English

Abstract

Little is known about the microbiology of passive mine drainage treatment systems, such as sulfate-reducing permeable reactive zones (SR-PRZs). We have recently developed a suite of molecular biology tools in our laboratory for characterizing the microbial communities present in SR-PRZs. In this study our suite of tools is used to characterize two different field bioreactors: Peerless Jenny King and Luttrell. Both bioreactors are located near the Ten Mile Creek Basin near Helena, MT, and both employ a compost-based substrate to promote the growth of sulfate-reducing bacteria (SRB) for production of sulfides and precipitation of metals. In summer, 2005, the reactors were sampled at multiple locations and with depth. DNA was extracted from the compost material and followed by cloning of polymerase chain reaction (PCR) amplified 16S rRNA genes, restriction digest screening, and DNA sequencing to provide insight into the overall composition of the microbial communities. To directly examine the SRB populations, a gene specific to SRB, apsA, was PCR-amplified, cloned, and sequenced. This revealed that Desulfovibrio spp. were prevalent in both Luttrell and Peerless Jenny King. At Peerless Jenny King, one Desulfovibrio spp. found was noted to be particularly aerotolerant. This analysis also revealed that Thiobacillus denitrificans were common at Peerless Jenny King. This is an organism that oxidizes sulfides in the presence of nitrate, which is undesirable for biozone function. In order to quantify SRB, quantitative real-time PCR (Q-PCR) was used targeting two specific groups of SRB, Desulfovibrio and Desulfobacteria. These results indicated that these two SRB groups, which have distinct substrate requirements, vary in distribution between the two bioreactors and with depth. It is hoped that an improved understanding of the microbiology of these systems will help to improve design and operation of passive treatment systems employing sulfate reduction.