The role of extracellular polymeric substances in bacterial adhesion onto variable charge soils

We investigated the role of extracellular polymeric substances (EPS) in the adhesion of Pseudomonas fluorescens, Bacillus subtilis, and Escherichia coli on four variable charge soils. Cation exchange resin was used to remove surface-bound EPS. It was observed that soil cation exchange capacity (CEC) and Fe2O3 contents greatly influenced their adhesion ability for the bacteria. The maximum adhesion capacity of Ultisol from Guangzhou for E. coli, P. fluorescens, and B. subtilis were 609.3, 1113.9, and 2169.2 mg g(-1), respectively. The values were 434.7, 837.5, and 2067.9 mg g(-1) for Oxisol and 134, 632.3, and 408.5 mg g(-1) for Alfisol. EPS removal decreased the adhesion of the bacteria in variable charge soils and thus increased their mobility in the soils. However, EPS removal did not greatly alter the electrokinetic properties of bacterial cells. There was significant (p > 0.05) difference in the rates of deprotonation between the different bacteria species. The deprotonation rates were 53.8, 71.7, and 5.6% for native P. fluorescens, B. subtilis, and E. coli, and 22.4, 63.9, and 6.5% for the EPS-free bacteria, respectively. Therefore, bacterial mobility in variable charge soils is greatly influenced by the concentration of EPS and CEC as well as Fe2O3 contents of the soils.