title: pH dependence of structure and surface properties of microbial EPS.
abstract: The flocculation of microorganisms plays a crucial role in bioreactors, and is substantially affected by pH. However, the mechanism for such an effect remains unclear. In this work, with an integrated approach, the pH dependence of structure and surface property of microbial extracellular polymeric substances (EPS), excreted from Bacillus megaterium TF10, and accordingly its flocculation is elucidated. From the Fourier transform infrared spectra and acid-base titration test results, the main functional groups and buffering zones in the EPS responsible for the microbial flocculation are indentified. The laser light scattering analysis reveals that the deprotonated or protonated states of these functional groups in EPS result in more dense and compact structure at a lower pH because of hydrophobicity and intermolecular hydrogen bonds. The zeta potential measurements identify the isoelectric point and indicate that the electrostatic repulsion action of EPS is controlled by pH. The highest flocculation efficiency is achieved near the isoelectric point (pH 4.8). These results clearly demonstrate that the EPS structure, surface properties, and accordingly the microbial flocculation are dependent heavily on pH in solution.
authors.affiliation: Department of Chemistry, University of Science & Technology of People's Republic of China.
authors.forename: Ling-Ling
authors.initials: LL
authors.lastname: Wang
authors.forename: Long-Fei
authors.initials: LF
authors.lastname: Wang
authors.forename: Xue-Mei
authors.initials: XM
authors.lastname: Ren
authors.forename: Xiao-Dong
authors.initials: XD
authors.lastname: Ye
authors.forename: Wen-Wei
authors.initials: WW
authors.lastname: Li
authors.forename: Shi-Jie
authors.initials: SJ
authors.lastname: Yuan
authors.forename: Min
authors.initials: M
authors.lastname: Sun
authors.forename: Guo-Ping
authors.initials: GP
authors.lastname: Sheng
authors.forename: Han-Qing
authors.initials: HQ
authors.lastname: Yu
authors.forename: Xiang-Ke
authors.initials: XK
authors.lastname: Wang
mesh_terms: D001410:Bacillus megaterium / Q000378:metabolism*; D019149:Bioreactors; D005427:Flocculation; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D011135:Polysaccharides, Bacterial / Q000737:chemistry* / Q000378:metabolism; D017550:Spectroscopy, Fourier Transform Infrared; D014865:Waste Disposal, Fluid
chemical_list: D011135:Polysaccharides, Bacterial