pH Dependence of Configurations and Surface Properties of Microbial Extracellular Polymeric Substances (EPS)

Abstract

The flocculability 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, the pH dependence of configuration and surface property of microbial extracellular polymeric substances (EPS), excreted from Bacillus megaterium TF₁₀, and accordingly its flocculability is elucidated. The main functional groups and buffering zones in the EPS were identified from FTIR and acid–base titration. The laser light scattering analysis revealed that the deprotonated or protonated states of these functional groups in EPS were governed by pH and resulted in more dense and compact structure at a lower pH because of hydrophobicity and intermolecular hydrogen bonds. The zeta potential measurements implied that the isoelectric point and the electrostatic repulsion action of EPS were controlled by pH. These results clearly demonstrate that the EPS configurations and accordingly microbial flocculability are heavily dependent on pH in solution.