European scientists investigated the metabolic pathways of microorganisms that live in the deep-sea subfloor. Interestingly, under energy-limited conditions, bacteria demonstrate great variability in energy conservation and carbon turnover.
Recent studies report the existence of microorganism communities living in the deep marine subsurface under conditions of extreme energy limitation. It remains to be determined how ATP is generated under such conditions, and in particular, how the ATP synthase protein complex adapts. Emerging evidence shows that the generated free energy is much higher than initially envisioned and unlikely to place selective pressure on the ATP synthesis machinery.
Further details: Energy production by deep sea microorganisms