(Submitted Abstract to the 2002 National Speleological Society Meeting, Camden, Maine)

Metabolic and isotopic diversity of chemoautotrophic sulfur-oxidizing bacteria from Lower Kane Cave, Wyoming

Annette Summers Engel¹,

Megan L. Porter²,

Libby A. Stern¹,

Philip C. Bennett¹

¹ Department of Geological Sciences, University of Texas at Austin, Austin, Texas 78712
² Department of Zoology, Brigham Young University, Provo, Utah 84602

Microbial communities from Lower Kane Cave (Wyoming) were investigated using phylogenetic analyses of 16S rRNA gene sequences and detailed isotopic surveys. Microbial mats from three sulfidic spring locations were discretely sampled along flow transects, from anaerobic waters in the spring orifices through the aerobic discharge channels, with mats extending 10-15 m from the orifices. Dense mats were 3 – 10 cm thick, and had short (<1 cm) and long (>10 cm) white filaments interconnected with white web-like films on the surface, and a gray-brown gel of filaments underneath. Discontinuous patches of yellow biofilms also intermixed with short filaments. Most of the microorganisms identified from the mats were sulfur-oxidizing bacteria. Thiobacillus spp. were detected from yellow patches, and short filaments along the stream channels were closely related to Thiothrix unzii. The most abundant bacterial populations in all the filamentous samples belonged to an uncharacterized group of sulfur-oxidizing bacteria within the e-Proteobacteria class. Similar organisms have been found in other sulfidic systems, including Cesspool Cave (Virginia) and Parker Cave (Kentucky). Microbial mats from Lower Kane had an average d¹³C value of -36 permil, demonstrating chemoautotrophic fractionation against ¹³C from an inorganic carbon reservoir (cave water was -8.9 permil). Each of the sulfur-oxidizing bacterial morphotypes, however, had distinct carbon isotope compositions, indicating that pathways for obtaining carbon may be slightly different. These complex populations provide energy for the cave ecosystem as chemoautotrophs, while driving speleogenesis due to sulfide oxidation and the production of sulfuric acid.

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