title: IscR regulation of capsular polysaccharide biosynthesis and iron-acquisition systems in Klebsiella pneumoniae CG43.
abstract: IscR, an Fe-S cluster-containing transcriptional factor, regulates genes involved in various cellular processes. In response to environmental stimuli such as oxidative stress and iron levels, IscR switches between its holo and apo forms to regulate various targets. IscR binding sequences are classified into two types: the type 1 IscR box that is specific for holo-IscR binding, and the type 2 IscR box that binds holo- and apo-IscR. Studying Klebsiella pneumoniae CG43S3, we have previously shown that iron availability regulates capsular polysaccharide (CPS) biosynthesis and iron-acquisition systems. The present study investigated whether IscR is involved in this regulation. Compared with that in CG43S3, the amount of CPS was decreased in AP001 (ΔiscR) or AP002 (iscR3CA), a CG43S3-derived strain expressing mutated IscR mimicked apo-IscR, suggesting that only holo-IscR activates CPS biosynthesis. Furthermore, a promoter-reporter assay verified that the transcription of cps genes was reduced in AP001 and AP002. Purified IscR::His6, but not IscR3CA::His6, was also found to bind the predicted type 1 IscR box specifically in the cps promoter. Furthermore, reduced siderophore production was observed in AP004 (Δfur-ΔiscR) but not in AP005 (Δfur-iscR3CA), implying that apo-IscR activates iron acquisition. Compared with those in AP004, mRNA levels of three putative iron acquisition systems (fhu, iuc, and sit) were increased in AP005, and both purified IscR::His6 and IscR3CA::His6 bound the predicted type 2 IscR box in the fhuA, iucA, and sitA promoters, whereas IscR3CA::His6 displayed a lower affinity. Finally, we analyzed the effect of external iron levels on iscR expression. The transcription of iscR was increased under iron-depleted conditions as well as in AP001 and AP002, suggesting an auto-repression exerted by apo-IscR. Our results show that in K. pneumoniae, IscR plays a dual role in the regulation of CPS biosynthesis and iron-acquisition systems in response to environmental iron availability.
authors.affiliation: Institute of Biochemistry and Molecular Biology, National Yang-Ming University, Taipei, Taiwan, Republic of China.
authors.forename: Chien-Chen
authors.initials: CC
authors.lastname: Wu
authors.affiliation: Department of Biotechnology, Asia University, Taichung, Taiwan, Republic of China.
authors.forename: Chien-Kuo
authors.initials: CK
authors.lastname: Wang
authors.affiliation: Department of Biomedical Informatics, Asia University, Taichung, Taiwan, Republic of China.
authors.forename: Yu-Ching
authors.initials: YC
authors.lastname: Chen
authors.affiliation: Division of Urology, Taichung Tzu Chi Hospital, The Buddhist Tzu Chi Medical Foundation, Taichung, Taiwan, Republic of China; Graduate Institute of Chinese Medicine, School of Chinese Medicine, China Medical University, Taichung, Taiwan, Republic of China.
authors.forename: Tien-Huang
authors.initials: TH
authors.lastname: Lin
authors.affiliation: Graduate Institute of Chinese Medicine, School of Chinese Medicine, China Medical University, Taichung, Taiwan, Republic of China.
authors.forename: Tzyy-Rong
authors.initials: TR
authors.lastname: Jinn
authors.affiliation: Graduate Institute of Chinese Medicine, School of Chinese Medicine, China Medical University, Taichung, Taiwan, Republic of China.
authors.forename: Ching-Ting
authors.initials: CT
authors.lastname: Lin
mesh_terms: D016667:Bacterial Capsules / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001665:Binding Sites; D015964:Gene Expression Regulation, Bacterial; D007501:Iron / Q000378:metabolism* / Q000494:pharmacology; D007506:Iron-Sulfur Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D007711:Klebsiella pneumoniae / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D011134:Polysaccharides / Q000096:biosynthesis*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D007506:Iron-Sulfur Proteins; D011134:Polysaccharides; D014157:Transcription Factors; D007501:Iron