Survival of non-psychrophilic methanogens exposed to martian diurnal and 48-h temperature cycles R.L. Mickol a, d , Y.A. Takagi b , T.A. Kral a, c, * a Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, AR, United States b Department of Biology, Oberlin College, Oberlin, OH, United States c Department of Biological Sciences, University of Arkansas, Fayetteville, AR, United States d American Society for Engineering Education, Washington, DC, United States ARTICLE INFO Keywords: Methane Methanogens Freeze/thaw Astrobiology Mars Permafrost ABSTRACT Polygonal ground and other geomorphological features reminiscent of recent freeze/thaw cycling are evident on Mars, despite the widespread belief that the planet is currently inhospitably cold and dry. On Earth, permafrost microbial communities are subjected to wide ranges in temperature and are often active at subfreezing temper- atures. The existence of active microbial communities within permafrost on Earth suggests that permafrost on Mars may constitute a habitable environment. Terrestrial microbial permafrost communities typically contain methane-producing Archaea, which is cause for concern as global temperatures rise, resulting in permafrost thaw and the release of the potent greenhouse gas. Similarly, on Mars, the overlap between patterned ground and detections of localized methane plumes suggest that the compound may have been released from thawing permafrost. Analyses of permafrost ice cores and soil samples on Earth note that (1) archaeal communities often contain both mesophiles and psychrophiles at different depths and (2) active methane is being produced at subfreezing temperatures over geological timescales. Thus, the purpose of the experiments described here was to determine the effect of extreme temperature changes (reminiscent of the martian diurnal temperature cycle) on the growth and survival of four non-psychrophilic methanogens previously used as models for potential life on Mars. The results indicate that non-psychrophilic methanogens are capable of survival during extreme diurnal and 48-h temperature changes, similar to those on Mars. 1. Introduction Mars experiences wide temperature variations over one sol, often ranging from temperatures just above freezing to 100  C and lower (Kieffer et al., 1977). Any microorganisms that could potentially inhabit Mars would at least need to be able to survive these temperatures, but also make use of any available liquid water or temporary increases in temperature in order to metabolize. Due to the very thin atmosphere and lack of other insulating factors, temperatures vary widely on Mars based on location and season. Temperatures from the primary Viking mission ranged between 143  C and 17  C(Kieffer et al., 1977), while mea- surements from the Thermal Emission Spectrometer (TES) depicted nighttime temperatures ranging between 123  C and 53  C(Chris- tensen et al., 2001). On Earth, methanogenic Archaea within permafrost communities are considered fairly active at subfreezing temperatures [1–2 nmol CH 4 /kg/ day at 16.5  C(Rivkina et al., 2004, 2007); 0.04–0.68 nmol CH 4 /h/g at 3  C to 6  C(Wagner et al., 2007)] and the same could potentially be true for regions on Mars (Gilichinsky et al., 2007; Steven et al., 2009; Wagner et al., 2002). Terrestrial permafrost communities are also sub- jected to wide variations in temperature over a particular season and may provide insight into the habitability of martian permafrost. On Earth, permafrost is defined by three temperature-dependent layers: the up- permost layer is considered the active layer, experiencing the widest range in temperatures (50  C–30  C) and ranging in thickness between 0.2 m and 2 m. Perennially-frozen permafrost sediments (10–20 m thick) constitute the middle layers and are subject to smaller temperature variations (15–0  C above the zero annual amplitude [constant tem- perature]). Lastly, deeper permafrost sediments are characterized by more stable temperatures, ranging between 10 and 5  C(Wagner, * Corresponding author. University of Arkansas, Department of Biological Sciences, SCEN 601, Fayetteville, AR 72701, United States. E-mail address: tkral@uark.edu (T.A. Kral). Contents lists available at ScienceDirect Planetary and Space Science journal homepage: www.elsevier.com/locate/pss https://doi.org/10.1016/j.pss.2018.03.012 Received 31 December 2017; Received in revised form 13 March 2018; Accepted 20 March 2018 Available online xxxx 0032-0633/© 2018 Published by Elsevier Ltd. Planetary and Space Science xxx (2017) 1–9 Please cite this article in press as: Mickol, R.L., et al., Survival of non-psychrophilic methanogens exposed to martian diurnal and 48-h temperature cycles, Planetary and Space Science (2017), https://doi.org/10.1016/j.pss.2018.03.012