RESUMEN
Yellowstone Lake (Yellowstone National Park, WY, USA) is a large high-altitude (2200 m), fresh-water lake, which straddles an extensive caldera and is the center of significant geothermal activity. The primary goal of this interdisciplinary study was to evaluate the microbial populations inhabiting thermal vent communities in Yellowstone Lake using 16S rRNA gene and random metagenome sequencing, and to determine how geochemical attributes of vent waters influence the distribution of specific microorganisms and their metabolic potential. Thermal vent waters and associated microbial biomass were sampled during two field seasons (2007-2008) using a remotely operated vehicle (ROV). Sublacustrine thermal vent waters (circa 50-90°C) contained elevated concentrations of numerous constituents associated with geothermal activity including dissolved hydrogen, sulfide, methane and carbon dioxide. Microorganisms associated with sulfur-rich filamentous "streamer" communities of Inflated Plain and West Thumb (pH range 5-6) were dominated by bacteria from the Aquificales, but also contained thermophilic archaea from the Crenarchaeota and Euryarchaeota. Novel groups of methanogens and members of the Korarchaeota were observed in vents from West Thumb and Elliot's Crater (pH 5-6). Conversely, metagenome sequence from Mary Bay vent sediments did not yield large assemblies, and contained diverse thermophilic and nonthermophilic bacterial relatives. Analysis of functional genes associated with the major vent populations indicated a direct linkage to high concentrations of carbon dioxide, reduced sulfur (sulfide and/or elemental S), hydrogen and methane in the deep thermal ecosystems. Our observations show that sublacustrine thermal vents in Yellowstone Lake support novel thermophilic communities, which contain microorganisms with functional attributes not found to date in terrestrial geothermal systems of YNP.
RESUMEN
Sublacustrine hydrothermal vents, geysers, and fumaroles impart regions of Yellowstone Lake with distinctive chemical compositions that generate unique freshwater habitats and support diverse microbial life. Some microbial communities within Sedge Bay manifest themselves as accumulations of white-colored films on the surfaces of aquatic macrophytes located within the hydrothermal flow of vents. It was hypothesized that the white films were the product of microbial growth, particularly sulfur-oxidizing bacteria. An investigation of the relevant biological compounds in the vent waters was conducted. Microscopy, non-culture molecular techniques, and phylogenetic analysis were used to assay the bacterial diversity associated with the films. Microscopic analysis of the white films revealed the presence of long filaments (>200 µm) that contained sulfur granules. Filaments with these characteristics were not detected on the normal macrophyte samples. Nucleic acids were extracted from the surface of macrophyte coated with the white film (SB1, SB2) and from the surface of an uncoated macrophyte (SC). 16S ribosomal (rRNA) genes were amplified with the polymerase chain reaction (PCR) and cloned. Amplified ribosomal DNA restriction analysis (ARDRA) was used to examine 100 clones from each library and identify unique phylotypes. S(Chao1) and the Shannon Index, mathematical measures of richness and heterogeneity, were employed to assess the ARDRA pattern diversity of each sample. The SC community contained 50 unique phylotypes, predominantly cyanobacteria and proteobacteria, and was the most heterogeneous. SB1 and SB2 communities were less heterogeneous and dominated by Thiothrix. Dilution to extinction PCR conducted with specific primers indicated that the relative abundance of Thiothrix 16S rRNA gene copies in all three samples were similar. However, reduced sulfur compounds from the vent resulted in a more narrow habitat that supported the sulfur-oxidizing Thiothrix in the white film to the exclusion of cyanobacteria and other proteobacteria found on the normal macrophyte. The majority of 16S rRNA gene sequences obtained in this study displayed similarities ≤98% to any known sequence in public data bases which suggests an abundance of new bacterial species in Sedge Bay.