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.

Characterization and Fungal Inhibition Activity of Siderophore from Wheat Rhizosphere Associated Acinetobacter calcoaceticus Strain HIRFA32

“…As already mentioned, siderophores are important in induced systemic resistance. Several reports state the structure of siderophores produced by PGP rhizobacteria such as schizokinen produced by Rhizobium leguminosarum IARI 917 [13]; pyoverdine by Pseudomonas fluorescens [39]; protochelin by Azotobacter vinelandii [11]; Rhizobactin by Rhizobium meliloti [30] and many more. However, there is no report of structural characterization of siderophore from PGP strain of Acinetobacter.…”

“…The (Fig. 1) and 13 C NMR techniques was performed and structure obtained by supported by HMQC, HMBC, NOESY and decoupling studies (Table 1). NMR studies confirmed presence of DHBA and revealed that two amino acids namely; hydroxyhistamine and threonine were present as the subunits.…”

“…All the fractions obtained were tested by CAS reagent. The fractions, which appeared yellow to brown in color, showed presence of siderophore and were pooled together and were concentrated in rotary evaporator (BUCHI Labortechnik AG CH-9230, Flawil, Switzerland) set at 50°C [13]. The dried sample was re-dissolved in 2 ml ddH 2 O and stored at 4°C till further use.…”

“…The siderophores produced by rhizosphere bacteria can supply iron to plants under iron limiting conditions [9] many strains of rhizobacteria, which are effective in biocontrol, produce siderophore. Siderophore also can act as one of the factors for inducing systemic resistance of plants and preventing growth of certain pathogenic bacteria and fungi in iron deficient conditions [10][11][12][13]. Their modes of action in suppression of disease may be based on competition for iron with the pathogen [9].…”

Tn5 siderophore producing mutants of Rhizobium and its role in nitrogen fixation and iron uptake in pigeonpea

“…On the other hand, hydroxamate type of siderophores is produced by chickpea, clover and pigeonpea rhizobia (Carson et al, 1992;Suneja et al, 1992;.Specific type of siderophores like rhizobactin, pseudobactin, schizokinen and some unknown types of siderophores are also known to be produced by different rhizobial and other bacterial strains (Reigh and O'Connell,1989;Lesueur et al, 1993;Schwyn and Neilands 1987;Storey et al, 2006;O'Hara, 2001).…”