Biofilms, surface-bound communities of microbes, are economically and medically important due to their pathogenic and obstructive properties. Among the numerous strategies to prevent bacterial adhesion and subsequent biofilm formation, surface topography was recently proposed as a highly nonspecific method that does not rely on small-molecule antibacterial compounds, which promote resistance. Here, we provide a detailed investigation of how the introduction of submicrometer crevices to a surface affects attachment of Escherichia coli. These crevices reduce substrate surface area available to the cell body but increase overall surface area. We have found that, during the first 2 h, adhesion to topographic surfaces is significantly reduced compared with flat controls, but this behavior abruptly reverses to significantly increased adhesion at longer exposures. We show that this reversal coincides with bacterially induced wetting transitions and that flagellar filaments aid in adhesion to these wetted topographic surfaces. We demonstrate that flagella are able to reach into crevices, access additional surface area, and produce a dense, fibrous network. Mutants lacking flagella show comparatively reduced adhesion. By varying substrate crevice sizes, we determine the conditions under which having flagella is most advantageous for adhesion. These findings strongly indicate that, in addition to their role in swimming motility, flagella are involved in attachment and can furthermore act as structural elements, enabling bacteria to overcome unfavorable surface topographies. This work contributes insights for the future design of antifouling surfaces and for improved understanding of bacterial behavior in native, structured environments.
We thank Karen Fahrner for helpful discussions about flagella and bacterial swimming behavior, and Michael Bucaro and Wendong Wang for helpful experimental discussions. This work was par- tially funded by the Office of Naval Research under the award N00014-11-1- 0641 and by the BASF Advanced Research Initiative at Harvard University. R.S.F. is supported by the National Science Foundation (NSF) Graduate Research Fellowship Program. Part of this work was carried out through the use of the Massachusetts Institute of Technology’s Microsystems Technology Laboratories and the Center for Nanoscale Systems at Harvard University, a member of the National Nanotechnology Infrastructure Network, sup- ported by the NSF under Award ECS-0335765.