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'.

Investigation of the Interplanetary Transfer of Microbes in the Tanpopo Mission at the Exposed Facility of the International Space Station

“…We have isolated Deinococcus aerius and Deinococcus aetherius, which are new species of Deinococcus, from air dust samples at the upper troposphere and lower stratosphere (Yang et al, 2008a(Yang et al, , 2009b(Yang et al, , 2010. Deinococcus aetherius forms cell aggregates during culture and exhibited higher resistance to UV than D. radiodurans and D. aerius (Yang et al, 2008a;Kawaguchi et al, 2013). The results suggest that the ability to form cell aggregates could be important for UV resistance at high altitude (Mancinelli and Klovstad, 2000;Horneck et al, 2001;Yang et al, 2008a;Smith et al, 2011).…”

“…Our previous report indicated that in aggregates, deinococcal cells near the surface layer were killed by UV radiation, and the layers of killed cells protected the cells underneath from UV damage (Kawaguchi et al, 2013). Deinococcus radiodurans, D. aerius, and D. aetherius are estimated to survive after 1 year of exposure under vacuum, temperature changes, heavy ions, and c rays (Kawaguchi et al, 2013). Submillimeter deinococcal aggregates shield internal cells against the intense solar UV, and such cells survive the LEO environment for 1 year.…”

“…Bacterial biofilms are surface-associated, multicellular, complex microbial communities (O'Toole et al, 2000;Stoodley et al, 2002). Our previous report indicated that in aggregates, deinococcal cells near the surface layer were killed by UV radiation, and the layers of killed cells protected the cells underneath from UV damage (Kawaguchi et al, 2013). Deinococcus radiodurans, D. aerius, and D. aetherius are estimated to survive after 1 year of exposure under vacuum, temperature changes, heavy ions, and c rays (Kawaguchi et al, 2013).…”

“…We would like to emphasize the importance of cell aggregates as the ark for interplanetary transfer of microbes. We named this concept massapanspermia (Kawaguchi et al, 2013). Massa means mass in Latin.…”

Space as a Tool for Astrobiology: Review and Recommendations for Experimentations in Earth Orbit and Beyond

“…TANPOPO (Sub-Theme 2) Kawaguchi et al (2013) have suggested the possible importance of cell-aggregate as an ark for terrestrial microbes to enable interplanetary transfer. The concept was named "massapanspermia hypothesis".…”