Glycerol inhibition of growth and dihydroxyacetone production byGluconobacter oxydans

Abstract

The evidence, kinetic aspects, and modelization of the inhibitory effect of glycerol on dihydroxyacetone (DHA) production byGluconobacter oxydans have been studied. The comparison of the maximal productivities and specific rates evaluated for initial concentrations of 31, 51, 76, 95, and 129 g L⁻¹ of substrate showed that glycerol exerts an inhibitory effect both on growth and DHA production: decrease of the growth-specific rate and of the specific rate of DHA production with increase of the initial glycerol content. The inhibition phenomenon was attributed to an immediate effect of glycerol on the biological activity. It was also established that the presence of glycerol at high concentration induces an increase in the time necessary for the cells to reach their maximal level of specific rates. This result tends to show that glycerol brings into play on the biological system the capacity to reach its optimal range of activity. The main models found in the literature dealing with substrate inhibition phenomena were then tested on experimental data. The exponential model describes at best the glycerol inhibition on growth (μ=0.53e^(−S/93.6)) and on DHA production (q_P=7e^(−S/76.7)). The kinetic study and modelization of the inhibition effect of glycerol on DHA production allows one, therefore, to fill the gap in the fundamental knowledge of this industrial fermentation, to show the maladjustment of the classical fermentation process used (batch), and to reconsider the conception for the optimization of the production (proposition of more adapted process like fed-batch and/or biphasic systems).