Effects of Ionizing Radiation and Long-Term Storage on Hydrated vs. Dried Cell Samples of Extremophilic Microorganisms.

Ida Romano,Akira Fujimori,Lisa Vaccari,Giovanni Birarda,Annarita Poli,Paola Di Donato,Carlo Camerlingo,Maria Lepore,Ralf Moeller

doi:10.3390/microorganisms10010190

Abstract

A main factor hampering life in space is represented by high atomic number nuclei and energy (HZE) ions that constitute about 1% of the galactic cosmic rays. In the frame of the “STARLIFE” project, we accessed the Heavy Ion Medical Accelerator (HIMAC) facility of the National Institute of Radiological Sciences (NIRS) in Chiba, Japan. By means of this facility, the extremophilic species Haloterrigena hispanica and Parageobacillus thermantarcticus were irradiated with high LET ions (i.e., Fe, Ar, and He ions) at doses corresponding to long permanence in the space environment. The survivability of HZE-treated cells depended upon either the storage time and the hydration state during irradiation; indeed, dry samples were shown to be more resistant than hydrated ones. With particular regard to spores of the species P. thermantarcticus, they were the most resistant to irradiation in a water medium: an analysis of the changes in their biochemical fingerprinting during irradiation showed that, below the survivability threshold, the spores undergo to a germination-like process, while for higher doses, inactivation takes place as a consequence of the concomitant release of the core’s content and a loss of integrity of the main cellular components. Overall, the results reported here suggest that the selected extremophilic microorganisms could serve as biological model for space simulation and/or real space condition exposure, since they showed good resistance to ionizing radiation exposure and were able to resume cellular growth after long-term storage.

Highlights

Introduction distributed under the terms andAn investigation of the limits of life is a key issue in astrobiology, either for the search of life on other planets or for the identification of terrestrial organisms that potentially could adapt to living beyond Earth
The space radiation is a main environmental factor that strongly limits the possibility of life outside of Earth due to its lethal effects: living organisms potentially travelling through space or living on the surface of planets lacking the protection that terrestrial atmosphere and magnetic field give, are exposed to the harmful effects of the radiation field
To identify new microbial species that potentially could resist space radiation and to test microorganisms that could be used for real space exposure, we proposed using two extremophilic microorganisms belonging to both the Archaea and Bacteria domains that, in our previous studies [6,7,8], showed promising resistance to multiple extreme parameters mimicking the space environment as biological samples

Summary

Introduction

Introduction distributed under the terms andAn investigation of the limits of life is a key issue in astrobiology, either for the search of life on other planets or for the identification of terrestrial organisms that potentially could adapt to living beyond Earth. The biological effects produced by an HZE have been extensively studied in a variety of space experiments or on ground simulation facilities using the biological dosimeter spores of Bacillus subtilis species [2,3,4,5]. These studies showed that the ionizing radiation effects depend upon both the delivered dose and the type of radiation; the LET value directly correlates with the number of changed cell structures and molecules that are passed through the particle’s path [2,3,4,5].

Methods

Results

Conclusion