Bacteria diversity, distribution and insight into their role in S and Fe biogeochemical cycling during black shale weathering

A group of black shale samples, which were collected sequentially along a continuous depositional unit from bottom fresh zone toward the surface regolith of the weathering profile at Chengkou County, Southwest China, were examined using mineralogical, geochemical and pyrosequencing techniques. The mineralogical and geochemical analyses indicated that the black shale profile provided a series of extremely acidic and chemical species that changed microbial habitats following the process of weathering. This finding is in contrast with a previous hypothesis that a low-diversity bacterial community existed in these harsh environments; the pyrosequencing analyses showed extremely diverse microbial communities with 33 different phyla/groups in these samples. Among these phyla/groups, proteobacteria, actinobacteria and firmcutes were more dominant than other phyla, and the phylogenetic structures of the bacterial communities vary with the progressive process of weathering. Moreover, the canonical-correlation analysis suggested that pH and sulfur in sulfate, followed by total Fe and sulfur in pyrite, are the significant factors that shape the microbial community structure. In addition, a large proportion of S- and Fe-related bacteria, such as Acidithiobacillus, Sulfobacillus, Thiobacillus, Ferrimicrobium and Ferrithrix, may be responsible for pyrite bio-oxidation, as well as for S and Fe biogeochemical cycling, in the black shale weathering environments.