The involvement of wood decay fungi and the importance of their enzymes in polyethylene degradation is well documented. Therefore, decay-resistant hardwood associated fungi should be better degraders with their versatile enzymatic systems. In the current study, decaying hardwood associated fungi were isolated and their ability to degrade low-density polyethylene (LDPE) was assessed. Thirty-three isolates were identified by sequencing the internal transcribed spacer region of nuclear ribosomal DNA. Randomly selected isolates were tested for laccase producing abilities. Three species were selected to test their potentials in LDPE sheet degradation. Fungi were incubated in Czapek-Dox broth containing 20-micron LDPE sheets at room temperature for 60 days. The biodegradation signatures were assessed by analyzing the changes in structural characteristics of LDPE using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), percent reduction of tensile properties, and weight loss. FTIR analysis revealed changes in certain functional groups compared with the control, indicating chemical changes resulting from the treatment. LDPE sheets incubated with fungi showed cracks and holes under SEM analysis, percent reduction in tensile properties, and weight loss, which are the signatures of degradation. This study revealed that the hardwood decaying basidiomycetes, Phlebiopsis flavidoalba, Schizophyllum commune, and Phanerodontia chrysosporium have the potential for in vitro LDPE degradation.
The involvement of microorganisms in low-density polyethylene (LDPE) degradation is widely studied across the globe. Even though soil, landfills, and garbage dumps are reported to be promising niches for such organisms, recently the involvement of wood decay fungi in polyethylene degradation is highlighted. In light of this, 50 fungal samples isolated from decaying hardwoods were assessed for their wood degradation ability and for their depolymerization enzymatic activities. For the LDPE deterioration assay, 22 fungal isolates having wood decay ability and de-polymerization enzymatic activities were selected. Fungal cultures with LDPE sheets (2 cm x 10 cm x 37.5 μm) were incubated in the presence and in the absence of wood as the carbon source (C) for 45 days. Degradation was measured by weight loss, changes in tensile properties, reduction in contact angle, changes of functional groups in Fourier-transform infrared spectroscopy, Scanning electron microscopic imaging, and CO2 evolution by strum test. Among the isolates incubated in the absence of wood, Phlebiopsis flavidoalba out-performed the other fungal species showing the highest percentage of weight reduction (23.68 ± 0.34%), and the lowest contact angle (64.28° ± 5.01). Biodegradation of LDPE by P. flavidoalba was further supported by 46.79 ± 0.67% of the mass loss, and 3.07 ± 0.13% of CO2 emission (mg/L) in the strum test. The most striking feature of the experiment was that all the isolates showed elevated degradation of LDPE in the absence of wood than that in the presence of wood. It is clear that in the absence of a preferred C source, wood decay fungi thrive to utilize any available C source (LDPE in this case) showing the metabolic adaptability of fungi to survive under stressful conditions. A potential mechanism for LDPE degradation is also proposed.
21Though Sri Lanka belongs to one of the 34 biodiversity hotspots of the world, its microfolora 22 specially fungi are not well studied and underrepresented in the global literature. Here we report 23 the fungal species diversity of decaying hardwood of a Sri Lankan dry zone forest for the first 24 time. Decaying hardwoods were collected from historically important Dimbulagala forest reserve, 25 Sri Lanka and fungi associated with these woods were isolated. Out of 35 fungal species identified 26 using morphological and molecular methods, 11 species were first records in Sri Lanka. All the 27 tested isolates were able to utilize wood as the sole carbon source and produced varying degrees 28 of laccase. Isolates of Perenniporia tephropora, Coriolopsis caperata, Gymnopilus dilepis, 29 Fusarium solani and Vanderbylia fraxinea were among the top six laccase producers. Except 30 Fusarium solani, the rest of the isolates showed more than 70% decolorization of the of 31 triphenylmethane dye and there was a significant positive correlation between laccase production 32 and dye decolorization. To the best of our knowledge laccase production and dye decolorization 33 ability of Vanderbylia fraxinea and Gymnopilus dilepis have never been reported in the fungal 34 kingdom before. Perenniporia tephropora was isolated from one of the strongest decay resistant 35 hardwood species, Ebony (Diospyros ebenum) also known as dark wood and V. fraxinea was 36 isolated from another medicinally important hardwood Neem (Azadirachta indica). Findings of 37 this study confirms that decaying hardwood of Sri Lanka provide unexplode a unique niche for 38 discovering fungal species with biotechnological applications such as high laccase producers and 39 dye decolorizers. 40 41 48metagenomics studies suggested that actual numbers might be closer to 3.5 to 5.1 million species 49 or much higher than this [3]. This uncertainty in the numbers is partially due to lack of advanced 50 molecular based thorough studies in the tropics where incredibly rich diversity has been reported 51 [4]. Hawksworth [5] also suggested that much of the undescribed fungal species could be present 52 in the tropics and it is reviewed in Aime and Brearley [4]. 53Sri Lanka, a tropical island in the Indian ocean along with the Western Ghats, belongs to one of 54 the 34 biodiversity hotspots in the world. Though its plant and animal diversity is well studied 55 [6,7], microbial studies, especially fungal studies remain in its infancy. Furthermore, biodiversity 56 hotspot concept of Sri Lanka should not be an exception for microbial diversity including fungi. 57However, most of the fungal studies in Sri Lanka have mainly focused on macro-fungi using 58 morphological characters [8]. Moreover, these studies have mainly concentrated on the wet zone 59 forests. On the other hand, dry zone forest ecosystems in the country spread over 22 % of area in 60 Sri Lanka, whereas the total forest cover is about 26.6%. Dimbulagala (7°51'40.5"N 61 81°07'05.5"E) is an isolated hill co...
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