High exogeneous concentrations of phenoxyacetic acid are crucial for a high penicillin V productivity in Penicillium chrysogenum

A high-penicillin-yielding strain of Penicillium chrysogenum was grown in continuous culture on a chemically defined medium with glucose as the growth-limiting component. The cultivations were operated at a constant dilution rate of 0.05 h-1 and the feed concentration of the penicillin V sidechain precursor phenoxyacetic acid was varied between 0 and 6.5 g l-1. Subsequent formation of penicillin V and by-products related to the penicillin biosynthetic pathway was monitored at steady state. It was established that the concentration of phenoxyacetic acid in the growth medium had to be kept high to obtain a high productivity of penicillin V. The specific production rate of penicillin V as a function of the phenoxyacetic acid concentration followed Michaelis--Menten-type kinetics, from which an overall apparent Km value of 42 mM for the incorporation of intracellular phenoxyacetic acid into penicillin V could be obtained. High phenoxyacetic acid concentrations tended to lower the formation of the by-products 6-aminopenicillanic acid and 8-hydroxypenillic acid. Furthermore the undesirable loss of the pathway intermediate isopenicillin N into the extracellular medium was lowered, whereas the opposite effect was observed for the pathway intermediate δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine and the by-product 6-oxo-piperidine-2-carboxylic acid, the δ-lactam form of α-aminoadipic acid.