Effects of substrate availability on growth and metabolism in soil microbes: Insights from theoretical modeling of studies of the Warburg effect and substrate-induced respiration

Carbon Use Efficiency (CUE) is a popular concept for measuring the efficiency of biomass production in different biological systems and, is frequently employed to understand effects of microbial processes on soil carbon dynamics. CUE in soil microbes is often measured through respiration-based studies, especially through the addition of a labile carbon substrate such as glucose. Therefore, exploring the response of microbial respiration to availability of labile substrates is crucial to understand microbial CUE in soils. In this work, we build upon a cellular model of the Warburg effect, where cells simultaneously utilize inefficient aerobic glycolysis/fermentation and efficient oxidative phosphorylation pathways for energy synthesis even at high oxygen availability, to predict microbial community response to various levels of substrate availability. We test our predictions systematically using a series of substrate-induced respiration (SIR) experiments to demonstrate prevalence of the Warburg effect in soil microbial communities. We further discuss the relevance of the underlying metabolic processes behind the Warburg effect in interpreting soil microbial CUE.