Bioenergetic interpretation on the S-o/X(o) ratio in substrate-sufficient batch culture

A batch culture of microorganisms can be classified to substrate-limited and substrate-sufficient growth according to the relative availability of the substrate to biomass, i.e. the S-0/X(0) ratio. It is generally observed that the growth yields are greater at lower S-0/X(0) ratios than at higher S-0/X(0) ratios. The excess substrate should cause serious uncoupling between anabolism and catabolism leading to energy spilling. Based on a balance on substrate reaction, the total quantity of substrate consumed by microorganisms is taken to be the sums of the quantity of substrate utilization for growth, the quantity of substrate utilization for maintenance and that due to energy spilling, a kinetic model is proposed to describe the dependence of the observed growth yield on the S-0/X(0) ratio for substrate-sufficient batch culture. It is demonstrated that decline in the observed growth yield with increasing the S-0/X(0) ratio is mainly due to energy spilling under substrate-sufficient conditions. The proposed model describes the literature data satisfactorily. Copyright (C) 1996 Elsevier Science Ltd