Extreme marine environments (brines, seeps, and smokers)

Several different extreme environments-characterized by geochemical and physical extremes-are found in the ocean and in seas and many of them appeared to be hot spots for microbial abundance and diversity, thanks to the overwhelming presence of substrates and energy sources that support microbial metabolism. The most studied oceanic extreme environments are the vent ecosystems, such as the hot deep-sea hydrothermal vents (DSHVs) or cold seeps and mud volcanoes, and the hypersaline ecosystems such as the deep anoxic hypersaline lakes, brine lakes on mud volcanoes, and brines contained within sea ice. However, new fascinating extreme habitats for microbial life in the ocean are being discovered continuously such as water droplets entrapped in oil deposits. These environments comprise a large variety of extreme physicochemical conditions, which contribute importantly to the composition and shaping of the residing microbial communities and select for extremophile populations of microorganisms. These extremophiles are the key players of the element cycles in these environments, often responsible for primary productivity, and endemic. Many of the extremophiles have not yet been obtained in pure culture. The study of the microbiota associated with extreme marine environments confirmed that they constitute an important source of Bacteria and Archaea with biotechnological potential, producing enzymes and metabolites-“extremozymes” and “extremolytes”-that might find industrial application.