title: Investigating the effects of simulated martian ultraviolet radiation on Halococcus dombrowskii and other extremely halophilic archaebacteria.
abstract: The isolation of viable extremely halophilic archaea from 250-million-year-old rock salt suggests the possibility of their long-term survival under desiccation. Since halite has been found on Mars and in meteorites, haloarchaeal survival of martian surface conditions is being explored. Halococcus dombrowskii H4 DSM 14522(T) was exposed to UV doses over a wavelength range of 200-400 nm to simulate martian UV flux. Cells embedded in a thin layer of laboratory-grown halite were found to accumulate preferentially within fluid inclusions. Survival was assessed by staining with the LIVE/DEAD kit dyes, determining colony-forming units, and using growth tests. Halite-embedded cells showed no loss of viability after exposure to about 21 kJ/m(2), and they resumed growth in liquid medium with lag phases of 12 days or more after exposure up to 148 kJ/m(2). The estimated D(37) (dose of 37 % survival) for Hcc. dombrowskii was > or = 400 kJ/m(2). However, exposure of cells to UV flux while in liquid culture reduced D(37) by 2 orders of magnitude (to about 1 kJ/m(2)); similar results were obtained with Halobacterium salinarum NRC-1 and Haloarcula japonica. The absorption of incoming light of shorter wavelength by color centers resulting from defects in the halite crystal structure likely contributed to these results. Under natural conditions, haloarchaeal cells become embedded in salt upon evaporation; therefore, dispersal of potential microscopic life within small crystals, perhaps in dust, on the surface of Mars could resist damage by UV radiation.
authors.affiliation: University of Salzburg, Division of Molecular Biology, Department of Microbiology, Salzburg, Austria.
authors.forename: Sergiu
authors.initials: S
authors.lastname: Fendrihan
authors.forename: Attila
authors.initials: A
authors.lastname: Bérces
authors.forename: Helmut
authors.initials: H
authors.lastname: Lammer
authors.forename: Maurizio
authors.initials: M
authors.lastname: Musso
authors.forename: György
authors.initials: G
authors.lastname: Rontó
authors.forename: Tatjana K
authors.initials: TK
authors.lastname: Polacsek
authors.forename: Anita
authors.initials: A
authors.lastname: Holzinger
authors.forename: Christoph
authors.initials: C
authors.lastname: Kolb
authors.forename: Helga
authors.initials: H
authors.lastname: Stan-Lotter
mesh_terms: D001105:Archaea / Q000166:cytology / Q000528:radiation effects* / Q000648:ultrastructure; D003460:Crystallization; D003470:Culture Media; D004307:Dose-Response Relationship, Radiation; D005118:Extraterrestrial Environment; D019015:Geologic Sediments / Q000382:microbiology; D019625:Halococcus / Q000166:cytology / Q000528:radiation effects* / Q000648:ultrastructure; D018535:Mars; D050296:Microbial Viability / Q000528:radiation effects; D012492:Salts / Q000737:chemistry; D018561:Space Simulation; D014466:Ultraviolet Rays
chemical_list: D003470:Culture Media; D012492:Salts