Cyclodextrin glycosyltransferase may be the only starch-degrading enzyme in Bacillus macerans

Cyclodextrin glycosyltransferase (CGTase) was released into the culture fluid by Bacillus macerans predominantly in the late stationary phase of growth and during autolysis in the presence of either glucose or starch as a carbon source. In both cases significant soluble intracellular enzyme activity could be observed in the early stationary phase, and a low non-soluble intracellular CGTase activity could be demonstrated also in the exponential growth phase in the presence of starch. At the end of the exponential phase the non-soluble specific intracellular enzyme activity was found to be constant with a value of 0.63 +/- 0.06 nkat/10(9) viable cells. Since amylase activity could not be detected in any intracellular or extracellular sample taken at any culture time, we conclude that cellbound CGTase is the only starch-digesting enzyme in growing B. macerans and, hence, may be fully responsible for the degradation of starch in the culture fluid.