Identification of Mn(II)-Oxidizing Bacteria from a Low-pH Contaminated Former Uranium Mine

Abstract

e Biological Mn oxidation is responsible for producing highly reactive and abundant Mn oxide phases in the environment that can mitigate metal contamination. However, little is known about Mn oxidation in low-pH environments, where metal contamination often is a problem as the result of mining activities. We isolated two Mn(II)-oxidizing bacteria (MOB) at pH 5.5 (Duganella isolate AB_14 and Albidiferax isolate TB-2) and nine strains at pH 7 from a former uranium mining site. Isolate TB-2 may contribute to Mn oxidation in the acidic Mn-rich subsoil, as a closely related clone represented 16% of the total community. All isolates oxidized Mn over a small pH range, and isolates from low-pH samples only oxidized Mn below pH 6. Two strains with different pH optima differed in their Fe requirements for Mn oxidation, suggesting that Mn oxidation by the strain found at neutral pH was linked to Fe oxidation. Isolates tolerated Ni, Cu, and Cd and produced Mn oxides with similarities to todorokite and birnessite, with the latter being present in subsurface layers where metal enrichment was associated with Mn oxides. This demonstrates that MOB can be involved in the formation of biogenic Mn oxides in both moderately acidic and neutral pH environments.

Nutrient input influences fungal community composition and size and can stimulate manganese (II) oxidation in caves

“…Whereas previous studies have demonstrated pH dependence of both fungal (Miyata et al ., ) and bacterial (Zhang et al ., ; Akob et al ., ) Mn(II) oxidation, our current study highlights the importance of the availability of carbon and other nutrients as important drivers of Mn(II) oxidation in environments such as caves. In addition, we show that microbial community composition and abundance can be intricately linked with the quality, quantity and form of the carbon input.…”

The role of natural biogeochemical barriers in limiting metal loading to a stream affected by mine drainage

“…Natural attenuation of trace metal loads commonly occurs via a complex set of processes (Akob et al, 2014;Byrne et al, 2014;De Giudici et al, 2009, 2014Fuller and Bargar, 2014) Root growth enhances soil permeability with the development of a macropore system called rhizopores (Archer et al, 2013;Ghestem et al, 2011). As reviewed by Vergani and Graf (2015), the overall effect of plants on soil permeability depends on the soil type, the density of vegetation and the vegetation cover type.…”

Biological Low-pH Mn(II) Oxidation in a Manganese Deposit Influenced by Metal-Rich Groundwater

“…The pH of environments that would be good targets for Mn oxide-mediated attenuation, e.g., drainage basins, mine tailings, and leaching heaps, is normally acidic due to the aerobic oxidation of sulfidic minerals (3). Although manganese is readily oxidized from Mn(II) to Mn(III/IV) at circumneutral pH by a variety of microorganisms (4), we have limited knowledge about the formation of biogenic Mn oxides in acidic environments (5,6).…”

“…In contrast, low-pH Mn(II) oxidation poses a challenge to microbes because the reaction is thermodynamically unfavored (5,6,19,20). Until recently, only the fungus Cephalosportium sp.…”

“…However, recently, Akob et al reported new isolates of low-pH MOB, including Duganella sp. strain AB_14 and Albidiferax ferrireducens strain TB-2, which oxidize Mn(II) at pH 5.5 (5). In addition, Bohu et al characterized Mesorhizobium australicum T-G1, a low-pH Mn(II) oxidizer, that forms a bixbyite-like phase via a multi-copper oxidase pathway rather than reactive oxygen species at acidic pH (6).…”