Halophile Archeabacteria at Different UV Doses: An Experiment for the UV Limits of Life

ABREVAYA, X. C.; ADAMO, H.; MAUAS, P.J.D.

Firenze, Italia.

Conferencia; 15th International Conference on the Origin of Life; 2008

International Society for the Study of the Origin of Life

Life is particularly vulnerable to ultraviolet radiation (UV). High exposure to UVC(wavelengths <290 nm) is lethal to most of the terrestrial biological systems and can set alimit for the development of extraterrestial life (Buccino et al., 2006). Halophile archeabacteriaare known inhabitants of halites and ancient evaporites in Earth. Since evaporites have beendetected in Martian meteorites (Zolensky et al. 1999, Whitby et al. 2000), these organisms areproposed as plausible inhabitants of Mars-like planets or other extrasolar planets (Stan-Lotter etal. 2004). Moreover, because halophiles are exposed to intense solar UV radiation in theirnatural environment they are generally regarded as relatively UV tolerant.We examine the effect of UVC on the haloalcalophile archea Natrialba magadii. To thisend cultures of N. magadii were grown to mid-exponential phase (around OD600=1) at37°C, in rich media (pH 10) containing (in g/l): yeast extract, 20; NaCl, 200; Na2C03, 18.5;and exposed to a Phillips 15 W Hg lamp 254 nm with constant mixing. Aliquots of theirradiated culture were withdrawn after different irradiation times, and the effect of the UVtreatment was assessed by diluting the sample and following the changes of the growthkinetics in media of identical composition. Growth was monitored by increasing in opticaldensity at 600 nm. Preliminary results show that even after significant UV damage, asjudged by the absence of detectable growth for more than 30 h, the surviving cells wereable to resume growth with nearly normal kinetics