Redox signaling modulates nitrite transport in a commensal Streptococcus.

Commensal streptococci modulate health and homeostasis in the oral cavity through the production of hydrogen peroxide (H2O2), a redox-active molecule with potent antimicrobial activity. Our group has previously shown that Streptococcus parasanguinis antagonizes oral and respiratory pathogens not only using H2O2, but also through the reaction of H2O2 with readily available environmental nitrite (NO2), which produces reactive nitrogen species (RNS), such as peroxynitrite (ONOO-). The production of H2O2 by oral streptococci requires the activity of pyruvate oxidase (PoxL), an enzyme that is essential for S. parasanguinis to inhibit neighboring pathogens and modulate homeostasis during polymicrobial infections. However, it remains unknown how H2O2 impacts NO2 acquisition in S. parasanguinis. In this study, we explored the role of PoxL in NO2 transport and NO2-dependent fitness and physiology in S. parasanguinis. Loss of PoxL resulted in decreased biofilm development and colonization in a Drosophila melanogaster model compared to wild-type bacteria, however, defective biofilm formation and colonization in the poxL mutant was restored by the addition of exogenous NO2. Further analysis of the poxL mutant revealed a decrease in intracellular NO2 compared to wildtype bacteria. In support of these findings, expression of the formate-nitrite transporter (Spaf_1142) was significantly decreased in the poxL mutant compared to wildtype, and also by the addition of catalase. Lastly, we observed decreases in several glycolytic proteins and a decrease in ATP production in the poxL mutant, which was increased by the addition of nitrite. Overall, this work highlights a coordinated regulatory interplay of PoxL activity and H2O2 production on NO2 transport and metabolism.