title: Characterization of 'Schizokinen'; a dihydroxamate-type siderophore produced by Rhizobium leguminosarum IARI 917.
abstract: The Rhizobia comprise one of the most important groups of beneficial bacteria, which form nodules on the roots (rarely on the stems) of leguminous plants. They live within the nodules and reduce atmospheric nitrogen to ammonia, which is further assimilated by plants into required nitrogenous compounds. The Rhizobia in return obtain nutrition from the plant. Rhizobia are free-living soil bacteria and have to compete with other microorganisms for the limited available iron in the rhizosphere. In order to acquire iron Rhizobia have been shown to express siderophore-mediated iron transport systems. Rhizobium leguminosarum IARI 917 was investigated for its ability to produce siderophore. It was found to produce a dihydroxamate type siderophore under iron restricted conditions. The siderophore was purified and chemically characterized. The ESMS, MS/MS and NMR analysis indicate the dihydroxamate siderophore to be 'schizokinen', a siderophore reported to be produced by Bacillus megaterium that shares a similar structure to 'rhizobactin 1021' produced by Sinorhizobium meliloti 1021. This is the first report of production of schizokinen by a strain of R. leguminosarum, therefore it was carefully investigated to confirm that it is indeed 'schizokinen' and not a degradation product of 'rhizobactin 1021'. Since ferric-siderophore complexes are transported across the outer membrane (OM) into the periplasm via an OM receptor protein, R. leguminosarum IARI 917 was investigated for the presence of an OM receptor for 'ferric-schizokinen'. SDS PAGE analysis of whole cell pellet and extracted OM fractions indicate the presence of a possible iron-repressible OM receptor protein with the molecular weight (MW) of approximately 74 kDa.
authors.affiliation: Department of Health Sciences, College of Public and Allied Health, East Tennessee State University, 37614 Johnson City, TN, USA. chakrabr@etsu.edu
authors.forename: E P
authors.initials: EP
authors.lastname: Storey
authors.forename: R
authors.initials: R
authors.lastname: Boghozian
authors.forename: James L
authors.initials: JL
authors.lastname: Little
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Lowman
authors.forename: R
authors.initials: R
authors.lastname: Chakraborty
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000032:analysis; D006877:Hydroxamic Acids / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular; D011956:Receptors, Cell Surface / Q000032:analysis; D016961:Rhizobium leguminosarum / Q000378:metabolism*; D017262:Siderophores / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013056:Spectrophotometry, Ultraviolet; D053719:Tandem Mass Spectrometry
chemical_list: D001425:Bacterial Outer Membrane Proteins; D006877:Hydroxamic Acids; D011956:Receptors, Cell Surface; D017262:Siderophores; C035902:siderophore receptors; C000766:schizokinen