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Response of Pseudomonas aeruginosa to the Innate Immune System-Derived Oxidants Hypochlorous Acid and Hypothiocyanous Acid.

ABSTRACT: Pseudomonas aeruginosa is a significant nosocomial pathogen and is associated with lung infections in cystic fibrosis (CF). Once established, P. aeruginosa infections persist and are rarely eradicated despite host immune cells producing antimicrobial oxidants, including hypochlorous acid (HOCl) and hypothiocyanous acid (HOSCN). There is limited knowledge as to how P. aeruginosa senses, responds to, and protects itself against HOCl and HOSCN and the contribution of such responses to its success as a CF pathogen. To investigate the P. aeruginosa response to these oxidants, we screened 707 transposon mutants, with mutations in regulatory genes, for altered growth following HOCl exposure. We identified regulators of antibiotic resistance, methionine biosynthesis, catabolite repression, and PA14_07340, the homologue of the Escherichia coli HOCl-sensor RclR (30% identical), which are required for protection against HOCl. We have shown that RclR (PA14_07340) protects specifically against HOCl and HOSCN stress and responds to both oxidants by upregulating the expression of a putative peroxiredoxin, rclX (PA14_07355). Transcriptional analysis revealed that while there was specificity in the 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 3 secretion system, sulfur and taurine transport, and the MexEF-OprN efflux pump. RclR coordinates part of the response to both oxidants, including upregulation of pyocyanin biosynthesis genes, and, in the presence of HOSCN, downregulation of chaperone genes. These data indicate that the P. aeruginosa response to HOCl and HOSCN is multifaceted, with RclR playing an essential role.IMPORTANCE The bacterial pathogen Pseudomonas aeruginosa causes devastating infections in immunocompromised hosts, including chronic lung infections in cystic fibrosis patients. To combat infection, the host's immune system produces the antimicrobial oxidants hypochlorous acid (HOCl) and hypothiocyanous acid (HOSCN). Little is known about how P. aeruginosa responds to and survives attack from these oxidants. To address this, we carried out two approaches: a mutant screen and transcriptional study. We identified the P. aeruginosa transcriptional regulator, RclR, which responds specifically to HOCl and HOSCN stress and is essential for protection against both oxidants. We uncovered a link between the P. aeruginosa transcriptional response to these oxidants and physiological processes associated with pathogenicity, including antibiotic resistance and the type 3 secretion system.

SUBMITTER: Farrant KV

PROVIDER: S-EPMC7950407 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description: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.

Project description:Antimicrobial resistance is a continuously increasing threat that severely compromises our antibiotic arsenal and causes thousands of deaths due to hospital-acquired infections by pathogens such as Pseudomonas aeruginosa, situation further aggravated by the limited development of new antibiotics. Thus, alternative strategies such as those targeting bacterial resistance mechanisms, virulence or potentiating the activity of our immune system resources are urgently needed. We have recently shown that mutations simultaneously causing the peptidoglycan recycling blockage and the β-lactamase AmpC overexpression impair the virulence of P.aeruginosa. These findings suggested that peptidoglycan metabolism might be a good target not only for fighting antibiotic resistance, but also for the attenuation of virulence and/or potentiation of our innate immune weapons. Here we analyzed the activity of the innate immune elements peptidoglycan recognition proteins (PGRPs) and lysozyme against P. aeruginosa. We show that while lysozyme and PGRPs have a very modest basal effect over P. aeruginosa, their bactericidal activity is dramatically increased in the presence of subinhibitory concentrations of the permeabilizing agent colistin. We also show that the P. aeruginosa lysozyme inhibitors seem to play a very residual protective role even in permeabilizing conditions. In contrast, we demonstrate that, once the permeability barrier is overpassed, the activity of lysozyme and PGRPs is dramatically enhanced when inhibiting key peptidoglycan recycling components (such as the 3 AmpDs, AmpG or NagZ), indicating a decisive protective role for cell-wall recycling and that direct peptidoglycan-binding supports, at least partially, the activity of these enzymes. Finally, we show that recycling blockade when occurring simultaneously with AmpC overexpression determines a further decrease in the resistance against PGRP2 and lysozyme, linked to quantitative changes in the cell-wall. Thus, our results help to delineate new strategies against P. aeruginosa infections, simultaneously targeting β-lactam resistance, cell-wall metabolism and virulence, ultimately enhancing the activity of our innate immune weapons.

Project description:To combat infections, the mammalian host limits availability of essential transition metals such as iron (Fe), zinc (Zn), and manganese (Mn) in a strategy termed "nutritional immunity." The innate immune protein calprotectin (CP) contributes to nutritional immunity by sequestering these metals to exert antimicrobial activity against a broad range of microbial pathogens. One such pathogen is Pseudomonas aeruginosa, which causes opportunistic infections in vulnerable populations, including individuals with cystic fibrosis. CP was previously shown to withhold Fe(II) and Zn(II) from P. aeruginosa and induce Fe and Zn starvation responses in this pathogen. In this work, we performed quantitative, label-free proteomics to further elucidate how CP impacts metal homeostasis pathways in P. aeruginosa. We report that CP induces an incomplete Fe starvation response, as many Fe-containing proteins that are repressed by Fe limitation are not affected by CP treatment. The Zn starvation response elicited by CP seems to be more complete than the Fe starvation response and includes increases in Zn transporters and Zn-independent proteins. CP also induces the expression of membrane-modifying proteins, and metal depletion studies indicate this response results from the sequestration of multiple metals. Moreover, the increased expression of membrane-modifying enzymes upon CP treatment correlates with increased tolerance to polymyxin B. Thus, the response of P. aeruginosa to CP treatment includes both single- and multimetal starvation responses and includes many factors related to virulence potential, broadening our understanding of this pathogen's interaction with the host. IMPORTANCE Transition metal nutrients are critical for growth and infection by all pathogens, and the innate immune system withholds these metals from pathogens to limit their growth in a strategy termed "nutritional immunity." While multimetal depletion by the host is appreciated, the majority of studies have focused on individual metals. Here, we use the innate immune protein calprotectin (CP), which complexes with several metals, including iron (Fe), zinc (Zn), and manganese (Mn), and the opportunistic pathogen Pseudomonas aeruginosa to investigate multimetal starvation. Using an unbiased label-free proteomics approach, we demonstrate that multimetal withholding by CP induces a regulatory response that is not merely additive of individual metal starvation responses, including the induction of lipid A modification proteins.

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Response of Pseudomonas aeruginosa to the Innate Immune System-Derived Oxidants Hypochlorous Acid and Hypothiocyanous Acid.

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