The Responses of the Black Fungus Cryomyces Antarcticus to High Doses of Accelerated Helium Ions Radiation within Martian Regolith Simulants and Their Relevance for Mars

Claudia Pacelli,Ralf Moeller,Akira Fujimori,Silvano Onofri,Alessia Cassaro,Lorenzo Aureli

doi:10.3390/life10080130

Abstract

One of the primary current astrobiological goals is to understand the limits of microbial resistance to extraterrestrial conditions. Much attention is paid to ionizing radiation, since it can prevent the preservation and spread of life outside the Earth. The aim of this research was to study the impact of accelerated He ions (150 MeV/n, up to 1 kGy) as a component of the galactic cosmic rays on the black fungus C. antarcticus when mixed with Antarctic sandstones—the substratum of its natural habitat—and two Martian regolith simulants, which mimics two different evolutionary stages of Mars. The high dose of 1 kGy was used to assess the effect of dose accumulation in dormant cells within minerals, under long-term irradiation estimated on a geological time scale. The data obtained suggests that viable Earth-like microorganisms can be preserved in the dormant state in the near-surface scenario for approximately 322.000 and 110.000 Earth years within Martian regolith that mimic early and present Mars environmental conditions, respectively. In addition, the results of the study indicate the possibility of maintaining traces within regolith, as demonstrated by the identification of melanin pigments through UltraViolet-visible (UV-vis) spectrophotometric approach.

Highlights

Mars is the prime target for the search of life beyond Earth, primarily because of the environmental conditions that have occurred in the past
The fungus was isolated in Malt Extract Agar Petri Dishes as reported in [16], and since it has been stored in the Culture Collection of Fungi From Extreme Environment (CCFEE) of University of Tuscia (Viterbo, Italy) that is a section of the Italian National Antarctic Museum
The survivability of the black fungus C. antarcticus after irradiation with accelerated He ions was determined by counting the numbers of colonies formed on Malt Extract Agar (MEA) plates, compared to the controls

Summary

Introduction

Mars is the prime target for the search of life beyond Earth, primarily because of the environmental conditions that have occurred in the past. Mars has evidence for past liquid water on the surface and an atmosphere that contains the essential elements for life [1,2]; the cold and dry conditions on the planet provide the opportunity that evidence for putative life may be well preserved. The Martian surface is characterized by an ionizing radiation environment significantly greater than that of Earth and represents the major limitations for microbial survival in dormant state on present-day Mars. The primary effects of UV radiation are a concern only on the surface of Mars, since the penetration of UV photons is limited to only a few micrometers [3] in the Martian near-subsurface or up to meters under a layer of snow or water [4].

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