Soil carbon cycling and ecosystem functioning can strongly depend on how
microbial communities regulate their metabolism and adapt to changing
environmental conditions to improve their fitness. Investing in
extracellular enzymes is an important strategy for the acquisition of
resources, but the principle behind the trade-offs between enzyme
production and growth is not entirely clear. Here we show that the
enzyme production rate per unit biomass may be regulated in order to
maximize the biomass specific growth rate. Based on this optimality
hypothesis, we derive mathematical expressions for the biomass specific
enzyme production rate and the microbial carbon use efficiency, and
verify them with experimental observations. As a result of this
analysis, we also find that the optimal enzyme production rate decays
hyperbolically with the soil organic carbon content. We then show that
integrating the optimal extracellular enzyme production into microbial
models may change considerably soil carbon projections under global
warming, underscoring the need to improve parameterization of microbial
processes.