Cloning and expression analysis of the pcbAB-pcbC β-lactam genes in the marine fungus Kallichroma tethys

Here we report the identification of the β-lactam biosynthesis genes pcbAB and pcbC from a cosmid genomic DNA library of the marine fungus Kallichroma tethys. A BLAST homology search showed that they share high sequence identity with the δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine (ACV) synthetases and isopenicillin N synthases, respectively, of various fungal and bacterial β-lactam producers, while phylogenetic analysis indicated a close relationship with homologous genes of the cephalosporin-producing pyrenomycete Acremonium chrysogenum. Expression analysis by reverse transciption-PCR suggested that both genes are highly regulated and are expressed in the late growth phase of K. tethys cultures. Complementation of an Aspergillus nidulans strain deficient in ACV synthetase suggested that at least pcbAB is functional, although attempts to isolate active antibiotic from K. tethys were unsuccessful.