Loving the Cold: Microbes from the Archeozoic Eon
On a snowy winter day there is nothing better than sitting next to a warm fire with a hot beverage dreaming of Cayo de Aqua beaches in Venezuela; however, in reality over 80% of the Earth never reaches above 5°C (3). Even more distant from our thoughts is that many microorganisms inhabit these inhabitable landscapes throughout our blue planet and call them home. These microbes are called psychrophiles, meaning “cold-loving,” and their evolution has allowed them to survive and proliferate at low temperatures. Their bitterly cold environments create biochemical limitations that range from decreased enzyme activity and membrane fluidity to inappropriate protein folding and intracellular ice formation (1). Despite challenges faced when living in extremely cold environments, psychrophiles have successfully colonized all permanently cold environments on Earth, including the deep sea, mountains, caves, and Polar Regions. In these environments biologist have found bacteria, archaea, fungi, algae, and viruses. Many of these amazing microbes can be found at Organic Lake in Antarctica’s Vestfold hills located in East Antarctica (3).
To show just how amazing their evolutionary adaptations can be, one psychrophile, Maritella profunda, has adapted to extremely cold living conditions in the deep sea with maximal growth rates at 2°C and a maximum growth temperature of only 12°C (1). Even more impressive, is the current record-holder for surviving in the cold, a microbe called Planococcus halocryophilus. Scientists from McGill University discovered this microbe in the permafrost of northern Canada. Recently, they demonstrated it grows at -15˚C and stays metabolically active at -25˚C (3). However, this doesn’t mean that these microbes have high reproductive rates. Life at these temperatures is incredibly slow and some species only divide six times per year. This is very little activity when compared to E. coli that can divide within 20 minutes in a laboratory setting (3).
One way psychrophiles convey adaptations that keep them more fluid in cold temperatures is through an altered composition of higher unsaturated, polyunsaturated and methyl-branched fatty acids, along with shorter acyl-chain lengths (1). By adjusting fatty acids that make them up and using more polyunsaturated fats, they can live more flexible lives. It is like cold margarine that has a lot of polyunsaturated fat versus cold butter; the butter will be rock hard and the margarine will still be spreadable (2). To overcome additional deterioration effects of low temperatures, psychrophiles utilize antifreeze proteins (AFPs) to prevent enzymes from rigidifying, affecting catalysts. These proteins have the ability to bind to ice crystals through a large complementary surface. In reaction to this binding, thermal hysteresis is created and lowers the temperature at which an organism can grow (1). Antifreeze proteins have been recently demonstrated in Antarctic lake bacteria like Marinomonas primoryensis. In tandem with antifreeze proteins, cold-shock proteins are highly expressed and can have crucial roles in protein folding, control of nucleic-acid secondary structure, transcription, and translation (1). These proteins allow psychrophiles to be much more flexible.
Impact on Humans
Not only have psychrophiles evolved to thrive in inhabitable environments, differences in their proteins can have an added benefit to our own lives. A few psychrophile proteins have already entered the marketplace. A Belgian company, Puratos, sells a cold-adapted protein for bread baking; it makes dough rise faster by breaking down cell walls quickly (3). Other applications of psychrophile proteins include detergents for washing clothes at even lower temperatures and enzymes for cleaning water filtration systems (3). As benefits begin to arise from scientifically understanding and using these microbes, there is a concern that their livelihood may be in danger.
Although the Earth is a mostly cold environment, places like Organic Lake are now facing threats, mainly from tourism and climate change. Global warming is hitting Polar Regions the hardest; this can become a huge concern as species adapted to warmer temperatures potentially outcompete our cold loving microbes.
1) D’Amico, S., Collins, T., Marx, J.-C., Feller, G., & Gerday, C. (2006). Psychrophilic microorganisms: challenges for life. EMBO Reports, 7(4), 385–389. http://doi.org/10.1038/sj.embor.7400662
2) Thrash, J. (2012, May 8). Microbes That Like it Cold: Psychrophiles. Retrieved December 2, 2015, from http://www.oneworldoneocean.com/blog/entry/psychrophiles-microbes-that-like-it-cold
3) Zimmer, C. (2013, June 11). Comfortable in the Cold: Life Below Freezing in an Antarctic Lake. Retrieved December 2, 2015, from http://www.pbs.org/wgbh/nova/next/nature/seeking- psychrophiles-in-antarctica/