Nature-inspired biodegradation of poly(butylene succinate-co-adipate): the potential of Cladosporium psychrotolerans isolated from marine copepods

Plastics pose a threat to both terrestrial and aquatic ecosystems due to slow degradation and pervasive presence. Bio-degradable plastics, such as Poly(Butylene Succinate-co-Adipate) (PBSA), offer potential solutions, but their impact in marine environment remains uncertain. This study explores the diversity of fungi associated with the carcasses of the marine copepod Acartia tonsa and their ability to degrade PBSA. The fungal strains belonging to Cladosporium, Fusarium, and Stemphylium were isolated, for the first time, from the copepod carcasses. Among these, Cladosporium psychrotolerans MUT6786 demonstrated significant carboxyl-ester hydrolase activity, enabling the degradation of PBSA in both emulsified and granule forms. Notably, in PBSA granules incubated with C. psychrotolerans a weight reduction of 80.5% occurred over 92 days of incubation. Progressive surface erosion and chemical alterations of the granules were confirmed with infrared spectroscopy (FTIR-ATR) and stereomicroscopy. Furthermore, thermogravimetric (TGA) and differential scanning calorimetry (DSC) analyses indicated selective hydrolysis of the amorphous polymer fraction. Molecular weight analyses further highlighted surface-specific degradation without significant changes to the bulk polymer structure. Moreover, the reduction of Carbonyl Index during 60 days of incubation provides additional evidence of the ability of C. psychrotolerans to hydrolyze the ester bonds. The findings highlight the importance of zooplankton-associated microbiomes in biopolymer degradation, offering insights into leveraging marine fungi for environmental restoration of bioplastics in aquatic ecosystems.