A recently discovered pigment that converts light into energy occurs in microbes throughout the world's oceans, researchers report today in the journal Nature. The first indication of the existence of a marine bacterium containing this photopigment, dubbed proteorhodopsin, came last fall. Now the new findings suggest that variations of proteorhodopsin abound in the seas and that the different variants are adapted to harnessing light at different depths in the water column.

To assess the commonness of active photopigments in the oceans, microbiologist Edward F. DeLong of the Monterey Bay Aquarium Research Institute and his colleagues first collected oceanic microbes from Hawaii, Antarctica and Monterey Bay. Subsequent analyses revealed photochemical activity in samples from each of the regions. But the proteorhodopsin genes from these microbes were not all the same. Rather they differed from region to region. And within regions, the team found groups of bacteria "whose energy-generating pigments are spectrally tuned to either shallow or deeper water light fields."

The concentration of photopigment in the microbes, the researchers note, suggests that it provides much of the energy needed for cell maintenance and reproduction. Furthermore, considering the abundance of proteorhodopsin-bearing bacteria, these microbes may significantly impact the oceans' carbon and energy cycles. Says DeLong, "Advances in technology are letting us view the marine microbial world in new ways."