Elucidation of Microbial Adhesion to Solid Surface

Abstract

Microbial adhesion to solid surface is known to play an important role in a wide variety of situations. In this study, the early stage of microbial adhesion to solid surface was investigated using the lactic acid bacterium. Microbial cells were washed using the sterile NaCl aqueous solution to remove the extracellular polymeric substances (EPS). The washed and intact cells were used for the experiments. Two types of beads were used as support materials: untreated silica (NTsilica) and AmP-silica with amino groups. The surface propeties of NT-silica and AmP-silica are negative/hydrophilic and positive/hydrophilic at the neutral pH, respectively. The surface potential and surface tension of microbial cells were analyzed by the measurements of electrophoretic mobility and contact angle. The percentage of cells adhering to support materials was calculated using the absorbance of microbial suspension before and after mixing. As a result, the percentage of cells adhering to AmP-silica was higher than to NT-silica. The percentage of cells adhering to AmP-silica decreased with an increase in the ionic strength. In contrast, the result of NT-silica was a tendency opposite to that of AmP-silica. These results could be explained by the extended DLVO theory using measured physico-chemical properties. Moreover, although there were slightly differences in the physico-chemical properties between washed and intact cells, the percentage of intact cells adhering was higher than that of washed cells. This result indicated that the EPS promoted the adhesion of the microbial cell to solid surface. Furthermore, the system to measure the adhesion force between the microbial cell and solid surface was constructed. As a result, it was found that the adhesion forces of the cell to slide glass at the ionic strength 5 mM was ca 3.4 pN.