The ComEA/ComEC Operon is Critical for Nitrosative Stress Tolerance by an Oral Commensal

Oral commensal streptococci play a large role in mediating microbial homeostasis. Our prior work has demonstrated that hydrogen peroxide (H2O2) produced by oral commensal streptococci can react with salivary nitrite (NO2) and generate peroxynitrite (ONOO-), a potent antimicrobial. We have shown that the combinatorial antimicrobial effects of NO2 and H2O2 produced from the commensal Streptococcus parasanguinis inhibit the colonization and pathogenesis of oral pathogens to promote homeostasis. Remarkably, S. parasanguinis is highly resistant to NO2 and ONOO-. However, it remains unclear how S. parasanguinis tolerates nitrosative stress. The goal of this study was to identify mechanisms used by S. parasanguinis to resist NO2-mediated nitrosative stress. Transcriptomics analysis revealed that the DNA uptake gene, comEA was upregulated during growth on 2 mM NaNO2. Further, loss of the ComEA/ComEC DNA uptake locus resulted in increased sensitivity to peroxynitrite and a decrease in biofilm development, intracellular nitrite transport, H2O2 production, and was defective for colonization in a Drosophila melanogaster colonization model. In summary, our data show that the ComEA/EC DNA uptake operon is critical for key aspects of S. parasanguinis physiology and potentially impacts S. parasanguinis's ability to colonize and modulate homeostasis in the oral cavity.