ISSN 2348-313X (Print) International Journal of Life Sciences Research ISSN 2348-3148 (online) Vol. 9, Issue 1, pp: (47-66), Month: January - March 2021, Available at: www.researchpublish.com
Physico-chemical characterization of biosurfactant secreted by Pseudomonas aeruginosa PU1 with its stability studies and application in microbial enhanced oil recovery Latha Domdi, Avinash Kant Lakra, Younus Mohd Tilwani, Venkatesan Arul* Department of Biotechnology, School of Life Sciences, Pondicherry University, Pondicherry 605014, India. *Corresponding author: varul18@gmail.com (V. Arul)
Abstract: 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 in surface tension of water from 70.23 mN/m to 29.77 mN/m at a concentration of 30 mg/L. The degradation of various oils by P. aeruginosa PU1 through gravimetric method showed maximum degradation of used transformer oil (95.55 ± 2.70%) followed by diesel oil (94.36 ± 1.86%), kerosene (76.17 ± 1.62%) and petroleum oil (66.03 ± 2.91%) in 10 days of the incubation period. 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 pseudomolecular 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 7th 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 sulfate (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. Keywords: Pseudomonas aeruginosa PU1, biosurfactant, rhamnolipid, emulsifying activity, oil recovery.
1. INTRODUCTION Biosurfactants derived from the microbes are heterogeneous in nature, surface-active agents, and can reduce surface as well as interfacial tension. Biosurfactants are composed of polar and non-polar moieties that include glycolipids, lipopeptides, and phospholipids, etc (Banat et al., 2000). Currently, numerous types of biosurfactants have been characterized. Among which the most extensively studied biosurfactant is rhamnolipid because it offers a wide range of environmental and industrial applications. Rhamnolipids are glycolipid in nature with lower molecular weight compounds, composed of hydrophilic rhamnose group and hydrophobic β-hydroxy fatty acids which are linked by glycosidic bonds (Rudden et al., 2005). Pseudomonas sp. is one of the most abundant isolated bacteria having the potential of degrading polycyclic aromatic hydrocarbons (PAHs) which are known to be organic pollutants, mutagens, and carcinogens (Bezza et al., 2006; Varjani and Upasani, 2016a; Varjani and Upasani, 2016b).
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