Chemolithoautotrophic microorganisms use inorganic molecules such as H2 or H2S as energy sources to drive carbon fixation from CO2 into biomass. Such organisms dominate the microbiota of deep-sea hydrothermal vents, where they are well adapted to elevated pressure, sharp thermal gradients, and highly variable redox conditions. Considering the contribution of these microbial communities to the global biogeochemical cycles, it is striking how little we know about the function and physiological responses of piezophiles to physical and chemical conditions resembling deep-sea habitats. Here, we conducted a series of high-pressure culture to gain insight into the adaptation mechanisms of piezophilic microorganisms to the environmental and bioenergetics conditions of subsurface biosphere. The model organism is a strictly anaerobic, nitrate reducing, thermophilic Epsilonproteobacterium (Nautilia strain PV-1) that we recently isolated from fluids discharged from an active deep-sea vent at the East Pacific Rise. This novel deep-sea vent bacterium is the only autotrophic organism among the piezophilic organisms isolated. Genomic and proteomic analysis revealed that the PV-1’s adaptation strategies under high pressure may involve upregulation of genes encoding for membrane fluidity, ATP transport, motility and production/conservation of energy, competence along with the downregulation of enzymes linked to the reductive citric acid cycle. Adaptation strategies to pressure and bioenergetic stresses may also be closely related to the presence of a temperate bacteriophage in the genome of PV-1. In the course of this project, we also investigated the physiology and functions of a suite of deep-sea and shallow-water chemolithoautrophic bacteria as both pure and mixed environmental cultures.