Implications of subzero metabolic activity on long-term microbial survival in terrestrial and extraterrestrial permafrost

• Main Authors: Amato, Pierre, Doyle, S., Christner, B.C.
• Other Authors: Synthèse et étude de systèmes à intêret biologique (SEESIB), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut de Chimie - CNRS Chimie (INC-CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2010
• Subjects: K5; permafrost
• Online Access: https://hal.science/hal-00493222

National audience The survival of microorganisms in permanently frozen environments such as permafrost over extended timeframes may be limited by damage to DNA caused by background ionizing radiation. In an effort to improve estimates for the survival of bacteria in icy terrestrial and extraterrestrial environments, we determined rates of protein and DNA synthesis at temperatures down to -15°C and the radiobiological sensitivity of bacteria isolated from 110-ky old Siberian permafrost (Psychrobacter cryohalolentis K5 and P. arcticus 273-4). Based on experiments conducted over ~400 days, the maximum macromolecular synthesis rates at -15°C at were 17 proteins cell-1 d-1 and 45 bp cell-1 d-1, respectively. The D37 (i.e. dose at which 37% of cells survive) of frozen suspensions of P. cryohalolentis at -6°C was 136 Gy, which was ~2-fold higher (71 Gy) than identical samples exposed as a liquid suspension. However, if laboratory measurements of the rate of DNA synthesis under frozen conditions are an accurate reflection of the bacterial physiological potential in natural icy environments, a sufficient level of DNA repair is possible to offset chromosomal damage incurred by dosages naturally existing in terrestrial and Martian permafrost. Our results suggest that damage incurred from ionizing radiation does not constrain the longevity of actively metabolizing microbes within permafrost and that the search for extant extraterrestrial life should not be exclusive to environments where water has recently existed in the liquid phase. In addition, though evidence for cellular activity under frozen conditions had been brought earlier, the way such a thermodynamic challenge is addressed is still poorly understood. We have recently demonstrated that a specific energy response consisting in elevating the concentrations of adenylates (adenosine-5'-phosphates, ATP and ADP) at decreasing temperature is involved in P. cryohalolentis. This is similar to that induced by osmotic shock and requires an operational respiratory chain. ...