Arginine deiminase inhibits surface-attached growth of Porphyromonas gingivalis

Objective: Using a novel screening method, we recently isolated an extracellular arginine deiminase (ADI) produced by a clinical isolate, Streptococcus intermedius, and found that this protein modulates surface attached growth (biofilm formation) by the periodontal pathogen Porphyromonas gingivalis.  The aim of this study was to determine if key factors (cell surface adhesons) involved in P. gingivalis biofilm formation are affected at the level of transcription by exposure to ADI.

Method: Biochemical methods were used to purify ADI from culture supernatants of S. intermedius. Microtiter dish biofilm assays were used to assess the affect of ADI on biofilm formation.  Total RNA was purified from P. gingivalis stationary phase cells that were exposed to ADI.  RNA was then evaluated for differential expression of genes encoding cell surface adhesons, using quantitative RT-PCR.

Result: ADI was shown to modulate P. gingivalis biofilm formation, specifically through the down-regulation of gene expression of the major and minor fimbriae, fimA and mfa1 respectively, both of which are required for proper biofilm formation.  Quantitative RT-PCR analysis showed a reduction of ~60% and ~50% of fimA (C_t 0.41± 0.2, p-value 0.006) and mfa1 (C_t 0.50 ± 0.2, p-value 0.011) in cells exposed to ADI when compared to untreated controls.

Conclusion: The observation that ADI can be released from the bacterial cell and act as effector proteins between different genera of prokaryotes is a major breakthrough in our understanding of the nature of inter-bacterial signaling molecules and of biofilm-mediated diseases.  Ultimately, this will advance the long-term goal to provide a basic understanding of the communication mechanisms that control colonization and out-growth of P. gingivalis.