EFFECT OF DISSOLVED-OXYGEN LEVEL ON ACV SYNTHETASE SYNTHESIS AND ACTIVITY DURING GROWTH OF STREPTOMYCES-CLAVULIGERUS

The multi-subunit enzyme, delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (ACV) synthetase catalyses the first step in the biosynthetic pathway of the beta-lactam antibiotic, cephamycin C. In batch fermentations of Streptomyces clavuligerus, ACV synthetase activity appeared during the rapid growth phase. Over the same period the dissolved oxygen (DO) content of the medium was depleted to zero and remained there for nearly 10 h. Maintainance of the DO at saturation throughout the fermentation did not change the maximum ACV synthetase specific activity, but did reduce the in-vivo stability of the enzyme. Oxygen saturation lowered the maximum intracellular ACV levels to one-sixth of those accumulated in the fermentor with no oxygen control, due principally to an improvement in the conversion of ACV to the penicillin N intermediate. Increased oxygenation also improved ACV conversion to cephamycin C, which demonstrated that the activity of both an early and a later enzymatic step in cephamycin biosynthesis was limiting antibiotic production under restricted oxygen conditions. The later step, catalysing the conversion of penicillin N to cephamycin C, showed the greatest sensitivity to the oxygen state of the culture.