A thermo‐alkaline lipase from a new thermophile <i>Geobacillus thermodenitrificans</i> AV‐5 with potential application in biodiesel production

Abstract

Abstract BACKGROUND A thermophilic lipase‐producing Geobacillus thermodenitrificans strain AV ‐5 was isolated from the Mushroom Spring of Yellowstone National Park in WY , USA and studied as a source of lipase for transesterification of vegetable oils to biodiesel. RESULTS A maximum activity of 330 U mL −1 was produced on 2% (v/v) waste cooking oil at 50 °C, pH 8, aeration rate of 1 vvm and agitation speed of 400 rpm. However, the higher lipase productivity (14.04 U mL −1 h −1 ) was found at a volumetric oxygen transfer coefficient ( k L a ) value of 18.48 h −1 . The partially purified lipase had a molecular weight, temperature and pH optimum of 50 kDa , 65 °C and pH 9, respectively, and was thermo‐alkali stable: at 70 °C, it retained 81% activity and 45% stability; at pH 10 it lost only 15% and 2.6% of its maximum activity and stability, respectively. Enzyme kinetic studies with p ‐nitrophenyl laurate as substrate revealed high substrate specificity ( k m of 0.440 mmol L −1 ) and kinetic activity ( v max of 556 nmol mL min −1 ) of lipase. CONCLUSIONS The k L a was found to be highly dependent on aeration and agitation rates. Following optimization of fermentation medium and parameters, a 7.5‐fold increase in lipase production by G. thermodenitrificans was attained. The lipase activity and substrate specificity (as k m ) are among the highest reported in the literature for bacterial lipases. It was demonstrated that the enzyme can produce biodiesel from waste cooking oil with a conversion yields of 76%. © 2015 Society of Chemical Industry