HIGHER PLOIDY IN SACCHAROMYCES-CEREVISIAE SUPPORTS ENHANCED HEPATITIS-B VIRUS S-CLONED GENE-EXPRESSION AT THE PILOT-SCALE

The effect of host strain ploidy on the production df hepatitis B surf ace antigen (HBsAg) in Saccharomyces cerevisiae was evaluated at the p ilot scale (75 L). We found that the accumulation of HBsAg normalized to cell protein was 2-fold higher for the diploid strain compared to i ts isogenic haploid. No detectable differences in many fermentation pa rameters were observed (e.g., rate of fermentation, growth rate, final cell yield). However, the enhancement of productivity in the diploid strain appeared to be associated with a slower rate of plasmid sheddin g (2 mu m element) and, thus, a higher average copy number (2-fold at stationary phase) compared to those of the haploid strain.