Date of Award

2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biotechnology Science and Engineering

Committee Chair

Luis R. Cruz-Vera

Committee Member

Joseph Ng

Committee Member

Nora Vazquez-Laslop

Committee Member

Debra M. Moriarity

Committee Member

Jerome Baudry

Subject(s)

Drug resistance in microorganisms--Genetic aspects., Gene expression., Escherichia coli.

Abstract

Mutational changes in bacterial ribosomes that confer antibiotic resistance decrease cell fitness. Determining the genetic factors that interconnect antibiotic resistance and cell fitness is critical in the fight against bacterial infections. This study describes gene expression and phenotypic changes presented in Escherichia coli cells carrying a uL22 K90D mutant ribosomal protein, which showed growth defects and resistance to macrolide antibiotics. Other uL4 and uL22 mutation, in basic, non-conserved residues, were examined for phenotypic changes, however the uL22 K90D mutation displayed the most consistent phenotypes when compared to the wild type strain, and thus was the focus of this study. Ribosome profiling analyses revealed reduced expression of operons involved in catabolism, electron transport, indole production, and lysine-decarboxylase acid resistance. In general, ribosome occupancy was increased at rare codons while translation initiation of proximal genes in several of the affected operons was substantially reduced. Reduction in the activity of these genes was accompanied by an increased expression of macrolide multidrug efflux pumps, the glutamate-decarboxylase regulon, and the autoinducer-2 metabolic regulon. In concordance with these changes, uL22 K90D mutant cells grew better in acidic conditions and generated more biofilm in static cultures than their parental strain. The results provide new insights on how mutations in ribosomal proteins induce the acquisition of macrolide and pH resistance and increase the ability to generate biofilms.

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