Nonspecific adherence by Actinobacillus actinouaycetemcomitans requires genes widespread in Bacteria and Archaea

The gram-negative coccobacillus, Actinobacillus actinomycetemcomitans, is t he putative agent for localized juvenile periodontitis, a particularly dest ructive form of periodontal disease in adolescents. This bacterium has also been isolated from a variety of other infections, notably endocarditis. Fr esh clinical isolates of A. actinomycetemcomitans form tenacious biofilms, a property likely to be critical for colonization of teeth and other surfac es. Here we report the identification of a locus of seven genes required fo r nonspecific adherence of A. actinomycetemcomitans to surfaces. The recent ly developed transposon IS903 phi kan was used to isolate mutants of the ro ugh clinical isolate CU1000 that are defective in tight adherence to surfac es (Tad(-)). Unlike wild-type cells, Tad- mutant cells adhere poorly to sur faces, fail to form large autoaggregates, and lack long, bundled fibrils. N ucleotide sequencing and genetic complementation analysis revealed a 6.7-kb region of the genome with seven adjacent genes (tadABCDEFG) required for t ight adherence. The predicted TadA polypeptide is similar to VirB11, an ATP ase involved in macromolecular transport. The predicted amino acid sequence s of the other Tad polypeptides indicate membrane localization but no obvio us functions. We suggest that the tad genes are involved in secretion of fa ctors required for tight adherence of A. actinomycetemcomitans. Remarkably, complete and highly conserved tad gene clusters are present in the genomes of the bubonic plague bacillus Yersinia pestis and the human and animal pa thogen Pasteurella multocida. Partial tad loci also occur in strikingly div erse Bacteria and Archaea. Our results show that the tad genes are required for tight adherence of A. actinomycetemcomitans to surfaces and are theref ore likely to be essential for colonization and pathogenesis. The occurrenc e of similar genes in a wide array of microorganisms indicates that they ha ve important functions. We propose that tad-like genes have a significant r ole in microbial colonization.