A new bacterial strain isolated from activated sludge, identified as Pseudomonas aeruginosa EMS1, produced a biosurfactant when grown on acidified
soybean oil as the sole
carbon source. An optimum biosurfactant production of 5 g/L was obtained with the following medium composition: 2% acidified
soybean oil, 0.3% NH4NO3, 0.03% KH2PO4, 0.03%
K2HPO4, 0.02% MgSO4.7H2O and 0.025% CaCl2.2H2O, with shaking at 200 rpm for an incubation period of 100 h at 30 degrees C. The production of the biosurfactant was found to be a function of cell growth, with maximum production occurring during the exponential phase.
Hemolysis of erythrocytes and thin-layer chromatography studies revealed that the secreted biosurfactant was
rhamnolipid. To overcome the complex environmental regulation with respect to
rhamnolipid biosynthesis, and to replace the opportunistic pathogen P. aeruginosa with a safe industrial strain, attempts were made to achieve
rhamnolipid production in a heterologous host, Pseudomonas putida, using molecular cloning of rhlAB rhamnosyltransferase genes with the rhlRI quorum sensing system, assuming that a functional rhamnosyltransferase would catalyze the formation of rhamnosyl-6-hydroxydecanoyl-6-hydroxydecanoate (
mono-rhamnolipid) in P. putida. It was shown that
rhamnolipid can be produced in the heterologous strain, P. putida, when provided with the rhamnosyltransferase genes.