RODUCTION AND PARTIAL CHARACTERIZATION OF LACCASE FROM OYSTER MUSHROOM (Pleurotus ostreatus) COLLECTED FROM THE BARK OF EUCALYPTUS TREE

The aim of the current study was to evaluate the effect of different growth substrates on laccase production and to partially characterize it in terms of the effect that pH, temperature and substrate concentration had on its activity. The study was conducted at the National Agricultural Biotechnology Research Center, Holetta. The fruiting bodies of Pleurotus ostreatus were collected from live old Eucalyptus tree barks. The potential of Pleurotus ostreatus in laccase production was evaluated on PDA plate containing guaiacol. After the 10th day of incubation, the fungus was able to produce dark brown color around the colonies. In solid state fermentation (SSF), bean straw produced more laccase with an activity of 0.1248 U/ml. The lowest activity was recorded from Cupressus lusitanica sawdust. Eucalyptus sawdust that was the second best medium in SSF was considered for further parameter optimization under SSF. Optimal laccase production (0.1198 U/ml) was obtained on the 10th day of incubation period and the optimum temperature and pH were 28°C and 5.5, respectively. Soluble starch and peptone were found to be the most preferred carbon and nitrogen sources for laccase production. Copper sulfate and asparagine induces more laccase production Copper sulfate being the most potent inducer. Generally, there was a 1.72-fold increase of laccase production in optimized media of Eucalyptus sawdust when compared to unoptimized one. The crude laccase extract showed maximum activity at pH 6.0 and a temperature of 50°C. When incubated overnight, laccase was found to be thermostable at lower temperature (20- 30°C). At pH 6.0, laccase nearly maintained 70% of its initial activity after 12 hrs incubation. There was a linear relation between laccase activity and its substrate concentration. The apparent calculated Vmax and Km were 0.922U/ml and 4.14mM, respectively showing its high affinity towards its substrate. Optimized medium of Eucalyptus sawdust gave more laccase production than unoptimized one and hence recommended for large scale production. Further study is recommended at a molecular level to enhance the production of laccase from P. ostreatus for animal feed treatment and other possible industrial applications.