Microbial Community Analysis Coupled With Geochemical Studies Reveal Factors Affecting Biotic Mn(II) Oxidation In Situ

Factors that affect biogeochemical cycling are important in ecosystems susceptible to anthropogenic input such as caves. The extent to which anthropogenic input can modulate the pathways and Mn cycling in caves is largely unknown. Microbial communities associated with Mn(III/IV) oxide deposits were assessed in both relatively pristine and anthropogenically impacted caves in the southern Appalachians. Fungal communities appeared to be independent of carbon infiltration, while the bacterial and archaeal communities appeared to be driven by long-term exogenous carbon loading. Cave sites were amended with various carbon sources that are commonly associated with anthropogenic input to determine whether exogenous anthropogenic input would stimulate biotic Mn(II) oxidation in situ. Sites where carbon incubations stimulated biotic Mn(II) oxidation microbial communities were significantly impacted, indicating that anthropogenic input can enhance biotic Mn(II) oxidation potentially shaping community dynamics. Geochemical analyses of sediment substrates suggest that some biotic Mn(II) oxidation pathways (e.g. MnP mediated oxidation) can be limited by carbon and low C:N ratios. Bacterially selective Mn(II)-oxidizer media supplemented with 100 µM Cu(II) inhibited Mn(II) oxidation, indicating that bacteria were using superoxide to oxidize Mn(II). In contrast, fungally selective media with Cu(II) stimulated Mn(II) oxidation, indicating that fungi were using MCO enzymes for Mn(II) oxidation.