MICROBIAL MN(II) OXIDATION AS AN INDICATOR OF ANTHROPOGENIC IMPACT IN CAVES: A CASE STUDY IN CARTER SALT PETER CAVE, CARTER COUNTY, TN
CSPC exhibits Mn(III/IV) oxide formation in biofilms associated with several groundwater seeps as well as on cave litter. Culturing and molecular data indicates that Mn(III/IV) oxide production in groundwater seeps is primarily associated with Mn(II) oxidizing bacteria, but culturing results reveal that Mn(III/IV) oxide production (predominantly poorly crystalline buserite, birnessite, or todorokite) on cave litter is also associated with Mn(II) oxidizing fungi. In 2008, one of the Mn oxide-rich seeps bloomed in a massive Mn(II) oxidizing biofilm, anecdotally related to a release of sewage in a nearby sinkhole. Molecular methods (16S rRNA) confirmed the presence of Bacteroides-Prevotella human fecal indicators in this seep, and most probable number (MPN) assays and ion chromatography of the associated seep water confirmed nutrient loading at the site. Phylogenetic analysis from clone sequences suggested a strong initial human-specific fecal signature (50% of the sequences clustering with human feces sequences) in July 2009, and a weaker human signature (20% clustering) by July 2011. From 2009-2011, the seep exhibited a dramatic visual reduction in Mn(IV) oxide production, which was hypothesized to correlate with a decrease in nutrient input. MPN analyses suggested that Mn(II) oxidation at the seep was correlated with heterotrophic activity (most likely due to reactive oxygen species production), in this case due to point source exogenous nutrient loading.
Preliminary phylogenetic analysis (using SSU, LSU, and ITS rRNA) to identify Mn(II) oxidizing fungi associated with cave litter revealed the presence of Plectosphaerellaceae sp. DCIF (growing on battery), and two Genus incertae sedis (Fungal sp. YECT1, and Fungal sp. YECT 3, growing on electrical tape) that are are not closely related to any known Mn oxidizing species.