The glutathione metabolism of the beta-lactam producer filamentous fungus Penicillium chrysogenum.

Glutathione (gamma-L-glutamyl-L-cysteinyl-glycine; GSH) shares structural similarities with the beta-lactam biosynthetic intermediate ACV-tripeptide (delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine). Not surprisingly, GSH has been reported to inhibit the beta-lactam biosynthetic machinery quite effectively and, hence, strategies to decrease the intracellular GSH concentrations without influencing negatively the physiological status of idiophasic mycelia would attract industrial interests. Here we present a detailed map of the GSH metabolic network of P. chrysogenum and show a promising way to keep the GSH pool selectively down under penicillin producing conditions. This procedure includes a well-controlled and transient lowering of pH at the beginning of the production phase, and it relies on the GSH-dependent detoxification of the protonophore penicillin side-chain precursors phenoxyacetic acid (POA) and phenylacetic acid (PA). Encouraging preliminary fed-batch fermentation experiments have been performed to test this technological proposal. Interestingly, the mechanism of the activation of POA and PA to the appropriate CoA derivatives has remained yet to be answered but the involvement of GSH seems to be rather unlikely in this case. Our data also challenge the hypothesis that the formation of different kinds of penicillins would be an alternative to GSH-dependent detoxification processes in P. chrysogenum.