A novel aerobic, gram-positive bacterium that is able to thrive at minus 15 degrees Celsius - the coldest temperature ever reported for bacterial growth – offers clues about microbial life on both Mars and the Saturn moon Enceladus, where similar briny subzero conditions are thought to exist, says a McGill University-led team of researchers.



The team discovered the bacterium Planococcus halocryophilus OR1 in 2011 after screening about 200 separate High Arctic microbes looking for the microorganism best adapted to the harsh conditions of the Arctic permafrost.

”We believe that this bacterium lives in very thin veins of very salty water found within the frozen permafrost on Ellesmere Island. The salt in the permafrost brine veins keeps the water from freezing at the ambient permafrost temperature (minus 16 degrees Celsius), creating a habitable but very harsh environment. It’s not the easiest place to survive but this organism is capable of remaining active to at least minus 25 degrees Celsius in permafrost,” said Prof Lyle Whyte, senior author of a paper published in the ISME Journal.

In order to understand what it takes to be able to do so, the researchers studied the genomic sequence and other molecular traits of Planococcus halocryophilus OR1. They found that the bacterium adapts to the extremely cold, salty conditions in which it is found thanks to significant modifications in its cell structure and function and increased amounts of cold-adapted proteins. These include changes to the membranes that envelop the bacterium and protect it from the hostile environment in which it lives.

The genome sequence also revealed that Planococcus halocryophilus OR1 is unusual in other ways. It appears to maintain high levels of compounds inside the bacterial cell that act as a sort of molecular antifreeze, keeping the microbe from freezing solid, while at the same time protecting the cell from the very salty exterior environment.

The scientists believe however, that such microbes may potentially play a harmful role in extremely cold environments such as the High Arctic by increasing carbon dioxide emissions from the melting permafrost, one of the results of global warming.

“I’m kind of proud of this bug. It comes from the Canadian High Arctic and is our cold temperature champion, but what we can learn from this microbe may tell us a lot about how similar microbial life may exist elsewhere in the Solar System,” Prof Whyte concluded.

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Bibliographic information: Nadia C. S. Mykytczuk et al. 2013. Bacterial growth at −15 °C; molecular insights from the permafrost bacterium Planococcus halocryophilus Or1. The ISME Journal 7, 1211–1226; doi: 10.1038/ismej.2013.8

Nadia C. S. Mykytczuk et al. 2012. Planococcus halocryophilus sp. nov., an extreme sub-zero species from high Arctic permafrost. IJSEM, vol. 62, no. Pt 8, 1937-1944; doi: 10.1099/ijs.0.035782-0