The Mycoplasma genitalium MG_454 Gene Product Resists Killing by Organic Hydroperoxides

Mycoplasma genitalium is the smallest self-replicating organism and a successful human pathogen associated with a range of genitourinary maladies. As a consequence of its restricted genome size, genes that are highly conserved in other bacteria are absent inM. genitalium . Significantly, genes that encode antioxidants like superoxide dismutase and catalase-peroxidase are lacking. Nevertheless, comparative genomics has revealed that MG_454 ofM. genitalium encodes a protein with putative function as an organic hydroperoxide reductase (Ohr). In this study, we found that anM. genitalium transposon mutant that lacks expression of MG_454 was sensitive to killing byt -butyl hydroperoxide and cumene hydroperoxide. To understand whether this sensitivity to hydroperoxides was linked to MG_454, we cloned this gene behind an arabinose-induciblePBAD promoter in plasmid pHERD20T and transformed this construct (pHERDMG454) into aPseudomonas aeruginosa strain having deletion in itsohr gene (ohr mutant) and showing sensitivity to organic hydroperoxides. TheP. aeruginosa ohr mutant harboring pHERDMG454, when induced with arabinose, was able to reverse its sensitivity to organic hydroperoxides, thus supporting the notion that the product of MG_454 resists organic hydroperoxides inM. genitalium . Surprisingly, real-time reverse transcription-PCR showed that expression of MG_454 inM. genitalium was not elevated in response to oxidative stress but was elevated in response to physical stresses, like salt (NaCl) and heat. Although failure of MG_454 to respond to oxidative stress inM. genitalium implies the absence of a known oxidative stress response regulator in the genome ofM. genitalium , elevated expression of MG_454 due to physical stress suggests its control by an unidentified regulator.