title: Role of DNA protection and repair in resistance of Bacillus subtilis spores to ultrahigh shock pressures simulating hypervelocity impacts.
abstract: 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) (alpha/beta-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.
authors.affiliation: German Aerospace Center (DLR), Institute of Aerospace Medicine, Radiation Biology Division, Department of Photo- and Exobiology, Linder Hoehe, D-51147 Cologne, Germany. ralf.moeller@dlr.de
authors.forename: Ralf
authors.initials: R
authors.lastname: Moeller
authors.forename: Gerda
authors.initials: G
authors.lastname: Horneck
authors.forename: Elke
authors.initials: E
authors.lastname: Rabbow
authors.forename: Günther
authors.initials: G
authors.lastname: Reitz
authors.forename: Cornelia
authors.initials: C
authors.lastname: Meyer
authors.forename: Ulrich
authors.initials: U
authors.lastname: Hornemann
authors.forename: Dieter
authors.initials: D
authors.lastname: Stöffler
mesh_terms: D001412:Bacillus subtilis / Q000502:physiology*; D015169:Colony Count, Microbial; D004260:DNA Repair; D004269:DNA, Bacterial / Q000378:metabolism*; D006874:Hydrostatic Pressure; D050296:Microbial Viability; D013171:Spores, Bacterial / Q000502:physiology*; D013314:Stress, Mechanical
chemical_list: D004269:DNA, Bacterial
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