Comparison of Fe(III) Reduction Rates by Iron-Reducing Bacteria within Sub Muros Samples from Quadrilátero Ferrífero Iron-Ore Caves, Brazil

Previous research investigating the speleogenesis of iron-ore caves (IOC) in the Quadrilátero Ferrífero, or “Iron Quadrangle,” of Brazil suggests that microbial iron reduction and subsequent dissolution of the surrounding Fe(III) rich rocks is responsible for cave formation. A soft intra-wall substance (sub muros) containing iron-reducing bacteria (FeRB) was discovered underneath the durable crusts of cave walls. The goal of the study was to determine if reduction rates were comparable between sub muros samples, while additionally observing how different electron donors affect microbial iron reduction. To do this, I compared Fe(III) reduction rates between sub muros samples collected from two different caves, and additionally between three electron donors for bacterial growth: succinate, lactate and fructose. Batch incubations were conducted and Fe(II) production was monitored over 68 days. The obtained data suggest differences in reduction rates between sub muros samples, although this could be a result of differences in FeRB population or abundance. Use of different electron donors demonstrated various effects on iron reduction and dissolution, where higher rates of both were observed in the fructose-amended group. Further analysis is needed to determine the reason behind differing reduction rates, specifically monitoring of microbial communities present in the incubations over time