Investigation of the physiological response of cold-adapted microorganisms to extreme environmental stress factors

Kurzfassung

Exploring the limits of life can help improve our understanding of how life has evolved on Earth and on other planets or moons. Exposing extremophiles to extraterrestrial conditions could highlight ways in which Earth microorganisms, but possibly also extraterrestrial life, survives in extreme environments. The icy moons Europa and Enceladus are the planetary targets of interest for this project. The peculiar characteristics of these moons, having a liquid subsurface ocean environment, potentially heated up by hydrothermal vents or tidal heating, makes them a great target for astrobiology investigations. This project not only investigates the characteristics of psychrophilic prokaryotic and eukaryotic organisms, from natural environments, but also organisms that have been isolated in clean rooms. Important to this project is also to avoid the contamination, during space travel, of planets or moons of astrobiological interest where there is a high probability they could support life. In this study we investigate a range of organisms including: the yeasts Rhodotorula frigidalcoholis, Rhodotorula mucilaginosa and the bacteria Pianococcus halocryophilus, Chromohalobacter sarecensis and Paenisporosarcina antarctica. With the exception of R. mucilaginosa, the other organisms have been isolated from extreme and arctic-like environments. We therefore hypothesized that these organisms would be tolerant to freezing conditions, given their isolation location, and to an extent to UV radiation, due to their pigmentation. We have been exposing the organisms to simulated space conditions, including desiccation, UV radiation, X-ray radiation and extreme cold temperatures (-80°C), in order to determine their limits of survival and potential risks for planetary protection. Ourresults have shown that surprisingly the yeasts are more tolerant to simulated space conditions than the bacteria, especially when exposed to UV-C (254 nm), polychromatic UV (200-400 nm) and X-ray radiation. When the organisms are exposed to desiccating conditions, at different temperatures, however, the difference between the two domains is not pronounced. This supports our hypothesis that lower temperatures are not the main limiting factor for these organisms. Furthermore, it should be emphasized that our results have been obtained with these microorganisms grown under minimal media conditions, supplemented with only one carbon source, D-gluconic acid or D-alanine replicating oligotrophic conditions similar to the ones assumed to prevail on Europa and Enceladus. Furthermore, we also want to investigate the mechanisms of survival through transcriptomics and metabolomics in order to highlight key pathways involved in survival during exposure to extreme conditions. We believe the results from this project be useful not only for understanding the mechanisms of survival at the extremes of life but also to define protocols for microbial exposure to simulated extreme environments.