The energetics of microbes at slow growth rates: Maintenance energies and dormant organisms

Abstract In continuous cultures at slow growth rates (less than about 10% maximum) bacterial growth yields from the carbon and energy source are higher than those expected. To account for this deviation it is proposed that dormant or non-viable cells with zero maintenance energy are generated at slow growth rates. From the growth yield variation, it is shown, the dormant fraction of the culture can be calculated. The few quantitative data available on the viability of bacteria in chemostat steady states at very slow growth rates are in agreement with the hypothesis. It is suggested that enzymic, chemical and morphological characters also may be used to distinguish between the growing and dormant fractions of a culture. The model provides a unifying theory for studies of microbial function at slow growth rates, which is a field of great practical importance.