Gram-negative synthase-dependent exopolysaccharide biosynthetic machines

Bacteria predominantly exist as matrix embedded communities of cells called biofilms. The biofilm matrix is made up of a variety of self-produced extracellular components including DNA, proteins, and exopolysaccharides. Bacterial exopolysaccharides have been implicated in surface adhesion, resistance to antibiotics, and protection from host immune systems. Herein we review the structure and function of the proteins involved in the production of the Gram-negative synthase-dependent exopolysaccharides: alginate, poly-beta(1,6)-N-acetyl-D-glucosamine (PNAG), cellulose, and the Pel polysaccharide. We highlight the similarities and differences that exist at the molecular level in these synthase systems.