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UBC Theses and Dissertations

Phototrophic iron oxidation and implications for biogeochemical cycling in the Archean Eon Thompson, Katharine Jean


Banded iron formations (BIFs), which host the world’s largest iron ore deposits, formed predominantly through the deposition of ferric iron (Fe[III]) from ferruginous oceans during the Archean Eon. Available evidence suggests that phototrophic iron oxidation (photoferrotrophy) may have played a key role in coupling the carbon and iron cycles during the Archean Eon, depositing BIFs, and, in doing so, underpinned global primary production at this time. To date, however, all known photoferrotrophs form a close association with the ferric iron metabolites they produce during growth. This intimate association calls into question the involvement of photoferrotrophs in BIF deposition, their ability to act as primary producers, and their role in sustaining the biosphere for millions of years. Furthermore, a lack of quantitative knowledge on the growth of photoferrotrophs and the interactions between them and other microorganisms limit our ability to constrain models of BIF deposition and the Archean ocean-atmosphere system as a whole. This dissertation generates new knowledge on extant photoferrotrophy that can be used to inform and constrain models of primary production and BIF deposition during the Archean Eon. I create new knowledge on photoferrotrophy under laboratory conditions and in natural environments through data collected on the physiology and metabolic capacity of pelagic photoferrotroph Chlorobium phaeoferrooxidans strain KB01. I also measure process rates and analyze the composition of the microbial community in a ferruginous lake--Kabuno Bay--that is dominated by photoferrotrophy. I subsequently integrate this new knowledge into models that examine the antiquity of nutrient acquisition in the photoferrotrophic Chlorobia and the role of photoferrotrophs as primary producers during the Archean. These models provide an explanation for the formation of BIFs as a by-product of the activity of photoferrotrophic bacteria. Additionally, I demonstrate how photoferrotrophs could have sustained the biosphere, likely fueled microbial methanogenesis, and, therefore, helped to stabilize Earth’s climate under a dim early Sun.

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