FIG 3.
Development of functionalized amyloid-dependent biofilms in Gram-negative and Gram-positive bacteria. (A) In E. coli, the major curli protein CsgA is engineered by fusing variable tags at its C terminus. Once in the extracellular medium, the fusion protein self-assembles into functional amyloid nanofibers. It is possible to obtain multifunctional biofilms by expressing engineered CsgA proteins under the control of different inducible promoters. The addition of measured concentrations of inducer molecules allows the expression and production of curli fibers containing precise multiple designed functions as a result of random extracellular self-assembly of CsgA monomers. (B) In the case of S. aureus, variable tags fused to the C-terminal part of the B domain of Bap could allow the formation of engineered Bap fibers. Since the B domain of Bap (amino acids 362 to 819) is sufficient to bestow multicellular behavior, it could be possible to express engineered Bap B-domain proteins under the control of an inducible promoter. The property of Bap to reversibly form amyloids according to pH and Ca2+ levels in the medium could be used as an external way to control the formation or disruption of functionalized biofilms.