Abstract:
Laccases are polyphenol oxidases that have numerous industrial and bioremediation applications. They are well known as lignin degrading enzymes. Majority of laccase activity has been demonstrated in fungal species and their physiological roles is mainly the oxidation of phenolic subunit which leads to biodegradation. In this study we evaluated the potential performance of fungal isolates from agro-wastes for laccase production. Fungal cultures were screened for laccase production by plate test method using 2’ 2’ – azinobis-(-3-ethyl benzthiazoline -6- suphonate) (ABTS). The isolates were further screened for laccase production in submerged culture using synthetic medium. Utilization of selected agro-wastes(sawdust, plantain and banana peels) residue for laccase production was evaluated. Out of 12 fungal cultures tested, 5 cultures were found to be laccase positive and these were identified as Geotrichum sp, Cephalosporium sp, Trichoderma sp, Trametes sp and Fusarium sp. These five fungal cultures were further used for quantitative screening with synthetic medium, Trichoderma sp gave the highest enzyme activity of 57.1U/l followed by Trametes sp with 51.99 U/l, Fusarium sp had 29.2 U/l. Geotrichum sp and Cephalosporium sp recorded the lowest activities with 28.04 U/l and 9.72 U/l respectively all at the fourth day of incubation. Trichoderma sp was selected as the most potent in producing enzyme and therefore used for further studies where the use of selected agro waste medium as different carbon sources, effect of different inoculum sizes, pH and use shaker was evaluated . With respect to agro-wastes used sawdust medium gave the highest with 151.17 U/l followed by plantain peel medium with 62.49U/l, banana peel medium was the lowest with 54.94U/l. Protein content obtained from sawdust medium was 45.8mg/ml, plantain peel medium had 29.2mg/ml while banana peel was the lowest with 16.8mg/ml all at the sixth day of the fermentation process. The optimum pH for banana peel, plantain peel and sawdust was 5.94, 5.83 and 5.95 respectively. When instead of the default static incubation, a shaker incubator (at 150 rpm) was introduced using sawdust as carbon source, the overall highest yield of laccase (310.45U/l) was obtained at pH 6 prior to incubation, temperature of 25˚C and inoculum size of 105 spores per ml. Thus, sawdust can serve as cheap substrate for laccase production.
