Characterization of extracellular polymeric matrix, and treatment of Fusobacterium nucleatum and Porphyromonas gingivalis biofilms with DNase I and proteinase K

BACKGROUND Biofilms are organized communities of microorganisms embedded in a self-produced extracellular polymeric matrix (EPM), often with great phylogenetic variety. Bacteria in the subgingival biofilm are key factors that cause periodontal diseases; among these are the Gram-negative bacteria Fusobacterium nucleatum and Porphyromonas gingivalis. The objectives of this study were to characterize the major components of the EPM and to test the effect of deoxyribonuclease I (DNase I) and proteinase K. METHODS F. nucleatum and P. gingivalis bacterial cells were grown in dynamic and static biofilm models. The effects of DNase I and proteinase K enzymes on the major components of the EPM were tested during biofilm formation and on mature biofilm. Confocal laser scanning microscopy was used in observing biofilm structure. RESULTS Proteins and carbohydrates were the major components of the biofilm matrix, and extracellular DNA (eDNA) was also present. DNase I and proteinase K enzymes had little effect on biofilms in the conditions used. In the flow cell, F. nucleatum was able to grow in partially oxygenated conditions while P. gingivalis failed to form biofilm alone in similar conditions. F. nucleatum supported the growth of P. gingivalis when they were grown together as dual species biofilm. CONCLUSION DNase I and proteinase K had little effect on the biofilm matrix in the conditions used. F. nucleatum formed biofilm easily and supported the growth of P. gingivalis, which preferred anaerobic conditions.