Extremophiles

Living organisms that can live in the world's extreme environments

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Extremophiles

Grand Prismatic Spring from Overlook

Looking down to Grand Prismatic Spring allows you to see the beautiful colors that extremophiles can create. Billions of living organisms living and working together are responsible for most of the color in thermal areas.

Extremophiles are microscopic organisms that thrive in that could be described as extreme conditions. In Yellowstone, these conditions can include extreme heat or an altered pH—either very low pH (acidic), very high pH (alkaline), or a combination of heat and altered pH

The environments of extremophiles would kill other organisms. However, if their environment would change to conditions that we would consider more hospitable, the extremophiles would perish.

Extremophiles are a type of microorganism, a small living thing that cannot be seen without a microscope. However, colonies, or large groups of microorganisms living together, are visible in many of Yellowstone’s thermal features.

Close in to the bacteria mat below Sapphire Pool.

There is a large flat area of runoff below Sapphire Pool. The runoff channel with the hottest water is green for a considerable distance from the pool. This orange mat is on higher ground, by a couple of inches, and is still hot. It has an intriguing display of bacteria and geyserite growing together. Looking closely, you may find the ephydrid flies walking on the water, eating bacteria.

Whirligig Geyser in Norris Geyser Basin

Norris Geyser Basin is predominately acidic. This means it supports acidophiles, actually thermoacidophiles, because the water is also hot.

Extremophiles in Yellowstone fall into two categories:

  • Thermophiles are microorganisms that live in extremely hot environments.
    • Thermophiles thrive in temperatures above 113° F (45° C).
    • Hyperthermophiles thrive in temperatures between 176° F (80° C) and 235° F (113° C).
  • Some extremophiles require hot conditions but also thrive in an altered pH environment.
    • Acidophiles thrive in environments with a pH level of 1 to 5. So, the acidophiles in Yellowstone are actually thermoacidophiles—they thrive in hot and acidic environments.
    • Alkaliphiles live and grow in environments with a pH level of 9 to 11.

Let us review what pH measurements mean; pH is a scale of acidity and alkalinity ranging from 1 to 14, with a pH of 7 indicating neutral, neither acidic nor alkaline. Any pH below 7 is considered acidic; anything above is alkaline or basic. A substance with a pH close to 1 would be a powerful acid; a pH close to 14 would be highly alkaline.

To better appreciate the impact of pH, comparing the conditions in Yellowstone’s thermal features to those tolerated by humans may be helpful. In the human body, our normal pH is 7.35 to 7.45. A pH above 7.8 or below 6.8 is generally fatal. Our pH may vary slightly from 7.35 to 7.45 during the day, but only by minute amounts.

pH Scale

Here is an example of the pH scale with items that match along the scale. Image by Freepik

Sulphur Caldron

Sulphur Caldron is south of Hayden Valley on the park's east side. Sulphur Caldron is one of the most acidic features in the park, with a pH of around 1.

Other extremophiles found throughout the world includes:

  • Barophiles microorganisms survive under great pressure.
  • Halophiles are aerobic (uses oxygen) microorganism that live and grow in high saline/salty environment.
  • Psychrophiles thrive in extreme cold. They grow best in environments of about 14° to 68° F (-10° to 20° C).
  • Xerophiles live in extremely dry environments.

“Normal” microorganisms are called mesophiles. They grow best in temperatures between 50° to 122° F (10° to 50° C).

Runoff from Excelsior Geyser

Excelsior Geyser runoff channel. The Geyser itself is 132°F (55.56°C). The runoff is cooler as it gets away from the heat source. Notice the green water is in a lower channel than the ground around it. The orange color is elevated above the green, and the color of the Extremophiles is darker because the water is cooler. The water is cooler because it runs slowly, not deep, and is exposed more to the wind.
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