The temperature in the permafrost on Ellesmere Island in the Canadian high Arctic is nearly as cold as that of the surface of Mars. So the recent discovery by a McGill University led team of scientists of a bacterium that is able to thrive at –15ºC, the coldest temperature ever reported for bacterial growth, is exciting. The bacterium offers clues about some of the necessary preconditions for microbial life on both the Saturn moon Enceladus and Mars, where similar briny subzero conditions are thought to exist.
”We believe that this bacterium lives in very thin veins of very salty water found within the frozen permafrost on Ellesmere Island,” explains Whyte. “The salt in the permafrost brine veins keeps the water from freezing at the ambient permafrost temperature (~-16ºC), creating a habitable but very harsh environment. It’s not the easiest place to survive but this organism is capable of remaining active (i.e. breathing) to at least -25ºC in permafrost.”
In order to understand what it takes to be able to do so, Mykytczuk, Whyte and their colleagues studied the genomic sequence and other molecular traits of P. halocryophilus OR1. The researchers 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 this permafrost microbe 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 researchers 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.
Whyte is delighted with the discovery and says with a laugh, “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.”
The small, icy moon Enceladus shown below is a major source of ionized material filling the huge magnetic bubble around Saturn. About 200 lb (about 90kg) of water vapour per second – about as much as an active comet – spray out from long cracks in the south polar region known as ‘tiger stripes’. The ejected matter forms the Enceladus plume – a complex structure of icy grains and neutral gas that is mainly water vapour. The plume gets converted into charged particles interacting with the plasma that fills Saturn’s magnetosphere.
Enceladus is emerging as the most habitable spot beyond Earth in the Solar System for life as we know it. "It has liquid water, organic carbon, nitrogen [in the form of ammonia], and an energy source," says Chris McKay, an astrobiologist at NASA's Ames Research Center in Moffett Field, California. Besides Earth, he says, "there is no other environment in the Solar System where we can make all those claims."
In addition, geyser-like jets spew ice crystals and gases into space, allowing a spacecraft to sample the subsurface by flying overhead. The current Cassini mission has done that several times already, but it's only equipped to find the building blocks of life, not more complex molecules.
This research was funded by: Natural Sciences and Engineering Research Council of Canada CREATE Canadian Astrobiology Training Program, Canadian Space Agency, the Polar Continental Shelf Program, Canada Research Chairs Program, and the Canada Foundation for Innovation.
The Daily Galaxy via https://www.mcgill.ca/newsroom