Researchers have found the first photosynthetic organism that lives off a light source other than the sun. The creature, a bacterium that resides in the inky depths of the ocean, appears to derive energy from a still mysterious light source near deep-sea hydrothermal vents. If true, the discovery could offer clues about life on early earth--or on other planets.
Since their discovery in 1977, deep-sea hydrothermal vents have offered up a surprising menagerie, including 2-meter tube worms and eyeless crabs, that thrives in total darkness (ScienceNOW, 29 April and (ScienceNOW 10 March, 1999). This world became slightly less gloomy two decades later when researchers proved that the water around the vents produces a shine beyond the infrared light from geothermal radiation. Although this curious vent glow is too weak to be detected by human eyes, it has a frequency well into the visible spectrum.
To determine if the so-called vent glow can sustain photosynthetic life, Cindy Van Dover, a marine biologist at the College of William and Mary in Williamsburg, Virginia, formed a research team that included Thomas Beatty, a microbiologist at the University of British Columbia in Vancouver, Canada, Robert Blankenship, a biochemist at Arizona State University in Tempe, and others. In 2003, the team descended 2.4 kilometers in the Woods Hole Oceanographic Institution research submarine ALVIN to retrieve samples from a pair of vents that lie along the volcanically active Pacific ridge.
The search paid off. Reporting online this week in Proceedings of the National Academy of Sciences, the team describes the first example of a photosynthetic organism that doesn't need the sun to live. As long as it gets sulfur and CO2, the bacterium--known as GSB1 for the time being--seems to get by on the kind of light provided by vent glow.
"The results break new ground and are indeed surprising," says Bob Buchanan, a microbiologist at the University of California, Berkeley. One open question, he says, is whether GSB1 "is a long term resident in the area surrounding the vent or whether it ... spends much of its life elsewhere." To quash such doubts, Beatty is already planning a mission to isolate photosynthesizers from other vents.