Function and diversity of sulfate- and iron-reducing bacteria in mine tailings submitted to various physico-chemical conditions

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Microbial  iron- and sulfate- reduction  have been proposed as a bioremediation technologies to attenuate acid mine drainage (AMD) in mining impacted environments (such as lakes) and mine tailings. Both microbial processes generate alkalinity which can reduce the existing acidity in the tailings and  sulfate reduction promotes the precipitation of toxic heavy metals as metal sulfides, therefore lowering the impact of AMD and heavy metal loading to adjacent aquatic and terrestrial ecosystems. Ongoing research in D. Fortin's laboratory has shown that iron-reducing bacteria (FeRB) and sulfate-reducing bacteria (SRB) are widespread in Cu-Zn and Au tailings, but their activity in tailings impoundments  is dependent on various biogeochemical factors, including availability or organic substrates, electron acceptors, pH, redox and temperature. For instance, sulfate reduction activity is greatly reduced in the spring in Cu-Zn tailings (after snowmelt), when the tailings are more acidic and low in organic carbon. On the other hand, FeRB populations tend to increase in the spring, likely as the result of the lack of competition with SRB populations. Such results indicate that microbial diversity and function of FeRB and SRB in mine tailings occurring under a wide range of physico-chemical conditions must first be understood before designing  appropriate bioremediation technologies for mine tailings residues residing in temperate climate regions. Bioremediation technologies must be effective all year around and not be dependent on  physico-chemical factors. The proposed research plans to use a microcosm approach to assess SRB and FeRB diversity and function in base-metal mine tailings submitted to various physico-chemical conditions.