Population structure of microbial communities associated with two deep, anaerobic, alkaline aquifers

Abstract

Microbial communities of two deep (1,270 and 316 m) alkaline (pH 9.94 and 8.05), anaerobic (E(h), -137 and -27 mV) aquifers were characterized by rRNA-based analyses. Both aquifers, the Grande Ronde (GR) and Priest Rapids (PR) formations, are located within the Columbia River Basalt Group in south- central Washington, and sulfidogenesis and methanogenesis characterize the GR and PR formations, respectively. RNA was extracted from microorganisms collected from groundwater by ultrafiltration through hollow-fiber membranes and hybridized to taxon-specific oligonucleotide probes. Of the three domains, Bacteria dominated both communities, making up 92.0 and 64.4% of the total rRNA from the GR and PR formations, respectively. Eucarya comprised 5.7 and 14.4%, and Archaea comprised 1.8% and 2.5%, respectively. The gram- positive target group was found in both aquifers, 11.7% in GR and 7.6% in PR. Two probes were used to target sulfate and/or metal-reducing bacteria within the delta subclass of Proteobacteria. The Desulfobacter group was present (0.3%) only in the high-sulfate groundwater (GR). However, comparable hybridization to a probe selective for the desulfovibrios and some metal- reducing bacteria was found in both aquifers, 2.5 and 2.9% from the GR and PR formations, respectively. Selective PCR amplification and sequencing of the desulfovibrio/metal-reducing group revealed a predominance of desulfovibrios in both systems (17 of 20 clones), suggesting that their environmental distribution is not restricted by sulfate availability.