Frequency- and Amplitude-Dependent Microbial Population Dynamics during Cycles of Feast and Famine

In nature microbial populations are subject to fluctuating nutrient levels. Nutrient fluctuations are important for evolutionary and ecological dynamics in microbial communities since they impact growth rates, population sizes, and biofilm formation. Here we show that when populations of Escherichia coli are subjected to cycles of nutrient excess (feasts) and scarcity (famine) their abundance dynamics during famines depend on the frequency and amplitude of feasts. We show that frequency and amplitude dependent dynamics in planktonic populations arise from nutrient and history dependent rates of aggregation and dispersal. These conclusions are enabled by precision measurements performed with automated continuous culture devices coupled to custom fluorescence microscopes. The instruments automatically sample, image and count single-cells drawn from continuously-cultured populations on a timescale of minutes for periods of weeks. The quality of the data enable us to construct a concise phenomenological model that recapitulates our experimental observations. Our results show that the statistical properties of environmental fluctuations have substantial impacts on spatial structure in bacterial populations driving large changes in abundance dynamics.