For biosurfactant production P. koreensis 2.74 was cultivated in
KB broth under the conditions described in Section 2.2, the cells
were centrifuged down, and the cell-free broth containing the
biosurfactant was autoclaved. The sterile broth was amended with
1% (w/v) Amberlite XAD-16 (Rohm and Haas Company, Philadelphia,
USA) and the slurry was shaken (150 rpm) for 12 h. After
this the resin was collected and washed with six volumes of
distilled water. The resin was then washed in 25% methanol, after
which it was washed once again with 50% methanol. The resin was
finally transferred to 100% methanol. After this step, the methanol
was collected and evaporated at 50 C and the dry weight of the
recovered biosurfactant was recorded. The critical micelle
concentration of the biosurfactant was 220 mg ml1, as determined
with SITA DynoTester (SITA, Messtechnik, GmbH) at 22 C, pH 7.0,
and the lowest surface tension value obtained was 23.5 mN m1.
The biosurfactant treatment was applied in the nutrient solution to
make a final concentration of 50 mg per mL.