CONICET | Buscador de Institutos y Recursos Humanos

The Halobacteriaceae family (order Halobacteriales) comprises a group of extremophile archaebacteria who inhabits in environments with high salt concentrations (3.4-5.1 M NaCl range for optimally growth). Some halobacterial species are acidophilic or alkaliphilic, growing in a pH range below 5 or in pH optima between 9 -11 respectively. It is known that halophile archaebacteria are inhabitants of halites and ancient evaporites in Earth. Since evaporites have been detected in Martian meteorites, these organisms are proposed as plausible inhabitants of Mars-like planets or other extrasolar planets. Ultraviolet (UV) radiation is an important environmental factor, because it can act as a genotoxic agent inducing DNA damage, or damaging a wide variety of proteins and lipids. In fact, high exposure to UV-C (wavelengths <290 nm) is lethal to most of the terrestrial biological systems. Because halophiles are exposed to intense solar UV radiation in their natural environment they are generally regarded as relatively UV tolerant. In an extraterrestrial environment the large amount UV radiation coming from certain type of stars (during events named flares), could set a limit for the development of extraterrestrial life. It is uncertain how these UV events can affect the evolution of life in these environments beyond the Earth, since life is particularly vulnerable to ultraviolet radiation. In this work we analyze the effect of UV-C on the haloalkalophile microorganism Natrialba magadii, who was isolated from Magadi lake in Kenya, Africa (ATCC.), To this end cultures of N. magadii were grown to mid-exponential phase (around OD600= 1) at 37.0 °C, in rich media (pH 10.0) containing (in g/l): yeast extract, 20.0; NaCl, 200; Na2C03, 18.5; and exposed to a Phillips 15W Hg lamp (254 nm emission peak) with constant mixing. Aliquots of the irradiated culture were withdrawn after different irradiation times, and the effect of the UV treatment was assessed by diluting the sample and following the changes of the growth kinetics in media of identical composition. Growth was monitored by increasing in optical density at 600 nm. Preliminary results show that even after significant UV damage, as judged by the absence of detectable growth for more than 30 hours, the surviving cells were able to resume growth with nearly normal kinetics.

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