Thermophilic Bacteria Examples

Thermophilic Bacteria Examples in Yellowstone National Park

Thermophilic bacteria are some of the most visually striking and biologically important organisms in Yellowstone National Park. They inhabit hot springs, geyser runoff channels, and geothermal basins where temperatures and chemical conditions would be lethal to most life. These bacteria are not random inhabitants of extreme environments but highly specialized organisms that occupy precise temperature and pH ranges. Many of them are photosynthetic, forming colorful microbial mats that transform Yellowstone’s geothermal features into living landscapes. Others rely on chemical energy instead of sunlight, demonstrating alternative ways life can persist under extreme conditions. 

The following examples highlight some of the most well-studied and ecologically significant thermophilic bacteria found in Yellowstone, showing how each species contributes to the park’s geothermal ecosystems.

Quick Reference: Thermophilic Bacteria Examples in Yellowstone National Park

Thermophilic Bacterium	pH Range	Temperature Range	Typical Color	Metabolism	Main Yellowstone Locations
Cyanobacteria 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
Cyanobacteria Phormidium	6–8	35–57°C (95–135°F)	Orange mats	Photosynthesis	Mammoth Hot Springs; Upper, Midway, and Lower Geyser Basins
Cyanobacteria Oscillatoria	6–8	36–45°C (96–113°F)	Orange mats	Photosynthesis; oscillating movement to adjust light exposure	Mammoth Hot Springs; Chocolate Pots
Cyanobacteria 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 Bacteria (Chlorobium)	6–9	32–52°C (90–126°F)	Dense dark green mats	Anoxygenic photosynthesis; produces sulfur and sulfate	Mammoth Hot Springs; Calcite Springs
Green Nonsulfur Bacteria (Chloroflexus)	7–9	35–85°C (95–185°F)	Green mats	Anoxygenic photosynthesis using organic compounds	Mammoth Hot Springs; Upper, Midway, and Lower Geyser Basins
Aquifex Hydrogenobaculum	3–5.5	55–72°C (131–162°F)	Yellow and white streamers	Chemosynthesis using hydrogen, hydrogen sulfide, CO₂; can use arsenic	Norris Geyser Basin; Amphitheater Springs
Aquifex Thermocrinis	5–9	40–79°C (104–174°F)	Bright red or orange streamers	Chemosynthesis; carotenoid pigments provide UV and heat protection	Lower Geyser Basin

1. Cyanobacteria Calothrix

Calothrix is a thermophilic cyanobacterium commonly found in Yellowstone’s moderately hot geothermal environments, particularly at Mammoth Hot Springs and across the Upper, Midway, and Lower geyser basins. It thrives in waters with a pH range between 6 and 9 and prefers temperatures from about 30 to 45 degrees Celsius. These conditions place Calothrix near the cooler edges of geothermal runoff channels, where sunlight is abundant and water chemistry is relatively stable.

Visually, Calothrix forms dark brown microbial mats that cling to rocks and mineral surfaces. These mats are dense and fibrous, helping the bacteria anchor themselves in flowing water. During daylight hours, Calothrix performs oxygenic photosynthesis, using sunlight to convert carbon dioxide and water into organic matter and oxygen. This process makes it a primary producer, supplying energy to other microorganisms within the mat. At night, when sunlight is unavailable, Calothrix switches to fermentation, allowing it to continue generating energy under dark conditions. This metabolic flexibility gives Calothrix a strong advantage in Yellowstone’s variable geothermal environments, where light and temperature fluctuate daily.

2. Cyanobacteria Phormidium

Phormidium is another important thermophilic cyanobacterium that contributes to the colorful appearance of Yellowstone’s hot springs. It is commonly found at Mammoth Hot Springs and throughout the Upper, Midway, and Lower geyser basins, where it inhabits waters with a pH between 6 and 8 and temperatures ranging from approximately 35 to 57 degrees Celsius. These conditions place Phormidium slightly deeper into the thermal gradient than Calothrix, allowing it to occupy hotter zones closer to geothermal sources.

Phormidium is easily recognized by the bright orange mats it forms along hot spring edges and runoff channels. These mats are smooth and often layered, reflecting the dense populations of photosynthetic cells packed together. Phormidium relies primarily on photosynthesis for energy, capturing sunlight and converting it into organic compounds that support both itself and other organisms in the microbial community. Its pigments are adapted to intense light and heat, allowing it to function efficiently under conditions that would stress most photosynthetic life. As a result, Phormidium plays a key role in shaping the visual and ecological structure of Yellowstone’s geothermal ecosystems.

3. Cyanobacteria Oscillatoria

Oscillatoria is a thermophilic cyanobacterium notable not only for its photosynthetic activity but also for its distinctive movement. It is commonly found in Mammoth Hot Springs and at Chocolate Pots, where it thrives in waters with a pH between 6 and 8 and temperatures from about 36 to 45 degrees Celsius. These moderate thermal conditions allow Oscillatoria to form stable populations while remaining close enough to geothermal activity to benefit from warm temperatures.

Oscillatoria forms orange microbial mats similar in color to those produced by Phormidium, but its behavior sets it apart. The bacteria exhibit an oscillating motion, slowly moving back and forth within the mat. This movement allows Oscillatoria to adjust its position in response to light intensity, moving closer to light sources during low-light conditions and retreating when light becomes too intense. Through photosynthesis, Oscillatoria contributes significantly to primary production in these geothermal systems. Its ability to reposition itself enhances its survival and demonstrates how even simple organisms can display complex responses to environmental conditions.

4. Cyanobacteria Synechococcus

Synechococcus is one of the most heat-tolerant photosynthetic bacteria in Yellowstone and plays a major role in some of the park’s hottest microbial ecosystems. It is found at Mammoth Hot Springs and across the Upper, Midway, and Lower geyser basins, thriving in waters with a pH between 7 and 9 and temperatures ranging from about 52 to 74 degrees Celsius. These temperatures approach the upper limits for photosynthetic life, making Synechococcus a key indicator of extreme thermal adaptation.

Synechococcus forms green microbial mats that are often found closer to the hottest parts of runoff channels. Like Calothrix, it performs photosynthesis during the day, capturing sunlight to produce energy-rich compounds. At night, it shifts to fermentation, allowing continued energy production in the absence of light. This day-night metabolic flexibility enables Synechococcus to dominate environments where conditions change rapidly. Because it thrives at such high temperatures, Synechococcus is often used by scientists to study the upper thermal limits of photosynthesis and the adaptations required for life in extreme heat.

5. Green Sulfur Bacteria Chlorobium

Chlorobium represents a different approach to photosynthesis in Yellowstone’s geothermal systems. This green sulfur bacterium is found at Mammoth Hot Springs and Calcite Springs, where it thrives in waters with a pH between 6 and 9 and temperatures from about 32 to 52 degrees Celsius. Unlike cyanobacteria, Chlorobium does not produce oxygen during photosynthesis.

Chlorobium forms dense, dark green microbial mats that often grow in low-light or shaded areas of geothermal runoff. Its metabolism relies on anoxygenic photosynthesis, using sulfur compounds instead of water as electron donors. As a result, Chlorobium produces sulfur and sulfate rather than oxygen. This metabolic pathway allows it to coexist with oxygen-producing cyanobacteria while occupying slightly different ecological niches. Chlorobium’s presence highlights the diversity of photosynthetic strategies in Yellowstone and shows how life can capture energy without contributing to atmospheric oxygen.

6. Green Nonsulfur Bacteria Chloroflexus

Chloroflexus is one of the most widespread and ecologically important thermophilic bacteria in Yellowstone. It is found at Mammoth Hot Springs and throughout the Upper, Midway, and Lower geyser basins, thriving in waters with a pH between 7 and 9 and temperatures ranging from about 35 to 85 degrees Celsius. This exceptionally broad temperature tolerance allows Chloroflexus to occupy large sections of geothermal runoff channels.

Chloroflexus forms green microbial mats that often appear layered beneath cyanobacteria. It performs anoxygenic photosynthesis but differs from Chlorobium in that it uses organic compounds during photosynthesis rather than relying solely on inorganic sulfur compounds. This metabolic flexibility allows Chloroflexus to take advantage of organic matter produced by neighboring microbes. In many microbial mats, Chloroflexus plays a key role in recycling organic carbon, linking different metabolic processes into a tightly integrated ecosystem.

7. Aquifex Hydrogenobaculum

Aquifex Hydrogenobaculum represents a very different type of thermophilic bacterium, one that relies entirely on chemical energy rather than sunlight. It is found in highly acidic geothermal environments such as Norris Geyser Basin and Amphitheater Springs, where pH values range from 3 to 5.5 and temperatures from about 55 to 72 degrees Celsius. These conditions are among the harshest in Yellowstone.

Hydrogenobaculum forms yellow and white streamer-like structures in fast-flowing geothermal waters. Its metabolism is based on chemosynthesis, using hydrogen, hydrogen sulfide, and carbon dioxide as energy sources. Remarkably, it can also use arsenic in place of hydrogen sulfide, a rare and extreme adaptation. By converting inorganic chemicals into organic matter, Hydrogenobaculum acts as a primary producer in environments where photosynthesis is impossible. Its presence demonstrates that life can thrive using chemical pathways alone, even in acidic and toxic conditions.

8. Aquifex Thermocrinis

Thermocrinis is another member of the Aquifex group and is commonly found in the Lower Geyser Basin. It thrives across a wide pH range from 5 to 9 and prefers temperatures between about 40 and 79 degrees Celsius. This versatility allows Thermocrinis to inhabit diverse geothermal settings, from acidic channels to more neutral springs.

Thermocrinis is visually distinctive, forming bright red or orange streamers in flowing hot water. These colors come from carotenoid pigments that act as a natural sunscreen, protecting the bacteria from intense sunlight and heat. Like Hydrogenobaculum, Thermocrinis relies on chemosynthesis, using chemical energy to fix carbon dioxide into organic matter. Its ability to withstand high temperatures and intense radiation makes it a key species for understanding thermal and chemical resilience in microbial life.