In addition, microorganisms have
developed various strategies to use the easily accessible
cell surface Sia as anchors for adhesion and subsequent
infection of the cell or destruction of the acidic
protective shield by secretion of hydrolytic enzymes.Thus, apart from their ‘‘internal’’ tasks, Sia permanently
interact with the environment of cells and whole
organisms. This ‘‘battle’’ is fought in conjunction with carbohydrate moieties bearing sialic acid residues. It will
be discussed that this defense barrier has continuously
and individually been adapted to new conditions, which
may also have driven the evolution of higher organisms