DFG Priority Program 1115: Mars and the terrestrial planets: Experimental study of the survival of endolithic microorganisms during impact and ejection of Martian meteorites: First phase of the transfer of life between Mars and Earth

In general terms, this interdisciplinary project represents an experimental contribution to the theory of “Lithopanspermia”. This theory has its roots in the work of Svante Arrhenius who formulated the theory of “Panspermia” in 1903 and postulated that microscopic forms of life, e.g. spores, can be dispersed in space by the radiation pressure from the sun, thereby seeding life from one planet to another. “Panspermia” has been replaced in the more recent past by the more realistic “Lithopanspermia” as defined by Melosh in 1988 and by Mileikowsky et al. in 2000. Lithopanspermia assumes that impactexpelled rocks serve as transfer vehicles for microorganisms colonizing those rocks. Our project has been focused on the potential transfer of primitive life from Mars to Earth. In view of the geological and climatological development of the planet Mars there seems to be quite a chance for the origin and evolution of life in the early history of Mars. There is also convincing evidence that a great number of surface rock material was ejected from Mars by impact processes and a substantial portion of them has been transferred to the Earth. The mineralogy of the Martian meteorites, so far collected, indicates an exposure to shock waves in the pressure range of 5 GPa to 50 GPa. As we know from Earth, terrestrial rocks are frequently inhabited by microbial communities. Therefore, rocks ejected by impact processes from a planet in the habitable zone of the solar system, may carry with them endolithic microorganisms, if microbial life exists on this planet. In this scenario, the microorganisms have to cope with three major steps: (1) escape from the planet by impact ejection, (2) journey through space over extended time periods, and (3) landing on another planet. Whereas step 2 of the scenario has been studied in depth in space experiments, there have been only limited data on the survivability of microorganisms of the first step, i.e. the impact ejection. Based on this situation, we initiated a comprehensive and systematic experimental study to determine the survival rate of resistant terrestrial microorganisms (bacterial endospores, epilithic and endolithic microbial communities) in the pressure range indicated by the Martian meteorites, in order to tackle the question whether and to what extent endolithic microorganisms ejected by impact processes may survive the high pressures (5 to 50 GPa) and high temperatures (in the range of ~150 °C to ~600 °C) which were derived for Martian meteorites on the basis of experimentally calibrated shock effects in the constituent minerals. Shock recovery experiments with an explosive set-up were performed at the Ernst-Mach-Institute für Kurzzeitdynamik in which three types of microorganisms inside various types of host rocks were exposed to strong shock waves: the endospore Bacillus subtilis, the lichen Xanthoria elegans, and the cyanobacterium Chroococcidiopsis sp. 029. In these experiments, three fundamental parameters were systematically varied: (1) the peak shock pressure, (2) the type of host rock and (3) the pre-shock ambient temperature. The applied pressures were in the range from 5 to 50 GPa. The pre-shock temperatures were set at 293, 233, and 193 K. The host rocks included non-porous igneous rocks (gabbro and dunite), porous sandstone, rock salt (halite), and artificial Martian regolith (MRS07)

2008 Service Award for Drew Barringer

The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Experimental evidence for the potential impact ejection of viable microorganisms from Mars and Mars-like planets

Bacterial spores (Bacillus subtilis), cyanobacteria (Chroococcidiopsis sp.), and lichen (Xanthoria elegans) embedded in martian analogue rock (gabbro) were exposed to shock pressures between 5 and 50 GPa which is the range of pressures observed in martian meteorites. The survival of Bacillus subtilis and Xanthoria elegans up to 45 GPa and of Chroococcidiopsis sp. up to 10 GPa supports the possibility of transfer of life inside meteoroids between Mars and Earth and it implies the potential for the transfer of life from any Mars-like planet to other habitable planets in the same stellar system

Role of DNA Protection and Repair in Resistance of Bacillus subtilis Spores to Ultrahigh Shock Pressures Simulating Hypervelocity Impacts▿

Impact-induced ejections of rocks from planetary surfaces are frequent events in the early history of the terrestrial planets and have been considered as a possible first step in the potential interplanetary transfer of microorganisms. Spores of Bacillus subtilis were used as a model system to study the effects of a simulated impact-caused ejection on rock-colonizing microorganisms using a high-explosive plane wave setup. Embedded in different types of rock material, spores were subjected to extremely high shock pressures (5 to 50 GPa) lasting for fractions of microseconds to seconds. Nearly exponential pressure response curves were obtained for spore survival and linear dependency for the induction of sporulation-defective mutants. Spores of strains defective in major small, acid-soluble spore proteins (SASP) (α/β-type SASP) that largely protect the spore DNA and spores of strains deficient in nonhomologous-end-joining DNA repair were significantly more sensitive to the applied shock pressure than were wild-type spores. These results indicate that DNA may be the sensitive target of spores exposed to ultrahigh shock pressures. To assess the nature of the critical physical parameter responsible for spore inactivation by ultrahigh shock pressures, the resulting peak temperature was varied by lowering the preshock temperature, changing the rock composition and porosity, or increasing the water content of the samples. Increased peak temperatures led to increased spore inactivation and reduced mutation rates. The data suggested that besides the potential mechanical stress exerted by the shock pressure, the accompanying high peak temperatures were a critical stress parameter that spores had to cope with

Microbial rock inhabitants survive hypervelocity impacts on Mars-like host planets: first phase of lithopanspermia experimentally tested

The scenario of lithopanspermia describes the viable transport of microorganisms via meteorites. To test the first step of lithopanspermia, i.e., the impact ejection from a planet, systematic shock recovery experiments within a pressure range observed in martian meteorites (5–50 GPa) were performed with dry layers of microorganisms (spores of Bacillus subtilis, cells of the endolithic cyanobacterium Chroococcidiopsis, and thalli and ascocarps of the lichen Xanthoria elegans) sandwiched between gabbro discs (martian analogue rock). Actual shock pressures were determined by refractive index measurements and Raman spectroscopy, and shock temperature profiles were calculated. Pressure-effect curves were constructed for survival of B. subtilis spores and Chroococcidiopsis cells from the number of colony-forming units, and for vitality of the photobiont and mycobiont of Xanthoria elegans from confocal laser scanning microscopy after live/dead staining (FUN-I). A vital launch window for the transport of rock-colonizing microorganisms from a Mars-like planet was inferred, which encompasses shock pressures in the range of 5 to about 40 GPa for the bacterial endospores and the lichens, and a more limited shock pressure range for the cyanobacterium (from 5–10 GPa). The results support concepts of viable impact ejections from Mars-like planets and the possibility of reseeding early Earth after asteroid cataclysms