HIGH-CONCENTRATION CULTURE OF BACILLUS-SUBTILIS-SPO- MUTANT STRAIN CARRYING A RECOMBINANT PLASMID

A Bacillus subtilis spo- mutant strain harboring a recombinant plasmid was cultured at a high cell density concentration by using a cross-flow filtration system. The cell concentration obtained was 300 as an optical density at 570 nm, which was six times as high as that of a fed-batch culture without using the cross-flow filtration system. However, the specific activity of plasmid-encoded beta-galactosidase decreased by filtration. To improve the specific activity, the carbon source was stepwisely changed from glucose to starch. By using a fed-batch culture combined with cross-flow filtration and the stepped change of carbon source, the production of the plasmid-encoded enzyme was improved 3 times compared with that of the fed-batch culture.