Isolation and characterisation of nitrilase producing Aspergillus species recovered from solid waste leachates at two dump sites in Lagos, Nigeria

Abstract

Aims: Nitrile compounds are cyanogenic intermediates, products, byproducts and waste products of agriculture, chemical and pharmaceutical industries and fossil fuels degradation. The enzymatic hydrolysis of nitriles to non-toxic carboxylic acids or amides plays an increasingly important role in environment remediation. This study aimed at exploring the potential of Aspergilli in the detoxification nitrile compounds at two selected dump sites in Lagos, Nigeria. Methodology and results: Decomposing solid waste leachate samples (SWL) were randomly collected at two selected dump sites namely Olusosun (Ojota) and Isolo (Oke-Afa). Samples per site were pooled, processed by selective enrichment and screened for the presence of Aspergilli by culture technique and intergenic spacer sequencing (ITS). Biomass generation and pH changes in the culture fluids were monitored at 4-days interval by dry weight measurements. Nitrilase production was determined spectrophotometrically. Two nitrilase producing Aspergillus strains: Aspergillus fumigatus strain WO2 with accession number MF78882 and Aspergillus niger strain WO7 with accession number MH542673 were identified. Growth investigation revealed biomass generations of 17.8 g and 23.8 g dry weight per one liter media for A. fumigatus strain WO2 and A. niger strain WO7 respectively. Progressive pH monitoring showed decline from 7.2 to 4.5 and 7.2 to 6.2 was obtained for strains WO2 and WO7 respectively, during nitrilase production at different yields of 0.0150 and 0.0161 mg/mL/min respectively. Conclusion, significance and impact of study: This study supports the studied dump sites as important sources of nitrilase-producing A. fumigatus and A niger strains with potentials as cost-effective environmental bioremediation agents in Nigeria.