A novel shared mechanism for Bacteroidota protein transport and gliding motility

Bacteria of the phylum Bacteroidota are major human commensals and pathogens in addition to being abundant members of the wider biosphere. Bacteroidota move by gliding and they export proteins using the Type 9 Secretion System (T9SS). Here we discover that gliding motility and the T9SS share a novel mechanism of energisation in which outer membrane proteins are covalently attached by disulfide bonds to a moving internal track structure which propels them through the membrane. We determined the structure of a representative Bacteriodota mobile track by obtaining the cryoEM structure of a 3 MDa circular mini-track from Porphyromonas gingivalis . Our discoveries identify a novel mechanistic and evolutionary link between gliding motility and T9SS-dependent protein transport.