Bacteria and biofilms under the influence of shear

In our attempts to improve the biofilm formation for productive bacteria (here the gram-negative seawater bacterium Paracoccus seriniphilus), we focus on the attachment of single bacteria to a solid surface as the first step of the biofilm formation process. Beside adhesion forces and elasticity of the bacteria, we investigate the minimal detachment forces due to lateral shear forces.

In order to investigate the influence of shear forces on already adhered bacteria in the laboratory, the Lateral Force Microscopy(LFM) was used first.The tip is moved laterally towards the adherent cell with different lateral forces until the cell detaches and thus the force required to shear the cell is determined.

By applying LFM, we found a correlation between the applied force and the number of moved bacteria as well as between the number of detached bacteria and the surface energy of the substrate. Further, any structuring of the substrate hinders the detachment substantially [1]. In agreement with the vertical adhesion forces, the bacteria are harder to detach at pH 4 than at pH 7.

In order to get closer to reality, the next step is to examine the (lateral) scanning force microscopic measurements under the influence of a flowing liquid and compare them with the LFM measurements. In combination with digital holography and proteome analysis, a better understanding of biofilm formation under the influence of a flowing liquid is to be achieved.

[1] K. Huttenlochner, N. Davoudi, C. Schlegel, M. Bohley, C. Müller-Renno, J. C. Aurich, R. Ulber, and C. Ziegle "Paracoccus seriniphilus adhered on surfaces: Resistance of a seawater bacterium against shear forces under the influence of roughness, surface energy, and zeta potential of the surfaces." Biointerphases 13.5 (2018)