Abstract
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° C. Specific α-amylase activity decreased with an increase in dilution rate. The specific activities of gluco-amylase 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° 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.
Published Version
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