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.