The Geobiology of Microbial Mediated Manganese Oxide Formation in an Environmental Remediation System.

Environmental remediation of contaminated sites requires a detailed understanding of the chemical and biological processes that occur 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 sludge formation in system components throughout the pump-and-treat system. To improve our understanding of the geobiological processes associated with manganese oxide formation, a multipronged investigation of the chemical composition and microbial community diversity within the sludge was conducted.  X-ray absorption spectroscopy, X-ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy revealed the 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. Efforts to isolate manganese oxidizing microbes resulted in the culturing of a phylogenetically diverse array of fungi and bacteria that are closely related to known manganese oxidizing organisms, most sharing high (>98%) sequence homology with fungal genus (Coniothyrium, Coprinellus, Fusarium, Paecilomyces, Paraconiotyrium and Phoma) and substantially fewer being bacteria (Rhodococci and Bacillus). After extracting genomic DNA from sludge samples, pyrosequencing of 16s and ITS genes of bacteria and fungi, respectively, revealed significant microbial diversity across the components of the treatment system, as well as the frequent presence of sequences closely related to both cultured and un-cultured manganese oxidizing organisms. Despite the presence of potentially toxic inorganic and organic contaminants, the results suggest that biological production of manganese oxides occurs in the system, and that isolates from the system may have utility in designed remediation systems where manganese oxide precipitation is sought.