pcd Mutants of Streptomyces clavuligerus Still Produce Cephamycin C

Biosynthesis of cephamycin C in Streptomyces clavuligerus involves the initial conversion of lysine to alpha-aminoadipic acid. Lysine-6-aminotransferase and piperideine-6-carboxylate dehydrogenase carry out this two-step reaction, and genes encoding each of these enzymes are found within the cephamycin C gene cluster. However, while mutation of the lat gene causes complete loss of cephamycin production, pcd mutants still produce cephamycin at 30% to 70% of wild-type levels. Cephamycin production by pcd mutants could be restored to wild-type levels either by supplementation of the growth medium with alpha-aminoadipic acid or by complementation of the mutation with an intact copy of the pcd gene. Neither heterologous PCR nor Southern analyses showed any evidence for the presence of a second pcd gene. Furthermore, cell extracts from pcd mutants lack detectable PCD activity. Cephamycin production in the absence of detectable PCD activity suggests that S. clavuligerus must have some alternate means of producing the aminoadipyl-cysteinyl-valine needed for cephamycin biosynthesis.