Microbes that Like it Cold: Arctic Critters
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 the second in a three-part series on microbes that thrive in extremely cold environments like the Arctic.
My previous post introduced you to cold-adapted microorganisms, or psychrophiles, and how they have evolved to thrive at temperatures well below freezing. Psychrophiles have only been studied in their native environments since the 1980s although they live in the oceans within both polar circles, and even within the sea ice itself. In the Arctic sea ice during the winter, temperatures can drop below -35˚C (-31˚F).
Detecting living microbes in the ice is challenging, particularly if one wants to observe metabolic activity in situ (in the normal setting in which it occurs). To determine the difference between a microorganism that is alive and metabolizing in ice, as opposed to just lying dormant, waiting for things to warm up, you cannot simply melt the ice and see if you can grow microorganisms in a petri dish. Instead, researchers have to maintain the ice near the temperatures where it was sampled, which is challenging. Imagine working in a -20˚C (-4˚F) freezer room, wearing a parka so you don’t freeze to death, staring down a microscope! While working in these conditions, researchers use specific dyes which bind DNA of microorganisms and can be seen with special fluorescence microscopes. Another fluorescent dye can be used to see if the microbes are actively metabolizing.
Because psycrophiles are highly adapted to life in the cold, we can look at Arctic microbes as “trapped” there – they cannot seek out other cold environments like Antarctica because they would have to cross warm regions like the equator, where they would die. This allows for interesting study of microbial biogeography, or how different populations of microorganisms develop different adaptations in different locations. There is evidence for both endemic (native to one geographic locale) and cosmopolitan (widely distributed) microbes at both poles, posing tantalizing questions about how such differences occur, why some microbes are at both poles and others not, and if there are genetic differences behind such variation. Such microbial biogeography is an area of active research.
Searching for life in these icy environments may seem a little like hunting aliens on strange worlds. In fact, research on psychrophiles has been partly driven by the fact that polar habitats offer the closest comparisons to extraterrestrial systems where water is still believed to be present, for example, on Europa, the icy moon of Jupiter. In the next post, we will turn to Antarctica and how it serves as a model for understanding how life may exist elsewhere in the solar system.
References and further reading:
1. Junge, K., Eicken, H. & Deming, J. W. Bacterial Activity at -2 to -20˚C in Arctic Wintertime Sea Ice. Appl. Environ. Microbiol. 70, 550–557 (2004).
2. Schütte, U. M. E. et al. Bacterial diversity in a glacier foreland of the high Arctic. Molecular Ecology 19 Suppl 1, 54–66 (2010).
3. Skidmore, M. L., Foght, J. M. & Sharp, M. J. Microbial life beneath a high arctic glacier. Appl. Environ. Microbiol. 66, 3214–3220 (2000).
4. Staley, J. T. & Gosink, J. J. Poles apart: biodiversity and biogeography of sea ice bacteria. Annu Rev Microbiol 53, 189–215 (1999).
5. Nikrad, M. P., Cottrell, M. T. & Kirchman, D. L. Abundance and Single-Cell Activity of Heterotrophic Bacterial Groups in the Western Arctic Ocean in Summer and Winter. Appl. Environ. Microbiol. 78, 2402–2409 (2012).
6. Margesin, R. & Miteva, V. Diversity and ecology of psychrophilic microorganisms. Research in Microbiologoy 162, 346–361 (2011).
7. Martiny, J. B. H. et al. Microbial biogeography: putting microorganisms on the map. Nat Rev Micro 4, 102–112 (2006).