Biochemical characterization and molecular genetics of nine mutants of Penicillium chrysogenum impaired in penicillin biosynthesis.

Nine mutants of Penicillium chrysogenum (npe1 to npe8 and npe10) impaired in penicillin biosynthesis were screened after nitrosoguanidine mutation. Mutants npe1, npe4, npe5, npe6, npe7, npe8, and npe10 failed to synthesize significant levels of penicillin, whereas strains npe2 and npe3 synthesized about 20% of the penicillin level produced by the parental strain. Mutants npe5 and npe10 did not show alpha-aminoadipylcysteinyl-valine (ACV) synthetase activity in vitro and did not form ACV in vivo. Immunoblotting analysis of the different mutants using antibodies raised against Aspergillus nidulans ACV-synthetase showed that mutants npe5 and npe10 lacked this multienzyme protein, which in the parental strain had a molecular mass of about 420 kDa, and mutants npe2 and npe3 formed reduced level of this protein. All mutants showed normal levels of isopenicillin N synthase, as shown by Western blot analysis and enzyme assays (except npe10 that lacked this enzyme and npe2 and npe3 that formed reduced levels); npe1, npe4, npe6, npe7, npe8, and npe10 lacked isopenicillin N acyltransferase. Southern hybridizations of total DNA of the parental strain and mutants npe5, npe6, npe8, and npe10 with probes internal to the pcbAB, pcbC, and penDE genes showed that mutants npe5, npe6, and npe8 had the same arrangement of the penicillin gene cluster carrying probably point mutations, but mutant npe10 lacked the three penicillin biosynthetic genes, suggesting that it had suffered a deletion of the entire penicillin cluster. Southern hybridization with a pyrG probe as control and fingerprinting analysis of total DNA of npe10 as compared to several P.chrysogenum strains and other Penicillium and Aspergillus species, confirmed that npe10 is a deletion mutant of P. chrysogenum that had lost the penicillin biosynthetic genes.