Porphyromonas gingivalis, a major periodontal pathogen, forms biofilm with other oral bacteria such as streptococci. Here, by using shotgun proteomics, we examined the molecular basis of mixed-biofilm formation by P. gingivalis with Streptococcus oralis. We identified a total of 593 bacterial proteins in the biofilm. Compared to the expression profile in the P. gingivalis monobiofilm, the expression of three proteins was induced and that of 31 proteins was suppressed in the mixed biofilm. Additionally, the expression of two S. oralis proteins was increased, while that of two proteins was decreased in the mixed biofilm, as compared to its monotypic profile. mRNA expression analysis of selected genes using a quantitative reverse transcription polymerase chain reaction confirmed the proteomics data, which included overexpression of P. gingivalis FimA and S. oralis glyceraldehyde-3-phosphate dehydrogenase in association with the biofilm. The results also indicated that S. oralis regulates the transcriptional activity of P. gingivalis luxS to influence autoinducer-2-dependent signaling. These findings suggest that several functional molecules are involved in biofilm formation between P. gingivalis and S. oralis.
Keywords: Porphyromonas gingivalis; Streptococcus oralis; biofilm; interaction; microbiology; quantitative RT-PCR; shotgun proteomics.