Geomicrobiology of pyrite (FeS2) dissolution: Case study at Iron Mountain,California

Geomicrobiology of pyrite weathering at Iron Mountain, CA, was investigated by molecular biological, surface chemical surface structural, and solution chemical methods in both laboratory and field-based studies. Research focu sed at sites bath within and peripheral to the ore-body. The acid-generatin g areas we have examined thus far at Iron Mountain (solution pH < 1.0, temp erature > 35 degrees C) were populated by species other than Thiobacillus f errooxidans. 16S rDNA bacterial sequence analysis and domain- and species-l evel oligonucleotide probe-based investigations confirmed the presence of p lanktonic Leptospirillum ferrooxidans and indicated the existence of other species apparently related to other newly described acidophilic chemolithot rophs. T. ferrooxidans was confined to relatively moderate environments (pH 2-3, 20-30 degrees C) that were peripheral to the orebody. Dissolution rat e measurements indicated that, per cell, attached and planktonic species co ntributed comparably in acid release. Surface colonization experiments in t he laboratory and field indicated that attachment was specific to sulfides instead of to silicates, occurred in crystallographically preferred orienta tions and. after cell division, resulted in a monolayer of cells at a maxim um density of 8 x 10(6) cells cm(-2). In situ geochemical characterization throughout the year revealed that the microbial community that controlled a cid generation varied and could be correlated with seasonal and spatial flu ctuations in geochemical conditions.