Abstract
A halophilic strain W33 showing lipolytic activity was isolated from the saline soil of Yuncheng Salt Lake, China. Biochemical and physiological characterization along with 16S rRNA gene sequence analysis placed the isolate in the genus Idiomarina. The extracellular lipase was purified to homogeneity by 75% ammonium sulphate precipitation, DEAE-Sepharose anion exchange and Sephacryl S-200 gel filtration chromatography. The molecular mass of the purified lipase was estimated to be 67 kDa by SDS-PAGE. Substrate specificity test indicated that it preferred long-chain p-nitrophenyl esters. Optimal lipase activity was found to be at 60 °C, pH 7.0-9.0 and 10% NaCl, and it was highly active and stable over broad temperature (30-90 °C), pH (7.0-11.0) and NaCl concentration (0-25%) ranges, showing excellent thermostable, alkali-stable and halotolerant properties. Significant inhibition by diethyl pyrocarbonate and phenylarsine oxide was observed, implying histidine and cysteine residues were essential for enzyme catalysis. In addition, the lipase displayed high stability and activity in the presence of hydrophobic organic solvents with log P(ow) ≥ 2.13. The free and immobilized lipases produced by Idiomarina sp. W33 were applied for biodiesel production using Jatropha oil, and about 84 and 91% of yields were achieved, respectively. This study formed the basic trials conducted to test the feasibility of using lipases from halophile for biodiesel production.
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