Uptake of pyocin S3 occurs through the outer membrane ferripyoverdine type II receptor of Pseudomonas aeruginosa

Abstract

Pyocin S3 was found to kill exclusively Pseudomonas aeruginosa isolates producing type II pyoverdine (exemplified by strain ATCC 27853). Killing was specifically inhibited by addition of type II ferripyoverdine. All Tn5 mutants resistant to pyocin S3 were defective for pyoverdine-mediated iron uptake and failed to produce an 85-kDa iron-repressed outer membrane protein. We conclude that this protein is probably the type II ferripyoverdine receptor that is used by pyocin S3 to gain entry into the cell.

FIG. 1

Plate showing the effects of different pyoverdines on the killing of P. aeruginosa ATCC 27853 by pyocin S3. To a lawn of P. aeruginosa ATCC 27853 on Luria-Bertani medium drops of purified pyocin S3 (20 μl, corresponding to 25 U ml⁻¹, defined as the reciprocal of the highest pyocin dilution inhibiting bacterial growth) were deposited at three places in the middle. Next, on each side of the pyocin drop, 20 μl of the following purified pyoverdines (2 μmol) was added: that from PAO1 (top), that from ATCC 27853 (middle), and that from clinical isolate PA6 (bottom). Only the cognate pyoverdine (ATCC 27853), recognized by the pyoverdine receptor, competes with pyocin S3, which uses the same receptor, inhibiting the killing.

FIG. 2

Sodium dodecyl sulfate-polyacrylamide gel (7%) electrophoresis of 10-μg quantities of outer membrane proteins from P. aeruginosa ATCC 27853 grown in CAA medium (lane 1) and in CAA medium plus FeCl₃ (50 μM) (lane 2), mutant ATCC 27853-5B (lane 3), mutant ATCC 27853-6A (lane 4), mutant ATCC 27853-9A1 (lane 5), and mutant ATCC 27853-16B1 (lane 6). Lane 7 contains the molecular mass markers (High molecular mass markers; Pharmacia-LKB, Uppsala, Sweden).