As scientists probe the limits of bacterial survival, their findings suggest microbes could withstand the intense shock of traveling on a meteor and crashing into another planetary body. This work lends support to the “panspermia” hypothesis; the idea that meteors and comets can spread life between habitable planets.
In a new paper in the journal Icarus , Deep Life Community members Rachael Hazael and Paul McMillan (both at University College London, UK) and colleagues report that a bacterium could survive a brief shock of high pressure up 2.5 gigapascals, about 25,000 times atmospheric pressure. Bacteria that had previously experienced high pressures had better survival rates than unaccustomed bacteria, suggesting they have physiological mechanisms in place to withstand high pressures.
Hazael and colleagues cultured strains of Shewanella oneidensis, an adaptable model microbe that can live with or without oxygen. By exposing the cultures to increasing pressure levels, they created a “pressure adapted” strain that survived 750 megapascals. The researchers teamed up with Gareth Appleby-Thomas and Brianna Fitzmaurice (both at Cranfield University, UK), to use their light gas gun, which generates a high-pressure shockwave. They gave the pressure-adapted strain an intense shock of pressures of 1.5 or 2.5 gigapascals, and then compared survival rates with unadapted bacteria receiving the same treatment.
A greater proportion of the pressure-adapted strain survived the shock than the regular bacteria. Both populations were more likely to live through a brief shockwave than constant pressure, which the researchers tested in a previous study, though the pressure-adapted population still had an edge. “In a shock event rather than a static one, you are seeing a lot more survivors,” said Hazael. “The fact that the bacteria that already have seen a pressure event are a lot more resilient shows we are seeing a build up of pressure resistance.”
“[The study] does indicate that survival of bacteria would be possible on a meteorite or a comet,” commented astrobiologist Barry Herschy (University of South Florida, USA) to New Scientist. “It actually shows life would be able to survive on a planet even if it was under bombardment.”
In future work, Hazael and her colleagues plan to expose their bacterial strains to high temperatures along with high pressures in order to better replicate the conditions an organism would experience as it passed through a planet’s atmosphere and struck the surface. They also are looking into the biological mechanisms that enable microbes to survive these high-pressure shocks. The pressure-adapted microbes may have acquired beneficial mutations and likely produce protective compounds that guard their structures against the pressure.
“Life’s ability to survive is amazing,” said Hazael. “It’s able to survive very difficult events and environments. If we keep looking, I’m sure we will find it in more difficult and inhospitable places.”