Hydrothermal systems, like the 'black smoker' chimneys at mid–ocean ridges, are some of the most dynamic and extreme environments colonized by life and may have been inhabited since early in Earth's history. Biofilms, or 'microbial mats', attached to rocks were amongst the first forms of microbial life discovered at hydrothermal vents thirty years ago and have since been found in terrestrial hot springs and shallow submarine hydrothermal habitats. Studies of high temperature microbial ecosystems have been a rich source of genetic and functional diversity and novel enzymes for biotechnology. While biofilms have been extensively characterized in medical and industrial settings, their role(s) in natural ecosystems are only now beginning to be elucidated. Some of the roles that biofilms may play include improving microbial resilience to environmental stresses and thereby expanding the range of potentially habitable conditions. Biofilms also serve to 'tether' microorganisms in the otherwise dynamic and rapidly–changing habitats found at deep sea vents. Furthermore, biofilms may bind nutrients and facilitate cooperative relationships between organisms, or serve as food for higher trophic levels. The growth of microbial communities as biofilms has a number of properties and a level of complexity that would be hard to recognize if studied individually.
Comparative studies of biofilm structure and composition in hydrothermal environments are beginning to make headway into understanding high temperature microbial 'slimes'. The interactions between biofilms and mineral surfaces at hydrothermal vents play a prominent role in many scenarios speculated for the origins of life on Earth, and surface–associated biofilms may contain a record of these molecular interactions. Insights from biofilm studies also provide us with a better extent of the depths and potential extent of the deep subsurface biosphere. Finally, findings from modern–day hydrothermal systems on Earth may help to focus life detection efforts on volcanically active planets elsewhere in the universe.