Date Published: August 15, 2013
Publisher: Public Library of Science
Author(s): José Maria Rodrigues da Luz, Sirlaine Albino Paes, Mateus Dias Nunes, Marliane de Cássia Soares da Silva, Maria Catarina Megumi Kasuya, Bernhard Ryffel.
Growing concerns regarding the impact of the accumulation of plastic waste over several decades on the environmental have led to the development of biodegradable plastic. These plastics can be degraded by microorganisms and absorbed by the environment and are therefore gaining public support as a possible alternative to petroleum-derived plastics. Among the developed biodegradable plastics, oxo-biodegradable polymers have been used to produce plastic bags. Exposure of this waste plastic to ultraviolet light (UV) or heat can lead to breakage of the polymer chains in the plastic, and the resulting compounds are easily degraded by microorganisms. However, few studies have characterized the microbial degradation of oxo-biodegradable plastics. In this study, we tested the capability of Pleurotus ostreatus to degrade oxo-biodegradable (D2W) plastic without prior physical treatment, such as exposure to UV or thermal heating. After 45 d of incubation in substrate-containing plastic bags, the oxo-biodegradable plastic, which is commonly used in supermarkets, developed cracks and small holes in the plastic surface as a result of the formation of hydroxyl groups and carbon-oxygen bonds. These alterations may be due to laccase activity. Furthermore, we observed the degradation of the dye found in these bags as well as mushroom formation. Thus, P. ostreatus degrades oxo-biodegradable plastics and produces mushrooms using this plastic as substrate.
Pollutants composed of plastic polymers have been removed from the environment using three approaches. The first approach is to store the waste in landfills. However, due to rapid population growth and the limited number of landfills, this approach only transfers the problem to future generations , . Plastic waste represents 20–30% of the total volume of solid waste contained in landfills because in addition to the large amount of waste generated, plastic waste is recalcitrant and remains deposited in these landfills for long periods of time . The second approach can be subdivided into two distinct parts: incineration and recycling , . The incineration of plastic waste often results in a significant release of carbon dioxide and other gases. The recycling process includes removing the plastic residue, separating plastic into categories according to type, and washing, drying, grinding and reprocessing the plastic waste . Thus, recycling is an expensive process, and the quality of the recycled plastic is lower than that of the primary material –. The final approach is the development of biodegradable polymers.
The nucleotide sequence obtained by the amplicon sequencing of the rDNA 18S of P. ostreatus PLO6 was deposited in GenBank (KC782771). The alignment of this sequence with other sequences found in the database showed a 92% similarity with the sequence EF514247.1, described as Pleurotus ostreatus strain CGMCC 5.37 . Thus, the sequencing confirmed the previous morphologic classification of the isolate PLO6 as the species P. ostreatus. This classification was made based in the basidiocarps (mushrooms) of this fungus , .
P. ostreatus is capable of degrading oxo-biodegradable plastic and producing mushrooms using the plastic waste without any prior physical treatment. The results of this study are important for elucidating the biodegradation process of plastic waste and revealing a new alternative for the proper treatment of these pollutants.