Streptococcus oralis supports Veillonella atypica in anaerobic saliva-fed biofilms

Objectives: to examine the ability of Streptooccus oralis 34 (So) to support growth of Veillonella atypica PK1910 (Va) in anaerobic biofilms using flowing saliva as the sole carbon/nitrogen source.

Methods:  So and Va were grown overnight anaerobically in, respectively, BHI and Veillonella broth.  Cultures were washed twice in sterile 25% saliva, resuspended to 0.05 OD₆₀₀ and injected into microscopy flowcells.  After 4 and 18 hours of anaerobic growth on flowing 25% saliva, biofilm biomass was determined by confocal microscopy, and lactic acid concentration was determined in the flowcell effluent using a fluorometric kit.

Results: Between 4 and 18 hours, So monoculture biomass increased 42-fold whereas Va monoculture biomass increased only 3-fold.  In coculture, So biomass increased 64-fold, while Va biomass increased 16-fold.  Lactic acid concentration in the 25% saliva input was 59 然.  In the flowcell effluent of the monoculture So biofilm, the lactic acid concentration after 4 hours growth was 55 然 and, after 18 hours growth, it rose to 99 然.  In the effluent from the monoculture Va biofilm, the lactic acid concentration was 38 然 after 4 hours and 44 然 after 18 hours.  In the coculture biofilm, the effluent lactic acid concentration was 55 然 at 4 hours and 58 然 at 18 hours.

Conclusion:  Under these nutrient-poor conditions, So biofilm grows well with a resultant increase in lactic acid concentration.  Va biofilm grows poorly and is limited by the organic acid concentration in saliva.  When the organisms are grown together, lactic acid supplied by So supports a Va biomass 5-fold higher than that reached in monoculture.  Saliva suffices as the sole carbon/nitrogen source for So to support Va growth.  This research is supported by NIDCR IRP.