As these results suggested a role for redox control of virulence genes, we tested the hypothesis that host reactive oxygen or nitrogen species may be sensed by the bacteria during infection to activate actA. However, growth of the suicide mutant was not rescued in BMMs lacking inducible nitric oxide synthase (NOS2-/-) or NADPH oxidase (NOX2-/-) (S3 Fig). Here, CYBB is linked to infection.