Influence of dissolved oxygen concentration on the biosynthesis of cephalosporin C

Abstract

Cephalosporin C was produced by a highly productive strain of Cephalosporium acremonium under industrial production conditions by fed-batch cultivation in a 40-l stirred-tank reactor using a complex medium containing 50 g l −1 peanut flour. The influence of dissolved oxygen concentration (pO 2, DOC), which was maintained at different constant levels between 5 and 40% of its saturation value, during the production phase by means of a parameter-adaptive pO 2-controller, on the cephalosporin C biosynthesis, was investigated. The concentrations of cephalosporin C (CPC) and its precursors penicillin N (PEN N), deacetoxycephalosporin C (DAOC), and deacetylcephalosporin C (DAC) were monitored by on-line HPLC. The concentrations of amino acids, valine (VAL), cysteine (CYS), α-amino-adipic acid (α-AAA), the dipeptide α-amino-adipyl-cysteine (AC), and the tripeptide α-amino-adipyl-cysteinylvaline (ACV) were determined by off-line HPLC. By reducing the pO 2 in the production phase from 40 to 5% of its saturation value, the CPC concentration diminished from 7.2 to 1.1 g l −1 and the PEN N concentration increased from 2.57 to 7.65 g l −1. The DAC concentration also dropped from 3.13 to 0.42 g l −1; however, the DAOC concentration was less influenced. The concentrations of AC and ACV were also less affected. The small DOC did not lead to an accumulation of the intermediate AC and ACV during the production phase. With increasing DOC in the range of 5–20%, the maximal specific production rate, the cell mass concentration-based and the substrate-based yield coefficients for CPC increased almost linearly, and fell back for PEN N. The critical pO 2 level was 20%; below this value a repression of cephalosporin C production occurred. Above 20%, DOC had less effect on the CPC production. The cyclization of the tripeptide to isopenicillin N was, however, hardly influenced by the DOC. The main effect of oxygen limitation was repression of the expandase enzyme, i.e., the conversion of PEN N to DAOC.