Extreme Habitats of Life

As is often the case, much is revealed about the mainstream by studying the fringe. Nowhere is this more evident than in studies of extreme habitats, which include high and low temperature and pressure; intense dehydration; enormous ranges of pH, salinity, and high concentrations of elements and compounds that prove to be extremely toxic in other settings. The metabolic flexibility that permits life to permeate such diverse habitats is not well understood. Neither are the enzymatic processes that effectively make every geochemically-provided source of chemical energy available to one microorganism or another. In recent years there has been great enthusiasm for extracting organisms, or at least their DNA, from extreme environments and transferring the organisms and biomolecules to the lab for study. In the process, many extreme environments have been largely ignored, despite their ability to provide novel organisms to microbiologists and molecular biologists. Reconnecting extremophiles with their environments requires a biogeochemical perspective, and the combination of careful chemical analyses, thermodynamic calculations, and clever experimental designs that include microbe growth as an integral part of geochemical processes. The res 5/5/04g how those processes permit life to thrive, and how life adapts to widely diverse habitats. The implications will extend from exploring the Earth's cryptic surface communities and subsurface biosphere to new quantitative tests of the potential for other planets to support life in ways that may not yet be considered.