identical to those in its ancestor Wisconsin54-1255. Controls were performed to rule out transformation-associated loss of penicillin-biosynthesis clusters. The correct PcvelA and PclaeA deletion strains revealed a small reduction of penicillin G productivity relative to the reference strain, which is a much smaller reduction than previously reported for prolonged batch cultures of similar P. chrysogenum mutants. Chemostat-based transcriptome analysis yielded only 23 genes with a consistent differential response in the PcvelAΔ and PclaeAΔ mutants when grown in the absence of the penicillin G side-chain precursor phenylacetic acid. Eleven of these genes belonged to two small gene clusters, one of which contained a gene with high homology to the aristolochene synthase. These results provide a clear caveat that the impact of the Velvet complex on secondary metabolism in filamentous fungi is strongly context dependent.