PRODUCTION AND APPLICATION OF LIGNOLYTIC ENZYMES of Halopiger aswanensis

Abstract

The present work focuses on studying the degradation of synthetic dyes and Kalson lignin using lignolytic enzymes produced from haloalkaliphile Halopiger aswanensis strain ABC_IITR. Synthetic dyes pose severe health hazards and a drastic impact on the aqueous environment, whereas lignin is a recalcitrant aromatic biopolymer required to synthesize biochemicals. In recent years, exploring the biocompatible process for lignin valorization and synthetic dyes degradation through extremozymes has gained attention. Lignolytic enzymes from other established genera such as fungi and bacteria have proven potential in the application as mentioned above; however, they exhibit low stability in harsh industrial conditions such as alkalinity, high temperature, and ionic strength/salt concentration. In the current scenario, both textile and paper industry effluents consist of the aforementioned industrial conditions. Although lignin can be valorized in the lignin-based industry in a homogenous phase by solubilizing lignin at higher alkaline pH, organic solvents, or biocompatible ionic liquids, it is the unavailability of compatible enzymes for the purpose. Hence, the current study explores the possibility of utilizing lignolytic enzymes in such conditions produced by H. aswanensis strain ABC_IITR. Lignolytic enzymes, Lignin peroxidase (LiP), Manganese peroxidase (MnP), and Laccase (Lac) were produced both in Submerged Fermentation (SmF) with glucose as a carbon source and Solid-State Fermentation (SSF) with wheat bran as a substrate. The optimized conditions obtained using a one-factor at a time experimental design. In optimized conditions of SmF, the activities of LiP, MnP were 2.95 ± 0.17 and 1.84 ± 0.11 IU/mL, respectively, while laccase activity was not detected. Whereas in optimized conditions of SSF, H. aswanensis produced LiP, MnP, and Lac with the activities of 272 ± 15, 41 ± 1, and 12 ± 1 IU/g, respectively. The reaction conditions of enzyme activity were optimized, including sodium chloride concentration, pH, and temperature. The optimized conditions for LiP & Lac: sodium chloride 2.5 M, pH 7, 55 ℃ and MnP: sodium chloride 2.5 M, pH 8.6, 60 ℃, which demonstrated their suitability towards lignin valorization in industrial conditions. Furthermore, metal ions influence and crude lignolytic enzyme stability was assessed in an organic solvent, cholinium laurate based ionic liquid (CLIL).