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Phylogeny and Predicted Functional Capabilities of a Sulfur-Oxidizing and Denitrifying Clade of Bacteroidetes from Sulfidic Environments
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Environments rich in sulfur compounds (sulfidic) are common in the ocean, and the ability to gain energy (dissimilatory) from sulfur redox reactions is widespread in bacteria. The Sulfiphilic Bacteroidetes (SB), have been found exclusively in sulfidic environments, but little is known about their metabolic potential and membership. The ability to perform dissimilatory sulfur redox would make them unique among Bacteroidetes, which are primarily known as heterotrophs that specialize in degrading complex organic molecules. Using 16S rRNA phylogeny and analysis of single amplified genomes (SAGs) from Saanich Inlet, a seasonally hypoxic basin, we elucidate the global distribution and potential metabolic capabilities of the SB clade. Phylogenetic analysis revealed that this clade was monophyletic and had a global distribution. It is hypothesized this clade combines heterotrophic amino acid and sugar uptake with denitrification and respiratory sulfur oxidation/polysulfide reduction. Putative genes for sulfur oxidation via polysulfide reductase (psr) were found in the combined genome, and phylogenetic analysis confirmed these genes were likely to be psrABC. A denitrification pathway was present and complete save for the absence of a gene catalyzing reduction of NO to N2O. The SB clade possesses the potential to grow by degrading a variety of polysaccharides and peptides, and possesses both aerobic respiratory and anaerobic fermentation pathways, including the TCA cycle, acetogenesis and ethanol fermentation. The presence of aerobic and anaerobic metabolic pathways makes the clade suited to environments experiencing periodic oxygen depletion. The inferred metabolic capabilities of the SB clade taken with their wide range suggest they are potentially important players in global nitrogen and sulfur cycling.
Zhou, Kecen (2018). Phylogeny and Predicted Functional Capabilities of a Sulfur-Oxidizing and Denitrifying Clade of Bacteroidetes from Sulfidic Environments. Master's thesis, Texas A & M University. Available electronically from