Diversity and Abundance of Microbial Community in NC Superfund Site Remediation System Biofilm, and Their Role in Mn Oxidation.

Environmental remediation of contaminated sites requires a detailed understanding of the chemical and biological processes occurring within the remediation system. Dissolved manganese from influent groundwater collected from Farm Lot 86 Superfund site (Raleigh, NC), is being microbially oxidized and precipitated, resulting in manganese oxide biofilm formation throughout the pump-and-treat system components. Following a prolonged system shut down due to biofilm caused congestion, a multipronged investigation of the chemical composition and microbial community within the biofilm was performed. Culture-based and high-throughput sequencing approaches were used to examine organisms inhabiting the Superfund Site treating scientific and agricultural wastewater. Additionally, microscopy and spectroscopy were used to improve our understanding of the geochemical processes associated with manganese oxide formation.

Despite the presence of potentially toxic inorganic and organic contaminants, efforts to isolate manganese oxidizing microbes resulted in the culturing of phylogenetically diverse fungal community, dominated by Ascomycete fungi, promoting Mn(II) oxidation in the biofilm. The isolated fungi obtained are closely related to known manganese oxidizing organisms, most sharing high (>98%) sequence homology with members of Ascomycota and Basidiomycota phyla assigned to the orders Hypocreales, Pleosporales, and Agaricales. Culture-independent techniques further show sequences of cultured fungi make up a large fraction of the total fungal sequences in each of the samples.

X-ray absorption spectroscopy, X-ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy revealed oxides to be layer type manganese(IV) oxides that contain significant concentrations of cobalt(III), zinc(II), and barium(II) adsorbed to specific crystallographic sites.

The culturing techniques used to determine Mn oxidation capabilities likely underestimate the microbial community presence contributing to the system wide formation of Mn. However, results from this study emphasize the role of microbes, particularly fungi, contributing to the biogeochemical cycling of Mn in the impacted remediation system, and suggest that the manganese oxides occurring in the system may have utility in designed remediation systems where heavy metal removal by manganese oxide precipitation is sought.