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

Abstract

Depending on the biomass yield on glucose and the cell morphology ofBacillus 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. AtD = 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 0.25–0.45 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.