Role of shear stress on biofilm formation of Candida krusei in a rotating disk system

In industrial conditions, biofilms formed on pipes, joints and heat exchangers are exposed to varying shear stress conditions caused by fluid flow. In this study we examined the effect of shear, created by the tangential liquid flow in a rotating disk system (RDS) on adhesion and biofilm formation of Candida krusei.C. krusei biofilms were formed on stainless steel (AISI 304 2B food grade) while being exposed to different shear stresses (from 0 to 91 N m−2) generated by two rotational speeds (350 and 800 rpm). The coupons were examined by fluorescein diacetate (FDA) at 24-h interval for 4 days.The morphology of the biofilms and the disposition of C. krusei cells in laminar and transitional flow were markedly different. The morphology of biofilm features in the transitional flow revealed the influence of hydrodynamic drag.The early stage of biofilm development resulted practically unaffected by shear stress. However, in a mature biofilm, shear stress determined the disposition of biofilm cells onto the surface. Microcolonies began to appear approximately at 48 h, at all tested shear stresses, and biofilm formation continued throughout the entire experimental period. Moreover, shape of biofilms was probably governed by the continuous applied shear stress. Finally, biofilms formed under higher shear stress differs significantly in their arrangement, as compared with those formed under lower shear conditions.