The role of microbial surface properties and extracellular polymer in Lactococcus Lactis aggregation

Microbial adhesion to an interface is known to have an important role in a wide variety of situations. In this study, we examine the effect of the surface physicochemical properties and extracellular polymers (ECP) of a lactic bacterium on microbial aggregation. Lactococcus lactis JCM 5805 was used in the current experiments to investigate the factors that control microbial aggregation. To this aim, we measured the electrophoretic mobility and contact angle of L. lactis. As a result, L. lactis was found to be a negatively charged and hydrophilic bacterium. The microbial aggregation was investigated using DLVO (Derjaguin, Landau, Verwey and Overbeek) theory. The percent aggregates of washed cells increased slightly with increasing ionic strength of the cell suspension. This tendency agreed with the prediction of the DLVO theory. By contrast, when the ECP was present in suspensions of intact cells or washed cells, the ECP was found to promote the aggregation of the microbial cells in the low ionic strength region due to an attractive bridging force. The percent aggregates of microbial cell decreased with increasing the ionic strength due to the repulsive steric or overlap forces between polymer-covered surfaces.