Microbial Rock Inhabitants Survive Hypervelocity Impacts on Mars-Like Host Planets: First Phase of Lithopanspermia Experimentally Tested

Abstract

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.

PCR-based analysis of microbial communities during the EuroGeoMars campaign at Mars Desert Research Station, Utah

“…Despite this extremely challenging situation for life, there are organisms on Earth which are potentially able to survive space travel: it has been shown that different micro-organisms can survive launch by spallation from a hypervelocity impact (Horneck et al 2008a;Fajardo-Cavazos et al 2009) and hypervelocity atmospheric transit (Fajardo-Cavazos et al 2005). Thus, it has been suggested that, for example, bacterial spores situated on or within meteorites could survive interplanetary transport (Fajardo-Cavazos et al 2009) and hypervelocity entry from space through Earth's atmosphere (Fajardo-Cavazos et al 2005;reviewed in Olsson-Francis & Cockell 2010).…”

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.…”

“…In flyer-plate experiments, we have shown that the asporogenous phototrophic cyanobacterium Chroococcidiopsis sp. was killed at shock pressures greater than 10 GPa Horneck et al 2007). This organism was chosen because it is naturally endolithic.…”

Special Issue: Abstracts From the 2008 Issol Meeting

“…40, 1665-1671. Horneck et al (2008). Microbial rock inhabitants survive hypervelocity impacts on Mars-like host planets: First phase of Lithopanspermia experimentally tested, Astrobiology, 8: 17-29.…”

“…But did it occur on Earth? As Earth was sterilized during the LHB, about 700 My after the formation of the solar system, seeding by lithopanspermia is a definite possibility (Horneck et al, 2008). If so, the question is what the place of origin could be in the solar system.…”