Bacteria found deep below ocean floor.

Earth's biosphere -- the area its living creatures call home -- is larger and has more life in it than scientists had realized. Studies of sediment laid down more than 4 million years ago in the Pacific Ocean reveal that bacteria are living at least 500 meters below the ocean floor.

"We have a much thicker veneer to our planet which is living and responding to chemical inputs and geothermal inputs than we previously thought," says R. John Parkes of the University of Bristol in England.

Scientists had believed that pressure and heat this far below the seafloor would prevent life from establishing a foothold there, he says. They also did not imagine that microorganisms could dine off the organic matter available at such depths. But some geochemists had begun to suspect that the degradation of organic material seen in the deep ocean could be attributed in part to bacteria, Parkes notes.

Other teams have reported finding microorganisms far beneath the ocean bottom, but investigators think those bacteria may have been introduced into the lower depths during drilling, Parkes asserts.

To ensure that this was not a problem in their work, Parkes and his colleagues took samples at a range of depths. They found populations of organisms that were much larger than the groups above them, the team reports in the Sept. 29 LANCET. Bacterial contamination during drilling couldn't account for the deeper groups' larger numbers, Parkes contends.

Using a microscope, the scientists observed the organisms directly in the sediments without growing them in laboratory cultures, he says. "Some of them we catch in the act of division" -- a sure sign of their viability, he adds.

The number and activity of bacteria vary with the availability of food, the team asserts. At 360 m below the seafloor, the researchers found a significant increase in both anaerobic bacteria and the methane and other hydrocarbons the creatures feed on.

The scientists cultured sulfate-reducing bacteria that they found 80 m below the seafloor. The DNA of these microorganisms resembles that of organisms living closer to the surface. However, "in terms of their growth and metabolism, they are very different. They are new," says Parkes. The researchers believe the sediment samples contain additional novel bacteria.

These hardy underseafloor creatures may one day prove useful in biotechnology, he adds.

The Parkes team "did a very thorough and careful job," says Derek Lovley of the U.S. Geological Survey in Reston, Va. In addition to showing that the biosphere is bigger than previously thought, the investigators demonstrated for the first time that microorganisms continue to act on ancient, deep-ocean sediments, he says. The findings also greatly extend previous research on deep terrestrial aquifers (SN: 3/5/88, p.149), he adds.