RESUMO
The present study describes the isolation, identification and screening of fugal isolates for the biosynthesis of extracellular lipase enzyme. Thirteen fungal cultures were isolated from cotton seeds, waste cake of cotton seed oil and spent bleaching earth, samples by serial dilution method. All isolates were initially selected qualitatively on tributyrin agar plates and were shifted to the slants of PDA for maintenance and storage at 4oC. Quantitative screening for extracellular lipase biosynthesis by isolated fungi was carried out in shake flasks and the most potent fungal isolate which producing 25 U ml[-1] of enzyme was selected. The isolate was then identified on the basis of standard morphological measurements and was assigned the code Aspergillus niger ADM 110. Enhanced lipase biosynthesis was observed at 25 °C, pH 7, 1.0 ml [4.60 × 10[7]] of spore inoculum and after 72 h of incubation. Olive oil 5 % was observed as the most effective carbon source and yeast extract 5.0 % as the most effective nitrogen source for lipase biosynthesis. The optimum shaking value was 200 rpm. Aspergillus niger ADM 110 was subjected to Gamma radiation in order to improve its lipolytic potential. Using the optimized conditions, maximum lipase biosynthesis has been obtained by using 0.14 kGy of gamma radiation with enzyme activity 53 U/ml as compared to the parent strain [unirradiated] with enzyme activity 30 U/ml