Effects of culture medium composition and temperature on hepatitis B surface antigen expression by recombinant yeast in fermentation processes.

Hepatitis B surface antigen (HBsAg, an exogenous protein) was produced by fermenting recombinant Saccharomyces cerevisiae containing the HBsAg gene. The relative HBsAg concentrations increased from 3.89 to 8.12 when glucose content was reduced and the culture medium was supplemented with glycerol and sucrose; specific activity also increased by a factor of 2.69. The temperature variation sequence for fermentation processes was established from experimental results. The amount of HBsAg gene expressed reached 13.51 in relative concentration terms. The stability of the recombinant plasmid containing the HBsAg gene was studied by the varying fermentation temperatures in a fed-batch process. There was a conversion activity distribution for the yeast containing the exogenous DNA, which affected HBsAg production by the genetically engineered yeast in fermentation processes.