Date of Award

Summer 8-2017

Embargo Period

8-18-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Advisor(s)

Robert Tilton

Abstract

This work is motivated by the need to understand the environmental risks posed by antimicrobial silver and copper nanoparticles, from consumer products and pesticides, and surfactants, used for oil remediation. Silver and copper nanoparticles have biocidal properties, and surfactants have similar chemical structures as autoinducers, molecules bacteria use to communicate (known as quorum sensing), which may alter bacterial communication. The introduction of both classes of chemicals may pose different threats to bacterial populations to affect normal ecosystem functions. The dissertation addresses the role natural organic matter and bacterial concentrations play to serve as silver and copper sinks to mitigate toxicity and probes the effects that surfactants have on bacterial quorum sensing. Pseudomonas fluorescens was used as a model biofilm forming bacterium to understand the role natural organic matter (NOM) and bacterial concentration play on bacterial survival and colonization of AgNP-decorated surfaces. It was seen that both NOM and P. fluorescens serve as silver sinks and the critical amount of bacteria-bound silver necessary to inhibit growth was on the same order of magnitude for each initial bacterial concentration. An increased silver sensitivity was observed when NOM was present. Escherichia coli was used as a model Gram-negative bacterium to study Cu2+ toxicity in the presence of NOM. NOM increased bacterial tolerance to Cu2+ over ten-fold. Copper responsive genes were measured with and without NOM at the same initial bacterial concentration and it was observed that copper sensitive gene expression was lowered with NOM. Vibrio harveyi was used as a model quorum sensing bacterium to study the effect of Tween 80 surfactant on quorum sensing. Bioluminescence is one form of quorum sensing response for V. harveyi, and the addition of Tween 80 caused a decrease in luminescence for similar bacterial concentrations. Liquid chromatography-mass spectrometry was used to study interactions between Tween 80 and N-butyryl homoserine lactone (AI-2). A decrease in autoinducer AI-2 signal was observed with Tween 80 suggesting that there is some interaction between the surfactant and AI-2 that may result in a decrease of available signal. These results indicate that further studies should be performed to better understand these observations.

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