Manganese Oxidation in the Photic Zone
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While the oxidation of Mn(II) has long been recognized as microbially-mediated, the role of bacteria in this process has only been attributed to direct enzymatic processes. Recently we have discovered an alternative Mn(II) oxidation pathway, which is coupled to a direct enzymatic pathway and occurs only in the presence of light. These findings illustrate that the reactions responsible for Mn(II) oxidation are more diverse than originally thought. The photoreduction of Mn is well-documented but the photo-oxidation of Mn(II) and it’s importance in the cycle of Mn has been largely dismissed. Thus, this mechanism challenges the long-held paradigm that Mn(II) oxidation is inhibited in the light and therefore presents a new role for photochemical reactions in the oxidative leg of the Mn cycle. |
Our current research seeks to identify the components of both enzymatic and light-enhanced oxidation pathways using Roseobacter sp. AzwK-3b as a model bacterium. Due to the numerical abundance, ecological diversity, and geochemical relevance (e.g. DMSP degradation) of Roseobacter species in surface environments, AzwK-3b serves as an environmentally relevant model organism. Furthermore, AzwK-3b is genetically tractable as the genome is now available allowing for complementary genome-based analysis. Using a combination of proteomics, genomics, cell/filtrate incubations, and chemical/mineralogical assays we are currently identifying the enzymes, genes, aqueous species, and mineral surface reactions involved in Mn(II) oxidation. |
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