UCLA

Periodontal disease is a highly common disorder believed to be triggered by colonization of bacteria on the surface of teeth. Although the relationship between many oral bacterial species has been shown to rely on physical adherence, the intracellular consequences that arise as a result of these intimate associations are currently unknown. Fusobacterium nucleatum (F.n), a Gram-negative periodontal pathogen that has the unique capability to adhere to Gram-positive primary colonizing and Gram-negative secondary colonizing oral bacteria was chosen to assess differential gene regulation that may occur in response to a primary colonizer, Streptococcus sanguinis (S.s.). A mutant strain of F.n that lacks RadD, an outer-membrane adhesin required for adherence and recognition of Gram-positive oral streptococci, was also used to determine if RadD-dependent gene regulation in response to S.s was present. RNA was extracted from wildtype F.n. and the ΔRadD mutant alone, as well as after co-incubation with S.s., and the expression profile of twenty-four F.n. genes selected from a previous microarray study for validation was determined via Real-Time Polymerase Chain Analysis (RT-PCR). We found that of the twenty-four genes tested, seventeen showed differential regulation in wildtype F.n. in the presence of S.s., twenty were regulated in the ΔRadD mutant in response to S.s., while five exhibited transcriptional differences due to lack of RadD independent of S.s. when the expression profile of the ΔRadD mutant was compared to wildtype. Compared to wildtype F.n., six genes showed opposite regulation in the ΔRadD mutant in response S.s., indicating that there is contact-dependent gene regulation mediated by the RadD adhesin. Aside from providing an intracellular understanding of contact-dependent adherence between two prominent oral bacteria, to the best of our knowledge, this is the first discovery of expression of genes that rely on the presence of an interspecies recognition based outer membrane adhesin in a bacterial species.