Survival of extremely and moderately halophilic isolates of Tunisian solar salterns after UV-B or oxidative stress

Abstract

Adaptation to a solar saltern environment requires mechanisms providing tolerance not only to salinity but also to UV radiation (UVR) and to reactive oxygen species (ROS). We cultivated prokaryote halophiles from two different salinity ponds: the concentrator M1 pond (240 g·L–1NaCl) and the crystallizer TS pond (380 g·L–1NaCl). We then estimated UV-B and hydrogen peroxide resistance according to the optimal salt concentration for growth of the isolates. We observed a higher biodiversity of bacterial isolates in M1 than in TS. All strains isolated from TS appeared to be extremely halophilic Archaea from the genus Halorubrum . Culturable strains isolated from M1 included extremely halophilic Archaea (genera Haloferax , Halobacterium , Haloterrigena , and Halorubrum) and moderately halophilic Bacteria (genera Halovibrio and Salicola ). We also found that archaeal strains were more resistant than bacterial strains to exposure to ROS and UV-B. All organisms tested were more resistant to UV-B exposure at the optimum NaCl concentration for their growth, which is not always the case for H2O2. Finally, if these results are extended to other prokaryotes present in a solar saltern, we could speculate that UVR has greater impact than ROS on the control of prokaryote biodiversity in a solar saltern.