Enhanced recombinant lipase production in Pseudomonas aeruginosa SDK-6: medium optimization using OFAT and RSM with purification and stability studies.

Abstract

Lipases are among the most significant biocatalysts that constitute the third most important group of enzymes due to their vast range of applications. The present research represents the first attempt to optimize the growth medium constituents to increase the production of recombinant lipase in Pseudomonas aeruginosa SDK-6. One factor at a time (OFAT) revealed castor oil, yeast extract, and ammonium nitrate as the most significant medium components affecting the recombinant lipase production. Further optimization via response surface methodology (RSM) resulted in lipase production of 115.50 U/mL with 0.5% (v/v) castor oil, 0.2% (w/v) yeast extract, and 0.1% (w/v) ammonium nitrate at pH 7. Statistical validation of the observed value via ANOVA revealed an F value of 117.02 at p < 0.01, with an R² of 0.9909. An overall 3.58-fold lipase production was achieved after optimization via OFAT and RSM. The purified lipase exhibited a specific activity of 102.73 U/mg, and the molecular mass was deduced to ~ 19.5 kDa via sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The optimum temperature and pH for the recombinant lipase activity were 40 °C and 10, respectively. The enzyme retained most of its initial activity up to 32 h when incubated at an elevated temperature of 40 °C. The purified enzyme also exhibited stability over alkaline pH, with remarkable stability at pH 12. The enzyme activity was enhanced in the presence of CaCl₂, MgCl₂, FeCl₂, NaCl, methanol, dichloromethane, and Triton X-100. The enzyme also retained most of its initial activity in the presence of all other screened organic solvents.