Wild type Xf produces pitmembrane-
degrading enzymes thought to aid movement
into neighboring xylem vessels. It is plausible that expression
of these enzymes is DSF-dependent. If so, a DSF
mutant might densely populate xylem vessels, causing
enhanced symptoms because it is unable to traverse the
pit membrane [55]. Fastidium exopolysaccharide is an
important virulence factor for Xf. Bacteria attach to xylem
vessels in the absence of the exopolysaccharide, while
matrix-encased bacteria appear mainly in densely colonized
vessels. Leite and co-workers proposed an adhesion
model in which cell surface-exposed thiol groups associated
with membrane features, impart a net negative cell
surface charge, promoting divalent ion bridging for bacteria-
to-bacteria and bacteria-to-host cell adhesion [56].
The same group found that artificial media based on
xylem chemistry stimulates Xf biofilm formation
membrane