Comparison of acid mine drainage microbial communities in physically and geochemically distinct ecosystems

This study presents population analyses of microbial communities inhabiting a site of extreme acid mine drainage (AMD) production, The site is the ina ctive underground Richmond mine at Iron Mountain, Calif, where the weatheri ng of a massive sulfide ore body (mostly pyrite) produces solutions with pH s of similar to0.5 to similar to1.0. Here we used a suite of oligonucleotid e probes, designed from molecular data recently acquired from the site, to analyze a number of microbial environments by fluorescent in situ hybridiza tion, Microbial-community analyses were correlated with geochemical and min eralogical data from those environments. The environments investigated were within the ore body and thus at the site of pyrite dissolution, as opposed to environments that occur downstream of the dissolution. Few organism typ es, as defined by the specificities of the oligonucleotide probes, dominate d the microbial communities. The majority of the dominant organisms detecte d were newly discovered or organisms only recently associated with acid-lea ching environments. "Ferroplasma" spp, were detected in many of the communi ties and were particularly dominant in environments of lowest pH and highes t ionic strength. Leptospirillum spp, were also detected in many slime and pyrite-dominated environments. In samples of an unusual subaerial slime, a new uncultured Leptospirillum sp, dominated. Sulfobacillus spp, were detect ed as a prominent inhabitant in warmer (similar to 43 degreesC) environment s. The information gathered here is critical for determining organisms impo rtant to AMD production at Iron Mountain and for directing future studies o f this process. The findings presented here also have relevance to the micr obiology of industrial bioleaching and to the understanding of geochemical iron and sulfur cycles.