Survival of bacteria and spores under extreme shock pressures

Abstract

Some rocky objects on Earth originated on other planets (e.g. Martian meteorites). Modelling of interplanetary transfer times (Mars–Earth) and calculations of the survival of cells and spores in the radiation environment of space show that this is not an insurmountable obstacle to the successful delivery of life from one planetary surface to another via these rocks. However, the initial launch into space and the subsequent arrival at a new planet involve short‐duration extreme accelerations, and shock pressures in the 1–100 GPa range. Recently it has been shown that survival of such accelerations and at such shock pressures is possible. Here we show that in hypervelocity impacts (which involve extreme short‐duration accelerations), as shock pressures vary from 1 to 78 GPa, the survival rate (N/N0) for Rhodococcus erythropolis cells falls from 10−4 to 10−7. Whilst survival rates are low at 78 GPa, they are still finite. For a different organism, Bacillis subtilis, the survival rate at 78 GPa was found to be of the order of 10−5, i.e. significantly greater than for the R. erythropolis, indicating that survival rates may vary greatly with different organisms. By contrast, the variation between the survival rate in impacts on agar at 78 GPa for B. subtilis spores versus active B. subtilis was found only to be a factor of 2, well within the experimental uncertainties and not significant. Overall, whilst extreme shock pressures clearly have a deleterious effect on survival rates, it is shown that, even at extreme shock pressures of near to 100 GPa, there is still a finite and sufficient survival rate for this not to be an insurmountable obstacle to successful natural transfer of life through space.

On the response of Escherichia coli to high rates of deformation

“…Further work into quasi-one-dimensionally shock loading E. coli at these pressures would help to verify these data and possibly reduce scatter while confirming where survival increases at the lower end of this scale. However, the apparent exponential decrease in survival with pressure increase in the present data does match up with previous work on E. coli and other types of bacteria [5,7], while demonstrating that the nature of the loading regime likely effects survival. It is also clear from both investigations that there is a drop in magnitude of survival within the 1-1.5 GPa range.…”

“…Dynamic pressure loading of B. subtilis cells by Burchell et al [7] even showed survival rates of 10 -7 at pressures of close to 100 GPa; within the region of pressures faced by rock ejection into space and asteroid impact. A more complex eukaryotic organism, Saccharomyces cerevisiae (baker's yeast), was also investigated in a similar manner by Price et al [8] and found to have a survival rate of ~10 -4 at a peak pressure of ~43 GPa.…”

The shock compression of microorganism-loaded broths and emulsions: Experiments and simulations

“…Given the violence associated with cavitation, it is perhaps surprising that these microorganisms demonstrate significant survivability. These results confirm the hardy nature of micro-organisms that have been subjected to shock loading as noted by Burchell et al [6,12].…”

“…For example, Burchell et al [12] has shown that when transient shock pressures are formed from hypervelocity impacts of spherical projectiles into targets, Rhodococcus erythropolis cells survive. The authors noted that although survival rates were low at a shock pressure of 78 GPa, they were still finite.…”

Planetary targets in the search for extrasolar oxygenic photosynthesis

“…A more deleterious stressor of organisms during the process of impact ejection is shock. Spores of Bacillus subtilis can survive shock pressures greater than 50 GPa (Burchell et al 2001(Burchell et al , 2004Horneck 2001a;Stöffler et al 2007;Horneck et al 2007), which would allow for the survival of ejection to Earth's escape velocity. In contrast, vegetative cells are susceptible to disruption by low shock pressures.…”