Fungal fish-oil factories.

Over the past decade, researchers have documented numerous health benefits -- including reduced risks of cancer, heart disease, and autoimmune disorders -- from fish oils rich in long-chain, omega-3 fatty acids. But many people object to the oil's fishy taste. So scientists at the Agricultural Research Service (ARS) in Philadelphia have engineered a fishless alternative: bioreactors that grow fungi rich in one of fish oil's most beneficial constituents, eicosapentaenoic acid (EPA).

In 1990, Eric W. Wessinger and his co-workers at ARS identified four species of Pythium fungi that naturally manufacture EPA. Though industrial systems can harvest such fermentation products from fungi grown in bioreactors, the strand-like structure of Pythium and other filamentous fungi precluded their efficient use in such reactors. So Dennis J. O'Brien and his ARS colleagues came up with a new design.

Most industrial fermenters grow free-floating clumps of fungus within a soup of nutrients. Key to the new ARS device is a rotating cylinder, half submerged in the fungus' nutrient soup. About a day after biochemists seed the soup with Pythium, the fungus begins locking onto the cylinder. O'Brien says the growing fungus feels like raw chicken skin and "looks similar to fibers on a paint roller." To obtain EPA, technicians periodically scrape mats of fungus off the cylinder.

Because the fungi also feed on whey, a by-product of cheese-making, the process may even provide dairy farmers a market for a waste they currently pay to get rid of, adds Wessinger, now with A.E. Staley Manufacturing Co. in Decatur, Ill.