Ice lovers

Most space environments are cold and NASA researchers are particularly interested in microbes that can survive at low temperatures.  Recently interest has focused on Lake Vostok in Antarctica.  NASA has had a research expedition working at the lake throughout 1998 and 1999.

Lake Vostok is a huge freshwater lake which has been frozen for perhaps a million years.  Ice samples have been retrieved from depths of nearly 4000m (1200 feet), and a diverse assortment of bacterial species has been recovered.  At these depths the microbes have been cut off from sunlight and other energy sources for a considerable time and are in a dormant state, but still metabolizing at a very low-level of activity.  These findings are a good sign for the possibility of life being able to survive on Europa, the ice-bound moon of Jupiter.

(above) © Sally Hodges, 1999

(Left) A microbe from beneath the Antarctic ice  © NASA, 1998
 

When water freezes, the life can go into suspension and remain that way almost indefinitely until temperatures increase to a level where activity can resume - ie liquid water.

In 1998, Richard Hoover of NASA's Marshall Space Sciences Laboratory and Dr S S Abyzov of the Russian Academy of Sciences found ice cores from Lake Vostok contained microbes like one (above) which is yet to be identified.  Other life forms recovered from the lake ice at depths as much as 3.5 km (about 2 miles) down have been more recognizable and include cyanobacteria, bacteria, fungi, spores, pollen grains, and diatoms.  These organisms are thought to have become trapped in the ice about 400,000 years ago.

(above) © Sally Hodges, 1999

t should be remembered that water boils at 100 C (212 F) only at normal (standard) atmospheric pressure (one atmosphere).  If we increase the pressure, the boiling point temperature increases.  In the ocean on the mid-ocean ridges there are volcanic vents that are constantly emitting hot water, gases and other materials from deep inside the Earth.  These vents are known as black smokers and they are located on the sea floor, at depths of thousands of feet.  Here the pressures are many atmospheres - the pressure underwater increases by one atmosphere for about every 10m (30 feet or so) depth.  So down at such depths the pressure can be 30 or more atmospheres and the boiling temperature very high.

Black smokers (above left) can produce temperatures of 350 C (662 F), but archaean microbes are still able to flourish, though possibly not main-stream of the scalding flow.  Nevertheless, they are close to it and must be living at very high temperatures.  The water at this depth is still liquid and not superheated steam, as it would be on the surface of the sea at this temperature.  One hyperthermophile that lives in this environment is Methanopyrus, which produces methane gas.  It is important in the development of life because it occupies a place at the bottom of the evolutionary tree.  So what does that tell us about early life on Earth - was life a hyperthermophile extremophile?  That seems likely, as the Earth was a firey cauldron during its early history.

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The current record for temperature tolerance is held by Pyrodictium Occultum, an archaean which survived 121 C (250 F) for an hour.  However, John Parkes of Bristol University has evidence of microorganisms living at 170 C (338 F) around volcanic vents on the ocean floor.

The extremophiles that live around the mid-ocean ridges live at extreme depths too, where the hydrostatic pressure is enormous.  But other organisms such as fish and crustaceans - lobsters - live at these depths too.  The secret is for the organism to balance or equalize the internal and external pressures.

Holger Jannasch leads a team of researchers at the Woods Hole Oceanographic Institution in Massachusetts.  Holger is one of the world's leading experts on life around mid-ocean hydrothermal vents.  The Woods Hole team found Pyrolobus fumarii, an Archaea,  at  the mid-Atlantic ridge in 1996.  Living at a depth of 3600 meters, and at temperatures of up to 113 C (235 F) the microbe was able to survive both in the presence of oxygen and without it.  It is a chemoautotroph, and survives with any intake of organic mater, on hydrogen, nitrates and sulfates.    It is one of best examples, so far discovered, of a a microbe that can survive not just at one extremes but in a variety of conditions.  The researchers claim that it is good evidence to reinforce the notion of life living in the watery depths below the ice of Europa.