Response ofPseudomonas aeruginosato the innate immune system-derived oxidants hypochlorous acid and hypothiocyanous acid

Abstract

ABSTRACTPseudomonas aeruginosais a significant nosocomial pathogen and associated with lung infections in cystic fibrosis (CF). Once established,P. aeruginosainfections persist and are rarely eradicated despite the host immune cells producing antimicrobial oxidants, including hypochlorous acid (HOCl) and hypothiocyanous acid (HOSCN). There is limited knowledge as to howP. aeruginosasenses, responds to, and survives attack from HOCl and HOSCN, and the contribution of such responses to its success as a CF pathogen. We investigated theP. aeruginosaresponse to these oxidants by screening 707 transposon mutants, with mutations in regulatory genes, for altered growth following HOCl exposure. We identified regulators involved in antibiotic resistance, methionine biosynthesis and catabolite repression, and PA14_07340, the homologue of theEscherichia coliHOCl-sensor RclR (30% identical), that were required for HOCl survival. We have shown that RclR (PA14_07340) protects specifically against HOCl and HOSCN stress, and responds to both oxidants by upregulating expression of a putative peroxiredoxin,rclX(PA14_07355). While there was specificity in the transcriptional response to HOCl (231 genes upregulated) and HOSCN (105 genes upregulated) there was considerable overlap, with 74 genes upregulated by both oxidants. These included genes encoding the type III secretion system (T3SS), sulphur and taurine transport, and the MexEF-OprN efflux pump. RclR coordinated the transcriptional response to HOCl and HOSCN, including upregulation of pyocyanin biosynthesis genes, and in response to HOSCN alone RclR downregulated chaperone genes. These data indicate that theP. aeruginosaresponse to HOCl and HOSCN is multifaceted, with RclR playing an essential role.