Degradation of different types of plastic with extremophillic fungi isolated from household appliances

Plastika je v današnjem svetu nepogrešljiv sintetični polimer. Recikliranje plastike poteka le v manjši meri, fizikalna ter kemijska obdelava pa sta energijsko potratni ter neugodni za okolje. Fizikalno-kemijska razgradnja plastike v vodi ali na kopnem vodi do nastanka mikroplastike, ki lahko vstopa v prehranjevalne verige. Mikrobiološka razgradnja plastike je trenutno ena najbolj obetavnih rešitev za zmanjšanje okoljskega bremena odpadne plastike s čim manj negativnih vplivov na okolje. Zajema uporabo mikroorganizmov, ki lahko plastiko uporabijo kot edini vir ogljika. Glive so znane kot naravni razkrojevalci. Naravne in sintetične polimere encimsko razgrajujejo z različnimi oksidoreduktazami in hidrolazami. V diplomski nalogi smo testirali 59 sevov gliv, ki so bile izolirane iz pralnih in pomivalnih strojev. V teh gospodinjskih aparatih so glive izpostavljene sintetičnim materialom, različnim organskim snovem, kemikalijam, visokim temperaturam, vodi ter visokemu pH. Izpostavitev različnim pogojem vodi v selekcijo poliekstremotolerantnih gliv. Ker so glive v gospodinjskih napravah kolonizirale predvsem plastične predele, nas je zanimalo, ali lahko rastejo na petih različnih plastikah brez dodanega vira ogljika. Uporabili smo sledeče tipe plastike: polietilen z nizko gostoto, poliamid, polietilen tereftalat, polipropilen in poliuretan. Glive smo tri mesece inkubirali na trdnem gojišču s posameznim tipom plastike. Njihovo rast in morfologijo smo opazovali s svetlobnim in elektronskim mikroskopom. Ugotovili smo, da so na plastikah najbolje rasle glive iz rodov Cladosporium in Exophiala, za katere je bilo v literaturi že dokazano, da lahko plastiko tudi razgrajujejo. Od 59 testiranih sevov jih je 50 raslo na več kot enem tipu plastike. Na vseh petih tipih plastike je raslo 20 sevov. Pri tem smo odkrili 43 vrst gliv, ki do sedaj v literaturi še niso bile opisane kot razgrajevalke plastike. Poliamid in polipropilen imata glede na literaturo le nekaj znanih razkrojevalcev – v našem eksperimentu je na poliamidu raslo 44 sevov ter na polipropilenu 43 sevov.Plastics are globally one of the most indispensable synthetic materials. However, the recycling remains limited. Since physical and chemical degradation is very energy consuming and toxic to the environment, physicochemical degradation of accumulated plastic on land or in the oceans leads to microplastics, which can enter various food chains. Microbial biodegradation is a promising solution to reduce plastic waste with minimal negative environmental impact. It involves the use of microorganisms to use plastic as their sole carbon source. Fungi, for example are known as such natural decomposers. They degrade natural and synthetic polymers enzymatically using oxidoreductases and hydrolases. Fifty-nine strains of fungi isolated from washing machines and dishwashers were used in this experiment. Fungi in household appliances are exposed to synthetic and organic materials, chemicals, high temperature, humidity, and pH. Exposure to several extreme conditions leads to the enrichment of polyextremotolerant fungi. The fact that fungi most frequently colonize plastic parts of household appliances led us to investigate whether they are able to utilize plastic as a sole carbon source. We screened the selected fungi for their ability to colonize five selected plastics: low density polyethylene, polyamide, polyethylene terephthalate, polypropylene and polyurethane. Fungal strains were incubated on a medium containing plastics for three months. Their growth and morphology were observed using light and electron microscopy. Fungi from the genera Cladosporium and Exophiala, previously proven to be able to degrade plastics, grew best. Of 59 strains tested, 50 strains grew on more than one type of plastic. Twenty strains grew on all five types of plastics. We identified 43 new species that grew on at least one type of plastic and had not previously been shown to degrade plastics. According to previous studies on fungal degradation of plastic, only a few strains are capable of degrading polyamide and polypropylene. We observed 44 strains colonizing polyamide and 43 strains colonizing polypropylene