Optimization of growth conditions for enhancing the production of microbial laccase and its application in treating antibiotic contamination in wastewater.

In this work, seven indigenous macrofungal isolates were selected to screen for their laccase production capability. Among them, isolates viz., Pleurotus eryngii, Pleurotus florida, Pleurotus sajor caju and Gandoderma lucidum were found to exhibit high laccase activity in the preliminary studies and were thus selected for the optimization studies with an aim to enhance laccase production. The pH optimization studies were carried out between pH range of 4-6. The laccase activity and biomass were found to be optimum at pH 4, 4.5, 4.5 and 5 for P. eryngii, P. florida, P. sajor caju and G. lucidum, respectively. Optimization studies with chemical inducers namely, tannic acid, 2,6 dimethoxyphenol and copper sulphate at three different concentration levels were conducted and tannic acid at 2 mM concentration was found to increase the laccase activity to about 45% followed by 2,6 dimethoxyphenol (2 mM) with an increase of about 43% and copper sulphate (0.1 mM) showing 21% increase in the yield. Biodegradation studies utilizing laccase isolated from P. eryngii, P. florida and P. sajor caju was carried out for a commonly detected fluoroquinolone antibiotic, levofloxacin, in water and pharmaceutical wastewater. The results indicated that the degradation efficiency of levofloxacin using laccase isolated from P. eryngii (88.9%) was comparable to commercial laccase (89%). When the cost economics of using crude laccase was evaluated against commercial laccase it was evident that the total cost of the treatment could be reduced by 71.7% if commercial grade laccase was replaced by crude enzyme extracted from indigenous macrofungi such Pleurotus eryngii, Pleurotus florida, and Pleurotus sajor caju indicating a promising and cost-effective alternative for wastewater treatment. © King Abdulaziz City for Science and Technology 2021.