Gliding Motility and Por Secretion System Genes Are Widespread among Members of the Phylum Bacteroidetes
ABSTRACTThe phylumBacteroidetesis large and diverse, with rapid gliding motility and the ability to digest macromolecules associated with many genera and species. Recently, a novel protein secretion system, the Por secretion system (PorSS), was identified in two members of the phylum, the gliding bacteriumFlavobacterium johnsoniaeand the nonmotile oral pathogenPorphyromonas gingivalis. The components of the PorSS are not similar in sequence to those of other well-studied bacterial secretion systems. TheF. johnsoniaePorSS genes are a subset of the gliding motility genes, suggesting a role for the secretion system in motility. TheF. johnsoniaePorSS is needed for assembly of the gliding motility apparatus and for secretion of a chitinase, and theP. gingivalisPorSS is involved in secretion of gingipain protease virulence factors. Comparative analysis of 37 genomes of members of the phylumBacteroidetesrevealed the widespread occurrence of gliding motility genes and PorSS genes. Genes associated with other bacterial protein secretion systems were less common. The results suggest that gliding motility is more common than previously reported. Microscopic observations confirmed that organisms previously described as nonmotile, includingCroceibacter atlanticus, “Gramella forsetii,”Paludibacter propionicigenes,Riemerella anatipestifer, andRobiginitalea biformata, exhibit gliding motility. Three genes (gldA,gldF, andgldG) that encode an apparent ATP-binding cassette transporter required forF. johnsoniaegliding were absent from two related gliding bacteria, suggesting that the transporter may not be central to gliding motility.