Defined hydrodynamic shear stresses influence the adhesion behaviors of marine Bacillus sp on stainless steel in artificial seawater

Formation of microbial biofilm on marine structures is crucial for subsequent attachment of macro fouling species and understanding the impact of fluid conditions on formation and growth of the biofilm is essential for preventing biofouling. Here we report the effect of shear stresses generated by laminar and weakly turbulent flow on the adhesion of typical marine bacterium Bacillus sp. biofilm on stainless steel. Numerical simulation was carried out to calculate the distribution of pressure and shear stress applied on adhered bacteria. The shear stress was proportional to both the distance from the center of rotating disk and rotation speed. The stress reached 18 Pa as the flow velocity was 2.4 m/s and the rotation speed was 600 rpm. Further adhesion testing revealed that development of the bacterial biofilm in early stage was unaffected by the shear stresses. However, shear stress regulated the adherence orientations of the bacteria on the steel surface. Turbulent flow obviously shaped development of the architecture of the biofilm, as revealed by CLSM and SEM characterization. Biofilm growth patterns were clearly observed under weakly turbulent flow, however, they were not seen under laminar flow. The microcolonies assumed elongated forms, possibly triggered by exerted pressure drag force. The results give insights into possibly controlling the formation of marine biofilm on marine infrastructures for desired anti-fouling performances