Preparation, characterization, and applications of rhamnolipids from pseudomonas aeruginosa SP4

Abstract

Pseudomonas aeruginosa SP4, isolated from petroleum-contaminated soil in Thailand, was used to produce a biosurfactant from a nutrient broth with palm oil as the carbon source. The biosurfactant extracted from the culture medium was a mixture of eleven rhamnolipid species, and the major component in the biosurfactant product was mono-rhamnolipid. Compared to synthetic surfactants — Pluronic F-68 and sodium dodecyl sulfate, the biosurfactant showed comparable surface activities, emulsification activities, and stabilities. The biosurfactant self-assembled to form spherical vesicles of various sizes (ranging from 50 nm to larger than 250 nm) at a concentration greater than its critical micelle concentration. To study the potential use of the biosurfactant vesicles in either delivery systems or other dispersed systems, the encapsulation experiment was done by using Sudan III, a water-insoluble dye, as a model substance. The encapsulation efficiency of the biosurfactant vesicles was slightly influenced by the addition of sodium chloride, but was significantly enhanced in the presence of either ethanol or cholesterol. To find the utilization in the biomedical field, the biosurfactant was used to modify the surface characteristics of two types of polymeric films, including silk fibroin and chitosan, via the adsorption process. The silk fibroin and chitosan films showed more hydrophobicity after the biosurfactant adsorption, but the surface topographies of both substrates was not significantly modified. The adsorbed biosurfactant layer was also found to differently affect the growths of the test cells—human dermal fibroblasts and human dermal keratinocytes.