Date of Graduation

12-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Cell & Molecular Biology (PhD)

Degree Level

Graduate

Department

Cell & Molecular Biology

Advisor/Mentor

Barabote, Ravi D.

Committee Member

Lessner, Daniel J.

Second Committee Member

Henry, Ralph L.

Third Committee Member

Ivey, D. Mack

Fourth Committee Member

Thallapuranam, Suresh

Keywords

Acidothermus cellulolyticus; Biological sciences; Graphene; Mycobacterium smegmatis; Thiosulfate sulfurtransferase

Abstract

Bacteria encounter a plethora of environmental stresses and have evolved different mechanisms to recognize and respond to various harmful conditions. Understanding and elucidating common themes as well as unique aspects of the molecular mechanisms underlying stress adaptation is important and can provide valuable strategies for applications. This study focuses on stress responses in three different bacteria, namely, Acidothermus cellulolyticus, Mycobacterium smegmatis and Escherichia coli. The thermophilic and acidophilic organism A. cellulolyticus was used as a model system to understand the effects of lignin phenolic acids on cellulolytic bacteria. Lignin phenolic acids pose a significant challenge to microbial deconstruction of lignocellulosic biomass for the commercial production of renewable products. Analysis of total proteins profiles of A. cellulolyticus revealed the enhanced expression of a predicted thiosulfate sulfurtransferase (TST) protein (Acel_0059) during exposure to phenolic acids. Expression of genes involved in sulfur assimilation into cysteine was also upregulated in the presence of phenolic acids. Heterologous expression of the Acel_0059 gene in E. coli alleviated growth inhibition of inhibitory phenolic acids. Analyses of the whole transcriptome of A. cellulolyticus revealed that exposure to these inhibitory lignin components induced the expression of genes coding for membrane proteins, efflux and transport proteins, oxidative stress response proteins, redox-sensors, TST, and sulfur assimilation pathway enzymes. Deletion of the Acel_0059 counterpart gene (MSMEG_5879) in a surrogate host M. smegmatis increased the sensitivity of the organism to a variety of stressors. The deletion of TST gene affected cysteine biosynthesis from inorganic sulfate under hypoxic conditions in M. smegmatis. In another study, E. coli was used as a model to assess the biological effects of oxidized graphene (OG), a carbon nanomaterial. Growth analysis revealed that the addition of OG inhibited the growth of E. coli. Analyses of the whole transcriptome of E. coli showed that the cytotoxicity of OG in E. coli could be attributed to oxidative stress, membrane stress and DNA damage. Overall the above studies provided new insights into the shared (eg. sulfur metabolism, oxidative stress adaptation) as well as unique (eg. TST, membrane proteins) aspects of bacterial responses to diverse stresses.

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