Veillonella Catalase Protects the Growth of Fusobacterium nucleatum in Microaerophilic and Streptococcus gordonii-Resident Environments

The oral biofilm is a multispecies community in which antagonism and mutualism coexist among friends and foes to keep an ecological balance of community members. The pioneer colonizers, such asStreptococcus gordonii , produce H2 O2 to inhibit the growth of competitors, like the mutans streptococci, as well as strict anaerobic middle and later colonizers of the dental biofilm. Interestingly,Veillonella species, as early colonizers, physically interact (coaggregate) withS. gordonii . A putative catalase gene (catA ) is found in most sequencedVeillonella species; however, the function of this gene is unknown. In this study, we characterized the ecological function ofcatA fromVeillonella parvula PK1910 by integrating it into the only transformable strain,Veillonella atypica OK5, which iscatA negative. The strain (OK5-catA ) became more resistant to H2 O2 . Further studies demonstrated that thecatA gene expression is induced by the addition of H2 O2 or coculture withS. gordonii . Mixed-culture experiments further revealed that the transgenic OK5-catA strain not only enhanced the growth ofFusobacterium nucleatum , a strict anaerobic periodontopathogen, under microaerophilic conditions, but it also rescuedF. nucleatum from killing byS. gordonii . A potential role of catalase in veillonellae in biofilm ecology and pathogenesis is discussed here.IMPORTANCE Veillonella species, as early colonizers, can coaggregate with many bacteria, including the initial colonizerStreptococcus gordonii and periodontal pathogenFusobacterium nucleatum , during various stages of oral biofilm formation. In addition to providing binding sites for many microbes, our previous study also showed thatVeillonella produces nutrients for the survival and growth of periodontal pathogens. These findings indicate thatVeillonella plays an important “bridging” role in the development of oral biofilms and the ecology of the human oral cavity. In this study, we demonstrated that the reducing activity ofVeillonella can rescue the growth ofFusobacterium nucleatum not only under microaerophilic conditions, but also in an environment in whichStreptococcus gordonii is present. Thus, this study will provide a new insight for future studies on the mechanisms of human oral biofilm formation and the control of periodontal diseases.