Plastic biodegradation: a metabolic understanding of the process
[eng] Microbial degradation of plastics has gained social and scientific interest in recent years, particularly regarding aliphatic recalcitrant plastics such as polyethylene (PE) and polypropylene (PP), both representing almost half of global plastic production. These polymers, among the most abund...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2025 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/695131 |
| Acceso en línea: | http://hdl.handle.net/10803/695131 |
| Access Level: | acceso embargado |
| Palabra clave: | Recalcitrant plastics Plastic biodegradation Plastic leachates Polyethylene Polypropylene Microbial degradation Proteomics Plásticos recalcitrantes Biodegradación de plásticos Lixiviados de plásticos Polietileno Polipropileno Degradación microbiana Proteómica Plàstics recalcitrants Biodegradació de plàstics Lixiviats de plàstics Polietilè Polipropilè Degradació microbiana Proteòmica Microbiologia 575 |
| Sumario: | [eng] Microbial degradation of plastics has gained social and scientific interest in recent years, particularly regarding aliphatic recalcitrant plastics such as polyethylene (PE) and polypropylene (PP), both representing almost half of global plastic production. These polymers, among the most abundantly produced and environmentally persistent, resist biodegradation due to their inert molecular structures and require initial abiotic oxidation to facilitate microbial assimilation. This thesis explores microbial metabolism to better understand the mechanisms driving the assimilation of weathered plastics. A comprehensive literature review led to defining polymer biodegradability, evaluating best practices for assessing microbial degradation, and summarising current knowledge on degradation mechanisms. Special attention is given to byproduct formation from abiotic plastic oxidation and the subsequent microbial assimilation of these molecules. This thesis advocates for improved methodologies in biodegradation research and, particularly, to elucidate molecular pathways. Experimental work focused on PE and PP degradation. Pure plastic pellets underwent thermal weathering at 80 °C resulting in the leaching of diverse organic molecules into water. The kinetics and chemical profiles of these leachates were analysed, revealing a complex mixture of oxidised molecules of varying sizes. These findings already suggested that microbial degradation requires a broad enzymatic repertoire to metabolise these molecules effectively. For PE degradation, 17 microbial isolates from the <i>Alcanivoracaceae<i>, <i>Halomonadaceae<i> and <i>Marinobacteraceae<i> families were studied for their abilities to assimilate PE leachates and correlated to their encoded metabolic potential. The results underscored the importance of β-oxidation genes redundancy over alkane degradation genes in enabling efficient assimilation of weathered PE. PP degradation was investigated using the <i>Rhodococcus erythropolis<i> PE4.1 isolate obtained from plastic collected at a 30-year-old landfill. This isolate demonstrated the ability to utilise thermally oxidised PP and PE as sole carbon and energy sources. Isotopic labelling confirmed plastic carbon assimilation. Genomic and proteomic analyses revealed a distinct array of oxidation-related enzymes, and for the first time, it identified a novel pathway involved in processing oxidised branched aliphatic molecules from PP. Overall, the findings presented in this thesis highlight the complexity of microbial plastic degradation, emphasising the enzymatic diversity required to metabolise weathered plastics and advancing our understanding of the molecular mechanisms involved. |
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