Laccase production by newly isolated white rot fungi under solid substrate fermentation conditions

Solid substrate fermentation (SSF) is a process occurring in the absence of free water, using natural substrates. This fermentation method which is an alternative method for biotechnologic processes uses lignocellulosic raw materials as solid substrates for laccase production with high activity and lower cost. Organisms utilize these solid substrates both as an attachment place and nutrition. Using lignocellulosic raw materials in bioprocesses may help to solve environmental problems. In this study, laccase production by newly isolated Funalia trogii, Ganoderma lucidum and Trametes versicolor was investigated during SSF process. The effect of different factors (solid substrate, temperature, pH, moisture content and inducers) on laccase production was tested. Among the tested lignocellulosic solid substrates wheat bran was determined the best solid substrate for laccase production. The effect of soy flour, tree leaves, yeast extract and copper on laccase production of fungi was also investigated. Wheat bran+soy flour medium supplemented with copper was the best medium for high laccase production. Optimum SSF conditions were 75% moisture content, 30°C and pH 5-6. SSF was also conducted using glass tray fermentor and high laccase activities as 22469±2622, 2008±826 and 2649±810 U/L were obtained for F.trogii, G.lucidum and T.versicolor, respectively. The effect of pH and temperature on crude laccase activity and stability, obtained from F.trogii, G.lucidum and T.versicolor grown on copper supplemented wheat bran+soy flour media were also tested. These crude laccases showed high activity especially at pH 2.5-3.5. They gave the highest activity in high temperatures. They were also detected as thermostable at high temperatures. Remazol Brilliant Blue R (RBBR) decolorization activity of crude laccase from G.lucidum showed that it could decolorize this textile dye (400 mg/L) as 61% within 20 minutes under optimal conditions. Results showed that, SSF has a potential for the laccase production and high amount of laccases could be obtained by these fungi under optimum conditions. It is important to determine the activity and stability profiles of these crude laccases for understanding the best application conditions. KEYWORDS: Solid substrate fermentation, Funalia trogii, Ganoderma lucidum, Trametes versicolor, lignocellulosic raw materials, crude laccase, dye decolorization