MARSBOx: Fungal and Bacterial Endurance From a Balloon-Flown Analog Mission in the Stratosphere.

Marta Cortesão,Prital Johnson,Ralf Moeller,Michael Lane,Katharina Siems,Elke Rabbow,Thomas Berger,Sonali D Verma,David J Smith,Samantha M Waters,Leandro James,Stella Koch,Kristina Beblo-Vranesevic

doi:10.3389/fmicb.2021.601713

Abstract

Whether terrestrial life can withstand the martian environment is of paramount interest for planetary protection measures and space exploration. To understand microbial survival potential in Mars-like conditions, several fungal and bacterial samples were launched in September 2019 on a large NASA scientific balloon flight to the middle stratosphere (∼38 km altitude) where radiation levels resembled values at the equatorial Mars surface. Fungal spores of Aspergillus niger and bacterial cells of Salinisphaera shabanensis, Staphylococcus capitis subsp. capitis, and Buttiauxella sp. MASE-IM-9 were launched inside the MARSBOx (Microbes in Atmosphere for Radiation, Survival, and Biological Outcomes Experiment) payload filled with an artificial martian atmosphere and pressure throughout the mission profile. The dried microorganisms were either exposed to full UV-VIS radiation (UV dose = 1148 kJ m−2) or were shielded from radiation. After the 5-h stratospheric exposure, samples were assayed for survival and metabolic changes. Spores from the fungus A. niger and cells from the Gram-(–) bacterium S. shabanensis were the most resistant with a 2- and 4-log reduction, respectively. Exposed Buttiauxella sp. MASE-IM-9 was completely inactivated (both with and without UV exposure) and S. capitis subsp. capitis only survived the UV shielded experimental condition (3-log reduction). Our results underscore a wide variation in survival phenotypes of spacecraft associated microorganisms and support the hypothesis that pigmented fungi may be resistant to the martian surface if inadvertently delivered by spacecraft missions.

Highlights

Mariner IV was the first successful robotic mission to Mars producing surface photos and preliminary data used to model atmospheric pressure, layer heights, and temperature (Leighton et al, 1965; Binder, 1966; Fjeldbo and Eshleman, 1968)
Onboard the MARSBOx payload, microbial samples were exposed as dried cells or spores desiccated on quartz disks in two different layers: a bottom layer that was shielded from UV radiation, and a top layer that was exposed to stratospheric UV conditions
In the event that these bacteria are brought to Mars, either in robotic missions for astrobiological research purposes; or by accident through crewled contamination in space missions (Avila-Herrera et al, 2020) our results suggest that bacterial bioburden embedded deep inside of spacecraft sent to Mars might remain viable for longer periods of time (>5 h)

Summary

Introduction

Mariner IV was the first successful robotic mission to Mars producing surface photos and preliminary data used to model atmospheric pressure, layer heights, and temperature (Leighton et al, 1965; Binder, 1966; Fjeldbo and Eshleman, 1968). In the middle stratosphere during daytime hours, the following Mars-like factors are simultaneously present: intense, full spectrum ultraviolet (UV) radiation, high energy ionizing radiation (including secondary scattering), desiccation, hypoxia, and ultralow temperatures and pressures (Clark and McCoy, 1965; Potemra and Zmuda, 1970; Vampola and Gorney, 1983; Keating et al, 1987; Clancy and Muhleman, 1993; Von Engeln et al, 1998; Seele and Hartogh, 1999; Shepherd, 2000; Lambert et al, 2007; Mertens et al, 2016; Caro et al, 2019) Taken together, these combined conditions cannot be found naturally anywhere on the surface of the Earth and would be challenging to reproduce in laboratory-based experiments

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