This study focused on screening, production and characterization of strains of microorganisms isolated from groundnut cake wastes capable of producing lipolytic enzyme. Over one hundred isolates were screened on Bromocresol green medium to detect the presence of lipase producing organisms by a colour change of the medium from green to yellow around the colonies at pH 3.8 – 5.6. Two of the isolates with NCBI Accession number ACJE01000015.1 and NT-166520.1 were identified as Aspergillus niger ATCC 1015 and A.niger CBS 513.88 respectively based on the nucleotide sequence of the domain of DNA gene. Other lipase producers include A. niger (B-05, B-17, B-33), A. oryzae (G -47, G- 51), and yeast, Candida sp. (H-06, H-11). Lipase activities of A. niger ATCC 1015 were evaluated at temperature (25 – 60 °C), pH 5 - 9 and enzyme loading (10 -35 %, v/v) for optimization.The effect of inducers on lipase production was also carried out by using coconut oil, physic nut oil, groundnut oil and olive oil.A. niger ATCC 1015 gave the largest halo on the medium with 102.4 U/g activity. Zones of hydrolysis also increased with time and ranged from 3 mm to 10 mm at 30 ºC for 96 h. The ability of cells to maintain sharp contrast between green medium and its clear zone without prior replication permits direct visualization and isolation of positive strains.
Optimum production of the enzyme (specific activity 216.7 Umg-1)was attained at temperature 45°C, pH 7, and enzyme loading (25% v/v) with physic nut oil (2%) inducer. Hence A. niger ATCC 1015 strain can be commercially exploited as a potential lipase producing strain for industrial application.
Bromocresol green medium; solid state fermentation; optimization; Aspergillus niger ATCC 1015