Autoinducer-2 from novel Veillonella tobetsuensis Influences on Oral Biofilm

Objective: Previously, 5 species, V. atypica, V. denticariosi, V. dispar, V. parvula and V. rogosae have been known as oral Veillonella. It is suggested that oral Veillonella has important roles to form oral biofilm as early colonizer, but these details including cell-cell communication have not been clarified. Recently, V. tobetsuensis has been established as a novel oral Veillonella species in our laboratory. Then our previous study demonstrated that the largest amount of biofilm was formed by Streptococcus gordonii as initial colonizer with V. tobetsuensis. In the present study, to determine the interactions between S. gordonii and V. tobetsuensis, biofilms formed by these two species were studied with culture supernatant from V. tobetsuensis. Also Autoinducer-2 (AI-2: a family of inter-convertible cell-cell signal molecules) activity in the supernatant was examined. 

Method: To form the biofilm, the wire method was used. The supernatant from V. tobetsuensis were prepared at late growth phase. After biofilms were formed by S. gordonii on the wires for 1 day, these wires were inserted into test tubes containing the supernatant from V. tobetsuensis. Then, biofilms on the wires were incubated for 6 days. Finally, genomic DNAs were extracted from these biofilms and planktonic cells to quantify their formation. Also, activity of AI-2 in the supernatants was tested by a previously described luminescence assay with Vibrio harveyi BB170. 

Result: The supernatant from V. tobetsuensis induced inhibition in the biofilm formed by S. gordonii (vs control, p< 0.01). Also, based upon AI-2 assay, V. tobetsuensis expressed higher activity of AI-2 than control strain (p< 0.01). 

Conclusion: The present study suggest that AI-2 or AI-2 like substances produced by V. tobetsuensis inhibit the biofilm formed by S. gordonii and bacterial cells of V. tobetsuensis has important roles to promote the growth of the biofilm formed by S. gordonii.