Filamentous “Epsilonproteobacteria” Dominate Microbial Mats from Sulfidic Cave Springs


Link to Full Text

Download Full Text

Publication Date

January 2003


Hydrogen sulfide-rich groundwater discharges from springs into Lower Kane Cave, Wyoming, where microbial mats dominated by filamentous morphotypes are found. The full-cycle rRNA approach, including 16S rRNA gene retrieval and fluorescence in situ hybridization (FISH), was used to identify these filaments. The majority of the obtained 16S rRNA gene clones from the mats were affiliated with the “Epsilonproteobacteria” and formed two distinct clusters, designated LKC group I and LKC group II, within this class. Group I was closely related to uncultured environmental clones from petroleum-contaminated groundwater, sulfidic springs, and sulfidic caves (97 to 99% sequence similarity), while group II formed a novel clade moderately related to deep-sea hydrothermal vent symbionts (90 to 94% sequence similarity). FISH with newly designed probes for both groups specifically stained filamentous bacteria within the mats. FISH-based quantification of the two filament groups in six different microbial mat samples from Lower Kane Cave showed that LKC group II dominated five of the six mat communities. This study further expands our perceptions of the diversity and geographic distribution of “Epsilonproteobacteria” in extreme environments and demonstrates their biogeochemical importance in subterranean ecosystems. Caves containing hydrogen sulfide-rich springs represent less than 10% of all known caves globally (42). However, these caves serve as access points into sulfidic groundwater aquifers, typically associated with geothermal regions and oil-field basins, which play an important role in global sulfur cycling. The microbial communities colonizing sulfidic cave habitats have recently received attention due to their chemolithoautotrophic metabolism that can sustain complex ecosystems in the subsurface (48) and their geomicrobiological impact due to acid production (14, 60). Filamentous bacteria dominate subaqueous cave microbial mats, and from phylogenetic analyses, stable isotope evidence, and aqueous geochemistry surveys,


Epsilonproteobacteria, Fresh Water, Phylogeny, Sulfide, Water, Microbiology

Document Type



Applied and Environmental Microbiology, Vol. 69, no. 9 (2003-01-01).