Cytochromes <i>c</i> Constitute a Layer of Protection against Nitric Oxide but Not Nitrite

It is widely accepted that the antibacterial effects of nitrite are attributable to nitric oxide (NO) formation, suggesting a correlation of bacterial susceptibilities to these two chemicals. However, compared to E. coli , S. oneidensis is highly sensitive to nitrite but resistant to NO, implying the presence of robust NO-protective systems. Here, we show that c -type cytochromes (cytochromes c ) play a main role in protecting S. oneidensis against damages from NO but not from nitrite. In their absence, impacts of proteins that promote NO tolerance and that are targets of NO inhibition become evident. Our data thus reveal the specific activity of cytochromes c in alleviating the stress caused by NO but not nitrite.