Background

Azo dyes represent a common textile dye preferred for its high stability on fabrics in various harsh conditions. Although these dyes pose high-risk levels for all biological forms, fungal laccase is known as a green catalyst for its ability to oxidize numerous dyes.

Methods

Trichoderma isolates were identified and tested for laccase production. Laccase production was optimized using Plackett–Burman Design. Laccase molecular weight and the kinetic properties of the enzyme, including K_m and V_max, pH, temperature, and ionic strength, were detected. Azo dye removal efficiency by laccase enzyme was detected for Congo red, methylene blue, and methyl orange.

Results

Eight out of nine Trichoderma isolates were laccase producers. Laccase production efficiency was optimized by the superior strain T. harzianum PP389612, increasing production from 1.6 to 2.89 U/ml. In SDS-PAGE, purified laccases appear as a single protein band with a molecular weight of 41.00 kDa. K_m and V_max values were 146.12 μmol guaiacol and 3.82 μmol guaiacol/min. Its activity was stable in the pH range of 5–7, with an optimum temperature range of 40 to 50 °C, optimum ionic strength of 50 mM NaCl, and thermostability properties up to 90 °C. The decolorization efficiency of laccase was increased by increasing the time and reached its maximum after 72 h. The highest efficiency was achieved in Congo red decolorization, which reached 99% after 72 h, followed by methylene blue at 72%, while methyl orange decolorization efficiency was 68.5%.

Conclusion

Trichoderma laccase can be used as an effective natural bio-agent for dye removal because it is stable and removes colors very well.