Early Earth lacked an ozone layer to act as a shield against high-energy solar radiation, but microbes flourished by adapting to or finding other forms of protection from the higher ultraviolet radiation levels. Now researchers have begun testing modern microbes to see if they could act as pioneers in the harsh conditions of extraterrestrial space and other planetary environments.
One such study from last year looked at Bacillus subtilis, a common soil bacterium which has become a model organism for experiments and holds the record for space survival after spending six years on NASA's Long Duration Exposure Facility spacecraft. The ordinary microbe proved capable of evolving a resistance to UV radiation of up to 3 times higher than that of the original ancestor or a non-UV-exposed group, after 700 generations lived and died in an Earth-based lab experiment.
By comparing the radiation-resistant mutants with their ancestor and the non-UV-exposed group, researchers could almost be certain that their adaptation to UV did not come from a UV-resistant specimen hiding among the original bacteria population.
"The significance is that a single organism is actively capable of reacting and adapting to changes in its environment," said Marko Wassmann, a radiation biology researcher at the German Aerospace Center's Institute of Aerospace Medicine in Germany.
That adaptation to radiation hints at how some microbes might have survived a journey to Earth aboard ancient asteroids, according to the theory known as Panspermia. Similarly, the adaptive ability indicates how Earth microbes might be able to colonize harsher extraterrestrial environments such as Mars, although even the most radiation-resistant bacteria would face other challenges if they tried to survive beyond Earth. The experiment also showed that B. subtilis was capable of adapting to UV levels even higher than those found on a primordial Earth – a harbinger of untapped potential that still lies within some organisms.