Harnessing fungi and bacteria to speed up the biodegradation of plastic mulch films

Plastics and microplastics are pervasive in agricultural systems, underscoring the need for effective mitigation strategies. Here, we explored microbial treatments to accelerate the degradation of plastic mulch films composed of commercial (LDPE-m) and additive-free (LDPE-p) low-density polyethylene and a blend containing polybutylene adipate-co-terephthalate and polylactic acid (PBAT-PLA). We tested four microbial treatments: a compost-derived microbial community (m1), a multi-strain Aspergillus consortium with Peribacillus simplex (B. simplex) (m2), an Aspergillus-only fungal consortium (m3), and an Aspergillus fumigatus-Pseudomonas aeruginosa co-culture (m4). These were incubated under carbon-free (CF), low-carbon (LC), autoclaved compost (AC), and raw compost (C) conditions (at 30 °C for 180 days), with and without abiotic pre-treatments (UV-aging and mineral oil amendment (MO)) to accelerate microorganisms association with plastics. Our results show that the Aspergillus-only consortium (m3) accelerated LDPE-m degradation (3.71 ± 0.86 WL, Mw = -17.2 kDa and OH and CO formation) while the fungal-bacterial co-culture (m4) quickened LDPE-m weight loss (2.79 ± 0.95%) and CO formation in CF media. Multi-strain Aspergillus consortium with B. simplex (m2) colonized the UV-aged LDPE-m plastisphere in AC, and the m1-dwelling Brucella combined with Aspergillus sp. optimized UV-aged LDPE-m degradation patterns. The co-occurrence of compost-dwellers Gordonia, Thermomyces, and Mycobacterium with inoculated Aspergillus sp. enhanced LDPE-p weight loss (4.91 ± 2.28%) and surface changes (CO formation) in compost under MO. Most Aspergillus treatments dominated the plastisphere in autoclaved compost and were eclipsed by Thermomyces in compost. Slower-than-expected degradation occurred for PBAT-PLA mulch films. This study sheds light on possible microbial treatments for accelerating the degradation of plastic mulches.