Molecular phylogenetic analysis of a bacterial community in Sulphur River,Parker Cave, Kentucky

Sulphur River in Parker Cave, Kentucky receives sulfurous water (11-21 mg s ulfide/L) from the Phantom Waterfall and contains a microbial mat composed of white filaments. We extend a previous morphological survey with a molecu lar phylogenetic analysis of the bacteria of the microbial mat. This approa ch employs DNA sequence comparisons of small subunit ribosomal RNA (SSU rRN A) genes obtained from the mat with those from an extensive database of rRN A sequences. Many of SSU rRNA gene clones obtained from the mat are most si milar to rRNA sequences from sulfur-oxidizing bacteria (Thiothrix spp., Thi omicrospira denitrtficans, and "Candidatus Thiobacillus baregensis"). The S ulphur River SSU rRNA gene clones also show specific affiliations with clon es from environmental surveys of bacteria from deep-sea hydrothermal vent c ommunities and subsurface microcosms. Affiliations with sequences from bact eria that are known to have the ability to obtain energy for CO, fixation f rom the oxidation of inorganic compounds (chemoautotrophs), in combination with the environmental conditions surrounding the microbial mat, indicate t hat chemoautotrophic metabolism of bacteria in this mat may contribute to t he biomass of Sulphur River. Cave communities, such as the one identified i n Sulphur River, provide sites to study such relatively autonomous chemoaut otrophic communities that are much more accessible than similar communities associated with deep-sea hydrothermal vents. Subsurface microbiology and t he contribution of microbial activity on cave development are also discusse d.