Lab experiments with primitive microbes taken from an Antarctic lake have shown that the hardy single-celled organisms can tolerate at least the warmest of the frigid temperatures found on Mars.

And they found that these species of microorganisms "huddled" together in colder temperatures to form a chemically linked unit called a biofilm. The finding marks the first time this phenomenon has been detected in the Antarctic species of so-called extremophiles.

The findings provide more evidence for the ideas that liquid found beneath Mars' surface could harbor microbial life and that life could exist elsewhere in the solar system and galaxy, which is generally incredibly cold.

Hardy creatures

Scientists with the Maryland Astrobiology Consortium focused on two species of cold-adapted microbes. One, called Halorubrum lacusprofundi, is highly salt-tolerant. The other, Methanococcoides burtonii, can live without oxygen and thrives on methane. (H. lacusprofundi is a type of microbe that was discovered first in spoiled foods that had been salted for preservation).

Both microbes are types of Archaea, one of the three major types of life along with Bacteria (another class of microbes) and Eukaryotes (a group that includes animals, plants, fungi and Protists, e.g. paramecium, algae, protozoa and slime molds). Archaea might be able to survive in many places in the universe beyond Earth, including some of the more than 180 extrasolar planets detected in the past decade, or on their terrestrial moons.

The team, led by Shiladitya DasSarma of the University of Maryland Biotechnology Institute, part of the consortium, grew the microbes and found they survived and reproduced at 30 and 28 degrees Fahrenheit (about -1 and -2 degrees Celsius), respectively, just below the freezing point of water.

"We have extended the lower temperature limits for these species by several degrees," DasSarma said. "We had a limited amount of time to grow the organisms in culture, on the order of months. If we could extend the growth time, I think we could lower the temperatures at which they can survive even more."

Slow it down

The cold temperatures of space could result in very slow growth, with generation times possibly longer than the average human lifespan, DasSarma said, and this forces a reconsideration of the duration of astrobiology laboratory experiments. "For example, is it living if one takes a century to replicate or divide?" he said.

H. lacusprofundi was chosen for the experiments because they could possibly thrive in the salty water thought to exist below Mars' surface, which can remain liquid at temperatures well below 32 degrees Fahrenheit. M. burtonnii was chosen because it could survive on a planet lacking oxygen, such as Mars.

The lab-grown archaea also adapted to the cold by aggregating to form biofilms or microbial mats, like the slimy plaque that accumulates on your teeth. Aggregating to form a mat or biofilm allows microbes to share nutrients and genetic material.

"The cold-adapted microorganisms studied in this investigation have not been observed to form biofilms in the past, and so the observation of biofilms in the cold was a surprise," DasSarma told

The genomes for these two species of archaea have already been partially sequenced. Their full sequences will soon be available, allowing scientists to learn which genes generate proteins, such as cold-shock proteins, that help the microbes adapt to extreme cold.

The findings were published online in the International Journal of Astrobiology.

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