Abstract
An unusually thick ( approximately 1 cm) slime developed on a slump of finely disseminated pyrite ore within an extreme acid mine drainage site at Iron Mountain, near Redding, Calif. The slime was studied over the period of 1 year. The subaerial form of the slime distinguished it from more typical submerged streamers. Phylogenetic analysis of 16S rRNA genes revealed a diversity of sequences that were mostly novel. Nearest relatives to the majority of sequences came from iron-oxidizing acidophiles, and it appears that iron oxidation is the predominant metabolic characteristic of the organisms in the slime. The most abundant of the 16S rRNA genes detected were from organisms related to Leptospirillum species. The dominant sequence (71% of clones) may represent a new genus. Sequences within the Archaea of the Thermoplasmales lineage were detected. Most of these were only distantly related to known microorganisms. Also, sequences affiliating with Acidimicrobium were detected. Some of these were closely related to "Ferromicrobium acidophilus," and others were affiliated with a lineage only represented by environmental clones. Unexpectedly, sequences that affiliated within the delta subdivision of the Proteobacteria were detected. The predominant metabolic feature of bacteria of this subdivision is anaerobic sulfate or metal reduction. Thus, microenvironments of low redox potential possibly exist in the predominantly oxidizing environments of the slime. These results expand our knowledge of the biodiversity of acid mine drainage environments and extend our understanding of the ecology of extremely acidic systems.
Highlights
Dissolution of sulfide ores exposed to oxygen, water, and microorganisms results in acid production and environmentally detrimental acid mine drainage (AMD) [35]
T. ferrooxidans, the organism often associated with AMD, has been detected at only low levels in samples collected within the ore body [43]
Cells detected with a Leptospirillum ferrooxidans-specific probe were distributed throughout these samples but made up small proportions of the cells attached to sediment particles [43]
Summary
Dissolution of sulfide ores exposed to oxygen, water, and microorganisms results in acid production and environmentally detrimental acid mine drainage (AMD) [35]. The understanding of biological enhanced pyrite oxidation is incomplete, but it is clear that microbial iron oxidation would replenish ferric ions for the above reaction. Numerous microorganisms are known for their acidiphily and iron-oxidizing capabilities, and it is apparent that different microorganisms have different mechanisms and perhaps different abilities for iron oxidation [7] It has been the endeavor of some investigations to increase the understanding of the microbial ecology of AMD systems [29, 43]. Our research is directed towards improving the understanding of AMD microbial ecology and changes in microbial community structure as a function of geochemical conditions at major sites of acid generation. Analysis of 16S rRNA gene sequences had previously detected Leptospirillum
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