WATER QUALITY, PIGMENT ANALYSIS, MICROSCOPY, AND GENOMICS DEFINE THE MICROBIAL DIVERSITY AND BIOGEOCHEMISTRY OF HOT SPRINGS BACTERIA IN THERMOPOLIS, WYOMING

Hot Springs State Park in Thermopolis is 160 km SE of Yellowstone National Park. The hot springs erupt along an east-west fault in Mesozoic sedimentary rocks that flank the north side of the Owl Creek Mountains. While not as hot as Yellowstone springs, the hot springs in Thermopolis (~52°C) is due to its proximity to the Yellowstone hotspot.

Two springs were studied: the Big Spring (TS) (a 5m pool at the main source of flow) and White Sulfur Springs (WSS) (exiting a small cave that is richly decorated in sulfur and other crystalline substances. A long-term study of water quality (pH, SC, selected ions) from the springs reveals little variation in geochemistry with time, season or rainfall. The only chemical variation observed is the degassing of H₂S.

On the macroscopic level, the morphology of the microbial communities changes along the 1-m wide, 150-m outflow channel from purple and green filaments with an underlying red-orange layer at the source, to thick white carbonate and sulfate dominated filaments, beginning approximately 10 m from the source. WSS exits a 10-m deep, <1-m wide cave, leaving a heavily precipitated (white) channel outlined with orange and green microbial mats. Microbial mats with trapped gas bubbles are found along the sides of the channel and toward the center of the outflow channel beginning 50 m from the hot spring source, extending to the cooling ponds at 100 m from the source. Microscopic, optical and electronic, morphology reveal a diversity of microbes.

Metagenomic analysis of the bacterial 16S rRNA gene shows a diverse microbial community of over 200 possible species. Dominant species at TS include Chloroflexus and Spirulina, with genera Pedobacter, Thiofaba, Sulfurovum, Venenivibrio, Enterobacter, Flavobacterium, and Sporobacterium. There are genera in WSS that are not found in the TS, and the samples are highly variable, except for the sample at the entrance of the cave, which is dominated by genus Venenivibrio and genus Thiofaba. Few are similar to Yellowstone microbes (likely because of the temperature differences between the two sites).

Characterization of the geochemical and microbial composition of these hot springs contribute to our knowledge of the regional diversity among the hot springs in and around the Greater Yellowstone Ecosystem, and may serve as modern homologs of life on ancient Earth.