Rhamnolipids Obtained from a PHA-Negative Mutant of Pseudomonas aeruginosa 47T2 ΔAD: Composition and Emulsifying Behavior

Pseudomonas aeruginosa 47T2 (NCBIM 40044) synthesizes polyhydroxyalkanoic acids (PHAs) and rhamnolipids (Rhls). The knockout mutant for PHAs biosynthesis, P. aeruginosa 47T2 ΔAD prepared in this study, increased the cellular yield of Rhls production by 28 %. The Rhls mixture (composed up to eight homologs) reduced the water surface tension to 31.67 mN/m with a critical micelle concentration of 105 mg/L. The IC₅₀ (μg/mL) of the neutral red uptake assay and methylthiazol tetrazolium assay ranged between 53.9 and 72 μg/mL, which is similar to that of sodium dodecyl sulfate (SDS). Rhamnolipids had a lower hemolytic effect at 110.8 μg/ml than SDS, a commercial anionic surfactant, at 43.6 μg/mL. This suggests that the Rhls mixture could be used in topical pharmaceutical and cosmetic applications or cleansers as a biosurfactant. The emulsifying properties in water/oil dispersions were determined using ternary phase diagrams at 25 °C. Isopropyl myristate, soybean oil, olive oil and Casablanca oil were used as the oil components. Total emulsions were obtained with most of the oils.