Reduced function of a phenylacetate-oxidizing cytochrome P450 caused strong genetic improvement in early phylogeny of penicillin-producing strains

The single-copy pahA gene from Penicillium chrysogenum encodes a phenylacet ate 2-hydroxylase that catalyzes the first step of phenylacetate catabolism , an oxidative route that decreases the precursor availability for penicill in G biosynthesis. PahA protein is homologous to cytochrome P450 monooxygen ases involved in the detoxification of xenobiotic compounds, with 84% ident ity to the Aspergillus nidulans homologue PhacA. Expression level of pahA d isplays an inverse correlation with the penicillin productivity of the stra in and is subject to induction by phenylacetic acid. Gene expression studie s have revealed a reduced oxidative activity of the protein encoded by pahA genes from penicillin-overproducing strains of P. chrysogenum compared to the activity conferred by phacA of A. nidulans. Sequencing and expression o f wild-type pahA from P. chrysogenum NRRL 1951 revealed that an L181F mutat ion was responsible for the reduced function in present industrial strains. The mutation has been tracked down to Wisconsin 49-133, a mutant obtained at the Department of Botany of the University of Wisconsin in 1949, at the beginning of the development of the Wisconsin family of strains.