Lessons From Extremophiles: Early Evolution And Border Conditions Of Life

Modern prokaryotes are the only forms of life featuring organisms capable of growth above 62°C, and inside each domain, the first phylogenetic analyses singled out the most extreme of these thermophiles as the earliest lines of descent: Aquificales and Thermotogales among Bacteria, different Euryarchaeota and Crenarchaeota among Archaea. A recent research study used a new algorithm automatically picking up “representative” proteins, including both ubiquitous and non-ubiquitous but rather well-conserved proteins; here Thermotoga and Aquifex remained together in a basal position with a weak bootstrap support. Modern thermophiles are the result of more than 3 billion years evolution, during which further adaptation has certainly occurred, and molecular adaptations to thermophily look rather elaborated in the only living organisms we can investigate. Temperature is an all-pervasive factor with straightforward effects on the physical state of the universal life solvent, which has to remain in the liquid state to allow suitably adapted organisms to grow. The world of extremophiles offers similar test cases; some of the most obvious ones concern extreme halophily and thermophily, conditions that impose adaptation to the whole proteome.