Dentilisin involvement in coaggregation between Treponema denticola and Tannerella forsythia

Periodontitis arises from a biofilm consisting of gram-negative anaerobic rods and spirochetes. Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia, termed the Red complex, have been co-isolated with high frequency from chronic periodontitis lesions, and these microorganisms are thought to be major pathogens of the disease. Coaggregation is an important strategy in the colonization of dental plaque biofilm by these bacteria. In the present study, we investigated the coaggregation of T. denticola strains with T. forsythia ATCC 43037 by use of visual grading or spectrophotometry. T. denticola ATCC 35405 coaggregated with T. forsythia, reaching a plateau at approximately 60 min. This coaggregation was inhibited by heat treatment of T. denticola ATCC 35405, but not of T. forsythia. Disaccharides such as sucrose, maltose, and lactose inhibited coaggregation by approximately 50%. The coaggregation reaction varied among T. denticola strains. There was somewhat less coaggregation between T. denticola ATCC 33520 and T. forsythia than between T. denticola ATCC 35405 and T. forsythia, although this difference was not statistically significant; T. denticola ATCC 33521 showed a trace level of coaggregation with T. forsythia. The magnitude of coaggregation among the three T. denticola strains was proportional to their dentilisin activities. Inactivation of dentilisin abolished coaggregation activity, but inactivation of the major outer sheath protein did not. In addition, phenylmethylsulfonyl fluoride did not affect coaggregation. These results indicate that dentilisin is involved indirectly in the coaggregation between T. denticola and T. forsythia, because its proteolytic activity is not required, possibly via ligand maturation.