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 Late range in which the microorganism uses mainly glucose, a dilution rate of 0.25-0.45 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.