Metabolite analysis of KA19
Siderophore production assay
Siderophore production of antagonists was assessed under
iron deprivation, at 30C for 72 h. To achieve iron deprivation, all media and glassware were treated according to
Cox (1994). Chrome azurol S (CAS) medium was prepared
according to Schwyn and Neilands (1987). The cell free
supernatant (0.5 ll) of each strain was obtained after
centrifugation of exponential phase culture at 10,0009g for
30 min followed by filter sterilization (0.22 l, Millipore).
This supernatant was inoculated on overlay chrome azurol
S (O-CAS) medium plates and incubated for 48 h to
observe the colour change (from blue green media colour
to orange haloes). The overlay medium was as follows:
CAS 60.5 mg, hexadecyltrimethyl ammonium bromide
(HDTMA) 72.9 mg, Piperazine-1, 4-bis (2-ethanesulfonic
acid) (PIPES) 30.24 g, and 1 mM FeCl3.6H2O in 10 ml
HCl of 10 mM. Agarose (0.9%, w/v) was used as gelling
agent. The 30 ml overlay of this medium was applied over
the plates containing cultivated microorganisms to be tested for siderophore production. After a maximum period of
15 min, a change in colour was observed in the overlaid
medium. The amount of siderophores excreted into the
culture medium was determined from the bacteria-free
supernatant. Concentration was calculated using absorption
maximum and the molar absorption coefficient (kmax =
400 nm and e = 20,000 M-1 cm-1) according to the
method of Meyer and Abdallah (1978). The M9 minimal
salts (minimal media, Sigma) containing 1% different
carbon sources and varying concentration of Fe (III) were
used to optimize siderophore production.