(Submitted Abstract to the 2002 International Symposium for Subsurface Microbiology -Copenhagen, Demark)
Annette Summers Engel1, Philip C. Bennett1, Libby A.,
Stern1, Megan L. Porter2, Natuschka Lee3, and
Michael Wagner3
1Department
of Geological Sciences, University of Texas, Austin, Texas 78712
2 Department of Zoology, Brigham Young University, Provo, Utah 84604
3Lehrstuhl für Mikrobiologie,
Technische Universität München, Freising, Germany 85350
Prokaryotic diversity was examined from microbial mats collected from three hydrogen sulfide-bearing springs that discharge into Lower Kane Cave, Wyoming, USA. Filamentous microbial mats and interconnected white web-like films were discretely sampled along 10-20 m flow transects, from anaerobic waters in the spring orifices through the aerobic discharge channels. Bulk mats had an average δ13C value of –36 permil, demonstrating chemolithoautotrophic fractionation against 13-C from an inorganic carbon source (cave water was –8.9 permil). DNA was extracted from the samples and the 16S rDNA was amplified by PCR. Clone assessment indicated Thiothrix spp. and two novel phylotypes (cluster I and II) within the epsilon-subclass of Proteobacteria. Cluster I was closely related to other uncultured environmental clones from sulfidic springs and groundwater, while cluster II had no known relatives. Microbial community composition of the mats was determined quantitatively using fluorescence in-situ hybridization with rRNA-targeted oligonucleotide probes for each of the two epsilon-clusters, confocal laser scanning microscopy, and digital image analysis. Of the samples investigated, cluster II was the most prevalent, accounting for an average of 68% of the total bacterial population. While Thiothrix is known to oxidize reduced sulfur compounds, our geochemical and isotopic evidence, and preliminary culturing of the microbial mat samples, suggest that the two novel clusters are also involved in sulfur cycling as sulfur-oxidizing bacteria. These results supplement the known diversity of epsilon-Proteobacteria in sulfur-based environments, and provide additional insight into the ecological significance of microbial populations responsible for sustaining chemolithoautotrophic ecosystems.
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