Undergraduate Honors Theses

Thesis Defended

Fall 2016

Document Type

Thesis

Type of Thesis

Departmental Honors

Department

Molecular, Cellular, & Developmental Biology

First Advisor

Dr. Shelley Copley

Second Advisor

Dr. Jennifer Martin

Third Advisor

Dr. Robert Kuchta

Abstract

Escherichia coli possesses a remarkable ability to adapt to new environments and overcome disruption of synthetic pathways. In this thesis, I show that E. coli with a deleted pdxB gene is able to bypass a disruption in the pyridoxal-5’-phosphate (PLP) synthesis pathway. The ΔpdxB strain cannot synthesize its own PLP via the traditional pathway, so it must create a new pathway to synthesize this essential vitamin. One way the ΔpdxB strain adapts is via serendipitous pathways that emerge as a direct result of mutations in PLP-depleted environments. These pathways appear when the strain is grown on both solid and liquid media.

Mutations restoring PLP synthesis occurred in the ΔpdxB strain when plated on solid M9 minimal medium supplemented with 0.2% (w/v) glucose or glycerol, or when supplemented with over 2% (w/v) pyruvate, succinate, and acetate. The ΔpdxB strain adapted in liquid M9/glycerol, but only in favorable conditions. These conditions, such as when the strain was supplemented with D-alanine or after the strain synthesized a proteome tailored to glycerol, allow survival of the bacterium by helping minimize the detriment of its weak cell wall. The longer the bacteria can survive, the more opportunity there is for mutations to appear. Whole-genome sequences of adapted strains were analyzed using breseq, revealing that the adapted ΔpdxB strains acquired mutations, which are assumed to result in the synthesis of PLP. It is currently unclear the exact effect these mutations have and whether or not they are all involved in a serendipitous pathway.

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