Lab experiments with primitive microbes taken from anAntarctic lake have shown that the hardy single-celled organisms can tolerateat 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 linkedunit called a biofilm. The finding marks the first time this phenomenon hasbeen detected in the Antarctic species of so-called extremophiles.
The findings provide more evidence for the ideas that liquidfound beneath Mars' surface could harbor microbial life and that life could exist elsewhere in the solar system and galaxy, which is generally incrediblycold.
Scientists with the Maryland Astrobiology Consortium focusedon two species of cold-adapted microbes. One, called Halorubrum lacusprofundi,is highly salt-tolerant. The other, Methanococcoides burtonii, canlive without oxygen and thrives on methane. (H. lacusprofundi is a typeof microbe that was discovered first in spoiled foods that had been salted forpreservation).
Both microbes are types of Archaea,one of the three major types of life along with Bacteria (another class ofmicrobes) and Eukaryotes (a group that includes animals, plants, fungi and Protists,e.g. paramecium, algae, protozoa and slime molds). Archaea might be able tosurvive in many places in the universe beyond Earth, including some of the morethan 180 extrasolarplanets detected in the past decade, or on their terrestrial moons.
The team, led by Shiladitya DasSarmaof the University of Maryland Biotechnology Institute, part of the consortium,grew the microbes and found they survived and reproduced at 30 and 28 degreesFahrenheit (about -1 and -2 degrees Celsius), respectively, just below thefreezing point of water.
"We have extended the lowertemperature limits for these species by several degrees," DasSarma said."We had a limited amount of time to grow the organisms in culture, on theorder of months. If we could extend the growth time, I think we could lower thetemperatures at which they can survive even more."
Slow it down
The cold temperatures of spacecould result in very slow growth, with generation times possibly longer thanthe average humanlifespan, DasSarma said, and this forces a reconsideration of the durationof astrobiology laboratory experiments. "For example, is it living if onetakes a century to replicate or divide?" he said.
H. lacusprofundi was chosenfor the experiments because they could possibly thrive in the salty waterthought to exist below Mars' surface, which can remain liquid at temperatureswell below 32 degrees Fahrenheit. M. burtonnii was chosen because itcould survive on a planet lacking oxygen, such as Mars.
The lab-grown archaea alsoadapted to the cold by aggregating to form biofilms or microbial mats, like theslimy plaque that accumulates on your teeth. Aggregating to form a mat or biofilmallows microbes to share nutrients and genetic material.
"The cold-adaptedmicroorganisms studied in this investigation have not been observed to form biofilmsin the past, and so the observation of biofilmsin the cold was a surprise," DasSarma told SPACE.com.
The genomes for these twospecies of archaea have already been partially sequenced. Their full sequenceswill soon be available, allowing scientists to learn which genes generateproteins, such as cold-shock proteins, that help the microbes adapt to extremecold.
The findings were publishedonline in the International Journal of Astrobiology.
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