How Do Bacterial Growth Rates Relate to Evolutionary Fitness Landscapes for Energy-Efficiency?

Abstract

We are interested in energy flows in bacteria, and how energy gets trafficked between producing ribosomal and nonribosomal proteins under different growth conditions. We describe an analytical model that leverages extensive data on experimental growth laws to infer the underlying fitness landscape in E. coli. This model gives insight into some of the complex nonlinear relationships between energy utilization and ribosomal and non-ribosomal production as a function of cell growth conditions. We draw inferences about what evolution has optimized in E. coli. Is E. coli optimized for growth speed or for energy efficiency? Experimental data shows that at its replication speed limit, E. coli produces 4 mass equivalents of non-ribosomal proteins for every mass equivalent of ribosomes. The model shows that this ratio is expected if the bacterial fitness function is the energy efficiency of fast-growing cells. We conclude that a principal evolutionary driving force for bacteria is the energy efficiency of the fastest growing cells.