Fusobacterium nucleatum apoptosis-inducing outer membrane protein

The periodontal pathogen Fusobacterium nucleatum induces apoptosis in lymphocytes. We previously identified the autotransporter protein Fap2 in F. nucleatum strain PK1594 that induced apoptosis in lymphocytes when expressed in Escherichia coli. In this study, we identified protein homologs of Fap2 in the transformable F. nucleatum strain ATCC 23726, to determine their role in the induction of apoptosis in lymphocytes. We used a new gene-inactivation vector conferring thiamphenicol resistance (pHS31) to construct a mutant deficient in one of the homologs, aim1. Transcriptional analyses demonstrated disruption of aim1 expression, and phenotypic analyses revealed a 41% decrease in the ability of the mutant to induce apoptosis in Jurkat cells, as compared with the parental strain. These studies demonstrate, in the native host cell background, the contribution of aim1 to F. nucleatum induction of apoptosis and, to the best of our knowledge, represent the first report of a genetically defined and phenotypically characterized mutation in F. nucleatum.