ROLE FOR THE SALMONELLA FLAVOHEMOGLOBIN IN PROTECTION FROM NITRIC-OXIDE

Hemoglobin homologs are being identified in an expanding number of uni cellular prokaryotic and eukaryotic organisms. Many of these hemoglobi ns are two domain proteins that possess a flavin-containing reductase in their C terminus. Determination of a function for these flavohemogl obins has been elusive. A Salmonella typhimurium strain harboring a de letion in the flavohemoglobin gene shows no difference in growth under oxidative stress conditions but displays an increased sensitivity to acidified nitrite and S-nitrosothiols, both of which produce nitric ox ide. The effect is seen aerobically or anaerobically, indicating that oxygen is not required for flavohemoglobin function. These results sug gest a role for the bacterial flavohemoglobins that is independent of oxygen metabolism and provide evidence for a bacterial route of protec tion from nitric oxide that is distinct from oxidative stress response s.