Production Parameters Optimization by Aspergillus flavus Isolated and Screened from different Environmental Sources in Lahore

Abstract

Laccases are industrially important oxidative enzymes, involved in degradation of phenolic and non-phenolic compounds, including lignin, reducing oxygen to water at the same time. Fungal laccase production has been widely studied because of enzyme secretion using agro-industrial wastes. This study includes isolation of laccase producing fungi from different environmental samples of water, collected from different sites in and around Lahore. In this study 58 fungal strains were isolated by serial dilution and plate method. They were cultured on potato dextrose agar (PDA) plates containing indicator compounds, guaiacol and tannic acid to screen fungal strain for laccase production ability. Among 58 isolated strains belonging to 12 different species, strains of 08 different species were found to be laccase producers. Quantitative analyses were carried out to select potent laccase producer among the strains of different species. Results showed that A. flavus (SAf5) isolated from industrial waste water produced large zone diameter and colony diameter while Pencillium strain showed least growth. The rest of strains belonging to different species showed variable behaviour for laccase biosynthesis. The production of laccase enzyme was investigated using isolated A. flavus strain (SAf5) under liquid state fermentation. The cultural parameters influencing laccase enzyme production by A. flavus strain (SAf5) were optimized. Guaiacol and acetate buffer were used to measure lacase activity. Lacase activity was highest on 7th day of incubation when operated under following conditions: 30 oC temperature, 5 pH, 3.5% sugarcane bagasse as carbon source (among other sources used including wheat straw, rice bran, glucose and maltose), 2% peptone as nitrogen source (among other sources including yeast extract, urea, ammonium sulphate and ammonium chloride). Scaled up study was carried out in a bench top fermenter, all previously optimized cultural conditions were used to grow A. flavus for improved production of laccase enzyme. Concentrated crude enzyme extract was obtained by filtration and centrifugation. It was concluded that A. flavus strain (SAf5) isolated from industrial waste water was the most promising one among eight other fungal strains isolated from different water sources, for laccase enzyme production.