Characterization of P. syringae 1448a pyoverdine NRPS knockouts. A. Wild type (WT) and pyoverdine NRPS knockouts (Δ1911, Δ1923-1926) on iron-limiting KB agar viewed under UV light. Only the wild type is able to synthesize fluorescent pyoverdine. Pyoverdine gene knockout strains are named according to the gene deleted, based on the Pspph gene numbering scheme in the published genome database . B. Wild type and pyoverdine null strain (Δ1925) inoculated into KB agar containing CAS dye and incubated for 24 h at 28°C. Only the wild type strain took up discernible levels of iron as evidenced by the orange halo surrounding this inoculum. All pyoverdine NRPS knockouts exhibited indistinguishable iron transport deficient phenotypes. C. Wild type, Δ1925 and Δ1925 complemented by pSX:1925 on iron-restricted KB agar containing 200 μg/ml EDDHA. Complementation by a functional gene copy in trans restored pyoverdine synthesis to near wild type levels in each of the NRPS knockout strains.