Outer membrane protein mediating iron uptake via pyoverdinpss, the fluorescent siderophore produced by Pseudomonas syringae pv. syringae

Abstract

In an iron-limited environment Pseudomonas syringae pv. syringae B301D produces a yellow-green fluorescent siderophore called pyoverdinp. which functions in high-affinity iron transport. Two-dimensional electrophoretic comparisons of the outer membrane proteins of strain B301D identified nine proteins which were expressed at low (50 nM) but not at high (10 ,uM) iron concentrations. Except for the minor protein 8e, the iron-regulated proteins exhibited high molecular weights ranging from approximately 74,000 to 80,000. A mutant of strain B301D incapable of iron uptake (lu-) from ferric pyoverdinp. lacked the 74,000-molecularweight protein 4a, which was the major iron-regulated outer membrane protein. In contrast, a nonfluorescent mutant (Flu-) unable to synthesize pyoverdinp8 showed no quantitative or qualitative difference in its outer membrane profile from that of the wild-type strain. In plant pathogenicity tests the Iu-and Flu-strains caused typical brown necrotic and sunken lesions in immature sweet cherry fruit which were indistinguishable from those of the wild-type strain. Thus, excretion of pyoverdinps and subsequent Fe(M) uptake do not have a determinative role in the pathogenicity or virulence of P. syringae pv. syringae.Iron is an abundant element, but it exists predominantly as insoluble complexes of Fe(III) in aerobic environments. Because iron is a nutrient required by all living cells, many microorganisms acquire iron by synthesizing siderophores, which are low-molecular-weight Fe(III) chelators that deliver iron to the cell via high-affinity transport systems (33-36). Virulence in several bacteria pathogenic to animals has been correlated with the production and utilization of siderophores during invasion (9, 48). The siderophores supply the iron essential for growth and pathogenesis by sequestering Fe(III) from body fluids, in which iron is mainly complexed with high-affinity proteins such as transferrin and lactoferrin (1). Infection continues only if the pathogen efficiently extracts and assimilates iron from these relatively small and guarded sources.Despite evidence that some siderophores modulate bacterial virulence in mammalian infections, the role of siderophores in plant pathogenesis is largely unexplored (36). Siderophore production nevertheless has been demonstrated for a number of plant pathogenic bacteria including Agrobacterium tumefaciens and Erwinia carotovora, which produce the catechol siderophores agrobactin and 2,3-dihydroxybenzoic acid, respectively (28, 37). Plant pathogenic and saprophytic fluorescent pseudomonads produce pyoverdin siderophores which usually contain a hydroxamate group (12,13,26,28,36,44). The pyoverdins are the yellow-green, water-soluble fluorescent pigments produced in media when iron is limited. Leong and Neilands (27) concluded that agrobactin production was not required by A. tumefaciens for infection and crown gall formation because agrobactin could not be isolated from infected tissues and agrobactin auxotrophs were not impaired in their ability t...

The Structure of the Pyoverdin Isolated from Various Pseudomonas syringae Pathovars

“…It is identical with that of 1. The same amino acid composition had also been found by Cody and Gross (1987) for the pyoverdin they had isolated from a P syringae pv. syringae strain.…”

Conservation of the gene for outer membrane protein OprF in the family Pseudomonadaceae: sequence of the Pseudomonas syringae oprF gene

“…Despite sharing rRNA homology, these two species have many differences including cell shape, optimal growth temperature, number of flagella, nutritional and metabolic properties, and guanosine plus cytosine (G+C) content of their DNA (67% for P. aeruginosa and 59 to 61% for P. syringae). Limited comparative studies on their outer membranes, however, have indicated some similarities (17, 19), although the outer membrane proteins of P. syringae, with the exception of the iron-regulated proteins (5), have received far less attention than have those of P. aeruginosa (17,26). In this study we examined in detail the well-characterized protein OprF and its structural gene to determine the extent of its conservation in the fluorescent pseudomonads and particularly in P. syringae.…”

Changes in cultivar-specificity toward pea can result from transfer of plasmid RP4 and other incompatibility group P1 replicons to Pseudomonas syringae pv. pisi.

“…A similar type of pigment from a different isolate of P. syringae pv. syringae was shown to be a pyoverdin siderophore (Cody & Gross, 1987).…”