Isolation and characterization of an Antarctic strain of Pedobacter sp. producing surfactant

Abstract:

[Background] With low toxicity, good biocompatibility, and biodegradability, biosurfactants are excellent substitutes for chemical surfactants. Most of the available biosurfactant-producing bacteria are mesophilic and it is of great significance to mine efficient biosurfactant-producing strains from cryogenic environments such as the Antarctic. [Objective] To screen psychrotolerant bacteria producing surfactants from the Antarctic soil samples and analyze the chemical structures and properties of the purified surfactants. [Methods] The biosurfactant-producing bacteria from the soil samples in Fildes Peninsula, Antarctic were screened by the oil spreading method. A strain with white solid particles on the colony surface was obtained and identified based on the morphology and the phylogenetic analysis of the 16S rRNA gene sequence. The components in the product were separated by high performance liquid chromatography (HPLC) and identified by nuclear magnetic resonance (NMR). The fermentation medium of the strain was optimized by single factor experiment and response surface design. The emulsifying ability of the product and the diesel oil-degrading ability of the strain were evaluated. [Results] Pedobacter sp. GW9-17 with high surfactant production was screened out. The optimal fermentation medium contained (g/L): soluble starch 18.0, tryptone 9.0, C₃H₃NaO₃ 4.4, K₂HPO₄ 3.6 and MgSO₄ 1.2, with pH value 7.0±0.2. The concentration of the product reached (3.0±0.5) g/L after the strain was incubated in the optimal medium at 28 ℃ and 180 r/min for 7 days with an inoculum amount of 10% (volume fraction). The main component of the surfactant was flavolipid-9U,9U, and the methanol-aqueous solution (the volume ratio is 1:1) of the surfactant crude extract had good emulsifying ability for liquid paraffin oil. In the medium with 5% diesel oil, the strain GW9-17 showed the diesel oil-degrading rates of 40.1% and 57.3% at 4 ℃ and 28 ℃, respectively. [Conclusion] A psychrotolerant strain, Pedobacter sp. GW9-17, efficiently producing the surfactant with a low molecular weight was isolated from the Antarctic soil. The product demonstrated the potential to degrade alkane pollutants and remediate the low-temperature environment of oil pollution.

Key words:biosurfactants;flavolipids;Pedobacter;diesel oil degradation