Temperature-sensing Genes as a Model for Lifes Adaptations in Dark Ocean Worlds

Biological rhythms on Earth are nearly ubiquitous, and are thought to confer fitness by allowing organisms to anticipate important periodic environmental events. While biological rhythms on Earth are generally entrained to sunlight, hypothetical life in the subsurface oceans of the icy moons Enceladus and Europa would lack this stimulus. However, both moons experience strong tidal forces, exerted by the moons parent planets and their sister moons, which are thought to result in the periodic stressing of their icy crusts and rocky interiors. As on Earth, tidal forces may drive fluid movement in the crust below the seafloor, creating thermodynamic disequilibria essential for life. If microbial life on these moons have evolved biological rhythms, they may entrain to tidally-driven rhythmic processes rather than light. To explore the idea of biological rhythms of possible life on icy moons, we first present possible alternative stimuli by which life on these moons might entrain biological rhythms. Temperature, a possible rhythmic stimulus on Enceladus and Europa, is already known to entrain biological rhythms in some organisms on Earth. We survey the ability of microbial life on Earth to sense temperature by identifying relevant temperature-sensing genes from the literature and summarizing the diversity and distribution of organisms possessing these genes. Biological functions associated with these genes are also catalogued. We expect that this work will pave the way for future exploration of non-light-entrained rhythms in Earth life, especially in model species for astrobiology and in organisms living in analog habitats for Enceladus and Europa.