Interdependence of gene expression for early steps of cephalosporin synthesis in Streptomyces clavuligerus

Study on genetic engineering of Acremonium chrysogenum, the cephalosporin C producer

Acremonium chrysogenum is an important filamentous fungus which produces cephalosporin C in industry. This review summarized the study on genetic engineering of Acremonium chrysogenum, including biosynthesis and regulation for fermentation of cephalosporin C, molecular techniques, molecular breeding and transcriptomics of Acremonium chrysogenum. We believe with all the techniques available and full genomic sequence, the industrial strain of Acremonium chrysogenum can be genetically modified to better serve the pharmaceutical industry.

Early cephamycin biosynthetic genes are expressed from a polycistronic transcript in Streptomyces clavuligerus

A polycistronic transcript that is initiated at the lat promoter has been implicated in the expression of the genes involved in early steps of cephamycin C biosynthesis in Streptomyces clavuligerus. pcbC is also expressed as a monocistronic transcript from its own promoter. However, an alternative interpretation involving expression via three separate yet interdependent transcripts has also been proposed. To distinguish between these possibilities, mutants lacking the lat promoter and containing a transcription terminator within the lat gene (Deltalat::tsr/term mutants) were created. This mutation eliminated the production of lysine-epsilon-aminotransferase (the lat gene product) but also affected the expression of downstream genes, indicating an operon arrangement. Production of delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase (ACVS) (the pcbAB gene product) was eliminated in Deltalat::tsr/term mutants, while production of isopenicillin N synthase (IPNS) (the pcbC gene product) was greatly reduced. The provision of alpha-aminoadipate to the Deltalat::tsr/term mutants, either via exogenous feeding or via lat gene complementation, did not restore production of ACVS or IPNS. Analysis of RNA isolated from the Deltalat::tsr/term mutants confirmed that the polycistronic transcript was absent but also indicated that monocistronic pcbC transcript levels were greatly decreased. In contrast, Deltalat mutants created by in-frame internal deletion of lat maintained the polycistronic transcript and allowed production of wild-type levels of both ACVS and IPNS.