The Microbial Community of a Black Shale Pyrite Biofilm and its Implications for Pyrite Weathering

Microbial biofilms preferentially colonized pyrite surfaces of black shale incubated in groundwater in the Newark Basin (northeastern United States) for 1 month. SEM observation revealed the co-occurrence of bacteria-shaped pits and secondary iron minerals on pyrite, which indicate biological involvement in pyrite weathering and secondary solid formation. Of the 24 16S rDNA sequences obtained from bacterial communities on pyrite, arsenopyrite and quartz sand, 22 belonged to the phylum proteobacteria, including 5 identified as β or ε-proteobacteria capable of oxidizing iron or sulfur, 16 identified as members of the Fe(III)-reducing Geobacteraceae in the δ-proteobacteria and one identified as the Fe(III)reducing Ferribacterium. Results indicate that microbes play an essential role in the oxidation of iron sulfides (via direct contact and indirect pathways) and the reduction of iron oxides in pyritebearing substrata of a slightly acidic black shale aquifer.