Enhancement of solubilization and biodegradation of polyaromatic hydrocarbons by the bioemulsifier alasan

Alasan, a high-molecular-weight bioemulsifier complex of an anionic polysac charide and proteins that is produced by Acinetobacter radioresistens KA53 (S. Navon-Venezie, Z. Zosim, A. Gottlieb, R. Legmann, S. Carmeli, E. Z. Ron , and E. Rosenberg, Appl. Environ. Microbiol. 61:3240-3244, 1995), enhanced the aqueous solubility and biodegradation rates of polyaromatic hydrocarbo ns (PAHs). In the presence of 500 mu g of alasan ml(-1), the apparent aqueo us solubilities of phenanthrene, fluoranthene, and pyrene were increased 6. 6-, 25.7-, and 19.8-fold, respectively. Physicochemical characterization of the solubilization activity suggested that alasan solubilizes PAHs by a ph ysical interaction, most likely of a hydrophobic nature, and that this inte raction is slowly reversible. Moreover, the increase in apparent aqueous so lubility of PAHs does not depend on the conformation of alasan and is not a ffected by the formation of multimolecular aggregates of alasan above its s aturation concentration. The presence of alasan more than doubled the rate of [C-14]fluoranthene mineralization and significantly increased the rate o f [C-14]phenanthrene mineralization by Sphingomonas paucimobilis EPA505. Th e results suggest that alasan-enhanced solubility of hydrophobic compounds has potential applications in bioremediation.