Feeding fungi plastic: uncovering LDPE-colonizing communities from silage wrap waste in Norwegian farms

Plastic pollution represents a major environmental challenge worldwide. In Norwegian agriculture, low-density polyethylene (LDPE) silage wrap waste is a dominant source of plastic pollution, accumulating on farms and in nearby ecosystems. A 2020 study by NORCE showed that up to 70% of the plastic contaminating rivers consists of agricultural plastic with dominance of silage wrap. Microbial degradation offers a sustainable alternative to conventional waste management approaches. Microbial attachment and colonization of plastic surfaces are essential initial stages of degradation. This study investigated the diversity of fungal communities associated with silage wrap waste and evaluated the LDPE-colonization potential of selected fungal isolates. A metabarcoding analysis of collected plastic silage wrap identified nine fungal orders from five major classes as predominant, with the members of the Cladosporiaceae family being most abundant. Community composition varied between geographic regions and original localization of the samples. Seven isolates were used in an exposure experiment in which commercial LDPE pieces were kept for 89 days together with active fungal cultures in three different media types. The colonization potential was visually ranked on a 0-3 ordinal scale according to the area covered by the colonizing fungi, and selected LDPE pieces were subsequently observed with SEM. During the experimental cultivation, Cladosporium uwebraunianum displayed the largest colonization area on LDPE surfaces, followed by Alternaria sp., as evidenced by colonization ranks and SEM, suggesting that they may be promising candidates for future studies of LDPE biodegradation. Glucose presence in the growth media supported spore germination and early hyphal growth of the tested isolates, promoting fungal attachment and development on LDPE surface. A pretreatment of LDPE pieces with UV-C lead to small structural surface damages generating anchoring points for microorganisms and thus enhanced fungal colonization efficiency. Our findings identify fungal taxa associated with Norwegian agricultural silage wrap, and highlight C. uwebraunianum as an efficient LDPE colonizer, suggesting that surface pre-treatment with UV-C may play a beneficial role in fungal plastisphere establishment and following biodegradation processes. Not applicable.