Characterization of Thermostable Lignolytic Enzymes from Penicillium italicum during Biomineralization of Polyethylene

Abstract

Penicillium italicum isolated from a local dumpsite in Ilara- mokin, Ondo state, Nigeria was used to bio-transform low-density polyethylene (LDPE). Biodegradation was carried out using surface-sterilized and autoclaved LDPE over 3 months experimental period. Bio-remediation was evaluated by determining the weight loss, and physical structure changes which were revealed by scanning electron microscopy. The result showed P. italicum was able to degrade autoclaved LD-PE (25%) more efficiently than surface-sterilized LD-PE (12%). Screening and characterization of lignolytic enzymes (manganese peroxidase (MnP) and laccase (Lac)) produced by P. italicum were also investigated using autoclaved LDPE as a carbon source over 3 months degradation period. The result showed that P. italicum produced optimum MnP and Lac activities in the 6th week of cultivation (90 U/mL and 100 U/mL respectively). Study of their physicochemical properties showed that MnP and Lac had optimum activities (100%) at pH 7.0 and pH 5.0 and were stable at the same pH with 74% residual activities each respectively. The enzymes also had optimum activity (100%) at 70oC and were stable over a wide temperature range (40oC–80oC) with 78% residual activities each after 120 min of incubation. These results show the ability of P. italicum to produce thermostable lignolytic enzymes with the potentials to bio-mineralize recalcitrant plastic polymers such as LDPE.