AMYLASE PRODUCTION BY A SCHWANNIOMYCES-OCCIDENTALIS MUTANT IN CHEMOSTAT CULTURE

In carbon-limited chemostat culture the cell yields of a Schwanniomyces occidentalis mutant increased slightly from 0.58 g cells.g-1 starch at a dilution rate of 0.05 h-1 to 0.64 at 0.2 h-1. The maintenance energy requirement was 0.012 g starch.g-1 cells.h-1 and the critical dilution rate was 0.22 h-1 at 30-degrees-C. Specific alpha-amylase activity decreased with an increase in dilution rate. The specific activities of glucoamylase and debranching activity initially increased with an increase in dilution rate up to 0.1 h-1, followed by a decrease in activity at higher dilution rates. Greatly higher levels of amylase activity were obtained in chemostat cultures than in batch cultures. The maximum temperature where a steady state was reached was 37-degrees-C, but production of amylases decreased with an increase in temperature. Amylase production was very sensitive to the dissolved oxygen tension (DOT), exhibiting a dramatic decrease at DOT values below 40% saturation. The critical DOT for growth was 31% of air saturation. On subjecting the mutant to anoxic conditions, growth as well as amylase production was arrested, but these continued after aeration was resumed.