PPGAS medium
is composed of NH4C1 (0.02 M), KCl (0.02 M), Tris-HCl
(0.12 M), glucose (0.5%), proteose peptone (1%), and
MgSO4 (0.0016 M), adjusted to pH 7.2 (3). This flask was
incubated at 37°C with gyratory shaking at 250 rpm, with
periodic aseptic removal of samples to monitor surface
tension. The initial surface tension of PPGAS medium was
66 dyn/cm. The surface tension of the medium started to
decrease at 6 h, coinciding with the production of a blue
pigment. By 48 h, the surface tension of the medium reached
29 dyn/cm and did not decline further. Rhamnolipid was
harvested at 60 h.