Caratterizzazione delle comunità microbiche implicate nella degradazione di bioplastica mediante tecniche biomolecolari.

Plastic has become an indispensable part of our modern society, and every year its production keeps increasing. Despite plastics’ desirable properties, there is a growing concern about their disposal and waste management. Some bioplastics, like petroleum-based plastics, are not biodegradable and end up in the ecosystem without proper disposal. Microbial biodegradation of bioplastics has gained considerable interest as an eco-friendly approach to reduce accumulation and enable sustainable waste management. Anaerobic digestion is a promising strategy for bioplastic degradation, allowing microorganisms to metabolise complex polymers under oxygen-free conditions and produce biogas as a renewable energy source. This approach couples waste reduction with energy recovery, offering a sustainable solution for end-of-life management of bioplastics. By optimising operational parameters such as temperature, inoculum source, and reactor configuration, anaerobic digestion can enhance microbial activity, degradation efficiency, and methane yield, making it a viable strategy for both industrial and municipal applications. Traditional identification methods rely on culture-dependent approaches for screening and characterisation of microbial communities associated with bioplastic degradation; these are time-consuming, labour-intensive and do not give insights into the synergy among the different microorganisms and the exact mechanisms, metabolic pathways and enzymes for bioplastic degradation. Major advancements in the field of bioengineering and sequencing technologies have led to new insights into the understanding of microbial metabolic pathways, novel genes, and enzymes associated with bioplastic degradation. This thesis aims to fill the gap in understanding microbial community acclimation, functional potential, and stability during anaerobic biodegradation of bioplastics. In Chapter 1, this thesis presents the current state of knowledge on microbial community acclimatization under thermophilic conditions and its effect on the biodegradation of polylactic acid (PLA) and starch-based (SBS) bioplastics, as well as associated biogas production. Chapter 2 investigates microbial community acclimation, demonstrating how selective enrichment under thermophilic batch conditions enhances bioplastic degradation and methane yield, with metagenomic analyses revealing key genera involved in polylactic acid (PLA) and starch-based bioplastics (SBS) breakdown. Chapter 3 evaluates the long-term stability and dynamics of microbial communities in thermophilic continuous stirred tank reactors (CSTRs), providing insights into microbial adaptation, acclimation, and sustained PLA and SBS degradation, integrating metagenomic profiling with PICRUSt2 functional predictions to link microbial composition with metabolic potential and sustained biogas production. Chapter 4 compares microbial community acclimation and stability during anaerobic bioplastic degradation and biogas production of SBS under mesophilic and thermophilic conditions across different digestates, using metagenomic analyses and PICRUSt2 predictions, to understand functional adaptations. Chapter 5 presents the conclusions of the thesis, highlighting the implications for sustainable bioplastic management and providing recommendations for future research. Overall, this thesis provides comprehensive insights into microbial dynamics, functional resilience, and renewable energy recovery, contributing to the development of effective strategies for anaerobic bioplastic biodegradation. By explicitly linking microbial acclimation, stability, and functional adaptation to improved polymer conversion and methane yield, this work advances both fundamental understanding and practical strategies for industrial-scale bioplastic valorisation within a circular bioeconomy framework. Keywords: Bioplastic, Anaerobic digestion, Microbial communities, Metagenomics, Acclimation.