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  • Mollasalehi, Somayeh
Publication Date
Aug 02, 2013
Manchester eScholar
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For over 50 years, synthetic petrochemical-based plastics have been produced in ever growing volumes globally and since their first commercial introduction; they have been continually developed with regards to quality, colour, durability, and resistance. With some exceptions, such as polyurethanes, most plastics are very stable and are not readily degraded when they enter the ground as waste, taking decades to biodegrade and therefore are major pollutants of terrestrial and marine ecosystems. During the last thirty years, extensive research has been conducted to develop biodegradable plastics as more environmentally benign alternatives to traditional plastic polymers. Polyvinyl alcohol (PVA) is a water-soluble polymer which has recently attracted interest for the manufacture of biodegradable plastic materials. PVA is widely used as a paper coating, in adhesives and films, as a finishing agent in the textile industries and in forming oxygen impermeable films. Consequently, waste-water can contain a considerable amount of PVA and can contaminate the wider environment where the rate of biodegradation is slow. Despite its growing use, relatively little is known about its degradation and in particular the role of fungi in this process. In this study, a number of fungal strains capable of degrading PVA from uncontaminated soil from eight different sites were isolated by enrichment in mineral salts medium containing PVA as a sole carbon source and subsequently identified by sequencing the ITS and 5.8S rDNA region. The most frequently isolated fungal strains were identified as Galactomyces geotrichum, Trichosporon laibachii, Fimetariella rabenhorsti and Fusarium oxysporum. G. geotrichum was shown to grow and utilise PVA as the sole carbon source with a mean doubling time of ca. 6-7 h and was similar on PVA with molecular weight ranges of 13-23 KDa, 30-50 KDa and 85-124 KDa. When solid PVA films were buried in compost, Galactomyces geotrichum was also found to be the principal colonizing fungus at 25°C, whereas at 45°C and 55°C, the principle species recovered was the thermophile Talaromyces emersonii. ESEM revealed that the surface of the PVA films were heavily covered with fungal mycelia and DGGE analysis of the surface mycelium confirmed that the fungi recovered from the surface of the PVA film constituted the majority of the colonising fungi. When PVA was added to soil at 25°C, and in compost at 25°C and 45°C, terminal restriction fragment length polymorphism (T-RFLP) revealed that the fungal community rapidly changed over two weeks with the appearance of novel species, presumably due to selection for degraders, but returned to a population that was similar to the starting population within six weeks, indicating that PVA contamination causes a temporary shift in the fungal community.

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