PRODUCTION OF LACCASE ENZYME USING FUNGAL ISOLATES FROM DECOMPOSED KHAT (Catha edulis (Vahl) Forsek.ex Endl) RESIDUE

Abstract

Laccase (EC 1.10.3.2, benzenediol oxygen, oxidoreductases) is typically extracellular monomeric glycoproteins that belong to the multicopper oxidase family. Laccase is widely distributed in higher plants, bacteria, fungi, and insects. Laccase play an important role in different industrial sectors, soil bioremediation and biodegradation of environmental phenolic pollutant and removal of endocrine disruptors. Laccase has been efficiently applied to nanobiotechnology due to their ability to catalyze electron transfer reactions without additional cofactor. Fungal isolates from decomposed khat (Catha edulis) residue for laccase enzyme production represent a unique source of biodiversity that has not been extensively studied. The present study has aimed to assess laccase production by fungal isolates from decomposed khat (Catha edulis) residue. The study involves sample collection from decomposed khat residues. After about five times dilution, the solution was plated onto agar medium. The screening for laccase producing fungal culture was conducted based on color changes followed by morphological identification of fungal species. The laccase activity test was conducted for fungal colonies with better activity. Thereafter, the optimization of parameters for laccase activity was conducted. The result morphological features of laccase producing fungal isolates from decomposed khat (Catha edulis) residue were identified by macroscopic visual color and microscopic observation using lactophenol cotton blue stain demonstrated the fungal isolates found to be belong to four genera including Pycnoporus sp, Melanocarpus sp, Podospora sp and Niesslia sp. The isolated fungal strains showed varying levels of laccase activity, with Podospora sp, and Melanocarpus sp being the most active ones. Melanocarpus sp has presented maximum laccase activity (425.04U/g) at pH 4 and (448.59U/g) at 45oC indicating that the optimum laccase activity for Melanocarpus sp isolate. By contrast, Podospora sp has recorded maximum laccase activity (403.12U/g) at pH 6 and (422.47U/g) at 40oC indicating that the optimum enzyme activity for Podospora sp isolate. The maximum laccase activity for Melanocarpus sp (367.21U/g) was recorded at 1mg/mL inoculums size whilst podospora sp has recorded maximum laccase activity (449.89U/g) at 1.50mg/mL inoculums size. It can be concluded from the result of the present study that laccase showed maximum activity at pH ranging from 2.0-7.0; temperature 35 to 50oC and inoculums size 0.5 to 2mg/mL in both Melanocarpus and Podospora spp. Lignocellulosic wastes have been widely used in fungal laccase production due to their low cost and good prospects. Although different lignocellulosic wastes were tested for laccase production by fungi, the principles for the selection of lignocellulosic substrates are lacking. In the present study laccase enzyme can be produced from locally available decomposed khat residues.