Objectives: In this study, we aimed to elucidate the effect of co-culture with P. gingivalis on T. denticola to gain insight into the interactions between these bacteria that may have relevance to periodontal disease pathogenesis.
Methods: Mono- and co-cultures were grown in continuous culture and cell density determined using real-time PCR. The transcriptomes of 6 mono- and 6 co-culture samples were compared using hybridization to in-house designed microarray chips. Metabolomic analyses were carried out using gas chromatography mass spectroscopy and chemotaxis assays were carried out in semisolid agarose.
Results: In co-culture there was a total cell density of 7 x 109 cells mL-1 and a ratio of P. gingivalis to T. denticola of 6:1. Scanning electron microscopy revealed that these organisms co-aggregated. 210 T. denticola genes (p-value < 0.01) were significantly differentially regulated in co-culture with P. gingivalis. Notably, T. denticola genes encoding a putative glycine/Na+ symporter and both the glycine cleavage and the glycine reductase systems were up-regulated in co-culture. There was altered expression of several genes encoding putative methyl-accepting chemotaxis proteins. T. denticola exhibited a chemotactic response towards glycine. Further metabolomic profiling carried out by growing T. denticola in batch culture revealed a rapid depletion of glycine from the growth medium.
Conclusion: These data indicate that T. denticola modifies its metabolism in the presence of P. gingivalis and that glycine is important in the co-association of these species. We hypothesize that glycine released by P. gingivalis is a chemoattractant for T. denticola which can use the glycine to derive energy. (NHMRC 400327)