Delignification and detoxification of peanut shell bio-waste using an extremely halophilic laccase from an...

Lignocellulose bioconversion is a harsh process requiring the use of surfactants and organic solvents. Consequently, the incorporation of laccases in this bioconversion requires the bioprospecting of enzymes that can remain stable under extreme conditions. An extracellular, highly stable laccase was produced by the halophilic isolate Aquisalibacillus elongatus in submerged liquid culture fermentation. Statistical and non-statistical strategies gave the highest enzymatic activity (8.02 U mL^-1) following addition of glucose (1.7 g L^-1), copper sulfate (0.8 g L^-1), urea (15 g L^-1), and CaCl₂ (0.8 g L^-1). The enzyme, after purification using a synthetic affinity support, delignified a peanut shell substrate by 45%. A pH of 8.0 and a temperature of 35 °C were optimal for delignification of this bio-waste material. Addition of [Bmim][PF₆], 1,4-dioxane, acetone, and HBT promoted this bio-waste delignification. Bio-treatment in the presence of 50% [Bmim][PF₆] gave a maximal lignin removal of 87%. The surfactants tested had no significant effects on the delignification yield. The laccase also detoxified the toxic phenols found in peanut shell waste. The high catalytic efficiency of this enzyme against a lignocellulosic sample under extreme conditions suggests the suitability of this laccase for industrial applications.