Surviving Life on Mars

It's heady stuff for a primitive organism.

But DR has a feature that is considered all-important in aerospace: redundancy. Its genetic code repeats itself many times so that damage in one area can be recognised and quickly repaired. Coupled with its range of other survival characteristics, DR has been dubbed an polyextremophile by Richmond, Sridhar, and Daly.

Extremophiles have been known to scientists for decades but often were regarded as laboratory oddities. The discovery of what appears to be nanobacteria (or nanobes, smaller than microbes) in a meteorite from Mars (see our article 'Life on Mars?') catapulted extremophiles into the spotlight as a model for possible lifeforms on Mars.

The debate over whether the meteorites forms ever were nanobes (or just non-living imitations) led to discoveries of probable nanobes living in such odd places as human kidney stones and in limestone 4 kilometres under the surface of the Earth.

A common link?
"We have a new door opening on the possibilities of lifeforms," Richmond said, "not just new species but whole new life forms that could connect to the origins of life on Earth and could be a common link to the possible beginnings of life on Mars."

Most extremophiles have optimised themselves for one or two extreme conditions and settled into wonderful ecological niches like the hot springs of Yosemite. Radiodurans has been dubbed a polyextremophile because it can endure many extremes, including the most dangerous space hazard, radiation.

"Radiation-induced DNA damage is an oxidising type of damage," Richmond said. It happens when radiation energises an atom enough to break a chemical bond and then act like an atom of oxygen and bind with another atom. Such free radicals have been implicated in a range of cancers and genetic mutations.

DR though, is hypothesised by Daly to resist such damage by virtue of repair specialised to utilise its redundant strands of DNA. This also means that it should resist damage from the chemistry of Mars, which chemical experiments done by the labs aboard the two Viking landers indicate may be highly oxidative.

DR was discovered in the 1950s. Scientists experimenting with radiation to kill bacteria and preserve food for long periods found that something kept growing back after treatment.