At this week’s meeting of the European Astrobiology Network, Tom Gheysens from Ghent University in Belgium and colleagues presented results of their research on the survival of bacterial spores exposed to very high temperatures.
Bacteria form resistant spore structures when environmental conditions become unfavorable. It was previously known that bacteria in this dormant form are much hardier than bacteria in the normal vital state. But it’s astonishing just how much heat they can handle.
The researchers collected microorganisms within soils from Jordan, Tunisia, Morocco and the Canary Islands, and showed that the hardiest of them, a Bacillus species from Morocco, could survive in a dried spore stage at temperatures up to 420o C. More than 90 percent of spores could be “resurrected” after heating to 300o C, and about 40 percent after being heated to 420o C.
How do the Bacillus spores do it? Gheysens thinks the bacteria must have a protein-based repair mechanism, or an RNA- or DNA-template that’s able to repair DNA damaged by excessive heat.
Whatever the mechanism, this tolerance to heat is startling, and it lends support to the old idea of panspermia, the possible transfer of life between planets. The new research broadens the environmental conditions under which such a transfer might be possible, particularly in the stages involving high temperatures, such as the ejection of a microbe-containing rock after an asteroid impact and its re-entry into the atmosphere of another planet.
To fully evaluate the panspermia theory, we still need to consider how bacterial spores would handle other environmental extremes such as pressure. And we should remember that the ability of bacteria to form spores (not all bacteria can do it) only evolved later on Earth—we’re not sure exactly when—which means that life has to reach a certain complexity before panspermia via spores becomes an option.
The new findings by Gheysens et al. also makes another idea more practical: directed panspermia, the intended transfer of life from one planet to the other. When we discover a truly habitable exoplanet, we could decide to “colonize” that world by sending dried Earth spores in a rocket to the alien ocean. Many would argue, however, that this should only be done if we are certain there is no indigenous life already existing on that planet. Some great minds, including Francis Crick, co-discoverer of the structure of DNA, and Leslie Orgel have suggested that we should consider that possibility when trying to figure out how life originated on Earth.