Figure 4.
Curli subunit sharing between adjacent cells, or interbacerial complementation, is made possible by the nucleation-precipitation mechanism of curli fiber assembly. A csgB mutant (or csgA+ donor strain) secretes soluble CsgA into the extracellular milieu. CsgA from a csgB mutant can polymerize on a csgA mutant (or csgB+ acceptor) that is presenting CsgB on the cell surface when grown in close proximity to one another on a plate. The left panel shows a csgB mutant streaked near a csgA mutant, and on the edge of the CsgB-expressing streak there is a Congo red staining region.