Optimization of simultaneous production of tyrosinase and laccase by Neurospora crassa

Abstract

Increasing demand for efficient and environmentally benign oxidation technologies has resulted in a focus on the use of oxidoreductases. Laccases and tyrosinases, which utilize molecular oxygen and produce water as by-product, are particularly attractive. Simultaneous production of laccase and tyrosinase was studied in Neurospora crassa FGSC #321 as the fungal strain which has the ability to produce tyrosinase intracellularly while producing laccase extracellularly. Using one-variable-at-a-time experiments and a Taguchi orthogonal L9 array demonstrated that a Vogel minimal medium containing 2.5% sucrose at pH 6.5 and 25 °C with no agitation or oxygen purging were the optimum conditions for N. crassa FGSC #321 growth. Conditions were adjusted to obtain the highest laccase and tyrosinase production. Results indicate that the control mechanisms for the production of both enzymes in N. crassa FGSC #321 are similar but not necessarily identical. Results revealed that transferring the harvested cells from the growth medium into the phosphate buffer (pH 6.8, 0.1M) containing cycloheximide (2 μM) and fluorouracil (2 mM) and increasing the temperature to 30 °C were the best conditions for simultaneous production of laccase and tyrosinase (1278 and 410 U/g of biomass, respectively). Nonetheless, starvation at 35 °C is proposed as the most cost-effective means for inducing laccase. The N. crassa laccase was characterized by using its molecular weight, pI value, optimal pH and temperature and stability.

Keywords:

• Optimization
• laccase
• tyrosinase
• Neurospora crassa
• starvation
• heat stress

Acknowledgements

Financial support of NIGEB and Ministry of Science, Research and Technology is kindly acknowledged. The invaluable help and collaboration of Chemical Engineering labs of Waterloo University and Biocatalysis Group of the CSIC (Madrid, Spain) are appreciated.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

Supplementary material available online