Proton and Zn<'2+> reactivity of xanthane, a model exopolysaccharide to assess metal sorption on bacterial biomass

摘要

Soil bacteria are biosorbent particles that may either favor the transfer of metals if they are mobile, or increase metal retention if they form biofilma. Bacteria reactivity studies performed with non-redox sensitive metals such as Zn, Cd, Pb, are numerous and focus mainly on the determination of the sorption capacity of the bacterial substrates and the determination of metal-ligand equilibrium constants. However, soil bacteria form biofilms which were shown to have an increased reactivity toward metals. We consequently consider that biofitrns compounds such as exopolysaccharides are involved in metal binding and eventually constitute the effective bacterial reactivity pool. Xanthane, a non-gelling model exopolysaccharide of known structure produced by Xanthomonas campestris strains was consequently investigated. Its acid-base reactivivity compares to that of its constituting monocarboxylic glucuronic and pyruvic acids. Contrarily, its Zn reactivity is higher than that of the constituting model ligands but fits the Zn binding constants typically found on bacterial cells. This indicates that the ternary structure of biopolymers may be involved in metal bindings processes. Xanthane's reactivity will be compared to that of Xanthomonas campestris mutants which produce no EPS. Our results support the idea of a key role of biopolymers in metal binding.