Deep green

Natural History, Dec, 2005 by Jennifer Evans

When most people think of photosynthesis, they think of sunlight. But most people aren't aware that black smokers--vents on the ocean floor that spew hot gases into the seawater--give off minute amounts of light, in addition to the heat and gas. Bacteria discovered near a deep-sea vent in the Pacific strongly suggest that photosynthesis can happen where the Sun doesn't shine.

J. Thomas Beatty, a microbiologist at the University of British Columbia in Vancouver, and his colleagues recently identified a new species of green sulfur bacteria off the west coast of Costa Rica, in water nearly 8,000 feet deep. Green sulfur bacteria make the food they need via photosynthesis, and, as a group, they have a knack of making do with exceptionally low levels of light. To drive photosynthesis, Beatty's bacteria absorb the faint geothermal light--also known as blackbody radiation--that emanates from active deep-sea vents. The photons are so scarce, though, that the bacteria must use the energy frugally: they don't move around (because they lack flagella), and they probably don't reproduce often.

The bacteria are the first organisms ever found that may rely solely on natural light that does not come from the Sun. Their discovery reinforces the likelihood that diverse life forms can live independent of the Sun--perhaps in such exotic habitats as beneath the ice on Jupiter's moon Europa--by relying on chemical, thermal, and alternative photic energy. (PNAS 102:9306-10, 2005)