Biodegradation tests. The biodegradation of octadecane
and rhamnolipid was determined by measurement of the
increase in the protein concentration as an indication of cell
growth and by rhamnolipid determination (based on rhamnose).
Octadecane mineralization was measured by the
quantification of 14CO2 and 14C-volatile compounds. For
protein and rhamnose determinations, octadecane was dissolved
in chloroform, and the mixture was used to coat the
bottom of 250-ml flasks. The chloroform was evaporated,
and 50 ml of mineral salts medium (16) containing rhamnolipid
was added to each flask. The flasks were warmed in a
370C 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 medium. The flasks were then
inoculated