title: The interplay between siderophore secretion and coupled iron and copper transport in the heterocyst-forming cyanobacterium Anabaena sp. PCC 7120.
abstract: Iron uptake is essential for Gram-negative bacteria including cyanobacteria. In cyanobacteria, however, the iron demand is higher than in proteobacteria due to the function of iron as a cofactor in photosynthesis and nitrogen fixation, but our understanding of iron uptake by cyanobacteria stands behind the knowledge in proteobacteria. Here, two genes involved in this process in the heterocyst-forming cyanobacterium Anabaena sp. PCC 7120 were identified. ORF all4025 encodes SchE, a putative cytoplasmic membrane-localized transporter involved in TolC-dependent siderophore secretion. Inactivation of schE resulted in an enhanced sensitivity to high metal concentrations and decreased secretion of hydroxamate-type siderophores. ORF all4026 encodes a predicted outer membrane-localized TonB-dependent iron transporter, IacT. Inactivation of iacT resulted in decreased sensitivity to elevated iron and copper levels. Expression of iacT from the artificial trc promoter (P(trc)) resulted in sensitization against tested metals. Further analysis showed that iron and copper effects are synergistic because a decreased supply of iron induced a significant decrease of copper levels in the iacT insertion mutant but an increase of those levels in the strain carrying P(trc)-iacT. Our results unravel a link between iron and copper homeostasis in Anabaena sp. PCC 7120.
authors.affiliation: JWGU Frankfurt/Main, Department of Biosciences, Molecular Cell Biology of Plants, Frankfurt, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Nicolaisen
authors.forename: Alexander
authors.initials: A
authors.lastname: Hahn
authors.forename: Marianne
authors.initials: M
authors.lastname: Valdebenito
authors.forename: Suncana
authors.initials: S
authors.lastname: Moslavac
authors.forename: Anastazia
authors.initials: A
authors.lastname: Samborski
authors.forename: Iris
authors.initials: I
authors.lastname: Maldener
authors.forename: Corinna
authors.initials: C
authors.lastname: Wilken
authors.forename: Ana
authors.initials: A
authors.lastname: Valladares
authors.forename: Enrique
authors.initials: E
authors.lastname: Flores
authors.forename: Klaus
authors.initials: K
authors.lastname: Hantke
authors.forename: Enrico
authors.initials: E
authors.lastname: Schleiff
mesh_terms: D017033:Anabaena / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology; D001483:Base Sequence; D001692:Biological Transport; D003300:Copper / Q000378:metabolism*; D007501:Iron / Q000378:metabolism*; D008969:Molecular Sequence Data; D017262:Siderophores / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D017262:Siderophores; D003300:Copper; D007501:Iron