Structure and shear strength of microbial biofilms as determined with confocal laser scanning microscopy and fluid dynamic gauging using a novel rotating disc biofilm reactor

The cohesive strength of microbial biofilms cultivated on a rotating disc has been measured using fluid dynamic gauging (FDG). The thickness of heterotrophic mixed culture biofilms was found to depend on substrate concentration and shear force at the biofilm surface during the cultivation. For high substrate concentrations and low shear forces the biofilm thickness increased to several 100 microm within 7 days. Low substrate concentration and higher shear forces yielded thin biofilms of about 100 microm thickness. Independent from cultivation conditions and thickness of the biofilms their cohesive strength ranged between 6.0 and 7.7 N m(-2). The ratio between cohesive strength measured with FDG and shear forces applied during biofilm cultivation have ranged from 200 to 1,100. Higher concentrations of iron in the cultivation media has a positive effect on the stability of the biofilms cultivated. By using the CLSM technique a stable base biofilm with a high amount of stained EPS glycoconjugates could be visualized after gauging. The thickness of the base biofilm was about 100 microm for all biofilms cultivated and was not removable under the applied shear conditions used during FDG.