Energy allocation theory for bacterial growth control in and out of steady state

Allocating energy resources efficiently to key physiological functions permits living organisms to grow in diverse environments and adapt to a wide range of perturbations. To understand how unicellular organisms quantitatively utilize energy in response to environmental changes, we introduce a theory of dynamic energy allocation which describes the dynamics of microbial growth based on the partitioning of metabolizable energy into growth, division, cell shape regulation, energy storage, and loss through dissipation. By optimizing the growth energy flux, we derive general equations governing the time-evolution of bacterial growth rate and morphology. The resulting model accurately captures experimentally observed dependencies of bacterial cell size on growth rate, superlinear scaling of metabolic rate with cell size, and predicts nutrient-dependent trade-offs in energy expenditure. By calibrating model pararameters with experimental data for the model organism E. coli, energy allocation theory is capable of describing growth control in dynamic conditions, including nutrient shifts and osmotic shocks. The model captures these perturbations with minimal added complexity and our unified approach predicts the driving factors behind a wide range of observed morphological and growth phenomena.