76th Annual Meteoritical Society Meeting (2013) 5071.pdf

METHANOGEN SENSITIVITY TO ULTRAVIOLET RADIATION: IMPLICATIONS FOR LIFE ON MARS N. Sinha1 and T. A. Kral1,2, 1Arkansas Center for Space and Planetary Sciences, 2Dept. of Biological Sciences, University of Arkansas, Fayetteville, AR, [email protected].

Introduction: We have been studying methanogens as models for life on Mars for the past 20 years (1, 2, 3, 4, 5, 6, 7, 8, 9). Methanogens are microorganisms that produce methane as a byproduct of metabolism. They are one possible explanation for the methane found in the Martian atmosphere (10, 11, 12). If an organism is to exist in the hostile Martian environment, it must be able to deal with a number of relatively extreme factors. One of those factors is ultraviolet radiation. Mars is continually bombarded with DNA-damaging ultraviolet (UV) radiation mostly between 200-400 nm due to lack of an ozone layer. Therefore, any life forms at or near the surface of Mars would have to adapt to radiation over time by repairing DNA damage caused by UV radiation. The goal of this study was to characterize the sensitivity of four species of methanogens to UV radiation. Methods: Liquid cultures (approximately 100 uL) of Methanothermobacter wolfeii, Methanosarcina barkeri, Methanobacterium formicicum and Methanococcus maripaludis were irradiated by a UVC lamp (254 nm/4 watts) simulating Martian-surface UV flux (approx. 4 W/m2). They were exposed to UV radiation for various lengths of time (0, 5, 10, 20, 30 min., 1, 2, 3, 4, 5, 6, 8, 12, 20, and 24 hrs) in a Coy anaerobic chamber. After exposure for these specified times, they were placed back into their respective sterile growth media and pressurized with hydrogen gas and incubated at their respective temperatures. The survivability of these methanogens was measured by methane production. Headspace gas of these sample tubes was analyzed for percentage of methane by a gas chromatograph at different time intervals. Results and Discussion: M. wolfeii survived up to 2 hours, M. barkeri up to 5 hours, M. formicicum up to 1 hour, and M. maripaludis survived for 12 hours of UV radiation. DNA repair enzymes may have played a crucial role for their survival after different amounts of UV radiation. The search for DNA repair enzymes, such as DNA photolyase and N-glycosylase, in these methanogens is in progress. Cells may adapt to radiation over time and can evolve on the surface of Mars as the conditions of early Earth were similar to that which exists on Mars today. Thus, this study provides insight into how early life on Earth may have responded to stress caused by unfiltered UV radiation, and it may have a significant implication for the possibility of life on Mars.

References: [1] Kral, T.A. et al. (1998) Origins Life Evol. Biosphere, 28, 311-319. [2] Kral, T.A. et al. (2004) Origins Life Evol. Biosphere, 34, 615-626. [3] Kendrick, M.G. and Kral, T.A. (2006) Astrobiology, 6, 546-551. [4] Ormond, D.R. and Kral, T.A. (2006) J. Microbiol. Meth., 67, 603-605. [5] McAllister, S.A. and Kral, T.A. (2006) Astrobiology, 6, 819-823. [6] Chas- tain, B.K. and Kral, T.A. (2010) Icarus, 208, 198-201. [7] Ulrich, R. et al. (2010) Astrobiology, 10, 643-650. [8] Chastain, B.K. and Kral, T.A. (2010) Astrobiology, 10, 889-897. [9] Kral, T.A. et al. (2011) Planetary Space Sci., 59, 264-270. [10] Formisano, V. et al. (2004) Science, 306, 1758-1761. [11] Krasnopolsky, V.A. et al. (2004) Icarus, 172, 537-547. [12] Mumma, M.J. et al. (2009) Science, 323, 1041-1045.