Effect of the dilution rate on the biomass yield of Bacillus thuringiensis and determination of its rate coefficients under steady state conditions

Depending on the biomass yield on glucose and the cell morphology of Bacillus thuringiensis, three different metabolic states were observed in continuous culture. At dilution rates between 0.18 h(-1) and 0.31 h(-1) vegetative cells, sporulating bacteria and spores coexisted, while glucose and amino acids were consumed. Only vegetative cells were observed at dilution rates between 0.42 h(-1) and 0.47 h(-1) and glucose was used as the main carbon and energy source. At D = 0.50 h(-1) the biomass yield on glucose decreases sharply. To define better the specific growth rate range in which the microorganism uses mainly glucose, a dilution rate of 0.25-0.35 h(-1) was studied. The experimental data could be adjusted to a Monod model and the following rate coefficients and growth yields were determined: maximum specific growth rate 0.54 h(-1), saturation constant 0.56 mg glucose ml(-1), biomass growth yields 0.43 g cells (g glucose)(-1), and 0.76 g cells (g oxygen)(-1) and maintenance coefficients 0.065 g glucose (g cells)(-1) h(-1) and 0.039 g oxygen (g cells)(-1) h(-1).