A rainforest may host breathtaking biodiversity, but it is no match for the ocean. William Fenical, PhD, director of the Center for Marine Biotechnology and Biomedicine at Scripps Institution of Oceanography in La Jolla, California, has been entranced by the sea for decades. Covering more than 70% the Earth's surface, the ocean harbors 34 of the 36 phyla of life found on the planet—double the 17 that live on land. Marine sources, he likes to point out, also account for more than 20 anticancer drugs now in clinicaltrials.

For Dr. Fenical, success in isolating potential therapies from the sea has meant aiming small. Several years ago, the inability to source enough material forced his group to abandon promising bioactive compounds from a soft coral off the western coast of Australia and from a bright orange sea squirt off the coast of Brazil. “We couldn't collect enough of these animals to even make gram quantities in many cases, much less 100 or 500,” he says. “So these discoveries went by the wayside.”

Over the past decade, he and his collaborators have pioneered new cultivation methods and harnessed molecular techniques, allowing them to exploit the teeming microbes found in shallow and deep-ocean sediments—as many as a billion per cubic centimeter. Forthe researchers,the microbes represent both the sources and mass producers of potential drugs.

Compounds from 2 marine microbes that Dr Fenical's team found near the Bahamas have been licensed by Nereus Pharmaceuticals (San Diego, Calif) and are progressing through phase 2 clinical trials. One, a molecule called marizomib that was derived from the deepwater Salinispora tropica bacterium, is being eyed as a potential therapy for multiple myeloma and lymphoma. Another drug known as plinabulin, a synthetic derivative of a molecule produced by a fungus found clinging to seaweed, has tentatively been earmarked for breast and ovarian cancer. “Now that we've invested all this time:' Dr. Fenical says, “we're riding a big high in the discovery of new compounds.”