Extremophile survives the transient pressures associated with impact-induced ejection from Mars
TL;DR
Imagine a massive asteroid hitting Mars so hard that it blasts chunks of rock into space - some of these rocks eventually land on Earth as meteorites. Scientists wanted to know: if there were tiny life forms (bacteria) living in those Martian rocks, could they survive the incredible shock of being launched into space? They took one of Earth's toughest bacteria, Deinococcus radiodurans (nicknamed "Conan the Bacterium"), and subjected it to the same crushing pressures that would occur during such an impact. Amazingly, most of the bacteria survived pressures that would instantly crush almost any other living thing. This suggests that life could potentially hitchhike between planets on rocks, surviving the violent journey through space.
Large-scale impacts are ubiquitous in the solar system, and the likelihood of survival of organisms after an impact event plays a key role in planetary protection, the search for extraterrestrial life, and the assessment of the panspermia hypothesis. Impacts generate very high stresses for short times, resulting in extreme pressures and high rates of loading. Can microorganisms survive such extreme conditions? Directly assessing the resilience of microorganisms subjected to impact stresses has been difficult because of challenges in experimental design for these extreme conditions, together with the choices of biological model system. Here, we describe an experimental approach that allows us to subject microorganisms to controlled extreme pressures for short times, recover these impacted microorganisms, and then assess their rates of survival, structural damage, and their molecular response to these extreme events. We focused on Deinococcus radiodurans, an extremophile that is known to survive space-like conditions. Our results suggested that microorganisms can survive much more extreme conditions than previously thought, potentially surviving conditions that result in the formation of ejecta that can move across planetary systems. We demonstrated that the extremophile D. radiodurans has remarkably high survivability and viability after being subjected to pressures of up to 3 GPa. As the pressure increases, D. radiodurans exhibited indicators of increased biological stress, as determined by the transcriptional analysis of impacted samples. The work has significant consequences for considerations of planetary protection, spacecraft mission design, our understanding of where we might find extraterrestrial life, and lithopanspermia.
- 1Deinococcus radiodurans achieved approximately 95% survival at 1.4 GPa impact pressure and 60% survival at 2.4 GPa, which is orders of magnitude higher than other microorganisms such as E. coli and S. oneidensis under similar conditions.
- 2Survival of D. radiodurans follows a power law relationship with pressure (S = 100 - a(P - Pi)^b), with survival predicted to fall below 10^-6 only at pressures reaching approximately 3.1 GPa, exceeding the estimated 0-5 GPa range relevant to Mars ejecta formation.
- 3Transcriptomic analysis revealed that at 2.4 GPa, D. radiodurans upregulated DNA repair, replication, recombination, and mobilome genes while downregulating cell wall biogenesis, energy production, and cell division pathways, indicating prioritization of damage repair over growth.
- 4TEM imaging confirmed that cells impacted at 1.4 GPa retained normal tetrad morphology and intact cell walls, while cells at 2.4 GPa showed ruptured membranes and internal damage consistent with reduced survival.
- 5A modified pressure-shear plate impact experimental approach enabled controlled, uniform, and measurable transient pressures (~1 microsecond duration) to be applied to living microorganisms with sufficient biological material recovery for transcriptomic analysis, representing the first such study of molecular responses to high-velocity impacts.
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