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Life in the extreme: Microbial activity discovered in Old Faithful

Yellowstone National Park’s Old Faithful Geyser is more than just a natural wonder. It’s also a thriving ecosystem for extremophiles – microscopic organisms that flourish in extreme environments, according to research published in the journal PNAS Nexus

Old Faithful is one of the most iconic and well-known geysers in the world. Its predictable eruptions and impressive force have made it a top attraction for millions of visitors each year. 


The geyser propels boiling hot water and steam up to 180 feet in the air every 90 minutes. While Old Faithful would hardly seem hospitable to any form of life, the new study shows that it’s a thriving ecosystem for extremophiles – microscopic organisms that flourish in extreme environments.

The research, conducted by Lisa M. Keller, revealed that two microorganisms – Thermocrinis ruber and Thermus aquaticus – have mastered the art of survival in this challenging environment.

Thermocrinis ruber

Thermocrinis ruber, the dominant bacteria in Old Faithful, accounts for over 60% of its microbial population. This chemoautotroph is essential not just for its own survival but also supports other microbial species in the geyser. 

Without the aid of sunlight for photosynthesis, Thermocrinis ruber harnesses CO2 emissions from the geyser, converting it into carbon forms. These can then potentially support heterotrophs, such as Thermus aquaticus.

Resilient bacteria

The resilience of these bacteria is a testament to nature’s ability to adapt and thrive. From hypersaline pools and oxygen-deprived zones to boiling waters, these microbes prove life’s uncanny ability to endure and flourish. 

Genomic diversity 

The geyser’s volatile nature, with its sporadic eruptions and variable steam and water temperatures, might seem disruptive, but it’s these very conditions that have nurtured a greater diversity of Thermocrinis strains in Old Faithful than any other non-geysing hot spring in Yellowstone. 

“We think that the highly dynamic geyser environment creates many different ecological niches that Thermocrinis can occupy, causing increased sub-species level diversity,” said Keller. These findings show that the dynamic environment of Old Faithful promotes genomic diversity.

How the research was conducted 

For the investigation, Keller gathered water samples from the geyser during eruptions using weighted sterile bins. Along with a National Park Service escort, she retrieved the samples 10 minutes post-eruption. 

In her lab, Keller subjected the samples to varying temperatures, replicating geyser and pool conditions. The results were astounding. The bacteria exhibited immediate signs of activity, confirming the hypothesis of active microbial life in Old Faithful.

Study implications 

This research has implications for our understanding of potential extraterrestrial life. Geysers on moons like Enceladus and Europa have caught the attention of the planetary community. 

“Everybody gets excited about sampling Enceladus plumes, but prior to this work we didn’t even have terrestrial geysers microbial samples. I thought, let’s take a step back and figure it out on our own planet first,” said Keller.

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