GSE124385
Response of Pseudomonas aeruginosa to the innate immune system-derived oxidants hypochlorous acid and hypothiocyanous acid
Purpose: The aim of this study was to determine the transcriptional response of P. aeruginosa PA14 to HOCl and HOSCN stress, and determine genes dependent on RclR (PA14_07340) regulation. Methods: PA14 WT and ?rclR exponential phase cultures were exposed to sub-lethal amounts of HOCl or HOSCN (2.2 or 0.8 mM, respectively), or untreated, and after 20 minutes of exposure, RNA was extracted and gene expression analysed by RNA-seq. Reads Per Kilobase per Million mapped reads (RPKM) were determined and the log2 fold change of the RPKM values of treated WT compared to untreated WT, or treated WT compared to treated ?rclR was calculated. Genes with a log2 fold change of >1.5 were considered upregulated and genes with a log2 fold change of <-1.5 were considered downregulated. Results: In the WT strain, HOCl exposure resulted in upregulation of 231 genes and downregulation of 20 genes, and HOSCN exposure caused upregulation of 105 genes and downregulation of 16 genes. There was considerable overlap in the transcriptional response to HOCl and HOSCN, with 74 genes being induced in response to both oxidants. Genes upregulated by HOCl and HOSCN included those involved in sulphur and taurine transport, those encoding the type 3 secretion system, the MexEF-OprN drug efflux pump, and the putative peroxiredoxin RclX (PA14_07355). Comparison of the treated WT and treated ?rclR strains revealed that in the presence of HOCl RclR upregulated 42 genes and downregulated 7 genes, and in the presence of HOSCN upregulated 132 genes and downregulated 213 genes. In the presence of both HOCl and HOSCN, RclR was required for upregulation of rclX as well as pyocyanin biosynthesis genes. In the presence of HOSCN, RclR downregulated a large number of genes, including those encoding chaperones. Conclusions: Our data have identified that the transcriptional response of P. aeruginosa to HOCl and HOSCN is multifaceted and appears to be linked to antibiotic resistance and the virulence factors pyocyanin and type 3 secretion. Determination of the regulon of the transcriptional regulator RclR after HOCl and HOSCN exposure suggests RclR has a role in coordinating the P. aeruginosa response to these oxidants. Overall design: PA14 WT and ?rclR exponential phase cultures were either untreated, exposed to 2.2 mM HOCl or 0.8 mM HOSCN for 20 minutes, in duplicate, and then RNA from the 12 samples was extracted, cDNA libraries were constructed, and RNA-seq was carried out using the Illumina NextSeq 500 system. Untreated WT samples were used as a reference to identify genes differentially expressed in the HOCl or HOSCN treated samples, and treated WT samples were used as a reference compared to treated ?rclR samples to identify RclR regulated genes.