title: An experimental evolutionary study on adaptation to temporally fluctuating pH in Escherichia coli.
abstract: In this study, we use the bacterium Escherichia coli to examine evolutionary responses to environmental acidity fluctuating temporally among pH 5.3, 6.3, 7.0, and 7.8 (5,000-15 nM [H(+)]). Two experimental protocols of temporal variation were used. One group (six replicate lines) of populations evolved for 2,000 generations during exposure to a cycled regime fluctuating daily between pH 5.3 and 7.8. The other group (also in six replicate lines) evolved during exposure for 2,000 generations to a randomly shifting regime fluctuating stochastically each day among pH 5.3, 6.3, 7.0, and 7.8. Adaptation to these fluctuating acidity regimes was measured as a change in fitness relative to the common ancestor by direct competition experiments in both constant and fluctuating pH regimes. For comparisons with constant pH evolution, a group evolved at a constant pH of 5.3 and another group evolved at pH 7.8 were also tested. This study initiated the first long-term laboratory natural selection experiment on adaptation to variable acidity and addressed key questions concerning patterns of adaptation (trade-offs, specialists, generalists, plasticity, transitions, and acclimation) in temporally fluctuating environments.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Irvine, California 92697, USA. bhughes@uci.edu
authors.forename: Bradley S
authors.initials: BS
authors.lastname: Hughes
authors.forename: Alistair J
authors.initials: AJ
authors.lastname: Cullum
authors.forename: Albert F
authors.initials: AF
authors.lastname: Bennett
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D004926:Escherichia coli / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D012641:Selection, Genetic