Survival of Extremophilic Yeasts in the Stratospheric Environment during Balloon Flights and in Laboratory Simulations

• Published in: Applied and environmental microbiology 2018-12, Vol.84 (23)
• Main Authors: Pulschen, André Arashiro, de Araujo, Gabriel Guarany, de Carvalho, Ana Carolina Souza Ramos, Cerini, Maria Fernanda, Fonseca, Lucas de Mendonça, Galante, Douglas, Rodrigues, Fabio
• Format: Article
• Language: English
• Subjects: Astrobiology; Balloons; Computer simulation; Desert environments; Deserts; Desiccation; Drying; Environmental Microbiology; Exposure; High altitude; High-altitude environments; Irradiation; Low pressure; Low temperature; Mars; Mars surface; Pressure; Simulation; Spores; Stratosphere; Survival; Survival analysis; Ultraviolet radiation; Viability; Yeast; Yeasts
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.01942-18

The high-altitude atmosphere is a harsh environment with extremely low temperatures, low pressure, and high UV irradiation. For this reason, it has been proposed as an analogue for Mars, presenting deleterious factors similar to those on the surface of that planet. We evaluated the survival of extremophilic UV-resistant yeasts isolated from a high-elevation area in the Atacama Desert under stratospheric conditions. As biological controls, intrinsically resistant spores were used. Experiments were performed in two independent stratospheric balloon flights and with an environmental simulation chamber. The three following different conditions were evaluated: (i) desiccation, (ii) desiccation plus exposure to stratospheric low pressure and temperature, and (3) desiccation plus exposure to the full stratospheric environment (UV, low pressure, and temperature). Two strains, ( ) 16LV2 and sp. strain 15LV1, survived full exposures to the stratosphere in larger numbers than did spores. (also known as ) 16LV1, however, suffered a substantial loss in viability upon desiccation and did not survive the stratospheric UV exposure. The remarkable resilience of and sp. 15LV1 under the extreme Mars-like conditions of the stratosphere confirms its potential as a eukaryotic model for astrobiology. Additionally, our results with strengthen the recent hypothesis that yeasts belonging to the genus are fit for aerial dispersion, which might account for the observed abundance of this species in high-elevation soils. Studies of eukaryotic microorganisms under conditions of astrobiological relevance, as well as the aerial dispersion potential of extremophilic yeasts, are still lacking in the literature compared to works with bacteria. Using stratospheric balloon flights and a simulation chamber, we demonstrate that yeasts isolated from an extreme environment are capable of surviving all stressors found in the stratosphere, including intense UV irradiation, scoring an even higher survival than spores. Notably, the yeast , which displayed one of the highest tolerances to the stratospheric environment in the experiments, was recently proposed to be adapted to airborne transportation, although such a hypothesis had not yet been tested. Our results strengthen such an assumption and can help explain the observed distribution and ecology of this particular yeast species.