Synthetic dyes removal by Fusarium oxysporum HUIB02 and stimulation effect on laccase accumulation

In this study, we reported a laccase producing fungus from hard wood samples. The isolation produced laccase as extracellular enzymes under liquid culture using rice straw and wood chips as carbon sources. The enzyme accumulated highest activity after 12 days and 6 days cultivation on rice straw and wood chips, reaching 186 U/mL and 2.5 U/mL, respectively. Fe^2＋ inhibited activity whereas Co^2＋, Cu²⁺, and Mg²⁺ significantly enhanced its activity. The optimal pH and temperature were 5.0 and 45°C, respectively. Molecular identification indicated that the isolation belonged in Fusarium genus and named as Fusairum oxysporum HUIB02. On the other hand, F. oxysporum HUIB02 showed excellent synthetic dyes decolouration for bromothymol blue, methyl orange, remazol brilliant blue R, indigo carmine with degree approximately 100%. The strain also exhibited great decolouration on malachite green and evans blue. These synthetic dyes enhanced laccase accumulation up to 12.6-fold in compared with culture in rice straw medium. SDS-PAGE zymogram analysis indicated F. oxysporum HUIB02 secreted two main laccases with molecular weight of 110 kDa (Lacc110) and 42 kDa (Lacc42). Laccase gene expression was affected by synthetic dyes. The Lacc110 expression level was suppressed whereas the Lacc42 expression level was induced. The results remarked F. oxysporum HUIB02 is a good source in laccase production and dye decolouration as well as synthetic dyes are directly affected on gene expression pathway in organism.