Influence of environmental factors on endo-beta-1,4-glucanase production by Bacillus HR68, isolated from a Zimbabwean hot spring.

Abstract

The production of endo-beta-1,4-glucanase by a Bacillus strain isolated from a hot spring in Zimbabwe was studied in batch culture, chemostat culture, and carbon dioxide-regulated auxostat (CO2-auxostat). The bacteria produced the enzyme in the presence of excess glucose or sucrose, but not under carbon-limited conditions in a chemostat using mineral medium. There was a specific growth rate dependent linear increase in enzyme production in glucose excess, nitrogen-limited chemostat cultures. A high specific growth rate of 2.2 h-1 and a high rate of enzyme production of 362 nkat (mg dry mass.h)-1 were attained under nutrient rich conditions in the CO2-auxostat. The bacteria had the highest specific growth rate and endo-beta-1,4-glucanase enzyme production at 50 degrees C. The maximum specific growth rate and the rate of enzyme production increased when yeast extract and tryptone were added in increasing amounts to the mineral medium used for cultivation in separate experiments. Increasing the glucose concentration in the CO2-auxostat cultures increased the rate of enzyme production but did not affect the specific growth rate.