Aspergillus niger lipases: induction, isolation and characterization of two lipases from a MZKI Al 16 strain

Aspergillus niger strain MZKI Al 16 was used to produce lipolytic enzymes in submerged culture. Lipase production was induced by addition of olive oil to a complex medium with an initial pH of 5.0. Maximal activity was reached after 70 h in a 15 1 bioreactor at 30°C with aeration of 0.5 vvm and agitation 400 rpm. Optimal temperature and pH conditions for the action of the lipases tested on tributyrin were 45°C and pH 7.0. Triacetin and tributyrin were shown to be the best substrates. The presence of iron and silver ions at low concentrations did not alter the activities. Two enzymes possessing lipase activity were isolated by acetone precipitation followed by ion-exchange chromatography. The molecular weights were 43 kDa and 65 kDa with isoelectric points of pH 4.1 and 4.2, respectively. The higher molecular weight lipase showed preference toward 1- and 3-positions of the triglyceride molecule and was stereoselective for the sn- 1 position with an enantiomeric excess of 20