Population dynamics of chemotrophs in anaerobic conditions where the metabolic energy acquisition per redox reaction is limited

Abstract

We present a new model of microbial population growth that focuses on the acquisition of metabolic energy through chemosynthesis and how this depends on the concentration of resources and byproducts. Due to entropy effects, organisms extract the greater energy (i.e., they produce the greater amount of adenosine triphosphate) when they use resources that are abundant and generates byproducts that are rare. This effect, which we call the “abundant resource premium,” has been neglected in traditional models of microbial growth because the total metabolic energy acquisition is generally far greater than this premium. This term, however, cannot be neglected for many microbes, such as sulfate reducers, iron oxidizers, and methanogens, which live under conditions of low-energy availability. Our model showed qualitatively different behaviors from those observed in traditional microbial population growth models, such as the Monod model. For example, the steady-state population density was maximum at an intermediate resource-utilizing ability, suggesting that high substrate acquisition is not always advantageous for a microbial population when the availability of metabolic energy is low. We discuss possible implications for evolutionary and ecosystem sciences.