School of Engineering and Science - Jacobs University

Results
P
P
A
Fig. 21. Isoelectic focusing and CAS-overlay detection of purified siderophores.
Lanes: A: reference pyoverdin of P. syringae; B: Psg1a; C: Pss22d; D: Pss22d∆Pvd;
E: Pss22d∆Sid; P= pyoverdin; A= achromobactin-like siderophore
Siderophore production of antagonist and pathogen were analysed in more detail
during growth in iron-free pipes medium (Fig.22). One aim of this analysis was to
distinguish between pyoverdin production and production of the achromobactinlike
siderophore. As demonstrated before, there is no fluorescence signal in
pyoverdin-negative Pss22d strains and the siderophore-negative mutant does
not show a reaction in the CAS-assay (Tab. 9). Thus comparison between CASmeasurement
and fluorescence determination was used to differentiate between
total siderophore production (= achromobactin-like siderophore plus pyoverdin)
and pyoverdin production.
In initial experiments, 250 ml of culture were incubated in a 1 L Erlenmeyer flask
(Fig.22A). The antagonist Pss22d reached stationary phase within 30 h at an
OD 600 of 2. Psg1a showed a slower growth and reached the stationary phase not
before 60 h, yet it reached the same OD 600 . In contrast to our expectations, the
siderophore activity produced by the antagonist Pss22d was significantly (about
10 times) lower than that of the pathogen Psg1a. While the activity of Psg1a was
in line with previous results (Fig.5B), siderophore production in Pss22d was
66