Figure 3.

Chen et al. (2014) created a tunable biomaterial using curli fibers, a constituent of Escherichia coli biofilms. Curli fibers are made up of CsgA subunits, which self-assemble into higher-order structures. The investigators modified CsgA with a His tag that confers metal-binding capability; when they alternated expression of modified CsgA with unmodified CsgA (based on two different small-molecule inducers), the resulting curli fibers had regions that bound gold nanoparticles alternating with regions that did not, as shown with scanning electron microscopy. Scale bar, 100 nm. AHL, Acyl-homoserine lactone. (Image courtesy of Allen Chen and Tim Lu, both at the Massachusetts Institute of Technology.)