Kinetic and thermodynamic characterization of novel alkaline lipase from halotolerant Bacillus gibsonii.

A halotolerant bacterial strain isolated and identified as Bacillus gibsonii was used for extracellular lipase production. The bacterial strain was able to grow up to 1200 mM salt concentration and showed maximum growth at 600 mM NaCl concentration. The present study includes production of extracellular lipase enzyme and characterization of partially purified lipase with respect to its kinetic and thermodynamic behaviour. Maximum lipase activity was observed at 60 °C under alkaline pH (9.0) condition. The kinetic parameters such as Vmax, Km and Kcat were calculated as 158.73 U/mL, 0.539 mM and 483.93 min-1 at 60 °C, respectively, suggested thermostable nature of the enzyme. The thermal inactivation energy [Ea(d)] was calculated as 66.98 kJ/mol. The values of Gibb's free energy (86.31 kJ/mol), enthalpy (64.26 kJ/mol) and entropy (- 66.21 × 10-3 kJ/mol/K) for the enzyme inactivation obtained at 60 °C corroborated the assumption that 60 °C was the optimum temperature. Further, the deactivation rate constant (kd) values calculated at 60 °C and 80 °C were found to be 0.0907 and 0.182 min-1, respectively, which suggested that enzyme was more stable at 60 °C and it was partly inactivated at 80 °C.