Bacillus licheniformis Extracellular Polymeric Substances Conditioning Layer Mediates the Bacterial Adhesion Behaviors toward Controlled Biofilm Formation

In aquatic environments, conditioning layers play a crucial role in modulating the adhesion and aggregation of planktonic bacteria, ultimately facilitating biofilm formation and the irreversible onset of biofouling. This study reports the construction of a simplified conditioning layer using extracellular polymeric substances (EPS) secreted by Bacillus licheniformis and its influence on the adherence behaviors of bacteria. The results reveal that the EPS conditioning layer remarkably inhibits the Staphylococcus aureus adherence yet promotes the aggregation of Escherichia coli. The surface of the EPS conditioning layer shows a flat morphology with the highest height of approximately 12.9 nm. The conditioning layer alters the physicochemical properties of the substrate materials on their surfaces, with water contact angles changing from 61.23° to 8.76° and the zeta potential changing from -1.0 to -25.0 mV. Despite these changes, the overall effect of the EPS conditioning layer on bacterial adhesion was found to be minimal. Further investigation on the bacterial adhesion and aggregation behaviors shows that two main components of EPS, namely, polysaccharides and bacitracin, affect the bacterial adhesion and aggregation behaviors. Bacitracin plays a predominant role in inhibiting the Staphylococcus aureus attachment, and the polysaccharides promote Escherichia coli aggregation. These findings would give inspiring insight into developing environmentally friendly efficient biological measures for combating the worldwide persisting biofouling.