Spiraling evolutionary patterns in cycling environments: The experimental evolution of physiologically superior ecological generalists.

摘要

This dissertation examines spiraling evolutionary patterns in cycling environments to rigorously test evolutionary hypotheses related to fitness and trade-offs, and also simulate realistic ecological conditions to bridge the disciplines of experimental evolution to environmental microbiology, using enteric bacterium Escherichia coli as an experimental system. The first study examines evolutionary responses of the bacteria to an environmental acidic-alkaline range between pH 5.3 and 7.8 (15-5000nM[H+]). General hypotheses about adaptation to abiotic variables and coliform organism response to changing environments were tested. Six replicate lines of E. coli evolved for 2,000 generations at one of four different constant pH conditions: pH 5.3, 6.3, 7.0 or 7.8. Both direct and correlated fitness changes in these environments were measured relative to the ancestor in direct competition experiments.;This second study examines evolutionary responses to environmental acidity fluctuating temporally among pH 5.3, 6.3, 7.0, and 7.8 (5000-15nM[H +]). Two distinct temporal variations were used. One group of populations evolved for 2000 generations in a cycled regime fluctuating daily between a constant pH 5.3 and 7.8 cycle. The other group evolved during exposure for 2000 generations to a randomly shifting regime fluctuating stochastically day-by-day between pH 5.3, 6.3, 7.0 or 7.8. Relative fitness changes were measured by direct competition experiments in both constant and stochastic pH regimes. This study initiated the first long-term natural selection experiment on adaptation to variable pH, investigating patterns of trade-offs, specialists, generalists, and acclimation in temporally fluctuating environments.;The third study investigated Escherichia coli growth and survival in a novel "Host to Coast" laboratory Analog simulating an 11-day sequence cycling through the pH and temperature conditions of the small intestine, colon, sewer, seawater, human stomach, and back into the small intestine. This study investigated the evolutionary roles of pH and temperature in evolving increased growth and survival fitness of E. coli in environments of coastal seawater and human host. Patterns, such as high alkalinity evolving high growth fitness in seawater, are discussed. Results may have future implications for wastewater treatment/release into marine waters for the prevention of evolving superior strains of pathogenic E. coli.