The high production and poor disposal of plastic materials have caused numerous environmental problems over the years. The need to find organisms capable of biodegrading these recalcitrant materials is still one of the main issues on which researchers focus; in fact, in 2018 alone, 359 million tons of plastic were produced, of which almost 40% is used for packaging. The purpose of this thesis was, therefore, to evaluate the biodegradation capacity of a fungal strain of Fusarium sp. against two types of plastics usually used in single use: polyethylene terephthalate (PET) and its compostable analogue, polylactic acid (PLA). For this purpose, a fungal strain was isolated from the soil of Bosco Siro Negri capable of colonizing PET baits, then identified morphologically and molecularly as Fusarium sp. After testing the enzymatic activities, the biodegradation tests involved the use of plastic fragments of 3x3mm size. The fragments were incubated with Fusarium sp. for 240. After this period, the percentage change in weight with respect to time zero and an uninoculated control was evaluated and a visual analysis of the surface by means of a scanning electron microscope (SEM) and an assessment of the change in bonds were also carried out chemicals using Fourier transform infrared spectroscopy (FT-IR). The results of the tests on the fragments showed an effective ability of the fungus to grow on top of both plastic polymers. The SEM photographs, in fact, show erosions and changes in the surface of the plastics also highlighting the presence of hyphae, while the FT-IR analyzes that revealed differences in the carbon bonds of both polymers. These data were confirmed by weight loss in the first 90 days of incubation, in which a maximum of 1.32% for PLA and 1.23% for PET was reached. In conclusion, it can be said that Fusarium sp. although it has a very slow metabolism, it is a possible biodegradation agent of plastic materials, useful for the formation of possible consortia. Thanks to its enzymatic activity, it is more effective against the biodegradation of compostable PLA than PET. From the results obtained after 240 days, unlike what was expected, the degradation of PLA is reduced at a temperature of 27 ° C, thus suggesting that their dispersion into the environment would not solve the pollution problem.
L’elevata produzione e il cattivo smaltimento dei materiali plastici hanno causato, negli anni, numerosi problemi ambientali. La necessità di trovare organismi in grado di biodegradare questi materiali recalcitranti è tutt’oggi uno dei temi principali su cui si concentrano i ricercatori; infatti, solo nel 2018, sono state prodotte 359 milioni di tonnellate di plastica, di cui quasi il 40% viene utilizzato per il packaging. Lo scopo di questo lavoro di tesi è stato, quindi, valutare la capacità biodegradativa di un ceppo fungino di Fusarium sp. nei confronti di due tipologie plastiche usualmente utilizzate nel monouso: il polietilene tereftalato (PET) e il suo analogo compostabile, l’acido polilattico (PLA). A tale scopo è stato isolato un ceppo fungino dal suolo del Bosco Siro Negri in grado di colonizzare esche di PET, identificato poi morfologicamente e molecolarmente come Fusarium sp. Dopo averne testato le attività enzimatiche, le prove di biodegradazione hanno previsto l’utilizzo di frammenti plastici di dimensioni 3x3mm. I frammenti sono stati incubati con Fusarium sp. per 240. Trascorso tale periodo è stata valutata la variazione percentuale di peso rispetto al tempo zero e ad un controllo non inoculato e sono state effettuate anche un’analisi visiva della superficie mediante microscopio elettronico a scansione (SEM) e una valutazione della variazione dei legami chimici attraverso la spettroscopia infrarossa in trasformata di Fourier (FT-IR). I risultati dei test sui frammenti hanno mostrato un’effettiva capacità del fungo di crescere sopra ad entrambi i polimeri plastici. Le fotografie al SEM, infatti, mostrano erosioni e cambiamenti nella superficie delle plastiche evidenziando anche la presenza di ife, mentre le analisi al FT-IR che hanno rilevato differenze a livello dei legami carboniosi di entrambi i polimeri. Questi dati sono stati confermati dalla perdita di peso nei primi 90 giorni di incubazione, in cui è stato raggiunto un massimo di 1,32% per il PLA e 1,23% per il PET. In conclusione, si può affermare che Fusarium sp. nonostante possieda un metabolismo molto lento, risulti essere un possibile agente di biodegradazione di materiali plastici, utile per la formazione di possibili consorzi. Grazie all’attività enzimatica di cui è dotato risulta più efficace nei confronti della biodegradazione del compostabile PLA rispetto al PET. Dai risultati ottenuti dopo 240 giorni, risulta evidente che diversamente da quanto ci si aspettasse la degradazione del PLA risulti ridotta alla temperatura di 27°C, suggerendo quindi che la dispersione in ambiente di queste non andrebbe a risolvere il problema dell’inquinamento.
BIODEGRADAZIONE DI POLIETILENE TEREFTALATO (PET) E ACIDO POLILATTICO (PLA) MEDIANTE Fusarium sp. E VALUTAZIONE DELL’ATTIVITÀ ENZIMATICA
MARTURANO, LAURA
2019/2020
Abstract
The high production and poor disposal of plastic materials have caused numerous environmental problems over the years. The need to find organisms capable of biodegrading these recalcitrant materials is still one of the main issues on which researchers focus; in fact, in 2018 alone, 359 million tons of plastic were produced, of which almost 40% is used for packaging. The purpose of this thesis was, therefore, to evaluate the biodegradation capacity of a fungal strain of Fusarium sp. against two types of plastics usually used in single use: polyethylene terephthalate (PET) and its compostable analogue, polylactic acid (PLA). For this purpose, a fungal strain was isolated from the soil of Bosco Siro Negri capable of colonizing PET baits, then identified morphologically and molecularly as Fusarium sp. After testing the enzymatic activities, the biodegradation tests involved the use of plastic fragments of 3x3mm size. The fragments were incubated with Fusarium sp. for 240. After this period, the percentage change in weight with respect to time zero and an uninoculated control was evaluated and a visual analysis of the surface by means of a scanning electron microscope (SEM) and an assessment of the change in bonds were also carried out chemicals using Fourier transform infrared spectroscopy (FT-IR). The results of the tests on the fragments showed an effective ability of the fungus to grow on top of both plastic polymers. The SEM photographs, in fact, show erosions and changes in the surface of the plastics also highlighting the presence of hyphae, while the FT-IR analyzes that revealed differences in the carbon bonds of both polymers. These data were confirmed by weight loss in the first 90 days of incubation, in which a maximum of 1.32% for PLA and 1.23% for PET was reached. In conclusion, it can be said that Fusarium sp. although it has a very slow metabolism, it is a possible biodegradation agent of plastic materials, useful for the formation of possible consortia. Thanks to its enzymatic activity, it is more effective against the biodegradation of compostable PLA than PET. From the results obtained after 240 days, unlike what was expected, the degradation of PLA is reduced at a temperature of 27 ° C, thus suggesting that their dispersion into the environment would not solve the pollution problem.È consentito all'utente scaricare e condividere i documenti disponibili a testo pieno in UNITESI UNIPV nel rispetto della licenza Creative Commons del tipo CC BY NC ND.
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https://hdl.handle.net/20.500.14239/12956