BIOGEOCHEMICAL ECOLOGY OF THIOTHRIX SPP IN UNDERWATER LIMESTONE CAVES

Thiothrix spp., sulfide-oxidizing mixotrophic bacteria, were sampled from visible colonies in the Floridan aquifer in several underwent caves, sinkholes, and springs below the water table in North Florida. Bacteria samples were collected by cave drivers certified by the National Speleological Society/Cave Diving Section. Sites sampled were ecological niches in the aquifer where visible colonies had a white slimy or filamentous appearance indicative of Thiothrix spp. Sterile sampling methods were adapted to the underwater cave setting. Bulk water samples for media preparation were collected by divers from bacteria sampling sites. Bacteria were isolated and cultured in growth media prepared with cave or spring water. Thiothrix spp. were identified by microbiological and immunological methods. Monoclonal antibodies specific for Thiothrix spp. were utilized in fluorescent antibody assays and enzyme-linked immuknosorbent assays (ELISA). Thiothrix was found in six of eight underwater caves sampled. Three of these caves had no discernible water flow at the time of sampling, indicating that Thiothrix in the Floridan aquifer does not necessarily require constantly flowing water. Most of the visible bacterial colonies that tested negative for Thiothrix were biofilms growing on limestone and iron oxyhydroxide substrates on the walls of clear-water and high-flow caves. The sulfur cycle in phreatic limestone conduits is described. The reactions and bacteria involved in the HS- cycle and pyrite cycle are discussed. Thiothrix generates sulfuric acid, which has the potential to disolve limestone below the water table. Results of this study should contribute to a better understanding of the role of colorless sulfur bacteria in the development of porosity in carbonate rocks and microbial ecology in these karst aquifer settings.