FIG 1.

Schematic model of the C. crescentus holdfast synthesis, secretion, and anchor machinery. The holdfast synthesis and polymerization machinery is comprised of proteins (PssY, PssZ, HfsEFGH, HfsJ, and HfsK) from several unlinked loci, all located in the cytoplasm or at the inner membrane of the cell. These proteins are responsible for manufacturing holdfast polysaccharide (green). The holdfast polymerases (HfsC and HfsI) and the holdfast secretion complex (HfsDAB) shuttle holdfast from the inner membrane and across to the outer membrane of the cell envelope. Holdfast polysaccharide is anchored on the cell surface by the holdfast anchor proteins (HfaABD). HfaB is located on the periplasmic side of the outer membrane, while HfaAD proteins are present on the outside.