biofilms are exceedingly difficult to eradicate once established. This resilience is facilitated, in part, by the secretion of polysaccharides that contribute to biofilm structural integrity. The cationic exopolysaccharide PEL plays an important role in disease pathogenesis; however, the mechanisms underlying its biosynthesis are poorly understood. In this work, we identify the
operon in more than 125 proteobacteria, demonstrating that its distribution was previously underestimated. We show that the essential outer membrane-anchored protein PelC forms a 12-subunit ring with an electronegative surface that we propose guides PEL toward the membrane-embedded secretion channel. Our work provides insight into a widespread outer membrane infrastructure unobserved in any other currently identified polysaccharide biosynthetic apparatus.