Date of Award

Spring 5-7-2014

Document Type

Thesis

Degree Name

Bachelor of Arts

Department

Microbiology, Molecular Biology and Biochemistry

First Advisor

Joan L. Slonczewski

Abstract

Escherichia coli is capable of growth in moderate acid (pH 4.5-5.0), and can survive exposure to extreme acid (< pH 3.0) without growth. We conducted a laboratory evolution experiment to isolate and analyze E. coli strains adapted to grow in moderate acid. Twenty-four independent populations of E. coli were propagated in complex media buffered to pH 4.8. The pH of the media was decreased to 4.6 following 730 generations of growth at pH 4.8. After a cumulative 2000 generations of growth, eight strains were isolated from four populations. Of the eight isolated strains, three had a greater early log phase growth rate than the ancestral wild type when cultured under the experimental acidic conditions, though no strains exhibited a growth advantage or disadvantage relative to the ancestral wild type when cultured at pH 7.0. In spite of growth rate differences, all strains had a fitness advantage when co-cultured with the ancestral wild type. The genomes of the eight acid-adapted isolates were sequenced in order to determine the genetic bases of adaptation to the acidic experimental conditions. The strains were found to have between two and six missense mutations, and each strain had acquired one missense mutation in one component of the RNA polymerase holoenzyme (rpoB, rpoC, or rpoD).

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