The Iron-Sulphur Cluster Biosynthesis Regulator IscR Contributes to Iron Homeostasis and Resistance to Oxidants in Pseudomonas aeruginosa

Abstract

IscR is a global transcription regulator responsible for governing various physiological processes during growth and stress responses. The IscR-mediated regulation of the Pseudomonas aeruginosa isc operon, which is involved in iron-sulphur cluster ([Fe-S]) biogenesis, was analysed. The expression of iscR was highly induced through the exposure of the bacteria to various oxidants, such as peroxides, redox-cycling drugs, intracellular iron-chelating agents, and high salts. Two putative type 1 IscR-binding sites were found around RNA polymerase recognition sites, in which IscR-promoter binding could preclude RNA polymerase from binding to the promoter and resulting in repression of the isc operon expression. An analysis of the phenotypes of mutants and cells with altered gene expression revealed the diverse physiological roles of this regulator. High-level IscR strongly inhibited anaerobic, but not aerobic, growth. iscR contributes significantly to the bacteria overall resistance to oxidative stress, as demonstrated through mutants with increased sensitivity to oxidants, such as peroxides and redox-cycling drugs. Moreover, the regulator also plays important roles in modulating intracellular iron homeostasis, potentially through sensing the levels of [Fe-S]. The increased expression of the isc operon in the mutant not only diverts iron away from the available pool but also reduces the total intracellular iron content, affecting many iron metabolism pathways leading to alterations in siderophores and haem levels. The diverse expression patterns and phenotypic changes of the mutant support the role of P. aeruginosa IscR as a global transcriptional regulator that senses [Fe-S] and directly represses or activates the transcription of genes affecting many physiological pathways.

Pseudomonas aeruginosa wound infection involves activation of its iron acquisition system in response to fascial contact

“…While activation of the siderophore pyochelin could be hypothesized to be a result of the recognition of iron limitation by P. aeruginosa , the overall gene expression pattern did not confirm this. Except for pyochelin, none of the other iron limitation-induced genes, however the iron-sulphur [Fe-S] cluster assembly genes (PA3812-PA3814, iscA , iscU , iscS ) (17) was up-regulated in our study (Fig.5C, supplemental table S1) possibly to reduce the total intracellular iron content increased due to pyochelin action. Genes encoding multidrug efflux pump MexGHI-OpmD (PA4207 mexI , PA4208 opmD ) were also activated.…”

Influence of the Hfq and Crc global regulators on the control of iron homeostasis in Pseudomonas putida

“…In E. coli , the expression of the isc genes is repressed by the IscR transcriptional regulator in response to high levels of these clusters (Schwartz et al ., ), as well as by the iron‐responsive sRNA rhyB (Desnoyers et al ., ). Interestingly, the increased expression of IscR in P. aeruginosa carrying a multicopy plasmid with iscR increases the total iron content of the cells and reduces siderophore production (Romsang et al ., ). In the present work, the mRNA levels of iscR (PP_0841) in the P. putida Hfq/Crc‐null strain were more than five‐fold higher than in the wild type strain (Supporting Information Table S3).…”

What a difference a cluster makes: The multifaceted roles of IscR in gene regulation and DNA recognition

“…4A). High level of promoter sequence conservation is found among Gram-negative bacteria, particularly pathogenic bacteria for which a number of putative IscR binding sites were recently identified [9,12,48].…”

“…P. aeruginosa iscR mutant was shown to be hypersensitive to H 2 O 2 and paraquat, due to decreased catalase A (KatA) enzyme activity [73]. More recently, it was shown that IscR regulated the P. aeruginosa isc operon under both physiological and stress conditions, conferring resistance to oxidative stress and contributing to iron homeostasis [48]. In Shigella flexneri, a facultative intracellular pathogen and the causative agent of bacterial dysentery, the expression of both suf and isc promoters increased when the pathogen was living intracellularly due to iron scarcity.…”