The sulfidic Frasassi cave system affords a unique opportunity to investigate niche relationships among sulfur-oxidizing bacteria, including epsilonproteobacterial clades with no cultivated representatives. Oxygen and sulfide concentrations in the cave waters range over more than two orders of magnitude as a result of seasonally and spatially variable dilution of the sulfidic groundwater. A full-cycle rRNA approach was used to quantify dominant populations in biofilms collected in both diluted and undiluted zones. Sulfide concentration profiles within biofilms were obtained in situ using microelectrode voltammetry. Populations in rock-attached streamers depended on the sulfide/oxygen supply ratio of bulk water (r ¼ 0.97; Po0.0001). Filamentous epsilonproteobacteria dominated at high sulfide to oxygen ratios (4150), whereas Thiothrix dominated at low ratios (o75). In contrast, Beggiatoa was the dominant group in biofilms at the sediment-water interface regardless of sulfide and oxygen concentrations or supply ratio. Our results highlight the versatility and ecological success of Beggiatoa in diffusion-controlled niches, and demonstrate that high sulfide/oxygen ratios in turbulent water are important for the growth of filamentous epsilonproteobacteria.
This study presents population analyses of microbial communities inhabiting a site of extreme acid mine drainage (AMD) production. The site is the inactive underground Richmond mine at Iron Mountain, Calif., where the weathering of a massive sulfide ore body (mostly pyrite) produces solutions with pHs of ϳ0.5 to ϳ1.0. Here we used a suite of oligonucleotide probes, designed from molecular data recently acquired from the site, to analyze a number of microbial environments by fluorescent in situ hybridization. Microbial-community analyses were correlated with geochemical and mineralogical 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 types, as defined by the specificities of the oligonucleotide probes, dominated the microbial communities. The majority of the dominant organisms detected were newly discovered or organisms only recently associated with acid-leaching environments. "Ferroplasma" spp. were detected in many of the communities and were particularly dominant in environments of lowest pH and highest 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 detected as a prominent inhabitant in warmer (ϳ43°C) environments. The information gathered here is critical for determining organisms important to AMD production at Iron Mountain and for directing future studies of this process. The findings presented here also have relevance to the microbiology of industrial bioleaching and to the understanding of geochemical iron and sulfur cycles.We have investigated microbial and geochemical characteristics of the extreme acid mine drainage (AMD) site at Iron Mountain, Calif. (15,32,36). At this location, extensive mining by underground tunneling and blasting has exposed a massive sulfide ore body, comprised of approximately 95% pyrite (FeS 2 ), to weathering by water and air (27). Dissolution of the pyrite ore body results from oxidation and produces acid according to the reaction FeS 2 ϩ 14Fe 3ϩ ϩ 8H 2 O315Fe 2ϩ ϩ 2SO 4 2Ϫ ϩ 16H ϩ (26). The water discharged from the mine is treated to neutralize the drainage and precipitate metals before the water is released into the Keswick reservoir.Chemolithotrophic prokaryotes such as Acidithiobacillus ferrooxidans (formerly known as Thiobacillus ferrooxidans [24]) and Leptospirillum ferrooxidans are known to enhance acid production in metal-leaching environments by oxidizing Fe 2ϩ and replenishing the oxidant Fe 3ϩ (34). To better understand details of microbially enhanced pyrite oxidation, much attention has been placed on characterizing A. ferrooxidans and L. ferrooxidans. However, acid-leaching environments support a diverse range of iron-and sulfur-oxidizing chemolithotrophs as well as heterotrophic microorganisms (22). Indeed, investigations of microbia...
Thermus aquaticus and Thermus thermophilus, common inhabitants of terrestrial hot springs and thermally polluted domestic and industrial waters, have been found to rapidly oxidize arsenite to arsenate. Field investigations at a hot spring in Yellowstone National Park revealed conserved total arsenic transport and rapid arsenite oxidation occurring within the drainage channel. This environment was heavily colonized by Thermus aquaticus. In laboratory experiments, arsenite oxidation by cultures of Thermus aquaticus YT1 (previously isolated from Yellowstone National Park) and Thermus thermophilus HB8 was accelerated by a factor of over 100 relative to a biotic controls. Thermus aquaticus and Thermus thermophilus may therefore play a large and previously unrecognized role in determining arsenic speciation and bioavailability in thermal environments.
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