微生物响应PBAT-PLA生物降解膜袋工业需氧堆肥降解机制

塑料污染已对全球环境造成严重威胁，生物降解塑料的推广使用及其工业堆肥是治理塑料污染的有效途径之一。该研究根据标准GB/T 19277.1-2011，在（58±2）℃的特殊高温条件下，对PBAT-PLA生物降解膜袋进行有氧堆肥降解，并选择微晶纤维素作为对照。通过对堆肥中的微生物进行16S/18S高通量测序，分析降解过程中细菌/真菌的群落种类和数量变化，包括物种多样性、物种组成、物种差异分析、样本比较分析，并结合扫描电镜下的微观形貌，深入探寻可降解塑料膜袋在工业需氧堆肥过程中的微生物响应降解机制。结果表明：微晶纤维素和生物降解膜袋在降解活跃期（第140天取样），其所在堆肥中大量存在的优势菌属为Sphaerobacter（球杆菌属，放线菌纲），分别占比20.25%和39.44%。与同样条件下不含降解材料的对照组堆肥相比，微晶纤维素/生物降解膜袋工业需氧堆肥降解过程中显著增长的4种菌属中有3种属于放线菌，说明放线菌对聚酯物的解聚以及纤维素的降解具有积极的作用。试验结果也表明了聚酯和纤维素的完整生物降解过程不依赖单一菌种，而是微生物协同作用的结果。

Microorganism responded biodegradation mechanism of PBAT-PLA biodegradable packaging under industrial aerobic composting

Abstract: Plastic pollution has posed a serious threat to the environment in the world. Biodegradable plastics can be widely expected to effectively mitigate plastic pollution. The subsequent industrial composting can also be treated to reduce the growing demand for landfills. In this research, the microorganisms responded to the biodegradation mechanism was proposed for the PBAT-PLA biodegradable packaging under the controlled industrial aerobic composting, according to the national standard (GB/T 19277.1-2011). Microcrystalline cellulose was used as reference material. The compost samples were taken on day 140 when the degradation was in the active period. The initial compost (before degradation), compost without any biodegradable material, compost with microcrystalline cellulose, and compost with PBAT-PLA packaging materials were then labeled as compost A, B, C, and D, respectively. The bacterial/fungal community was analyzed during degradation, including the species diversity, speciation, and species difference. A sample comparison was made through 16S/18S high-throughput sequencing of microorganisms in compost. The microscopic morphologies of PBAT-PLA packaging materials and microcrystalline cellulose were characterized by a Scanning Electron Microscope (SEM), in order to explore the intrinsic microbial response to the degradation mechanism. The results showed that the bacterial diversity of compost B under the industrial composting at 58 ± 2°C was significantly lower than that of initial compost A since only some thermophilic bacteria survived. The bacterial diversities in compost C and D were significantly higher than that of compost B, due to the addition of cellulose or biodegradable packaging materials which provided carbon sources. There was no significant change in the fungal diversity, due to unsuitable for most fungi to survive at high temperatures. The fungal abundance changed, due to the temperature and carbon source in the compost, where the compost B (blank sample) showed the lowest fungal abundance. The dominant bacteria in the compost C and D were Sphaerobacter, Longispora, norank_f_norank_o_Actinomarinales, and Rubrobacter, which belonged to Actinomycete. The student''s T-test was used to compare the composition of bacteria and fungi in the compost C and D with those in the compost B. The significant growing bacteria in the compost C and D, including norank_f_Euzebyaceae, unclassified_c_Actinobacteria, and Actinobacteria, belonged to Actinomycetes. Therefore, there were similar degrading microorganisms of PBAT-PLA membrane bag and microcrystalline cellulose at (58±2)°C. The SEM images showed that the surface of PBAT-PLA packaging after degradation was covered with a layer of biofilm. The biofilm was mainly composed of the clusters of ellipsoid bacteria, which were inferred to be Sphaerobacter. Actinomycetes presented a positive effect on the depolymerization of polyester and the degradation of cellulose under industrial composting conditions. The complete biodegradation of polyester and cellulose depended on the microbial synergy, rather than a single strain. Therefore, the dominant bacteria and significant growth bacteria of biodegradable materials under industrial composting conditions can be expected to serve as a theoretical basis for screening key biodegradation bacteria in the future. It can also greatly contribute to breaking through the technical barriers of the long detection cycle with the current biodegradation for higher efficiency and speed. The identification of microbial communities can be an important indicator to evaluate the impact of the compost produced by biodegradable plastics on crops growth, and agricultural ecological environment. Consequently, a theoretical foundation can be made to optimize the industrial composting and biodegradable plastic testing standards. The finding can also provide a scientific basis for the large-scale promotion of biodegradable plastic films and the application of the compost produced from biodegradable plastics in advanced (or modern) agriculture