Azevedo, Ricardo B. R.2019-12-17December 22019-12December 2Portions of this document appear in: Phillips, Kelly N., Gerardo Castillo, Andrea Wünsche, and Tim F. Cooper. "Adaptation of Escherichia coli to glucose promotes evolvability in lactose." Evolution 70, no. 2 (2016): 465-470. And in: Phillips, Kelly N., Scott Widmann, Huei-Yi Lai, Jennifer Nguyen, J. Christian J. Ray, Gábor Balázsi, and Tim F. Cooper. "Diversity in lac Operon Regulation among Diverse Escherichia coli Isolates Depends on the Broader Genetic Background but Is Not Explained by Genetic Relatedness." mBio 10, no. 6 (2019).https://hdl.handle.net/10657/5608Selection in fluctuating environments can lead to novel adaptations that may limit or facilitate evolution. I used Escherichia coli populations experimentally evolved in limited-glucose and -lactose environments to examine the effect of historical contingency and test for compensation of the cost normally produced by an evolved non-functional lac operon repressor (lacI-) in glucose. I surveyed 23 diverse strains for natural variation in regulatory function of the E. coli lac operon, which integrates transcriptional control of the lac operon with environmental signals from glucose and lactose availability. Although lac operon regulation has been extensively studied, a considerable amount of research is based on a small number of closely related strains. I found that populations initially evolved in a limited-glucose environment, and clones randomly selected from these populations, were more evolvable than the common ancestor during 1k generations of evolution in a lactose-limited environment, indicating specific genetic changes throughout glucose selection led to increased evolvability. Genome sequencing of the pre-evolved glucose clones revealed mutations in the gene iclR as candidates for increasing evolvability. Next, I tested for compensation of the glucose cost of lacI- in experimentally evolved populations after 8k generations of selection in minimal glucose and lactose fluctuating environments. Competitions measuring the lacI- fitness effect indicated that compensation rarely alleviated the cost in glucose, but epistasis commonly increased the benefit in lactose compared to the ancestor. A reporter introduced into these evolved clones indicated lac operon expression changed but had different fitness effects. Finally, using the same reporter but placed into 28 distinct strains, I measured E. coli lac operon expression in inducers combined at different concentrations. The results encompassed regulatory functions of a vast range, and aspects that were associated with genetic relatedness were the most effective at predicting initial lactose growth. Hybrid reference strains containing lacI and the lac operon of five different natural isolates indicated regulatory elements that had more control over expression could be either global or local. My results demonstrate selection can lead to diverse adaptations that can depend on selective history, mutation interactions, or idiosyncrasies.application/pdfengThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. UH Libraries has secured permission to reproduce any and all previously published materials contained in the work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).AdaptationEvolvabilityExperimental evolutionEpistasisCompensatory mutationsLac operon regulation2019-12-17Thesisborn digital