title: The possible interplanetary transfer of microbes: assessing the viability of Deinococcus spp. under the ISS Environmental conditions for performing exposure experiments of microbes in the Tanpopo mission.
abstract: To investigate the possible interplanetary transfer of life, numerous exposure experiments have been carried out on various microbes in space since the 1960s. In the Tanpopo mission, we have proposed to carry out experiments on capture and space exposure of microbes at the Exposure Facility of the Japanese Experimental Module of the International Space Station (ISS). Microbial candidates for the exposure experiments in space include Deinococcus spp.: Deinococcus radiodurans, D. aerius and D. aetherius. In this paper, we have examined the survivability of Deinococcus spp. under the environmental conditions in ISS in orbit (i.e., long exposure to heavy-ion beams, temperature cycles, vacuum and UV irradiation). A One-year dose of heavy-ion beam irradiation did not affect the viability of Deinococcus spp. within the detection limit. Vacuum (10(-1) Pa) also had little effect on the cell viability. Experiments to test the effects of changes in temperature from 80 °C to -80 °C in 90 min (± 80 °C/90 min cycle) or from 60 °C to -60 °C in 90 min (± 60 °C/90 min cycle) on cell viability revealed that the survival rate decreased severely by the ± 80 °C/90 min temperature cycle. Exposure of various thicknesses of deinococcal cell aggregates to UV radiation (172 nm and 254 nm, respectively) revealed that a few hundred micrometer thick aggregate of deinococcal cells would be able to withstand the solar UV radiation on ISS for 1 year. We concluded that aggregated deinococcal cells will survive the yearlong exposure experiments. We propose that microbial cells can aggregate as an ark for the interplanetary transfer of microbes, and we named it 'massapanspermia'.
authors.affiliation: Laboratory for Extremophiles, Department of Applied Molecular Biology, School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo, 192-0392, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Kawaguchi
authors.forename: Yinjie
authors.initials: Y
authors.lastname: Yang
authors.forename: Narutoshi
authors.initials: N
authors.lastname: Kawashiri
authors.forename: Keisuke
authors.initials: K
authors.lastname: Shiraishi
authors.forename: Masako
authors.initials: M
authors.lastname: Takasu
authors.forename: Issay
authors.initials: I
authors.lastname: Narumi
authors.forename: Katsuya
authors.initials: K
authors.lastname: Satoh
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Hashimoto
authors.forename: Kazumichi
authors.initials: K
authors.lastname: Nakagawa
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Tanigawa
authors.forename: Yoh-Hei
authors.initials: YH
authors.lastname: Momoki
authors.forename: Maiko
authors.initials: M
authors.lastname: Tanabe
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Sugino
authors.forename: Yuta
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Shimizu
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yoshida
authors.forename: Kensei
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Yokobori
authors.forename: Akihiko
authors.initials: A
authors.lastname: Yamagishi
mesh_terms: D034301:Deinococcus / Q000502:physiology* / Q000528:radiation effects*; D018559:Exobiology; D005118:Extraterrestrial Environment; D020450:Heavy Ions / Q000009:adverse effects; D013026:Space Flight; D013045:Species Specificity; D013696:Temperature; D013997:Time Factors; D014466:Ultraviolet Rays / Q000009:adverse effects; D014618:Vacuum