Deep-Sea Bacterium Uses Heat Radiation for Photosynthesis

A deep-sea bacterium discovered in 2005 can photosynthesize without sunlight, using thermal radiation from a hydrothermal vent 2,400 meters below the ocean.

Biology

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In 2005, researchers described a green sulfur bacterium found near a deep-sea hydrothermal vent more than two kilometers below the ocean surface. The striking part was not simply that it lived in darkness, but that its photosynthetic system could make use of geothermal radiation coming from the hot vent environment rather than relying on sunlight. The organism absorbs long-wavelength light around the edge of the visible and infrared range, with a major absorption peak near 750 nanometers. Hydrothermal vents emit thermal radiation because their hot fluids and surrounding materials radiate electromagnetic energy, even where sunlight cannot reach. The bacterium is a green sulfur bacterium and uses anoxygenic photosynthesis, meaning its metabolism does not produce oxygen in the way plant photosynthesis does. Instead, sulfur compounds can serve as the electron source, with elemental sulfur produced during the process. The discovery broadened the range of environments known to support light-driven microbial life and raised interesting questions about how organisms might harvest energy in other dark environments, including potentially habitable settings beyond Earth. The findings do not show that life exists elsewhere, but they demonstrate that photosynthetic organisms can exploit light sources very different from ordinary sunlight.

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