The deep-sea biosphere: Constraints and implications

John Baross
School of Oceanography
University of Washington

Wednesday, October 28, 1998
3:00 p.m.—Pacific Forum

The isolation of hyperthermophiles (microorganisms that grow at 90C and above) from both deep-sea (< 2 km) subseafloor fluids immediately following a volcanic eruption and from diffuse flow vent fluids associated with stable hydrothermal vents indicates the existence of a deep-sea, subsurface microbial biosphere. These organisms are apparently growing in the porous, extrusive layers of the crust that reach depths of greater than 500 m below the deep-sea floor. Moreover, models from seismic data indicate that cracking may occur at depths exceeding 6,000 m in the crust. The physical and chemical properties of the subseafloor environment put constraints on the metabolic versatility and physiologies of the microbial communities. These constraints can be used to identify microorganisms uniquely adapted to the subseafloor. Hyperthermophiles isolated from plume fluid following the North Gorda Ridge eruption can grow both heterotrophically and autotrophically and over a wide temperature range. The evidence suggests that subsurface environments associated with hydrothermal systems can support microbial life in the absence of nutrients derived from photosynthesis. These findings have implications for understanding the earliest microbial communities on earth and potential life on other hydrothermally active solar bodies.

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