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Title Photosynthetic and Fermentative Bacteria Reveal New Pathways for Biological Mercury Reduction
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University/Publisher University of Ottawa
Abstract Mercury (Hg) is a global pollutant and potent neurotoxin that bioaccumulates in aquatic and terrestrial food webs as monomethylmercury (MeHg). Anaerobic microbes are largely responsible for MeHg production, which depends on the bioavailability of inorganic Hg substrates to methylators. Hg redox cycling pathways such as Hg reduction play a key role in determining Hg’s availability in the environment. Although abiotic photochemical Hg reduction typically dominates in oxic surface environments, Hg reduction pathways mediated by photosynthetic and anaerobic microbes are thought to play an important role in anoxic habitats where light is limited and MeHg production occurs. Currently, the physiological mechanisms driving phototrophic and anaerobic Hg reduction remain poorly understood. The main objective of my thesis is to provide mechanistic details on novel anaerobic and phototrophic Hg reduction pathways. I used a combination of physiological, biochemical and trace Hg analytical techniques to study Hg reduction pathways in a variety of anaerobic and photosynthetic bacteria. I demonstrated that Hg redox cycling was directly coupled to anoxygenic photosynthesis in aquatic purple non-sulphur bacteria that reduced HgII when cells incurred a redox imbalance. I discovered that terrestrial fermentative bacteria reduced Hg through pathways that relied on the generation of reduced redox cofactors. I also showed that sulphur assimilation controlled Hg reduction in an anoxygenic phototroph isolated from a rice paddy. In addition, I developed methods to explore cryptic anaerobic Hg redox cycling pathways using Hg stable isotope fractionation. At its core, my thesis underscores the intimate relationship between cell redox state and microbial Hg reduction and suggests a wide diversity of microbes can participate in anaerobic Hg redox cycling.
Subjects/Keywords Mercury; Redox cycling; Anaerobic bacteria; Photosynthetic bacteria; Heliobacteria; Purple non-sulphur bacteria; Stable isotope fractionation; Sulphur assimilation; Redox homeostasis; Anoxygenic photosynthesis; Bioremediation; Climate change; Fermentation
Language en
Country of Publication ca
Record ID handle:10393/38722
Repository ottawa
Date Retrieved
Date Indexed 2019-01-30
Issued Date 2019-01-18 00:00:00

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Heliobacteria reveal fermentation as a key pathway for mercury reduction in anoxic environments ............................................................................... 144 5.1 ABSTRACT…

…distinct families of anoxygenic phototrophs. In this study, I chose to work with Heliobacterium modesticaldum Ice1, a thermophilic representative from the family Heliobacteria. Heliobacteria are a metabolically versatile family of terrestrial spore-forming…

…obligate anaerobes that can grow photoheterotrophically and chemotrophically via fermentation 66, 67 . The decision to work with Heliobacteria was motivated by the fact that many Heliobacteria isolates originate from environments such as rice paddies 66…

…68, 69 where Hg accumulation is becoming a food safety issue 70, 71. Although H. modesticaldum was isolated from volcanic soils, it was selected as a model because its carbon metabolism is well-characterized 72 and it is the only Heliobacteria strain…

…Heliobacillus mobilis Romero/Guest 6, a mesophilic Heliobacteria originally isolated from a rice paddy in Thailand. This strain can grow on a variety of oxidized and reduced sulphur sources 75. Thanks to this metabolic versatility, I was able to test the…

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