title: The components of the putative iron transport system in the cyanobacterium Anabaena sp. PCC 7120.
abstract: Iron uptake in Gram-negative bacteria involves four distinct steps: (i) siderophore synthesis, (ii) siderophore secretion into the extracellular space, (iii) iron chelation by the siderophores, and (iv) siderophore/iron uptake via complexes in the outer membrane and the intermembrane space as well as in the plasma membrane. This process is well characterized for some proteobacterial systems, but largely unexplored and scarcely investigated in cyanobacteria such as the heterocyst-forming cyanobacterium Anabaena sp. PCC 7120. Two putative siderophore synthesis clusters have been recently identified in this cyanobacterium. In addition, the export system for the main siderophore, schizokinen, secreted by Anabaena sp. PCC 7120 was described as well as the outer membrane transporter for its import from the extracellular space. We present the identification of components of three additional systems involved in siderophore-mediated iron uptake under iron-limiting conditions, namely TonB3, the ExbB3/ExbD3 and the Fhu systems. The transcription level of these genes is elevated under iron limitations and decreased under excess iron, while the expression levels of other members of these gene families and systems are impacted in distinct ways by other environmental conditions. Mutants of the tonB3, exbB3/exbD3 and fhu genes show an iron starvation phenotype. Thus, Anabaena sp. has a similar, yet distinct system for siderophore-dependent iron uptake compared with other proteobacteria.
authors: JWGU Frankfurt am Main, Department of Biosciences, Molecular Cell Biology of Plants, Max-von-Laue Strasse 9, Frankfurt, Germany.
authors: Mara
authors: M
authors: Stevanovic
authors: Alexander
authors: A
authors: Hahn
authors: Kerstin
authors: K
authors: Nicolaisen
authors: Oliver
authors: O
authors: Mirus
authors: Enrico
authors: E
authors: Schleiff
mesh_terms: D017033:Anabaena / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D015964:Gene Expression Regulation, Bacterial; D006877:Hydroxamic Acids / Q000378:metabolism; D007501:Iron / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D005810:Multigene Family; D017262:Siderophores / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D006877:Hydroxamic Acids; D026901:Membrane Transport Proteins; D017262:Siderophores; C000766:schizokinen; D007501:Iron