Curli are adhesive surface fibers produced by many Enterobacteriaceae, such as Escherichia coli and Salmonella enterica. They are implicated in bacterial attachment and invasion to epithelial cells. In this study, atomic force microscopy was used to determine the effects of curli on topology and mechanical properties of live E. coli cells. Young's moduli of both curli-deficient and curli-overproducing mutants were significantly lower than that of their wild-type (WT) strain, while decay lengths of the former strains were higher than that of the latter strain. Surprisingly, topological images showed that, unlike the WT and curli-overproducing mutant, the curli-deficient mutant produced a large number of flagella-like fibers, which may explain why the strain had a lower Young's modulus than the WT. These results suggest that the mechanical properties of bacterial surfaces are greatly affected by the presence of filamentous structures such as curli and flagella.
Bibliographical noteFunding Information:
This study was supported by the grant “Scientific-Technological Co-operation (WTZ)” from the Austrian Federal Ministry of Science and Research and the Korean Ministry of Education, Science, and Technology. Y.J.O. was funded by a Marie Curie International Incoming Fellowship of the 7th European Community Framework Program. Y.C., H.K., and Y.L. were funded by the National Research Foundation (NRF) grants (#20110021114, 20120000647, and 20120000054) in Korea. Y.C. was supported by the Ewha Global Top 5 Grant 2011.