The chloroform was evaporated
to allow the octadecane to coat the bottom of the test
tubes. After evaporation of the solvent, 1 ml of rhamnolipid
solution was added. The test tubes were incubated at 37°C in
a water bath for 30 s, to melt the coated octadecane and then
cooled at room temperature until the octadecane solidified
on the surface of the solution. The test tubes were then
incubated at 23°C at an appropriate shaking speed. After 24
h, 0.1 ml was carefully removed from the bottom of the test
tubes to avoid floating of any particulate octadecane on the
top of the liquid surface and was added to 5 ml of Scintiverse
BD (Fisher, Pittsburgh, Pa.). Radioactivity was determined
with a Packard (Meriden, Conn.) Tri-Carb liquid scintillation
counter (model 1600 TR).