D'Ambrosio, Gennaro (2025) A multidisciplinary approach to sustainable plastic depolymerization through microalgae enzymatic biocatalysis. [Tesi di dottorato]

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Abstract

Plastic pollution represents one of the most urgent environmental challenges of the Anthropocene, particularly due to the persistence of micro- and nanoplastics in ecosystems. This PhD thesis investigates a sustainable bioremediation strategy based on green microalgae, focusing on their enzymatic potential for initiating the degradation of common synthetic polymers such as polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET). A multidisciplinary approach combining bioinformatics, molecular enzymology, spectroscopy, and physiological assays was adopted to characterize the activity of laccase-like multicopper oxidases (LMCOs) and hydrolases in identified microalgae accessions. In silico analyses revealed the presence of diverse laccase-like multicopper oxidase (LMCO) genes in several green microalgae supported by and functional enzymatic assays. Microalgae accessions exhibited extracellular laccase activity in response to polypropylene(PP) exposure, associated with early oxidative modifications on the polymer surface. Plastic debris influenced microalgae growth dynamics and pigment profiles, showing species-specific stress responses. Additionally, identified accessions demonstrated the ability to promote PET surface oxidation under both light and dark conditions, suggesting photo-independent enzymatic oxidation. These findings provide new insights into the enzymatic potential of native microalgae in the early-stage transformation of synthetic polymers. By demonstrating their ability to tolerate plastic stress and induce oxidative modifications on polymer surfaces, microalgae emerge as dual-function agents: photoautotrophic biocatalysts initiating plastic depolymerization and sustainable platforms for enzyme production. The work also considers techno-economic feasibility, regulatory aspects, and scalability challenges, contributing to the development of integrated, low-impact solutions for plastic waste management in line with circular bioeconomy principles.

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