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Cell Microbiol. 2019 Dec 24:e13154. doi: 10.1111/cmi.13154. [Epub ahead of print]

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

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Asia-Pacific Centre for Animal Health, Melbourne Veterinary School, The University of Melbourne, Parkville, Australia.
Metabolomics Australia, Bio21 Institute of Molecular Science and Biotechnology, The University of Melbourne, Parkville, Australia.
Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity, The University of Melbourne, Melbourne, Australia.


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.


Coxiella burnetii; NADP(H) metabolism; oxidative stress; short chain dehydrogenase


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