<i>Bacillus lichenformis</i> γ-Glutamyl Exopolymer: Physicochemical Characterization and U(VI) Interaction

Abstract

Complexation by microbially produced exopolymers may significantly impact the environmental mobility and toxicity of metals. This study focused on the conformational structure of the bacterial exopolymer, γ-d-poly(glutamic acid) and its interactions with U(VI) examined using ATR-FTIR spectroscopy. Solution pH, polymer concentration, and ionic strength affected the conformation of the exopolymer, and U(VI) binding was monitored. At low pH, low concentration, or low ionic strength, this exopolymer exists in an α-helical conformation, while at high pH, concentration, or ionic strength the exopolymer exhibits a β-sheet structure. The change in exopolymer conformation is likely to influence the number and nature of exposed surface functional groups, sites most responsible for metal complexation. We found the polyglutamate capsule binds U(VI) in a binuclear, bidentate fashion; in contrast the glutamate monomer forms a mononuclear, bidentate complex with U(VI). The apparent polynuclear binding of U(VI) may induce β-sheet structure formation provided the U(VI) concentration is sufficiently high.