Isolation and screening of lipase producing fungi from selected oil contaminated soils

Abstract

Oil spills pose a significant threat to the environment, resulting in complex changes to soil properties and microbial ecology. This study investigated the variations in soil characteristics and enzymatic potential of indigenous fungi across several oil-contaminated sites within Ilorin Metropolis, with the aim of isolating and screening for lipase production. Soil samples were collected from three distinct locations: Tanke Tipper Garage, Tanke Ile-iwe, and Ago Market, representing areas contaminated with engine oil, groundnut oil, and palm oil, respectively. Standard methods were employed to determine key soil properties. The analysis revealed diverse soil profiles across the sites, with texture varying from sandy to clayey and loamy/sandy. Soil acidity also ranged from slightly acidic to neutral to alkaline. Six distinct fungal species were isolated and identified namely: Aspergillus niger, Aspergillus flavus, Rhizopus stolonifer, Geotrichum candidum, Fusarium oxysporium, Penicillium chrysogenum. The isolates were screened for lipase production by measuring the diameter of the zone of clearance on appropriate medium using standard methods. The fungal species exhibited varying degrees of lipase activity,  Aspergillus niger emerged as the highest lipase producer with a 54.50mm diameter zone of clearance, followed by Rhizopus stolonifer (29.50mm), Geotrichum candidum (13.00mm), Fusarium oxysporium (12.00mm), and Penicillium chrysogenum (9.00mm) as the least producer. Notably, the most proficient lipase producer, Aspergillus niger, was isolated from the engine oil-contaminated soil, which was determined to be the most toxic and recalcitrant contaminant analyzed. The significant variations in soil properties and microbial adaptability highlight the intricate interplay between contaminant type and local soil characteristics.