Escherichia coli robustly expresses ATP synthase at growth rate‐maximizing concentrations

Fitness‐enhancing adaptations of protein expression and its regulation are an important aspect of bacterial evolution. A key question is whether evolution has led to optimal protein expression that maximizes immediate growth rate (short‐term fitness) in a robust manner (consistently across diverse conditions). Alternatively, they could display suboptimal short‐term fitness, because they cannot do better or because they instead strive for long‐term fitness maximization by, for instance, preparing for future conditions. To address this question, we focus on the ATP‐producing enzyme F1F0 H+‐ATPase, which is an abundant enzyme and ubiquitously expressed across conditions. Its expression is highly regulated and dependent on growth rate and nutrient conditions. For instance, during growth on sugars, when metabolism is overflowing acetate, glycolysis supplies most ATP, while H+‐ATPase is the main source of ATP synthesis during growth on acetate. We tested the optimality of H+‐ATPase expression in Escherichia coli across different nutrient conditions. In all tested conditions, wild‐type E. coli expresses its H+‐ATPase remarkably close (within a few per cent) to optimal concentrations that maximize immediate growth rate. This work indicates that bacteria can indeed achieve robust optimal protein expression for immediate growth‐rate maximization. To experimentally validate whether Escherichia coli maximizes its growth rate by optimal expression of its ATP synthase, we titrated the expression level of this enzyme in a mutant strain, using an isopropyl β‐ d‐1‐thiogalactopyranoside‐titratable construct. We confirmed that: i. an optimal expression level exists at which the growth rate is maximal, and ii. the wildtype strain achieves this same maximal growth rate across conditions.