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Physiological and Genetic Investigations into Putative Sulfur Oxidation Systems of Methylococcales.
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- Author / Creator
- Waddingham, Marc
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Methylotrophic bacteria are ecologically widespread chemotrophs which utilize single carbon compounds as their primary energetic and assimilatory substrate for biomass. Those which utilize methane are commonly referred to as methane oxidizing bacteria (MOB), or methanotrophs. The majority of known MOB are strict aerobes, as they rely on availability of molecular oxygen for the activation of methane via the key enzyme complex particulate methane monooxygenase (pMMO), and for respiration when replete with oxygen. Our understanding of the metabolic diversity of MOB continues to expand, with autotrophy, nitrogen reduction, and most recently sulfur oxidation having been reported across diverse methanotrophic clades. Analysis of MOB genomes from Gammaproteobacteria, order Methylococcales, have revealed the presence of a putative thiosulfate-oxidizing multienzyme system (TOMES) across multiple species, raising the prospect of dissimilatory catabolic sulfur oxidation in these bacteria. However, the observation of a sulfur/methane mixotrophic growth phenotype or direct sulfur oxidation by Methylococcales species has remained elusive. Herein the lack of discernable growth benefit of thiosulfate for Methylotuvimicrobium buryatense 5GB1C and Methylicorpusculum oleiharenae XLMV4 is confirmed in the conditions tested, verified through growth, substrate gas consumption, and sulfate production measurements. Neither oxygen nor methane limiting conditions resulted in significant change in parameters measured; rather, the growth of Mp. oleiharenae XLMV4 was shown to be inhibited by lanthanum and thiosulfate in combination. This effect was replicable, and resulted in slowed doubling rates, lowered final optical density readings, with a commensurate decrease in headspace gas depletion rates for both methane and oxygen for XLMV4 cultures grown in thiosulfate/lanthanum conditions. This effect is hypothesized to be due to competitive inhibition of the lanthanide-dependent methanol dehydrogenase (MDH) XoxF by thiosulfate, inferred through high sequence similarity between XoxF-type MDHs and thiol dehydrotransferase (ThdT), a novel thiosulfate oxidizing enzyme first identified in the betaproteobacterium Advenella kashmirensis. These results indicate that the presence of a conserved sulfur oxidation system across multiple Methylococcales species may not be for of energy conservation or carbon fixation, but rather to alleviate competitive inhibition of XoxF-type MDH function by thiosulfate. While this inhibitory interaction between the XoxF MDH and thiosulfate requires validation through targeted enzymatic and metabolomic assays, these data may serve as the basis for future investigations into the role of TOMES in Methylococcales. Moreover, the implications of XoxF inhibition may well encompass bacterial clades beyond Methylococcales, as XoxF-type MDHs are highly abundant within marine sediment microbial communities and may be similarly affected by thiosulfate.
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- Subjects / Keywords
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- Graduation date
- Fall 2023
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.