We don’t usually associate Arctic environments with life, but one species of cyanobacteria, Phormidesmis priestleyi, not only flourishes there but shapes the glaciers on which it lives. University of Bristol scientists have shown it relies on a layer of protective sugars to keep it from freezing.
As a cyanobacteria, P. priestleyi is capable of photosynthesis. In conditions where no plant can live, it represents the base of the food chain. By darkening the ice, P. priestleyi and other cyanobacteria inhabiting a similar niche contribute to higher temperatures and increased melting. In a warming world, this makes them very important to understand.
There is a reason so few species manage to conquer these environments. Water's unusual trait of expanding when frozen can cause it to break cell walls, just as a full bottle of water can shatter in a freezer. In humans, this is one of the contributors to frostbite in our extremities. To survive in such an environment, P. priestleyi must have developed some defense mechanisms.
For the study, a sample of P. priestleyiBC1401 was collected for sequencing from a meltwater pond on a Greenland glacier and compared with strains from more temperate climates.
PhD student Nathan Chrismas said in a statement: "Many cold adapted organisms, or psychrophiles, have distinct signatures in their genomes related to how they are adapted to survival in the cold. By isolating and sequencing its genome of Phormidesmis priestleyi, we could look for distinctive signatures at the genome level. We found its genome is similar to related organisms from much warmer environments. This new genome suggests that Phormidesmis priestleyi mainly survives in cold environments by producing a special protective coating made from sugars."
The sugars form a layer that prevents cells from freezing, but the genes responsible are repurposed versions of those used elsewhere, rather than new versions unique to freezing conditions, as some other cold-adapted microbes have developed.
"Interestingly, other cyanobacteria species use similar strategies in order to survive in other extreme habitats. Such strategies have allowed cyanobacteria to colonize some of the most inhospitable places on our planet,” said senior author Dr Patricia Sánchez-Baracaldo.
Besides the cold, P. priestleyi also has to survive exposure to intense ultraviolet light in summer and months of darkness in winter. Many closely related species have not managed to adapt to such conditions, but strains of P. priestleyi have been found in Antarctica as well, apparently similarly relying on the sugar protection.
The authors suggest that future work could explain how P. priestleyi's gene expression varies with environment.
Important as it is to understand the cyanobacteria itself, future work could also indicate how it shapes the polar ecosystem, particularly the mixtures of tiny rock particles, soot, and microbes known as cryoconite, of which P. priestleyi is a major constituent.