Siderochromes from Pseudomonas fluorescens. I. Isolation and characterization.

Several iron-binding pigments (siderochromes) produced by Pseudomonas fluorescens have been isolated and partially characterized. They include ferribactin and various forms of pyoverdine, as well as some previously unreported compounds. In particular, the existence of ferribactin has been independently confirmed for the first time. Column and thin layer chromatographic procedures have been developed to fractionate, purify, and identify the siderochromes. We find ferribactin to contain nine amino acids, one residue each of glutamine, tyrosine, and glycine, and two each of serine, lysine, and N-hydroxyornithine, rather than 10 as earlier reported. Pyoverdine is a peptide with the same composition as ferribactin except for the absence of glutamine and the substitution of a fluorescent chromophore for tyrosine. Paper electrophoresis reveals an extra ionizable group in ferric pyoverdine relative to pyoverdine or ferribactin which provides that complex a definite cathodic mobility at pH 3. Optical spectra of the pyoverdine fluorescent component indicate that, in conjunction with the two hydroxamate groups, it is involved in the metal ion coordination, conferring on pyoverdine a dramatically increased affinity for Fe(III) relative to ferribactin.