Microbes That Like it Cold: Psychrophiles
Microbes don’t always get as much attention as charismatic animals like polar bears or whales, but as we discussed previously, they impact the ocean more than any other marine organism. This is a three-part series on microbes that thrive in extremely cold environments like the Arctic.
In general the Universe is very, very cold, except in places like the inside of stars and planets, where intense gravity fields cause compaction. Outside those areas, things get cold in a hurry. Most of the Earth’s biosphere, which is mostly ocean, is also cold, at least by human standards. However, there are microorganisms that thrive at temperatures inhospitable to humans throughout the Earth’s habitats, from the deep oceans to polar ice.
Temperature of ocean water at depth. Even though this data is from a tropical transect, temperatures drop rapidly as you move away from the surface. The numbers at left indicate depth in meters. The color key at right refers to temperature in Celsius. Source: Pacific Islands Fisheries Science Center.
These kinds of microorganisms are called psychrophiles, meaning “cold-loving,” in contrast to mesophiles that prefer relatively balmy conditions, like humans do. Psychrophiles often grow at below-freezing temperatures and some can even carry out active metabolism when they should be frozen solid, at temperatures as cold as -27˚F (-33˚C).
They do this in several ways. Some produce substances that reduce the freezing temperature of water. While salt already lowers the freezing temperature of water (for example, most of the underwater scenes in To The Arctic were filmed in ocean water that had cooled below freezing temperature (29F), due to high salt content), some psychrophiles produce an ice-binding protein that prevents recrystallization of ice. Think of it as a microbial anti-freeze, like what you would put in your radiator. Psychrophiles have evolved enzymes that actually work better at colder temperatures, and become unstable and don’t function well when in warmer conditions. Also, these microorganisms can have differences in their proteins and cell membranes that keep them more fluid in cold temperatures, thus preserving motions essential to both proper membrane and protein function. This is like putting more butter in your cookies: they stay chewier, even when cold.
An example of the diversity of morphotypes of microbes found in polar ice at Vostok Station. Scanning electron micrographs provided courtesy of Dr. Scott Rogers (results of collaborative work between T. D’Elia, R. Verrapeneni, M. Cayer and S.O. Rogers).
These amazing adaptations are part of why psychrophiles can live in the deep cold oceans, in glaciers, in the winter sea ice of the Arctic, and more than two miles under the surface ice of Antarctica at Vostok Station. We will explore polar microorganisms in the upcoming posts.
References and further reading:
1. D’Elia, T., Veerapaneni, R. & Rogers, S. O. Isolation of Microbes from Lake Vostok Accretion Ice. Appl. Environ. Microbiol. 74, 4962–4965 (2008).
2. Raymond, J. A., Christner, B. C. & Schuster, S. C. A bacterial ice-binding protein from the Vostok ice core. Extremophiles 12, 713–717 (2008).
3. Valentine, D. L. Adaptations to energy stress dictate the ecology and evolution of the Archaea. Nat Rev Micro 5, 316–323 (2007).
4. Cavicchioli, R. Cold-adapted archaea. Nat Rev Micro 4, 331–343 (2006).
5. D’Amico, S., Collins, T., Marx, J.-C., Feller, G. & Gerday, C. Psychrophilic microorganisms: challenges for life. EMBO Rep 7, 385–389 (2006).
6. Scherer, S. & Neuhaus, K. Life at low temperatures. The Prokaryotes 2, 210–262 (2006).
7. Feller, G. & Gerday, C. Psychrophilic enzymes: hot topics in cold adaptation. Nat Rev Micro 1, 200–208 (2003).
8. Saunders, N. F. W. et al. Mechanisms of thermal adaptation revealed from the genomes of the Antarctic Archaea Methanogenium frigidum and Methanococcoides burtonii. Genome Research 13, 1580–1588 (2003).