Our group is unraveling the basic mechanisms that underlie pathogenicity and commensalism in bacteria from the phylum Bacteroidetes, a phylum including common members of the intestinal and oral flora of mammals. Some of them are human pathogens, like Bacteroides fragilis, Capnocytophaga canimorsus and Porphyromonas gingivalis. Our model organism is Capnocytophaga canimorsus, a commensal of dogs mouth that causes generalized infections with a high mortality rate in humans that have been bitten, scratched or licked by a dog. We characterize the surface structures that may interact with the host and other virulence factors. We also study virulence factors encoded by Polysaccharide Utilization Loci (PUL), complex systems involving a new lipoprotein transport pathway.