Thermophilic Bacteria

Small ridges of rock filled with water
Almost every hot spring or geyser in Yellowstone hosts bacteria. The travertine terraces in Mammoth Hot Springs host thermophilic bacteria.



The word “bacteria” is often associated with disease, but only a few kinds of bacteria cause problems for humans. The other thousands of bacteria, although all simple organisms, play a complex role in Earth’s ecosystems. In fact, cyanobacteria made our oxygen-rich atmosphere possible. They were the first photosynthesizers, more than 3 billion years ago. Without bacteria, we would not be here.

Almost any hot spring or geyser you see hosts bacteria. Some chemosynthesize, changing hydrogen or sulfur into forms other thermophiles can use. Most photosynthesize, providing oxygen to other thermophiles. All of the cyanobacteria and green nonsulfur bacteria photosynthesize. Some fulfill both roles. For example, Thermus sp.—which are photosynthetic—also may be able to oxidize arsenic into a less toxic form.

Individual bacteria may be rod or sphere shaped, but they often join end to end to form long strands called filaments. These strands help bind thermophilic mats, forming a vast community or mini-ecosystem. Other groups of bacteria form layered structures resembling tiny towers, which can trap sand and other organic materials.


Thermophilic Bacteria in Yellowstone National Park


Name pH Temperature Color Metabolism Location
Calothrix 6–9 30–45°C (86–113°F) Dark brown mats Photosynthesis by day; fermentation by night Mammoth Hot Springs; Upper, Midway, and Lower geyser basins
Phormidium 6–8 35–57°C (95–135°F) Orange mats Photosynthesis Mammoth Hot Springs; Upper, Midway, and Lower geyser basins
Oscillatoria 6–8 36–45°C (96–113°F) Orange mats Photosynthesis; oscillating moves it closer to light sources. Mammoth Hot Springs, Chocolate Pots
Synechococcus 7–9 52–74°C (126–165°F) Green mats Photosynthesis by day; fermentation by night Mammoth Hot Springs; Upper, Midway, and Lower geyser basins

Green Sulfur

Name pH Temperature Color Metabolism Location
Chlorobium 6–9 32–52°C (90–126°F) Dense, dark green mats Anaerobic photosynthesis—produces sulfate and sulfur, not oxygen Mammoth Hot Springs, Calcite Springs

Green non-sulfur

Name pH Temperature Color Metabolism Location
Chloroflexus 7–9 35–85°C (95–185°F) Green mats Anaerobic photosynthesis Mammoth Hot Springs; Upper, Midway, and Lower geyser basins


Name pH Temperature Color Metabolism Location
Hydrogenobaculum 3–5.5 55–72°C (131–162°F) Yellow and white streamers Uses hydrogen, hydrogen sulfide and carbon dioxide as energy sources; can use arsenic in place of hydrogen sulfide Norris Geyser Basin, Amphitheater Springs


Name pH Temperature Color Note Location
Thermus 5–9 40–79°C (104–174°F) Bright red or orange streamers Contains carotenoid pigments that act as sunscreen Lower Geyser Basin
Archaea are found in place like the mudpots of Mud Volcano.

Thermophilic Archaea

Archaea are the most extreme of all extremophiles.

Green colors line a thermal runoff pool.

Thermophilic Eukarya

Microscopic plants and animals live in the extreme environments of Yellowstone's hydrothermal features.

Blue waters of Congress Pool are host to thermophilic viruses

Thermophilic Viruses

Viruses, a logical part of thermophilic ecosystems, have been found in some pools in Yellowstone.

Orange-colered bacterial column growing in geyser runoff water.

Thermophilic Communities

Thermophilic communities are very diverse, depending on the microbes living there, the pH, and the water temperature.

View of the

Thermophiles in Time & Space

Yellowstone's hydrothermal features and thermophilic communities are studied by scientists searching for evidence of life on other planets.

A dark blue hot spring with a white crested edge rimmed by orange water

Life in Extreme Heat

Hydrothermal features are habitats for microscopic organisms called thermophiles: "thermo" for heat, "phile" for lover.

Last updated: August 21, 2017

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