| Summary: | My dissertation investigated the role played by microbially synthesized iron chelating molecules known as siderophores, and other naturally occurring organic chelators, on a microbial anaerobic respiratory pathway known as dissimilatory iron respiration in anaerobic thawed soils from a wetland basin chronosequence in the Arctic coastal plain, AK, which consists of a wet sedge tundra ecosystem. Iron cycling in Arctic soils is an understudied biogeochemical process that affects the carbon cycle in different ways. The first chapter of this dissertation reviewed different reactions in the iron cycle that are coupled to feedback mechanisms in the carbon cycle and explored the possible effects and changes to existing feedbacks in the carbon cycle future climate change might present. My second chapter investigated the response of dissimilatory iron reduction, to the addition of two types of chelators; a synthetic analogue of a microbially synthesized siderophore, deferroxamine mesylate, and an abiotically sourced naturally occurring organic chelator, trisodium nitrilotriacetic acid, to soils sampled from the wetland basin chronosequence in the Arctic coastal plain, AK. The addition of siderophores, and other chelating molecules to these soils, showed an increased response in dissimilatory iron reduction in the oldest basin of the chronosequence, the ancient basin, that had lower concentrations of dissolved iron, solid phase iron, and lower concentrations of ambient siderophores. My third and final chapter was an investigation of the microbial ecology of Arctic tundra soils from the perspective of siderophore utilization by the microbial populations within the soil. The investigation was performed using metagenomic analyses, a pure culture study, and mass spectrometry analyses. Metagenomic analyses revealed an ecological mechanism known as xenosiderophore uptake employed by different taxa found in the soil metagenomes. The mass spectrometry analyses and pure culture analyses revealed the importance of the genus ...
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