Physico-chemical characterization of biosurfactant from Pseudomonas aeruginosa PU1 and its application in microbial enhance oil recovery

Biosurfactant-producing bacteria were isolated from transformer oil-contaminated soil. The strain was identified as Pseudomonas aeruginosa PU1 based on its molecular characterization by 16S rRNA gene sequencing. The extraction of biosurfactant was done by acid precipitation method using 2 N hydrochloric acid and further purified by silica-gel column chromatography. The highest rhamnolipid biosurfactant production (8.92 ± 0.08 g/L) was obtained using molasses (6%, w/v) and ammonium nitrate (5%, w/v). The purified biosurfactant showed a reduction of surface tension of water from 70.23 mN/m to 29.77 mN/m at a concentration of 30 mg/L. The functional groups were characterized by fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (¹H NMR). The liquid chromatography-mass spectrometry (LC-MS) analysis showed six different rhamnolipid congeners with psuedomolecular ions (m/z) of 305, 361, 451, 505, 532 and 621. X-ray diffraction (XRD) analysis and the thermal analysis showed crystalline nature and thermal stability of the biosurfactant. The stability study of the biosurfactant reveals that the emulsifying activity was much stable at various ranges of temperature (4-120 °C), pH (2-12), and NaCl concentration (2-10%, w/v) even on the 7^th day. The purified biosurfactant PU1 was found to be effective in oil recovery and showed 68.53 ± 3.07% of oil recovery in the sand pack column under saline condition, which was higher than anionic surfactant sodium dodecyl sulphate (SDS). The physico-chemical properties and the stability studies of the biosurfactant suggested that it has enormous potential in oil recovery in the soil contaminated with the oils.