The response of Porphyromonas gingivalis to Treponema denticola

Porphyromonas gingivalis and Treponema denticola are often found to co-exist in the deep subgingival pockets of patients with chronic periodontitis. Studies have shown that they display synergism in growth promotion and nutrient acquisition. Furthermore, co-infections of T. denticola and P. gingivalis exhibit a synergistic pathogenesis in animal models of infection. Objectives: In this study, we aimed to elucidate the effect of co-culture with T. denticola on P. gingivalis gene expression. Methods: Mono- and co-cultures were grown in continuous culture and the transcriptomes of 6 mono- and 6 co-culture samples were compared using hybridization to in-house designed microarray chips. Results: 135 P. gingivalis genes were significantly differentially regulated (p-value < 0.05, fold change ≥ 1.4) in co-culture with T. denticola. While most of the genes coding enzymes involved in metabolism remain unaltered, P. gingivalis genes encoding putative enzymes involved in thiamine biosynthesis and transport were significantly upregulated during co-culture suggesting possible thiamine competition with T. denticola which is unable to synthesize thiamine relying on exogenous thiamine to grow. Furthermore, there was decreased expression of genes encoding enzymes involved in heme/iron uptake and lipid metabolism. Differential expression of genes coding a two-component signal transduction system, several transposable elements, virulence factors and cell surface proteins awaits further investigation. Conclusion: These data indicate that P. gingivalis modifies its metabolism and physiology in the presence of T. denticola. Possible competition and cooperation between P. gingivalis and T. denticola may have relevance to the progression and severity of periodontal disease (NHMRC 400327).