Impact of Siderophore Production by Pseudomonas syringae pv. syringae 22d/93 on Epiphytic Fitness and Biocontrol Activity against Pseudomonas syringae pv. glycinea 1a/96▿

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   FIG. 1.

   Influence of culture media on siderophore production. P. syringae pv. syringae 22d/93 (filled bars) and P. syringae pv. glycinea 1a/96 (open bars) were cultivated in various low-iron media at 28°C for 48 h. The siderophore activity of supernatants was determined by the CAS assay and normalized to an OD₆₀₀ of 1.0. The data are the means and standard deviations of three independent experiments.
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   FIG. 2.

   Isoelectric focusing and CAS overlay for detection of siderophores in P. syringae. Siderophores were extracted from concentrated culture supernatants using XAD-4 resin at pH 3.0. After separation by isoelectric focusing, the polyacrylamide gel was overlaid with a thin layer of CAS agar to visualize siderophore activity. Lane 1, P. syringae pv. syringae 22d/93ΔSid; lane 2, purified pyoverdin of P. syringae; lane 3, P. syringae pv. syringae 22d/93; lane 4, P. syringae pv. glycinea 1a/96; lane 5, P. syringae pv. syringae 22d/93ΔPvd.
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   FIG. 3.

   (A) Siderophore production by P. syringae pv. syringae 22d/93 and siderophore mutants of this strain on CAS agar. CAS agar plates were inoculated with 5-μl portions of suspensions (>10⁶ CFU/ml) of the different strains and incubated at 28°C for 48 h. Siderophore production is indicated by the formation of haloes. 1, P. syringae pv. syringae 22d/93; 2, P. syringae pv. syringae 22d/93ΔAch; 3, P. syringae pv. syringae 22d/93ΔSid; 4, P. syringae pv. syringae 22d/93ΔPvd. (B) Growth of P. syringae pv. syringae 22d/93 and siderophore mutants of this strain in PIPES medium at 28°C, as determined by measurement of the OD₆₀₀. The data are the means and standard deviations of three independent cultures. □, P. syringae pv. syringae 22d/93; ▿, P. syringae pv. syringae 22d/93ΔAch; ▵, P. syringae pv. syringae 22d/93ΔPvd; ⧫, P. syringae pv. syringae 22d/93ΔSid.
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   FIG. 4.

   Population dynamics of P. syringae pv. glycinea 1a/96, P. syringae pv. syringae 22d/93, and P. syringae pv. syringae 22d/93 siderophore mutants after single inoculation (solid lines) and coinoculation (dashed lines) into soybean leaves using wound inoculation. Single inoculations were used to evaluate the epiphytic fitness of the strains and as controls for comparison with the coinoculation experiment. (A) Coinoculation of P. syringae pv. glycinea 1a/96 (□) with P. syringae pv. syringae 22d/93 (▪) and controls; (B) coinoculation of P. syringae pv. glycinea 1a/96 (□) with P. syringae pv. syringae 22d/93ΔPvd (▪) and controls; (C) coinoculation of P. syringae pv. glycinea 1a/96 (□) with P. syringae pv. syringae 22d/93ΔAch (▪) and controls; (D) coinoculation of P. syringae pv. glycinea 1a/96 (□) with P. syringae pv. syringae 22d/93ΔSid (▪) and controls. The data are the means and standard deviations of four independent experiments.

• American Society for Microbiology