Microbial Communities In Acid Mine Drainage From Dabaoshan Mine And Succession Of Communities Under The Selective Stress Of Ferrous Iron

Acid mine drainage (AMD) refers to the outflow of acidic water from metal mines or coal mines. AMD is formed by a series of complex geo-chemical and microbial reactions that occur when water comes in contact with sulfide, refuse or the overburden of a mine operation. Subsurface mining often progresses below the water table, in which case water must be constantly pumped out of the mine in order to prevent flooding. AMD is highly acidic and generally enriched with aluminum, iron, sulfate and heavy metals such as chromium and cadmium.While these waters are major causes of environmental pollution and are toxic to the majority of prokaryotic and eukaryotic organisms, some life forms thrive within them. Although the small numbers of metabolically beneficial reactions are available in the extreme circumstance, "acidophiles" comprise a surprisingly wide diversity of microorganisms in terms of both physiology and phylogeny. And microbial communities often were much different in diverse sites. To date, although there are many existing reports on bacterial ecology in AMD, to the best of our knowledge such studies in Chinese mines are rare. In this study, we investigated the bacterial, archaeal and geochemical characteristics of 3 AMD sites in Dabaoshan Mine, China.By using the technology of the Amplified Ribosomal DNA Restriction Analysis (ARDRA) or Restriction Fragment Length Polymorphism (RFLP) analysis, microbial diversity and community structure could be exploited quickly and exactly. We identified major bacterial components in 3 AMD samples by 16S rRNA and gyrB gene libraries. 16S rRNA and gyrB gene libraries represented the similar result. In samples, Proteobacteria, Nitrospira, Actinobacteria and Acidobacteria were found, but Firmicutes was absent. The bacterial community structures were mainly composed of the members of Gammaproteobacteria (mainly A. ferrooxidans), Alphaproteobacteria (mainly Acidiphilium species) and Nitrospira (mainly Leptospirillum species) in acid mine drainage from Dabaoshan mine. Furthermore, Ferroplasma was abundant in all samples from Dabaoshan mine. Most Archaea were related to two undefined groups of Thermoplasmatales division.To quantitatively measure diversity in the samples, we used the inverse of Simpson's index (1/D). AMD environments examined in our study exhibited very low microbial diversity indices. However, bacterial diversities were obviously distinct among different AMD sites. Furthermore, by compared between 16S rRNA and gyrB gene libraries, the gyrB genes sequences may be higher resolution than 16S rRNA. It is more obvious in the low microbial diversity and abundant Acidithiobacillus spp of communities.Principal component analysis (PCA) studies revealed that the correlation between bacterial communities and physiochemical characteristics seemed to be indistinct in samples from all 3 sites. Samples JX and LC had similar biogeochemical properties, but bacterial communities obviously differed. In contrast, Samples JX and FS were dissimilar in biogeochemical properties but similar in bacterial community composition. We discovered two important factors that affect bacterial communities - the concentrations of ferrous iron and toxic ions. Microbial community structure wasn't closely connected with the biogeochemical properties. Shift of ferrous iron or toxic ions might greatly change community structure.Acidithiobacillus ferrooxidans had a competitive relationship with other bacterial species capable of making use of ferrous iron. A. ferrooxidans grows first under conditions of high ferrous iron concentrations. The competitive relationship among different A. ferrooxidans likewise existed. Two kinds of A. ferrooxidans could gradually capture living space of other A. ferrooxidans under the selective stress of ferrous iron.Two factors that affect bacterial communities - the concentrations of ferrous iron and toxic ions - could be correlated with time. Therefore, AMD could be regarded as a dynamic environment, and the different bacterial community structures of 3 AMD samples could simply reflect different periods of an evolution process.