A new strain of Rhodotrula mucilaginosa producing sophorolipid biosurfactant as an effective agent in microbial oil extraction

Biosurfactants have wide applications in the microbiology of food and oil. The aim of this research was to investigate the production of stable biosurfactant in high temperature and salinity from yeasts isolated from oil-contaminated soil. Bushnell Haas culture medium was used to screen biosurfactant producing yeasts. The presence of biosurfactant was evaluated using oil dispersion and surface tension reduction tests. The best biosurfactant producing strain of Radotrulla mucilaginosawas named GBMEIAUF1 and its 5.8s-rDNA gene sequence was registered inthe NCBI gene bank under accession number CBS11162. The results of thin layer chromatography and Fourier transform infrared spectroscopy confirmed that the extracted biosurfactant was sophorolipid with significant surface activity. Purified sophorolipid decreased the surface tension of water from 72 mN/m to 1.29 mN/m. The highest emulsification index, E24%, the extracted biosurfactant was 53% and retained 63.71 to 58.09% of its initial activity at 80 to 120 degrees Celsius. This biosurfactant also retained 82.67 and 89.41% of its initial activity at pH 10.5, and 12, 59.66% of its initial activity at 10% salinity. This research is the first report of sophorolipid production by the yeast Redotrula mucilaginosa.Due to its thermal stability and high pH and salinity tolerance, sophorolipid produced by Redotrula mucilaginosa can be strongly recommended as an effective emulsifying agent for application in microbial enhanced oil extraction programs as well as food industry.