Bacillus lichenformis gamma-glutamyl exopolymer: Physicochemical characterization and U(VI) interaction

Complexation by microbially produced exopolymers may significantly impact t he environmental mobility and toxicity of metals. This study focused on the conformational structure of the bacterial exopolymer, gamma-D-poly(glutami c acid):and its interactions with U(VI) examined using ATR-FTIR spectroscop y. Solution pH, polymer concentration, and ionic strength affected the conf ormation of the exopolymer, and U(VI) binding was monitored. At low pH, low concentration, or low ionic strength, this exopolymer exists -in an alpha- helical conformation, while at high pH, concentration, or ionic strength th e exopolymer exhibits a beta-sheet structure. The change in exopolymer conf ormation is likely to influence the number and nature of exposed surface fu nctional groups, sites most responsible for metal complexation. We found th e polyglutamate capsule binds U(VI) in a binuclear, bidentate fashion; in c ontrast the glutamate monomer forms a mononuclear, bidentate complex with U (VI). The apparent polynuclear binding of U(VI) may induce beta-sheet struc ture formation provided the U(VI) concentration is sufficiently high.