The ECPs can mediate both cohesion and adhesion of cells, and play a vital role in maintaining structural integrity of microbial matrix. On the other hand, the metabolic blocking of exopolysaccharides synthesis would prevent microbial aggregation (Schmidt and Ahring, 1994; Cammarota and Sant'Anna, 1998). It had been reported that ECPs could change the surface negative charge of the bacteria, and thereby bridge two neighboring cells physically to each other, and with other inert particulate matters (Shen et al., 1993; Schmidt and Ahring, 1994, 1996). Chen and Lun (1993) observed that increasing the organic loading rate resulted in significant growth of Methanosarcina which secreted much more ECPs to form larger clumps, and subsequently Methanothrix tended to fill in the Methanosarcina clumps.
1DLVO theory accounts for the interaction between charged colloidal particles. It is based on the sum of a van der Waals attractive potential and a screened electrostatic potential arising from the "double layer" potential screened by ions in solution.
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