Causes and consequences of mine waste microbial community structure

Abstract

Acid mine drainage (AMD) is a widely studied environment in microbiology and geochemistry. However, there have been far fewer detailed studies of the microbiology and biogeochemistry of historic sulfidic mine wastes giving rise to AMD. Key questions have yet to be answered about the ecological mechanisms underlying the relationship between microbial communities and mineral substrates, the environmental features imposing selective pressure on such communities compared to nearby soils and the main ecological principles that can be used to explain such complex relationships. The South West of England has been subject to intensive mining activity, resulting in a variety of mine wastes and disused underground tunnels left undisturbed for decades. The microbial consortia inhabiting these environments make an interesting case study, as they derive from the same region and yet their similarity is unknown. Samples of mine waste and nearby soils were collected from twelve sites in Cornwall and West Devon. Geochemistry and microbial ecology were analysed to study the environmental drivers of microbial community composition. Metals from different fractions of the samples were analysed (total, readily extractable and pore water) and their compositions related to the microbial community. The microbial ecology of most sites appeared to be largely associated with pH, and to a lesser extent to the bulk metals composition. and communities were more diverse in waste sites than nearby soils. This suggested the possibility of strong local adaptation or dispersal limitation. Information on local adaptation of consortia is potentially useful for further manipulations as it provides insights into their performance in defined conditions. Therefore, inocula prepared from the twelve mine wastes were assessed for local adaptation to sympatric and allopatric substrates via a reciprocal transplant experiment. Results revealed that, with the exemption of a few sites, microbial communities were not generally locally adapted. Bioleaching performance (pyrite dissolution) was further analysed to understand how this is improved (or not) through community mixing and coalescence. Four inocula were mixed in all possible sixteen combinations to form new coalesced inocula whose performance was tested in pyrite, showing that coalescence potentially increases performance. The results give insights for the use of communities in biotechnologies such as biohydrometallurgy, as well as the microbial ecology of AMD-generating wastes. This study contributes to the knowledge of the microbial ecology of acidophiles in the scenario of whole communities coalescence and transplant.