Phagocytic superoxide specifically damages an extracytoplasmic target to inhibit or kill Salmonella.
BACKGROUND
The phagocytic oxidative burst is a primary effector of innate immunity that protects against bacterial infection. However, the mechanism by which reactive oxygen species (ROS) kill or inhibit bacteria is not known. It is often assumed that DNA is a primary target of oxidative damage, consistent with known effects of endogenously produced ROS in the bacterial cytoplasm. But most studies fail to distinguish between effects of host derived ROS versus damage caused by endogenous bacterial sources. We took advantage of both the ability of Salmonella enterica serovar Typhimurium to survive in macrophages and the genetic tractability of the system to test the hypothesis that phagocytic superoxide damages cytoplasmic targets including DNA.


RESULTS
SodCI is a periplasmic Cu-Zn superoxide dismutase (SOD) that contributes to the survival of Salmonella Typhimurium in macrophages. Through competitive virulence assays, we asked if sodCI has a genetic interaction with various cytoplasmic systems. We found that SodCI acts independently of cytoplasmic SODs, SodA and SodB. In addition, SodCI acts independently of the base excision repair system and RuvAB, involved in DNA repair. Although sodCI did show genetic interaction with recA, this was apparently independent of recombination and is presumably due to the pleiotropic effects of a recA mutation.


CONCLUSIONS
Taken together, these results suggest that bacterial inhibition by phagocytic superoxide is primarily the result of damage to an extracytoplasmic target.
Craig
Maureen
M
Department of Microbiology, University of Illinois, Urbana, Illinois, USA.
Slauch
James M
JM
D000818:Animals; D004260:DNA Repair; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008264:Macrophages / Q000166:cytology / Q000382:microbiology / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D052247:Nitric Oxide Synthase Type II / Q000235:genetics / Q000378:metabolism; D010586:Phagocytes / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D011938:Rec A Recombinases / Q000235:genetics / Q000378:metabolism; D011995:Recombination, Genetic; D016897:Respiratory Burst / Q000502:physiology*; D012486:Salmonella typhimurium / Q000378:metabolism* / Q000472:pathogenicity; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*
D018398:Homeodomain Proteins; D017382:Reactive Oxygen Species; D013481:Superoxides; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D013482:Superoxide Dismutase; D011938:Rec A Recombinases