Inhibition of the flocculation of bacteria by biopolymers

Bacterial flocculation is an important phenomenon in secondary waste treatment. Polymers produced by bacteria control the flocculation process. We used the bacterium Leuconostoc as a model in a study of the effect of bacterial polymers on flocculation.Leuconostoc mesenteroides is known to synthesize extracellular dextran when sucrose is used as a substrate. Dextran is not normally produced by glucose-grown cells. Sucrose-grown cells of Leuconostoc failed to flocculate, while glucose-grown cells formed visible flocs. Removal of dextran from sucrose-grown cells stimulated aggregation. Artificial polymers and clays interacted with stable suspensions of Leuconostoc to yield aggregates. The presence of large quantities of natural or artificial polymers can act to stabilize bacterial suspensions and prevent flocculation.