Photosynthetic bacteria may be able to live without solar light, instead using thermal radiation from hot fluid for energy, according to a study in this week's PNAS. Researchers led by J. Thomas Beatty of the University of British Columbia, Vancouver, have found obligately photosynthetic green sulfur bacteria at a deep-sea hydrothermal vent more than a mile below the ocean surface.

"They're seeing photosynthesis where there's no sunlight," said Carl Bauer of Indiana University, who was not involved in the study. "That's amazing."

Submarine hydrothermal vents, often called black smokers, host complex ecosystems that are largely fueled by chemicals dissolved in geothermally heated vent water. Chemotrophic bacteria near the vent orifice can get energy by breaking down inorganic compounds such as hydrogen sulfide, and the organic material these bacteria produce feeds other microbes and invertebrates.

Beatty and colleagues cultured water samples taken from various depths over the East Pacific Rise,...