Mars May Be Cosy
Place for Hardy Microbes
(19 October 2006) A class of especially hardy microbes that live in some of the harshest Earthly environments could flourish on cold Mars and other chilly planets, according to a research team of astronomers and microbiologists.
A class of especially hardy microbes that live in some of the harshest Earthly environments could flourish on cold Mars and other chilly planets, according to a research team of astronomers and microbiologists. In a two-year laboratory study, the researchers discovered that some cold-adapted microorganisms not only survived but reproduced at 30 degrees Fahrenheit, just below the freezing point of water. The microbes also developed a defense mechanism that protected them from cold temperatures. These close-up images, taken by an electron microscope, reveal the tiny one-cell organisms, called halophiles and methanogens, that were used in the study. (courtesy: Maryland Astrobiology Consortium, NASA, and STScI)
In a two-year laboratory study, the
researchers discovered that some cold-adapted micro-organisms not only survived
but reproduced at 30 degrees Fahrenheit, just below the freezing point of
water. The microbes also developed a defence mechanism that protected them from
cold temperatures. The researchers are members of a unique collaboration of
astronomers from the Space Telescope Science Institute and microbiologists from
the University of Maryland Biotechnology Institute's Center of Marine
Biotechnology in Baltimore, Md. Their results appear on the International
Journal of Astrobiology website.
"The low temperature limit for life is
particularly important since, in both the solar system and the Milky Way
Galaxy, cold environments are much more common than hot environments," said
Neill Reid, an astronomer at the Space Telescope Science Institute and leader
of the research team. "Our results show that the lowest temperatures at which
these organisms can thrive fall within the temperature range experienced on
present-day Mars, and could permit survival and growth, particularly beneath
Mars's surface. This could expand the realm of the habitable zone, the area in
which life could exist, to colder Mars-like planets."
Most stars in our
galaxy are cooler than our Sun. The zone around these stars that is suitable
for Earth-like temperatures would be smaller and narrower than the so-called
habitable zone around our Sun. Therefore, the majority of planets would likely
be colder than Earth.
In their two-year study, the scientists tested the
coldest temperature limits for two types of one-cell organisms: halophiles and
methanogens. They are among a group of microbes collectively called
extremophiles, so-named because they live in hot springs, acidic fields, salty
lakes, and polar ice caps under conditions that would kill humans, animals, and
plants. Halophiles flourish in salty water, such as the Great Salt Lake, and
have DNA repair systems to protect them from extremely high radiation doses.
Methanogens are capable of growth on simple compounds like hydrogen and carbon
dioxide for energy and can turn their waste into methane.
The halophiles
and methanogens used in the experiments are from Antarctic lakes. In the
laboratory, the halophiles displayed significant growth to 30 degrees
Fahrenheit (minus 1 degree Celsius). The methanogens were active to 28 degrees
Fahrenheit (minus 2 degrees Celsius).
"We have extended the lower
temperature limits for these species by several degrees," said Shiladitya
DasSarma, a professor and a leader of the team at the Center of Marine
Biotechnology, University of Maryland Biotechnology Institute. "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. The brine culture in which
they grow in the laboratory can remain in liquid form to minus 18 degrees
Fahrenheit (minus 28 degrees Celsius), so the potential is there for
significantly lower growth temperatures."
The scientists also were
surprised to find that the halophiles and methanogens protected themselves from
frigid temperatures. Some arctic bacteria show similar behaviour.
"These
organisms are highly adaptable, and at low temperatures they formed cellular
aggregates," DasSarma explained. "This was a striking result, which suggests
that cells may 'stick together' when temperatures become too cold for growth,
providing ways of survival as a population. This is the first detection of this
phenomenon in Antarctic species of extremophiles at cold
temperatures."
The scientists selected these extremophiles for the
laboratory study because they are potentially relevant to life on cold, dry
Mars. Halophiles could thrive in salty water underneath Mars's surface, which
can remain liquid at temperatures well below 32 degrees Fahrenheit (0 degrees
Celsius). Methanogens could survive on a planet without oxygen, such as Mars.
In fact, some scientists have proposed that methanogens produced the methane
detected in Mars's atmosphere.
"This finding demonstrates that rigorous
scientific studies on known extremophiles on Earth can provide clues to how
life may survive elsewhere in the universe," DasSarma said.
The
researchers next plan to map the complete genetic blueprint for each
extremophile. By inventorying all of the genes, scientists will be able to
determine the functions of each gene, such as pinpointing the genes that
protect an organism from the cold.
Many extremophiles are evolutionary
relics called Archaea, which may have been among the first homesteaders on
Earth 3.5 billion years ago. These robust extremophiles may be able to survive
in many places in the universe, including some of the roughly 200 worlds around
stars outside our solar system that astronomers have found over the past
decade. These planets are in a wide range of environments, from so-called "hot
Jupiters," which orbit close to their stars and where temperatures exceed 1,800
degrees Fahrenheit (1,000 degrees Celsius), to gas giants in Jupiter-like
orbits, where temperatures are around minus 238 degrees Fahrenheit (minus 150
degrees Celsius).
The discovery of planets with huge temperature
disparities has scientists wondering what environments could be hospitable to
life. A key factor in an organism's survival is determining the upper and lower
temperature limits at which it can live.
Although Martian weather
conditions are extreme, the planet does share some similarities with the most
extreme cold regions of Earth, such as Antarctica. Long regarded as essentially
barren of life, recent investigations of Antarctic environments have revealed
considerable microbial activity. "The Archaea and bacteria that have adapted to
these extreme conditions are some of the best candidates for terrestrial
analogues of potential extraterrestrial life; understanding their adaptive
strategy, and its limitations, will provide deeper insight into fundamental
constraints on the range of hospitable environments," DasSarma said.
The
team's research was supported through grants from the Space Telescope Science
Institute's Director's Discretionary Research Fund, a National Science
Foundation, and the Australian Research Council.
The Space Telescope
Science Institute is operated for NASA by the Association of Universities for
Research in Astronomy, Inc., Washington.
One of five centres forming the
University of Maryland Biotechnology Institute (UMBI) the Center of Marine
Biotechnology, located in Baltimore's Inner Harbor, employs researchers who
apply the tools of modern biology and biotechnology to study, protect, and
enhance marine and estuarine resources.
With research centres in
Baltimore, Rockville, and College Park, the University of Maryland
Biotechnology Institute is the newest of 13 institutions forming the University
System of Maryland. UMBI has 85 ladder-ranked faculty and a 2006 budget of US$
60 million. Celebrating the institution's 20th year of service to Maryland and
the world, UMBI is led by microbiologist and former biotechnology executive Dr.
Jennie C. Hunter-Cevera.
(source: Space Telescope Science
Institute)