Survival of the Halophilic Archaeon Halovarius luteus after Desiccation, Simulated Martian UV Radiation and Vacuum in Comparison to Bacillus atrophaeus

Niloofar Feshangsaz,Euan P Monaghan,Kamran Nazmi,Saeed Hesami Tackallou,Andreas Riedo,Farid Semsarha,Jack J W A Van Loon

doi:10.1007/s11084-020-09597-7

Abstract

Extraterrestrial environments influence the biochemistry of organisms through a variety of factors, including high levels of radiation and vacuum, temperature extremes and a lack of water and nutrients. A wide variety of terrestrial microorganisms, including those counted amongst the most ancient inhabitants of Earth, can cope with high levels of salinity, extreme temperatures, desiccation and high levels of radiation. Key among these are the haloarchaea, considered particularly relevant for astrobiological studies due to their ability to thrive in hypersaline environments. In this study, a novel haloarchaea isolated from Urmia Salt Lake, Iran, Halovarius luteus strain DA50T, was exposed to varying levels of simulated extraterrestrial conditions and compared to that of the bacteria Bacillus atrophaeus. Bacillus atrophaeus was selected for comparison due to its well-described resistance to extreme conditions and its ability to produce strong spore structures. Thin films were produced to investigate viability without the protective influence of cell multi-layers. Late exponential phase cultures of Hvr. luteus and B. atrophaeus were placed in brine and phosphate buffered saline media, respectively. The solutions were allowed to evaporate and cells were encapsulated and exposed to radiation, desiccation and vacuum conditions, and their post-exposure viability was studied by the Most Probable Number method. The protein profile using High Performance Liquid Chromatography and Matrix Assisted Laser Desorption/Ionization bench top reflector time-of-flight are explored after vacuum and UV-radiation exposure. Results showed that the change in viability of the spore-forming bacteria B. atrophaeus was only minor whereas Hvr. luteus demonstrated a range of viability under different conditions. At the peak radiation flux of 105 J/m2 under nitrogen flow and after two weeks of desiccation, Hvr. luteus demonstrated the greatest decrease in viability. This study further expands our understanding of the boundary conditions of astrobiologically relevant organisms in the harsh space environment.

Highlights

We investigated the survival of two different microorganisms in simulated space and Mars-surface conditions: the halophilic archaeon Hvr. luteus strain DA50T and the spore-forming bacteria B. atrophaeus
We explored the resistance of halite-embedded cells of Hvr. luteus strain DA50T and PBS-embedded cells of resistant bacteria B. atrophaeus to UV radiation (200––400 nm), low and high vacuum conditions, and desiccation
This study is the first work reporting the survival of a novel extremely halophilic archaeon compared to a resistant spore-forming bacterium under simulated space conditions

Summary

Introduction

There are many signatures of life, from biomolecules to viable microbes, and it is important to understand the ability of these biosignatures to survive and persist, as the most stable signatures may still be preserved and have the potential to be detected during future missions. Ultraviolet (UV) radiation is ubiquitous in the Solar System and it is understood that UV radiation causes damage to cells and increases the rate of DNA mutation and eventually leads to death (Horneck 1999). UVB and UVC make up only 2% of the entire solar spectrum, these wavelengths are the ones primarily responsible for cell damage due to the high absorption of this wavelength range by DNA (Henning et al 1995; Mancinelli 2015)

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Conclusion