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The role of electroactive organisms in biomineralization reactions involving transition metals, nitrogen and humic substances under suboxic/anoxic conditions
VALERO, Astolfo
Electroactive microorganisms sustain their respiratory metabolisms by retrieving or transferring electrons to extracellular conductive particles. Electroactive metabolisms based on iron respiration can trigger the precipitation of Fe(III)-oxyhydroxides or changes in their crystallinity. Iron biomineralization has a sound effect on the geochemical cycles of elements because it also influence the solubility of other elements such as phosphorus and arsenic. Thus, siderophile elements are removed from solution within precipitated particles or they are released back after mineral stabilization. However, major insights are often deduced by studying lab isolates of model microorganisms and using simplified substrates. This does not reflect environments where the presence of redox stratification boosts the overlapping of nitrogen- and iron-based metabolisms and interspecies interactions regarding thermodynamics constraints of minimal energetic loss for microbial respiration. For example, reactive nitrogen species (i.e., nitrate and ammonia) serve as alternative electron sources as sinks during iron biomineralization in nature. This can be also furthered by the presence of re-oxidable moieties of humic substances, which are used as electron shuttlers to reach extracellular materials. Therefore, this doctoral research aimed to describe how the availability of redox-reactive humic substances and reactive nitrogen species, as alternative electron donors or acceptors, affect electroactive metabolisms and linked iron biomineralization in the anoxic water column of a redox-stratified lake with high metal load (Lake Medard, NW Czech Republic). This was addressed by assessing the geochemical and hydrobiological features of the uppermost layers of sediment and the redox-stratified ferruginous water column of Lake Medard, and then, (ii) using the resulting dataset as input conditions in bioelectrochemical experiments to model the lake's biomineralization reactions by inducing microbe-mineral interactions under controlled electric potentials.
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