Resilience and adaptation to extreme environments: the special case of Euplotes focardii, a strictly psychrophilic Antarctic ciliate

Antarctica and the Sothern Ocean are the coldest and harshest places on the Planet. Antarctic marine organisms face a number of environmental challenges, in particular the adverse effects on key biological processes of cold and oxidative stress, the latter due to increased oxygen solubility in cold waters. Over the past 50 years, the west coast of the Antarctic Peninsula has been one of the most rapidly warming parts on the Earth. Antarctic species are dramatically impacted by thermal changes. As single cells directly exposed to environmental cues, marine Antarctic protozoa represent excellent models to unravel the full suite of cellular functions that allowed the ecological success of psychrofiles and the biological responses to fast environmental changes. To optimally address resilience and adaptation, it is necessary to access to large sample sizes of sequences in order to enable evaluation via statistical and computational approaches. Only genome or transcriptome sequencing can provide such data sets. In this context, we are studying the Antarctic hypotrichous marine ciliate Euplotes focardii by an “omic” approach, focussing principally on the genome and transcriptome, the latter obtained under both physiological and stress conditions.The analysis of these large data set allowed us to approch the study from three different points of view: the analysis of gene expression under stress, the biochemical characterization of “cold-adapted” enzymes and the study of a bacterial consortium associated to this ciliate. Our results strongly indicate that ciliates represent a good model to unravel the evolutionary mechanisms that determine environmental adaptation. The biology of E. focardii highlights the impact of environmental constrain on evolution and adaptation and indicates the strategy used by this microorganism to survive in fast evolving environmental conditions.