Selection of Enterobacter cloacae Strain POPE6 for Fermentative Production of Extracellular Lipase on Palm Kernel Oil Processing Effluent

Abstract

An Enterobacter cloacae strain was isolated from palm oil processing effluent and demonstrated ability to elaborate extracellular lipase on Tween 80-minimal medium using the rapid plate assay of precipitate formation. Peak productivity of the enzyme in submerged culture occurred at 72 h with lipase concentration of 95 μg/mL. Enzyme activity, monitored using different carbon-chain lengths of p-nitrophenol (p-NP)-triacylglycerol substrates, revealed that stearate was the most suitable substrate for the lipase. Preliminary optimization of major medium variables revealed highest lipase concentration in palm kernel oil processing effluent (Carbon source; P = 2.22E-05; Time, P = 1.99E-25; P < 0.05). Ammonium nitrate (NH4NO3) emerged as best nitrogen source with Na2HPO4/KH2PO4 (2:1) selected as phosphate combination with best buffering capacity. A fermentation medium incorporating the selected carbon, nitrogen and phosphorus sources, and supplemented with 2% (v/v) inoculum volume containing 108 cells/mL led to the production of 147.59 μg/mL lipase within 72 h of incubation. The lipase was found to possess highest activity of 2.031 U/mL at 35°C, pH 7 within 10 min, with stearate as substrate. One unit of lipase activity was defined as the amount of enzyme required to release 1 mM of p-nitrophenol per min from p-NP-stearate under the assay conditions of pH 7 and temperature of 35°C. The bacterium is recommended for lipase production on palm oil processing effluent as an oily waste management option.