Two Bacillus species were studied which produced bioemulsifiers; however, they were distinctly different compounds. Bacillus sp. strain IAF 343 produced unusually high yields of extracellular biosurfactant when grown on a medium containing only water-soluble substrates. The yield of g/liter was appreciably better than those of most of the biosurfactants reported previously. This neutral lipid product, unlike most lipid biosurfactants, had significant emulsifying properties. It did not appreciably lower the surface tension of water. On the same medium, Bacillus cereus IAF 346 produced a more conventional polysaccharide bioemulsifier, but it also produced a monoglyceride biosurfactant. The bioemulsifier contained substantial amounts of glucosamine and originated as part of the capsule layer. The monoglyceride lowered the surface tension of water to 28 mN/m. It formed a strong association with the polysaccharide, and it was necessary to use ultrafiltration to effect complete separation. The removal of the monoglyceride caused the polysaccharide to precipitate. It is suggested that earlier reports of biopolymers which both stabilized emulsions and lowered surface tension were actually similar aggregates of lipid and bioemulsifier. Both the lowering of the surface tension of water and the stabilization of oil and water emulsions can be accomplished by using biological materials. A large variety of biosurfactants have been reported (3, 8, 16, 20, 23). In fact, any lipid probably has some degree of surface activity (3; D. G. Cooper and B. G. Goldenberg, Appl. Environ. Microbiol., submitted for publication). Most lipids are minor components of a cell, however. To have commercial potential as a biosurfactant, a lipid must be produced in high yield to reduce cost and must be excreted into the medium to facilitate efficient product recovery (2, 3, 7). Most of the bioemulsifiers that have been characterized have been polymeric, usually polysaccharides (1, 3, 16, 19, 20, 24; Cooper and Goldenberg, submitted). Several polymeric biosurfactants have been reported to both stabilize emulsions and significantly lower surface tension (8, 17, 20, 22). It is possible, however, that further fractionation of the crude products would isolate different components that are responsible for each activity (17; Cooper and Goldenberg, submitted).
