Culture Volume Influences theDynamics ofAdaptation under Long-Term Stationary Phase

Abstract

Escherichia coli and many other bacterial species, which are incapable of sporulation, can nevertheless survive within resource exhausted media by entering a state termed long-term stationary phase (LTSP).We have previously shown that E. coli populations adapt genetically under LTSP in an extremely convergentmanner. Here,we examine howthe dynamics of LTSP genetic adaptation are influenced by varying a single parameter of the experiment-culture volume.We find that culture volume affects survival under LTSP, with viable counts decreasing as volumes increase. Across all volumes, mutations accumulate with time, and the majority of mutations accumulateddemonstrate signals ofbeing adaptive.However,positive selection appears toaffectmutation accumulation more strongly at higher, compared with lower volumes. Finally, we find that several similar genes are likely involved in adaptation across volumes. However, the specificmutationswithin these genes that contribute to adaptation can vary in a consistent manner. Combined, our results demonstrate how varying a single parameter of an evolutionary experiment can substantially influence the dynamics of observed adaptation.