A unique bacterial secretion machinery with multiple secretion centers

Abstract

Significance The newly described type IX secretion systems (T9SSs) translocate virulence factors and can mediate specialized gliding motility among bacterial pathogens of the Fibrobacteres–Chlorobi–Bacterioidetes superphylum. We visualized the spatial organization of the T9SS in its native context in the Porphorymonas gingivalis cell by cryoelectron tomography. The T9SS exhibits distinct symmetries across the bacterial cell envelope: a cytoplasmic complex requiring PorL and PorM for assembly exhibits 12-fold symmetry; a periplasmic complex composed of PorM exhibits 18-fold symmetry and attaches to a PorKN ring near the outer membrane; and eight Sov translocons are arranged with 8-fold symmetry at the cell surface. The T9SS is the largest of the known bacterial secretion systems and evidently arranges as multiple, independently functioning translocation motors.