Isopenicillin N synthase and desacetoxycephalosporin C synthase activities during defined medium fermentations of Streptomyces clavuligerus: effect of oxygen and iron supplements.

When the level of dissolved oxygen was increased to saturation in defined media fermentations of Streptomyces clavuligerus, the total duration of activity of the penicillin ring cyclization enzyme, isopenicillin N synthase (IPNS), was extended by at least 20 h; however, no increase in the stability of the ring expansion enzyme, desacetoxycephalosporin C synthase (DAOCS), was observed. Consequently, the conversion of the excreted intermediate penicillin N to cephamycin C was 15-20% less efficient at this high oxygen concentration. The increased dissolved oxygen level also led to the complete loss of IPNS and DAOCS activities for 4 h during the period of fastest growth, and the rate of specific cephamycin C production fell to zero. A several hundred fold increase in the level of iron in the defined media resulted in a sixfold improvement in the rate of specific cephamycin C production after 60 h fermentation. This increased rate appeared to be due to an elevation in the in vivo activities of a number of the cephamycin biosynthetic enzymes, particularly those catalysing later pathway steps.