Production of cyclodextrin glycosyltransferase by batch and chemostat culture of Bacillus macerans in chemically defined medium

Abstract

AbstractA chemically defined medium for cultivation of Bacillus macerans is reported. Growth rates and cyclodextrin glycosyltransferase (CGT) titres obtained were similar to those obtained using media containing potato extract. The proteins in supernatant fluids from a batch culture were separated by disc electrophoresis and results obtained showed that CGT was produced after growth ceased, in agreement with results of activity measurements. The maximum growth rate in the chemostat considerably exceeded that in batch culture; this anomalous effect is unexplained. High CGT titres were produced at low dilution rates (0.03 to 0.05 h−1) but residual starch was present at higher dilution rates and CGT synthesis was repressed. Enzyme titres obtained in chemostat cultures at D = 0.03 h−1 using defined medium containing 13 g starch/1 were 2.75 times greater than the maximum obtainable by batch cultivation and about 20 times greater than those reported by other workers using medium containing diced potato and CaCO3. A two‐stage chemostat cultivation was performed using dilution rates of 0.1 h−1 and 0.033 h−1 in the first and second stages, respectively. The CGT activity in the second stage increased by 57 per cent when a maintenance feed of starch was supplied at 0.08 g g−1 dry biomass h−1. Only negligible CGT titres were obtained when a dilution rate of 0.5 h−1 was used in the first stage. For reasons not understood, DM medium would not support biomass yields greater than 5 g 1−1. This limitation was not due to production of an inhibitor, or to deficiency of N, Fe, Zn, Mn, thiamine or biotin.