L-Arg availability affects the physiological state of porphyromonas gingivalis

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Project Summary/Abstract Many chronic inflammatory diseases, including periodontal infections, are biofilm-based pathologies mediated by indigenous microbiota persisting within complex host-associated microbial communities. Determining the environmental cues that direct the physiological state (commensal versus pathogenic state) of oral anaerobes, is fundamental to development of therapeutic strategies for periodontal diseases. Recent studies indicate that the pathogenic potential of the anaerobic bacterium Porphyromonas gingivalis is not solely dependent on its ability to colonize and proliferate within the subgingival biofilm; its physiological state and its associations within the microbial consortium are fundamental to development of pathology. The central hypothesis for this application is that the availability of L-arginine is a key signal/substrate that impacts P. gingivalis surface translocation, expression of virulence determinants, and biofilm formation. Studies have reported that the levels of arginine increase 2-fold (from ~5µM to 10µM) in gingival crevicular fluid during periodontal disease. The reason for this increase is not known but may reflect a decrease in metabolism by the microbial community, a decrease in uptake by host cells, or an increase in bacterial arginine biosynthesis. One known factor is the activity of the arginine - specific cysteine proteases (Arg-gingipains) produced by P. gingivalis, along with its carboxypeptidase that releases the terminal arginine residues from peptides produced by Arg- gingipains. Our analysis shows that both intracellular and extracellular accumulation of L-arginine has a negative impact on P. gingivalis physiology, confirming that the levels of L-arginine are monitored and controlled. Our studies have shown that under L-arginine deplete conditions, P. gingivalis down regulates expression of fimbriae, inhibiting biofilm formation; and, in contrast, addition of L-arginine boosts fimbrial expression and surface colonization. Thus, P. gingivalis adjusts its lifestyle in response to changes in extracellular L-arginine. What remains unclear is the sensing and regulatory mechanisms that control this change in physiology. The goal of this application is to determine how P. gingivalis controls extracellular and intracellular arginine concentrations and in particular the effect of changes in arginine concentration on its ability to surface translocate. Importantly, L-arginine is known to be an important modulator of the host immune response to pathogens, so we posit that there is a delicate balance between host and pathogen responses to arginine during disease progression and that P. gingivalis has evolved with the ability to sense and respond to this key amino acid as a fundamental strategy for persistence. The rationale for these studies is that identifying the signals that control colonization and the physiological state of oral pathogens will provide prime targets for the development of therapeutic strategies. Thus, the long-term objective is to determine if this mechanism of signaling can be targeted for treatment and prevention of biofilm-induced diseases in humans.