Date of Award

Spring 5-11-2016

Document Type

Thesis

Degree Name

Bachelor of Arts

Department

Biology

First Advisor

Joan L. Slonczewski

Abstract

Escherichia coli are able to grow in a wide external pH range of 5 to 9 through the use of acid and base regulatory systems. In order to identify genes that allow for moderate acid growth, we established a laboratory evolution experiment, in which twenty-four populations of E. coli K-12 W3110 were cultured in moderately acidic medium for 2,000 generations. Four populations with consistently higher growth endpoints had individuals isolated and submitted for whole genome sequencing to identify the mutations potentially correlated to increased growth in external moderate acid exposure. In our study, we characterized each acid-evolved strain’s amino acid decarboxylase activity. Each population had a unique combination of active amino acid decarboxylase systems. None of the isolated strains had all three decarboxylase systems active. Only the strains isolated from the F9 population had an active lysine decarboxylase. In addition to this, F9 strains had the least number of mutations. F9 strains are able to maintain optimal cell shape under moderate acid stress, while the ancestral W3110 strain had irregular elongated cells. In further characterization of the mutations found, the rpoC and wzzE mutations were reverted to original wild-type expression. The reverted F9 strains were directly competed against the original acid-evolved strain. There was a significant decrease of fitness in the F9-2 strain when either the rpoC or wzzE mutation was reverted to ancestral expression. The decrease in fitness indicates that the mutations in rpoC and wzzE may play a significant role in the acid-evolved strain’s ability to grow under constant moderate acid stress.

Share

COinS