UC Berkeley

Respiration is a set of metabolic reactions and processes that release chemical energy to fuel cellular activity. While humans can only breathe oxygen, microorganisms are able to respire other terminal electron acceptors such as chlorate and perchlorate [collectively (per)chlorate]. My graduate thesis aims to elucidate the molecular mechanisms and physiology of (per)chlorate respiration in the model (per)chlorate reducing bacteria, Azospira suillum PS; and to transform our fundamental knowledge of perchlorate reduction into applied technologies to solve practical industrial problems.

The first chapter of this dissertation is a published review article. This chapter represents an overview of my thesis and summarizes the potential biotechnological applications of (per)chlorate reduction, including enzymatic perchlorate detection; enhanced xenobiotic bioremediation; oil reservoir biosouring control; chemostat hygiene control; aeration enhancement in industrial bioreactors; and biogenic oxygen production for planetary exploration.

The second chapter of this dissertation is a published research article. This chapter aims to identify the redundancy between perchlorate and nitrate reduction pathways. Our results demonstrate two genes (pcrQ and pcrO) that encode electron transfer cytochromes are essential for perchlorate respiration; but completely redundant and fully replaceable with their respective homologous genes napC and napO in the denitrification pathway. While (per)chlorate reducers are known to preferentially reduce nitrate in the presence of both nitrate and perchlorate, by rewiring the terminal electron transport pathways in PS we were able to engineer strains that preferentially reduce perchlorate or concurrently reduce both nitrate and perchlorate.

The third chapter of this dissertation is a transcriptomic analysis of PS under different growth conditions. These data establish the expression profiles of proteins involved in the nitrate, chlorate, perchlorate, and aerobic respiration pathways. This information also serves as a hypothesis-generating foundation for future investigations in microbial (per)chlorate reduction.

The fourth chapter of this dissertation describes a biocide/biocide-resistant system for bacteriophage and microbial contamination prevention and treatment during biomanufacturing. This technology is based on the biocide chlorite(ClO2-), a toxic intermediate generated during perchlorate respiration, and the corresponding detoxifying enzyme, chlorite dismutase (Cld).

The fifth chapter of this dissertation discusses the implications of this research for future investigations regarding the biology and the biotechnology of microbial (per)chlorate reduction.

The sixth chapter is the conclusion of this dissertation.