This thesis is missing a page between pages 60 and 70, and three pages between pages 70 and 81. Since the pages are not all numbered, the specific page numbers cannot be determined. Theses missing pages are not in the other copies of the thesis. -Digitization Centre / Replicate isogenic populations of E. coli were propagated and maintained for over 4000 generations in order to investigate the adaptation of E. coli to increased levels of the mutagen methanesulfonic acid ethyl ester (EMS). Control "C" cell lines were propagated through daily serial culture in the absense of any mutagenic treatment. EMS adapted cell lines "E" / "e" were propagated through daily serial culturing and treated daily with 25Jul of EMS following serial dilution. Mutation frequency and survival assays conducted in this investigation strongly suggest that prior long-term low dose exposure to EMS results in significantly higher levels of resistance to the lethal and mutagenic effects of larger challenge doses of EMS relative to long-term evolved control cell lines "C". In addition, both survival and inhibition disk assays suggest a cross adaptive response between EMS and MNNG, showing enhanced survival and reduced growth inhibition zones in cells adapted to EMS and challenged with MNNG. Preliminary competition experiments suggest relative fitness for the EMS adapted cell lines ( "E" / "e") compared to the "C" control cell lines in both the presence of EMS. Unexpectedly the fitness estimates also suggest a higher relative fitness for the "E" / "e" EMS adapted cell lines in the absence of EMS treatment, suggesting that the EMS specific adaptation may also result in improved fitness in novel environments. Despite the adaptive advantage for the "E" / "e" cell lines suggested by the fitness estimates, the results from the competition experiments are insignificant due to the high degree of variability among replicate fitness estimates. Attempts to induce the adaptive response repair pathway were not successful in either the control "C" or the EMS adapted "E" / "e" cell lines suggesting that enhanced resistance seen in the adapted "E" / "e" cell lines could likely be a result of enhanced activity of the constitutive transferase Ogt and the constitutive glycosylase Tag. The ada and the ogt genes encode the induced and the constitutively-active DNA methyl transeferases in E. coli. As such they appeared to be the most likely candidates for genetic changes responsible for the enhanced resistance to the lethal and mutagenic effects of large doses of alkylating agents in the long-term EMS adapted "E" / "e" cell line. However, the DNA sequences analyzed for the ogt and the ada genes for both the long-term evolved control E. coli cell line "C" and the long-term-evolved EMS adapted "E" / "e" cell line indicate no sequences differences between these two cell lines. Previous studies have primarily observed E. coli's ability to phenotypically acclimate over very short time intervals to EMS. This analysis has shown that long-term genetic adaptation to low doses of EMS results in enhanced resistance to both the lethal and mutagenic effects of larger challenge doses of EMS. / Thesis / Master of Science (MS)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/24421 |
| Date | 05 1900 |
| Creators | Muller-Meloche, Monique |
| Contributors | Golding, G. Brian, Biology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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