By Michelle Chamberlain
Yellowstone National Park contains a rainbow colored hot spring called Grand Prismatic Spring. No, somebody didn’t dump food coloring into the spring. The colors are actually due to the presence of microorganisms! These microorganisms are tiny, single-celled bacteria that contain special chemicals, called pigments, which give them their color. The pigments absorb certain wavelengths of light and reflect others – the wavelengths that they reflect determine their color.
Grand Prismatic Spring is a hot spring with temperatures reaching as high as 87°C (188.6°F), with the highest temperatures occurring at the middle of the pool and cooling off as you move towards the edge. All microorganisms, also called microbes, living within the spring are considered thermophiles, meaning that they can survive and thrive at high temperatures. Although some organisms can tolerate the highest temperatures at the center of the pool, most cannot. The changing colors that give the Grand Prismatic Spring its rainbow appearance are due to differences in the temperatures where the different types of microbes can survive.
The center of the pool is too hot for life, so the blue color is due to the absorption of light. Water absorbs red light and scatters blue light, resulting in the blue appearance. Moving outward, a yellow ring appears within the pool when the temperature is about 163.4°F. This yellow ring is due to Synechococcus, a type of photosynthetic bacteria within the Cyanobacteria phylum. It contains chlorophyll, which is the primary pigment in photosynthesis and is what makes plant leaves appear green. But Synechococcus also contains carotenoids, which give the bacteria a yellow appearance. Moving outward, the water cools down to about 65°C and the Chloroflexi become the most common microbe. Like Synechococcus, these bacteria also have carotenoid pigments, but in this case they appear orange. Beyond the orange zone the water cools to around 55°C and more types of bacteria and archaea are able to survive the elevated temperatures. This reddish-brown ring contains an abundance of Cyanobacteria called Calothrix. The reddish color is due to a pigment called scytonemin which acts as a sunscreen for the bacteria.
The Grand Prismatic Spring is not only a great site to see when visiting Yellowstone National Park, but it’s an example of how different microorganisms vary in their ability to tolerate high temperatures.
