Anaerobic biodegradation of PLA at mesophilic and thermophilic temperatures: methanation potential and associated microbial community

Polylactic acid (PLA) is the most promising bio-based alternative to traditional petrochemical plastics across diverse applications. In this study, the biodegradation performance of PLA plastic under two potential end-of-life scenarios: mesophilic and thermophilic anaerobic digestion (AD) were investigated. The biotic and abiotic influence factors were evaluated through short-time exposure experiments. The potential bacteria and archaea involved in PLA anaerobic biodegradation were identified by high-throughput 16S rRNA sequencing analysis. The results showed that PLA had different biodegradation performance at mesophilic and thermophilic digestion (the biogas yield: 36.70 ± 0.2vs 398.6 ± 1.1 mL/g VS). The increased temperature at thermophilic conditions improved the biodegradability of PLA, but an attack by microorganisms was more crucial for biodegradation. The bacteria engaged in PLA hydrolysis and acidification were closely associated with proteolytic microbes. Mesophilic biodegradation of PLA involved <i>Clostridia</i> (14.94%), <i>Anaerolineae</i> (22.6%) and acetoclastic <i>Methanothrix</i> (53.0%). Thermophilic biodegradation of PLA was mainly accomplished by syntrophic microbes, <i>Clostridia</i> (38.2%), <i>Synergistia</i> (18.99%) and <i>Thermotogae</i> (17.82%), in tandem with hydrogenotrophic <i>Methanothermobacter</i> (20.5%). The results provide some insights for understanding mechanisms governing PLA biodegradation under AD conditions.

聚乳酸（Polylactic acid, PLA）是目前各类应用场景中最具潜力的可替代传统石油基塑料的生物基材料。本研究针对两种潜在的废弃末端处理场景——中温厌氧消化（Anaerobic Digestion, AD）与高温厌氧消化——下的PLA塑料生物降解性能展开了探究。本研究通过短期暴露实验，评估了生物与非生物因素对降解过程的影响，并采用高通量16S rRNA测序技术，对参与PLA厌氧生物降解的潜在细菌与古菌进行了菌种鉴定。结果表明，PLA在中温和高温厌氧消化条件下展现出截然不同的生物降解性能（以挥发性固体计，沼气产率分别为36.70±0.2和398.6±1.1 mL/g VS）。高温条件下的温度提升可改善PLA的生物降解性，但微生物的侵袭对降解过程更为关键。参与PLA水解与酸化过程的细菌与蛋白水解微生物类群密切相关。PLA的中温生物降解过程涉及梭菌纲（Clostridia，占比14.94%）、厌氧绳菌纲（Anaerolineae，占比22.6%）以及乙酸营养型产甲烷八叠球菌属（Methanothrix，占比53.0%）。PLA的高温生物降解过程主要由互营微生物完成，涉及梭菌纲（Clostridia，占比38.2%）、互营杆菌纲（Synergistia，占比18.99%）以及热袍菌门（Thermotogae，占比17.82%），并伴生有氢营养型产甲烷热杆菌属（Methanothermobacter，占比20.5%）。本研究结果为解析厌氧消化条件下调控PLA生物降解的机制提供了有益参考。