A systems biology view on bacterial response to temperature shift

The term " extreme environments " is used to defi ne ecological niches characterized by harsh chemical/physical conditions that challenge most of the life forms, at the point they are characterized by a restricted species diversity. Even though extremophiles can be found across all the domains of life, as well as among viruses, the most prevalent ones are the microbes, mainly due to their ability to adapt to sharp environmental changes, to their metabolic versatility and to their capability of surviving in oligotrophic environments. Living organisms inhabiting these environments have developed peculiar mechanisms to cope with these extreme conditions, in such a way that they mark the chemical-physical boundaries of life on Earth. In general, a distinction can be made between adaptation (i.e. the process of genetic change that accumulates over many generations in response to an organism's specifi c environmental niche) and acclimation (short-term physiological adjustments in response to transitory changes in environmental conditions) (Morgan-Kiss et al. 2006 ). The study of the mechanisms adopted by extremophilic organisms to overcome the selective pressure acting in the ecological niches they occupy is interesting fromboth applied and basic biology viewpoint. Cold-adapted microorganisms, for example, can be exploited in the construction of low-temperature protein expression, facilitating the overproduction of thermo-labile proteins (Papa et al. 2007 ; Miyake et al. 2007 ). Furthermore, cold-active enzymes from these microorganisms have proven to be useful for many areas of biotechnology (e.g. food-processing enzymes) and molecular biology (e.g. the use of alkaline phosphatase for dephos-phorylating DNA vectors before cloning) (Cavicchioli et al. 2011 ).