School of Engineering and Science - Jacobs University

Results
reduced in comparison to these prior experiments. As the production of
siderophores is known to be tightly regulated, we next analyzed potential
regulatory parameters in order to reconstitute the original phenotype. Indeed,
siderophore production of Pss22d could be increased by addition of the trace
elements Zn 2+ , Cu 2+ , and Ca 2+ . This supplementation did not influence
siderophore production in Psg1a, but the CAS activity in Pss22d supernatants
was increased to approx. 150 µM DFOM equiv. at OD 600 =1. As the first
measurements were performed in the lab of our cooperation partner Dr. Beate
Völksch in Jena, chemicals from other commercial suppliers had been used to
prepare the medium. Thus a slight variation in medium composition due to
variable trace element content has an impact on the quantity of siderophores
produced. To investigate this hypothesis, Pipes medium was prepared with
chemicals and water supplied by the laboratory in Jena. Doing so, the
siderophore activity produced by Pss22d could be slightly increased; under the
conditions approximately 200 µM DFOM equiv. an OD 600 =1 were produced by
Pss22d.
Finally, the influence of culture volume on siderophore production was
investigated. Again, the total siderophore activity produced by Psg1a did not
change, but the response of Pss22d to different ratios of culture vessel to culture
volume became obvious. 250 ml of culture volume were incubated, but this time
a 2 L Erlenmeyer flask as used instead of a 1 L-flask (Fig.22B). Under these
conditions, the original phenotype could be reconstituted. At the same time,
growth of Pss22d was delayed, indicating a possible stress response. The two
growth curves gave an interesting insight into regulation of siderophore
biosynthesis in Psg1a and Pss22d. Under conditions of lower oxygen supply
(250 ml culture in a 1 L-Erlenmeyer flask), Pss22d produced lower amounts of
siderophores but relatively high fluorescence. Under high oxygen conditions
(250 ml culture in 2 L-Erlenmeyer flask), Pss22d produced approximately the
same amount of fluorescence but more than 10 times the siderophore activity.
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