The goal of this proposal is to gain insight into the metabolic and molecular adaptations of deep-sea and subseafloor bacteria exposed to crustal pressures (200-500 atm). The model organism will be an anaerobic nitrate-reducing bacterium (Nautilia strain PV-1) isolated from subseafloor fluids discharged from an active vent at the East Pacific Rise (2500 m depth). The microorganism was retrieved from a series of shipboard continuous culturing incubations conducted aboard the R/V Atlantis. We will investigate the rates of carbon fixation and anaerobic respiration of PV-1 by using our high-pressure chemostat. Further, we propose to investigate the synthrophic growth kinetics of a co-culture composed of the fermentative, hydrogen-producing piezophile, Marinitoga piezophila, and the hydrogenotrophic Nautilia strain PV-1. To our knowledge this would the first experimental study to describe the effects of pressure on chemolithoautotrophic bacteria that were sampled from deep-sea hydrothermal vents and cultured at seafloor pressure conditions prior to their isolation. We anticipate that understanding the pressure adaptations of this strain PV-1, as well as its interactions with heterotrophic bacteria with whom it shares its ecological niche, will provide a unique opportunity to define the spatial and temporal variability of the subseafloor biosphere in the Earth's oceanic crust.