SdrA, an NADP(H)‐regenerating enzyme, is crucial for Coxiella burnetii to resist oxidative stress and replicate intracellularly

SUMMARY Coxiella burnetii, the causative agent of the zoonotic disease Q fever, is a Gram‐negative bacterium that replicates inside macrophages within a highly oxidative vacuole. Screening of a transposon mutant library suggested that sdrA, which encodes a putative short‐chain dehydrogenase, is required for intracellular replication. Short‐chain dehydrogenases are NADP(H)‐dependent oxidoreductases, and SdrA contains a predicted NADP+ binding site, suggesting it may facilitate NADP(H) regeneration by C. burnetii, a key process for surviving oxidative stress. Purified recombinant 6×His‐SdrA was able to convert NADP+ to NADP(H) in vitro. Mutation to alanine of a conserved glycine residue at position 12 within the predicted NADP binding site abolished significant enzymatic activity. Complementation of the sdrA mutant (sdrA::Tn) with plasmid‐expressed SdrA restored intracellular replication to wild‐type levels, but expressing enzymatically inactive G12A_SdrA did not. The sdrA::Tn mutant was more susceptible in vitro to oxidative stress, and treating infected host cells with L‐ascorbate, an anti‐oxidant, partially rescued the intracellular growth defect of sdrA::Tn. Finally, stable isotope labelling studies demonstrated a shift in flux through metabolic pathways in sdrA::Tn consistent with the presence of increased oxidative stress, and host cells infected with sdrA::Tn had elevated levels of reactive oxygen species compared with C. burnetii NMII.