Controlled expression of heterologous cytochrome P450e cDNA in Saccharomyces cerevisiae. II. Development of cultivation process for heterologous cytochrome P450e production

Cytochrome P450e was expressed in Saccharomyces cerevisiae under the regime of the PHO5 promoter and terminator. Derepression of the expression system was achieved by shifting the cells from C- to P-limited growth in a continuous culture. Alongside the production of heterologous cytochrome P450e, a change from purely oxidative to oxido-reductive glucose metabolism was initiated by the shift. The expression of cytochrome P450e was not stable and production ceased after a cultivation period of approximately 25 days. A shift to higher dilution rate accelerated the loss of expression activity which was paralleled by a decrease in relative plasmid copy number. To avoid the disadvantages of the continuous production system, which is a reduction of biomass yield as a consequence of the shift in metabolism with the beginning of P-limited growth, a repeated fed-batch process was evaluated for heterologous product formation.