Antarctic bacteria float through winter

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As the Northern Hemisphere shivers through winter, bacteria in Antarctica are employing an inventive strategy to survive the extreme cold: they use a specialized antifreeze protein to latch onto the ice and stay afloat.

Antifreeze proteins generally protect their hosts from freezing by controlling the growth of destructive ice crystals. They were first found in fish swimming in icy waters (see this paper about the evolution and transfer of these proteins between different fish species), and have also been found in plants and bacteria.

The bacterial case now has an interesting twist, published earlier this winter. The authors of the recent study isolated and characterized the antifreeze protein from Marinomonas primoryensis, found in ice-covered Ace Lake in Antarctica. They determined that the bacteria display the protein on their surface, where it can bind directly to ice crystals and anchor the microorganism to the ice. This behavior is a significant departure from what is known about similar proteins, which act inside cells to protect against internal ice crystallization. The image above shows the results from one of the experiments that confirmed the protein is found on the bacterial surface, rather than the interior.

It may not be immediately obvious how binding to ice benefits the bug, but the researchers suggest that it helps the bacteria stay closer to the water surface, where oxygen and nutrients are more abundant. Instead of requiring protection from freezing, these bacteria take advantage of the ice, essentially turning lemons into lemonade – although that may be a metaphor for a different season.

Citations:

Graham LA, Lougheed SC, Ewart KV, Davies PL (2008) Lateral Transfer of a Lectin-Like Antifreeze Protein Gene in Fishes. PLoS ONE 3(7): e2616. doi:10.1371/journal.pone.0002616

Guo S, Garnham CP, Whitney JC, Graham LA, Davies PL (2012) Re-Evaluation of a Bacterial Antifreeze Protein as an Adhesin with Ice-Binding Activity. PLoS ONE 7(11): e48805. doi:10.1371/journal.pone.0048805

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