Promotion of Mn(II) Oxidation and Remediation of Coal Mine Drainage in Passive Treatment Systems by Diverse Fungal and Bacterial Communities

Abstract

Biologically active, passive treatment systems are commonly employed for removing high concentrations of dissolved Mn(II) from coal mine drainage (CMD). Studies of microbial communities contributing to Mn attenuation through the oxidation of Mn(II) to sparingly soluble Mn(III/IV) oxide minerals, however, have been sparse to date. This study reveals a diverse community of Mn(II)-oxidizing fungi and bacteria existing in several CMD treatment systems.Acidic, metal-laden mine drainage is a significant problem for many regions in the United States and throughout the world. In Appalachia, centuries of coal mining has left thousands of abandoned mines that are discharging waters containing elevated levels of metals-particularly Mn, with concentrations as high as 150 mg liter Ϫ1 (see reference 9 and references therein and reference 23). In the eastern United States, one of the most common methods to remediate coal mine drainage (CMD) is the use of biologically active limestone treatment beds. In essence, dissolved metals, such as Mn(II), are immobilized in the treatment bed via precipitation of sparingly soluble oxide minerals (23, 24) that effectively remove other metal contaminants (e.g., Ni, Co, and Zn) through coprecipitation and surface adsorption reactions (26,31,47).The importance of microbial activity in the remediation of Mn-contaminated waters has frequently been observed (6,20,21,24,25). Several strains of Mn(II)-oxidizing bacteria have even been used for treating manganiferous mine waters (49). Recently Mariner et al. (32) identified Mn(II)-oxidizing fungi, in addition to bacteria, successfully growing in a Mn-attenuating bioreactor for treatment of mine waters. We also observed that the addition of fungicides inhibited Mn(II) oxidation in laboratory-based CMD treatment simulations (W. D. Burgos, H. Tan, C. M. Santelli, and C. M. Hansel, presented at the National Meeting of the American Society of Mining and Reclamation, Pittsburgh, PA, 5 to 11 June 2010), suggesting a role for fungal activity in Mn remediation. The identities, growth characteristics, and oxidation mechanisms of the microbial community contributing to CMD remediation, however, remain largely unresolved. The objective of this study was to define the Mn(II)-oxidizing microbial community existing in passive treatment systems designed to remove dissolved Mn(II) from CMD. Because the mechanisms of microbial Mn(II) oxidation are not fully elucidated and are not genetically tractable (13, 18), we initiated an extensive culture survey to identify microorganisms that catalyze Mn(II) oxidation and precipitate Mn(III/IV) oxide minerals. These results provide the foundation for future explorations identifying the key players in CMD remediation and factors impacting their activity.In October 2007, we sampled four Mn attenuation bedsSaxman Run (SRC1) and DeSale phases I, II, and III (DS1 to DS3)-in central Pennsylvania that are currently treating exceptionally high Mn concentrations (up to 119 mg liter Ϫ1 ; 2.2 mM) generated from abandoned coal mines. Ea...

Mn(II) oxidation by an ascomycete fungus is linked to superoxide production during asexual reproduction

“…To date, the physiological reason for Mn(II) oxidation by bacteria and Ascomycete fungi is unknown, and this process has not been linked to energy conservation by these organisms (12,36). The rate and extent of growth by these organisms is not enhanced in the presence of Mn(II) (12,36) and superoxide formation by Roseobacter and Stilbella does not appear to be a response to Mn (II)-for example, cell differentiation is not enhanced in the presence of Mn(II)-and thus we hypothesize that for these organisms Mn(II) oxidation is likely an unintentional side reaction. Interestingly, this finding also introduces a surprising homology between some prokaryotic and eukaryotic organisms in the mechanisms responsible for Mn(II) oxidation.…”

“…Thus, the reason microbes expend energy to enzymatically oxidize Mn(II) is presently unknown (7) and brings into question any evolutionary basis for this process. The Mn(II)-oxidizing Ascomycota belong to a number of different genera, such as Pyrenochaeta, Alternaria, Phoma, and Acremonium (11,12). Although the mechanism of Mn(II) oxidation by Ascomycete fungi remains unknown, the multicopper oxidase enzyme laccase has been implicated recently (11).…”

“…Here, we use a combination of compound-specific chemical assays, microspectroscopy, and electron microscopy to explore the potential for fungal-derived ROS formed during cell differentiation to impact the cycling of metals. We focus this investigation on an Ascomycete filamentous fungus, Stilbella aciculosa, that we recently isolated from a passive treatment system used to remediate Mn-laden coal mine drainage water (12). S. aciculosa serves as a model organism because of its widespread occurrence in diverse soil and sedimentary environments, including terrestrial soils, estuarine, and marine bottom sediments (24).…”

Profiling Microbial Communities in Manganese Remediation Systems Treating Coal Mine Drainage

“…The remediation of Mn-contaminated waters is thought to rely largely on such organisms. Indeed, culture-based studies of Mn(II) removal systems in Wales, United Kingdom (19), and across Pennsylvania (5,20) have identified numerous resident bacteria and fungi that oxidize Mn(II), although the abundance and activity of these isolates relative to the total microbial communities in the treatment systems is unknown. Since Mn(II) oxidation is not an energy conservation process (i.e., respiration) in any known Mn(II)-oxidizing microorganism (21,22), it is possible that it does not correlate positively with abundance.…”

Geochemical controls on the distribution and composition of biogenic and sedimentary carbon

“…The two bacterial species are well-characterized Mn(II) oxidizers isolated from coastal surface sediments (Erythrobacter; Francis et al, 2001) and a coastal estuary (Roseobacter; Hansel & Francis, 2006). The two fungi are cosmopolitan species found in a wide variety of terrestrial habitats that were isolated from Mn-rich wetlands treating coal mine drainage (Santelli et al, 2010). Minerals were precipitated in cell-free filtrate following the procedure outlined in .…”