title: Reactions between bacterial exopolymers and goethite: A combined macroscopic and spectroscopic investigation.
abstract: The adsorption to goethite of extracellular polymeric substances (EPS) isolated from Pseudomonas putida was investigated using batch adsorption experiments, electrophoretic mobility (EM) measurements, Fourier transform infrared (FTIR) spectroscopy, isothermal titration calorimetry (ITC) and X-ray absorption fine structure (XAFS) spectroscopy. The adsorption of EPS decreased the point of zero charge of goethite from 7.6 to 3.2, suggesting the formation of negatively charged inner-sphere surface complexes. The adsorption isotherms of EPS on goethite conformed to the Langmuir equation. The adsorption energy constant (K) of EPS on goethite was in the sequence of EPS phosphate-containing moieties > nitrogen-containing moieties > carbon-containing moieties, indicating those containing phosphate were the most strongly adsorbed. FTIR showed ligand exchange of phosphate groups of EPS with surface hydroxyls on goethite. Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopy results further demonstrated phosphate groups of EPS can form monodentate inner-sphere complexes at lower pH 3.0, while form bidentate inner-sphere complexes at higher pH 9.0. The oxidation state of iron in goethite was not changed after the reaction with EPS at different pH values. The information obtained in this study is of fundamental significance for the understanding of the interaction mechanisms between bacteria and minerals in soil and aquatic environments.
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China; State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, Yangling 712100, China.
authors.forename: Linchuan
authors.initials: L
authors.lastname: Fang
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Cao
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China; Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River), Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China.
authors.forename: Qiaoyun
authors.initials: Q
authors.lastname: Huang
authors.affiliation: Department of Chemical and Environmental Engineering, University of California, Riverside, CA 92521, USA.
authors.forename: Sharon L
authors.initials: SL
authors.lastname: Walker
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China; Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtse River), Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, China. Electronic address: cp@mail.hzau.edu.cn.
authors.forename: Peng
authors.initials: P
authors.lastname: Cai
mesh_terms: D000327:Adsorption; D006863:Hydrogen-Ion Concentration; D058085:Iron Compounds / Q000737:chemistry*; D008903:Minerals / Q000737:chemistry*; D011135:Polysaccharides, Bacterial / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D058085:Iron Compounds; D008903:Minerals; D011135:Polysaccharides, Bacterial; C094886:goethite