Direct measurements of interactive forces on the components of biofilm using atomic force microscopy

Abstract

Sulphate-reducing bacteria (SRB) are the predominant colonizers on metals surfaces that induce biofilm formation which subsequently gives rise to biocorrosion and biofouling problems in many industrial systems. In order to better understand the mechanism of biofilm adhesion onto metal substrates, it is necessary to investigate the force interactions on the biofilm. In this study, we report on the use of atomic force microscopy to directly measure the interactive forces between a silicon nitride tip and various components of the biofilm, formed by two sulphate-reducing bacteria (Desulfovibrio desulfuricans and a local marine isolate), in the nano-newton (nN) force range. A mono-species bacterial biofilm was formed by immersing a polished stainless steel AISI 316 into enriched artificial seawater with sulphate-reducing bacteria for 14 days. Five locations on the heterogeneous biofilm were selected: (i) on the bacteria cell, (ii) at the cell periphery, (iii) on the deposit, (iv) at the deposit periphery, and (v) on the substratum. The interactive force on the bare metal was also measured. When the interactive forces at these locations were compared, significantly higher force at the cell surface was measured than that on the deposit (P <0.05). The force on the cell was the same as that at the cell periphery, while the force on the deposit was significantly lower than that at the deposit periphery. The adhesion force on the marine isolate cell was much higher than that on the cell of D. desulfuricans. Compared to the bare metal, the surface after the biofilm formation was more adhesive. These data indicate that the bacterial species influence the biofilm adhesion, and the biofilm formed attracts more substances which subsequently adsorb onto the surface. The difference in interactive forces on the various components of biofilm is possibly due to the distribution of extracellular polymeric substances.