Biodeterioration of low-density polyethylene by mangrove-associated endolichenic fungi and their enzymatic regimes

Abstract

Abstract Fungal involvement in the biodeterioration of low-density polyethylene (LDPE) has received great attention in recent years. Among diverse groups of fungi, endolichenic fungi (ELF) are adapted to thrive in resource-limited conditions. The present study was designed to investigate the potential of mangrove-associated ELF, in the biodeterioration of LDPE and to quantify key-depolymerizing enzymes. A total of 31 ELF species, isolated from 22 lichens of mangrove ecosystems in Negombo lagoon, Sri Lanka were identified using DNA barcoding techniques. ELF were inoculated into a mineral salt medium, containing LDPE strips and incubated at 28 ± 2°C, for 21 days, under laboratory conditions. After incubation, biodeterioration was monitored based on percent reductions in weights and tensile properties, increments in the degree of water absorption, changes in peaks of infrared spectra and surface erosions using scanning electron microscopy. Out of 31 species, Chaetomium globosum, Daldinia eschscholtzii, Neofusicoccum occulatum, Phanerochaete chrysosporium, Schizophyllum commune and Xylaria feejeensis showed significant changes. Production of depolymerizing enzymes by these species was assayed qualitatively using plate-based methods and quantitatively by mass-level enzyme production. Among them, Phanerochaete chrysosporium showed the highest enzyme activities as (9·69 ± 0·04) × 10−3, (1·96 ± 0·01) × 10−3, (5·73 ± 0·03) × 10−3, (0·88 ± 0·01), (0·64 ± 0·06), (1·43 ± 0·01) U ml−1 for laccase, lignin peroxidase, manganese peroxidase, amylase, lipase and esterase, respectively.