聚乳酸的生物降解

聚乳酸(polylactic acid, PLA)因其良好的理化性能、生物相容性和生物降解性而备受关注，已被认为是石油基塑料最具潜力的替代者，但在实际应用中仍然存在降解缓慢循环周期长的问题，因此对PLA的生物降解深入研究对于解决塑料垃圾污染和缓解能源危机至关重要。近年来，有关微生物(放线菌、细菌和真菌)和酶(蛋白酶、脂肪酶、酯酶和角质酶)降解PLA的研究已经取得了一定的进展。本文从降解微生物、降解酶和降解机制等方面综述了PLA生物降解的研究进展，并展望了PLA生物降解研究未来的发展趋势。     

聚乳酸(PLA)生物降解的研究进展

聚乳酸(Polylactic Acid,PLA)是一种新兴的,由可再生资源--乳酸聚合而成的高分子聚酯.因为其具有优良的物理化学性能、生物相容性及生物可降解性,且对环境及人体无毒害作用,而被认为是一种最具潜力的绿色生物塑料.作为环境友好材料,聚乳酸日益受到人们的重视.基于可循环利用的考虑,其生物降解的研究也成为当前研究的一个重要方面.本文综述了PLA生物降解领域的相关进展,包括降解的微生物学、相关酶学及分子生物学,系统阐述了PLA可能的生物降解机制.并对生物系统处理PLA废弃物的可行性进行了探讨.     

中欧组织间合作研究项目MIX-UP助力实现“碳中和”

随着全球塑料循环体系的变革升级,提高塑料的回收利用不仅可以减少塑料在生命周期中的碳排放,还可以解决废塑料潜在的生态环境危害。文中介绍了2019年国家自然科学基金组织间国际 (地区) 合作研究项目“废塑料资源高效生物降解转化的关键科学问题与技术 (MIXed plastics biodegradation and UPcycling using microbial communities,MIX-UP)”。该项目聚焦“塑料污染”这一全球化的问题,围绕中欧双方确定的“塑料生物降解菌群”研究领域,联合中欧双方14家优势科研单位,开展实质性的重大前沿合作研究。针对废塑料生物降解中存在的解聚与重塑两个难题,项目以难降解石油基塑料 (PP、PE、PUR、PET和PS) 以及生物可降解塑料 (PLA和PHA) 的混合废塑料作为研究对象,从塑料微生物降解途径解析及关键元件的挖掘与改造、塑料高效降解混菌/多酶体系的构建与功能调控、塑料降解物的高值化炼制途径设计与利用策略3个方面展开研究。本项目将突破废塑料生物降解转化中高效降解元件挖掘、塑料降解物高值化利用的关键科学问题与技术,探索一条废塑料资源化、高值化、循环化、低碳化的新塑料循环路线,建立以“降塑再造”为核心理念的废塑料生物炼制体系,丰富我国固废资源化生物技术利用平台。项目的实施不仅有助于提升我国塑料 (生物) 循环经济的理论基础和关键技术水平,还可以推动我国与国际科研院所的多边交流与合作,促进我国在生物技术领域的创新发展,助力我国碳中和目标的实现。     

石油基塑料的微生物降解

石油基塑料种类繁多、数量巨大、应用广泛,常见的有聚乙烯(PE)、聚丙烯(PP)、聚苯乙烯(PS)、聚氯乙烯(PVC)、聚对苯二甲酸乙二醇酯(PET)、聚氨酯(PUR)等。这些合成塑料因其高分子量、高疏水性及高化学键能的特点难以被微生物降解,从而在环境中长期存在和累积,"白色污染"已经成为一个全球性问题。因此安全经济的微生物降解合成塑料是人类面临的一个选择和难题。文中从微生物资源及相关酶学研究方面综述了聚苯乙烯、聚乙烯、聚丙烯、聚氨酯、聚对苯二甲酸乙二醇酯和聚氯乙烯这6种石油基塑料的生物降解的研究现状。目前关于上述6种石油基塑料的微生物降解研究依然大多停留在微生物资源的寻找中,已发现的具备相关能力的菌株种类较少,并且微生物降解效率均非常缓慢;对于其降解机理及关键基因和酶的研究比较少。文中为进一步开展塑料生物降解研究,寻找高效的塑料降解菌株资源以及进一步在遗传、分子和生化水平研究塑料生物降解机理研究,从而最终实现合成塑料的彻底降解和高值化利用提供了借鉴。     

国内生物基材料产业发展现状

近年来,生物基材料正逐步成为引领当代世界科技创新和经济发展的又一新的主导产业。文章综述了国内生物基材料产业的最新进展,对整个生物基材料产业市场进行了综合分析,包括生物基化学品如乳酸、1,3-丙二醇、丁二酸等,可生物降解生物基塑料如二元酸二元醇共聚酯、聚乳酸、二氧化碳共聚物、聚羟基烷酸酯、聚己内酯、热塑性生物质塑料,非生物降解生物基塑料如生物基聚酰胺、聚对苯二甲酸丙二醇酯、生物基聚氨酯,以及生物基纤维等材料的产业现状。     

可降解塑料的微生物降解研究进展

塑料材料的广泛使用给环境带了巨大的污染和处理压力,使用可降解塑料替代传统塑料是解决这一问题的重要途径。可降解塑料的生物降解是由相应的微生物和降解酶来完成的。综述了目前常见的生物降解塑料的微生物降解研究和进展情况,明确了微生物在可降解塑料生物降解中的重要性。     

微生物降解塑料的研究进展

塑料广泛应用于人类的生活中,其中约80%的塑料垃圾被填埋,最终成为陆地和海洋垃圾。由于管理与处置不善,这些废弃物造成了巨大的环境污染,目前回收再利用是较好的处置方式,但对某些塑料废弃物并没有妥善的处置方式。生物降解作为环境友好的处置方式,具有巨大的应用潜力。本文对聚对苯二甲酸乙二醇酯、聚乙烯、聚氯乙烯、聚丙烯、聚苯乙烯和聚氨酯这6种常用塑料的降解微生物及生物降解机制进行了总结,对目前微生物降解塑料存在的问题进行了分析,并提出了促进微生物降解塑料应用的途径,为生物降解塑料菌株和降解酶的开发应用、降解机制研究提供理论参考。     

微生物降解石油污染物机制研究进展

石油污染是当前紧迫的水环境问题,研究石油污染物降解机制有助于探索石油污染修复技术路径。重点介绍了微生物降解石油污染物过程中的微生物种类、降解机制和反应机理,即具有代表性的细菌、真菌和藻类,石油烃的有氧降解(链烷烃、环烷烃和芳香烃)和厌氧降解(脱氢羟基化、延胡索酸盐加成)。并对微生物降解石油组分的影响因素进行了讨论,具体包括:烃类结构(支链多结构越复杂,越难降解)、微生物种类(混合菌的生化降解能力更强)、环境因子(pH、温度、盐度、含氧量和营养物质),进一步指出了生物修复技术应用于石油污染修复治理研究中的优缺点。此外,还对现有微生物降解技术的应用做了简要概述,归纳总结现有研究中存在的问题,尝试性的提出了今后生物降解石油污染物的研究重点,即生物降解石油的机制还需进一步明确,并重点分析了生物电化学方法在降解去除石油污染物方面可行性。综述石油烃生物降解机制和反应机理,以期为生物修复水体石油污染提供参考和借鉴作用。     

塑料生物降解检测方法的研究进展

塑料处理不当造成的污染问题已成为全球性难题。目前的解决办法除回收利用与使用可生物降解塑料替代之外,最主要途径仍是寻求高效的塑料降解方法。其中,采用微生物或酶处理塑料的方法因其具有条件温和、不产生次生环境污染的优势而受到越来越多的关注。塑料生物降解技术的核心是高效解聚微生物/酶,然而当前的分析检测方法无法满足塑料生物降解资源的高效筛选,因此开发准确、快速的塑料降解过程分析方法,对于生物降解资源筛选和降解效能评价具有重要意义。本文介绍了近年来在塑料生物降解领域的常用分析检测技术,包括高效液相色谱、红外光谱、凝胶渗透色谱以及透明圈测定等,重点讨论了荧光分析策略在快速表征塑料生物降解过程中的应用,为进一步规范塑料生物降解过程的表征与分析研究,以及开发更高效的塑料生物降解资源筛选方法提供借鉴。     

生态概念的依赖度有限生物塑料要有优良性能

生产原料部分或全部是生物质的塑料叫生物塑料。此前使用的生物塑料主要是在石油基塑料产品中混入淀粉、木质素的混合塑料和糖质发酵所得乳酸经聚合的聚乳酸（PLA）。在利用这种生物塑料加工的商品中,被业界有关人士称为迄今最成功的产品是日本可口可乐公司的PET（聚对苯二甲酸乙二醇酯,polyethylene terephthalate）瓶装饮用水伊洛哈斯（IL0HAS）。     

生物可降解塑料在不同环境条件下的降解研究进展北大核心CSCD

当前社会塑料制品的使用需求持续增加,塑料垃圾处理压力不断增大,减缓塑料污染成为当务之急,生物可降解塑料因可在一定生物活性环境下较快降解而备受关注,具有广阔的应用前景。生物可降解塑料降解条件复杂,影响因素众多,对不同生物可降解塑料降解规律,降解微生物和功能酶的透彻掌握,是实现其全面利用和高效资源化处理处置的基础和前提。文章系统梳理了常见生物可降解塑料的种类、性能、优缺点和主要用途,全面综述了生物可降解塑料的降解机理、降解微生物和功能酶,以及生物可降解塑料在不同环境条件下的降解周期和程度,以期为生物可降解塑料的微生物降解研究提供借鉴,为生物可降解塑料废弃物的高效处理处置和彻底降解提供科学参考。     

Biological degradation of plastics: a comprehensive review

Lack of degradability and the closing of landfill sites as well as growing water and land pollution problems have led to concern about plastics. With the excessive use of plastics and increasing pressure being placed on capacities available for plastic waste disposal, the need for biodegradable plastics and biodegradation of plastic wastes has assumed increasing importance in the last few years. Awareness of the waste problem and its impact on the environment has awakened new interest in the area of degradable polymers. The interest in environmental issues is growing and there are increasing demands to develop material which do not burden the environment significantly. Biodegradation is necessary for water-soluble or water-immiscible polymers because they eventually enter streams which can neither be recycled nor incinerated. It is important to consider the microbial degradation of natural and synthetic polymers in order to understand what is necessary for biodegradation and the mechanisms involved. This requires understanding of the interactions between materials and microorganisms and the biochemical changes involved. Widespread studies on the biodegradation of plastics have been carried out in order to overcome the environmental problems associated with synthetic plastic waste. This paper reviews the current research on the biodegradation of biodegradable and also the conventional synthetic plastics and also use of various techniques for the analysis of degradation in vitro.     

塑料添加剂向生态环境中的释放与迁移研究进展

塑料废弃物,尤其是粒径小于5 mm的微塑料造成的环境污染问题已引起全球的普遍关注。塑料制品在生产过程中常使用多种添加剂,以提高聚合物的性能并延长其使用寿命。然而,在废弃塑料制品的回收及自然老化过程中,这些添加剂会不断释放出来,对生态环境的安全与人类的健康产生威胁。综述了近年来国内外塑料添加剂的使用情况及其向生态环境释放与迁移等方面的研究进展,具体包括常用塑料添加剂的种类、废弃物塑料回收和塑料老化过程中添加剂向生态环境中的释放与迁移及机制等。未来需要更加关注绿色塑料添加剂的研发、废弃塑料回收工艺的改进以及关于塑料添加剂的释放、在各类环境介质中的迁移转化以及在生态系统各个圈层间的相互作用方面的系统性的研究,并构建相应的迁移模型评估塑料添加剂产生的生态风险。     

Life cycle assessment of single use thermoform boxes made from polystyrene (PS), polylactic acid, (PLA), and PLA/starch: cradle to consumer gate

Purpose

Currently, the bio-based plastics have been drawing considerable attention from the packaging industry as a sustainable solution for replacing petroleum-based plastics in order to reduce the accumulation of plastic waste in the environment. This work has benchmarked the environmental impact of bio-based against petroleum-based plastics for single use boxes. In this paper, the cradle to consumer gate environmental impact data of these boxes was calculated and reported as part 1. End-of-life options of both bio- and petroleum-based boxes are an important subject which will be further studied for part 2. The energy sources in this work were taken from the Thailand energy database namely: Thai electricity grid mix (TEGM), Thai coal electricity (TCE), Thai natural gas combine cycle (TNGCC), and Thai coal integrated gasification combine cycle (TIGCC).

Methods

The materials studied were polystyrene (PS) derived from petroleum, polylactic acid (PLA) derived from corn, and PLA/cassava starch blend (PLA/starch). The tray with lid (herein after called box) was processed in a plastic manufacturing in Thailand using cast sheet extrusion and then thermoforming techniques. The functional unit is specified as 10,000 units of 8.0?×?10.0?×?2.5 cm of PS, PLA, and PLA/starch boxes which weigh 447.60, 597.60, and 549.56 kg, respectively. Three impact categories; namely global warming potential including direct greenhouse gas, and indirect land use change (LUC) emissions, acidification, and photochemical ozone formation are investigated. Finally, the normalization results including and excluding LUC consideration were compared and reported.

Results and discussion

The results from this study have shown that the total environmental impact including LUC emission of bio-based boxes were different when the various energy sources were supplied throughout the life cycle production stage. It can be seen that the PS box has lower environmental impact than PLA and PLA/starch boxes when TEGM, TCE, TNGCC, and TIGCC were used as energy supplied. LUC of renewable feedstocks, such as corn and cassava, were considered as the biggest impact of absolute scores of PLA and PLA/starch boxes. These results are consistent with Piemonte and Gironi (2010).

Conclusions

PLA and PLA/starch boxes give a slightly higher environmental impact than the PS box by 1.59 and 1.09 times, respectively, when LUC was not accounted in the absolute scores and clean energy TIGCC was used throughout the life cycle.     

Biochemical properties and biotechnological applications of microbial enzymes involved in the degradation of polyester-type plastics

Application of polyester-degrading enzymes should be considered as an eco-friendly alternative to chemical recycling due to the huge plastic waste disposal nowadays. Many hydrolases from several fungi and bacteria have been discovered and successfully evaluated for their activity towards different aliphatic polyesters (PHA, PBS, PBSA, PCL, PLA), aromatic polyesters (PET, PBT, PMT) as well as their co-polyesters (PBST, PBAT, PBSTIL). This revision gives an up-to-date overview on the main biochemical features and biotechnological applications of those reported enzymes which are able to degrade polyester-based plastics, including different microbial polyester depolymerases, esterases, cutinase-like enzymes and lipases. Summarized information includes available protein sequences with the corresponding accession numbers deposited in NCBI server, 3D resolved structures, and data about optimal conditions for enzymatic activity and stability of many of these microbial enzymes that would be helpful for researchers in this topic. Although screening and identification of new native polyester hydrolases from microbial sources is undeniable according to literature, we briefly highlight the importance of the design of improved enzymes towards recalcitrant aromatic polyesters through different approaches that include site-directed mutagenesis and surface protein engineering.     

Metabolic engineering for the synthesis of polyesters: A 100-year journey from polyhydroxyalkanoates to non-natural microbial polyesters

As concerns increase regarding sustainable industries and environmental pollutions caused by the accumulation of non-degradable plastic wastes, bio-based polymers, particularly biodegradable plastics, have attracted considerable attention as potential candidates for solving these problems by substituting petroleum-based plastics. Among these candidates, polyhydroxyalkanoates (PHAs), natural polyesters that are synthesized and accumulated in a range of microorganisms, are considered as promising biopolymers since they have biocompatibility, biodegradability, and material properties similar to those of commodity plastics. Accordingly, substantial efforts have been made to gain a better understanding of mechanisms related to the biosynthesis and properties of PHAs and to develop natural and recombinant microorganisms that can efficiently produce PHAs comprising desired monomers with high titer and productivity for industrial applications.Recent advances in biotechnology, including those related to evolutionary engineering, synthetic biology, and systems biology, can provide efficient and effective tools and strategies that reduce time, labor, and costs to develop microbial platform strains that produce desired chemicals and materials. Adopting these technologies in a systematic manner has enabled microbial fermentative production of non-natural polyesters such as poly(lactate) [PLA], poly(lactate-co-glycolate) [PLGA], and even polyesters consisting of aromatic monomers from renewable biomass-derived carbohydrates, which can be widely used in current chemical industries.In this review, we present an overview of strain development for the production of various important natural PHAs, which will give the reader an insight into the recent advances and provide indicators for the future direction of engineering microorganisms as plastic cell factories. On the basis of our current understanding of PHA biosynthesis systems, we discuss recent advances in the approaches adopted for strain development in the production of non-natural polyesters, notably 2-hydroxycarboxylic acid-containing polymers, with particular reference to systems metabolic engineering strategies.     

A hot topic: thermophilic plastic biodegradation

Biological degradation of plastic waste is an environmentally and economically friendlier alternative to current recycling practices and enables the cycling of plastic monomers back into virgin-quality plastics. However, due to slow reaction rates, there is a lack of an industrially viable biodegradation strategy for most plastics. Here, we highlight the applicability of a thermophilic biodegradation strategy over a mesophilic approach, to enhance enzyme accessibility and catalyze plastic biodegradation. Thus, at reactions closer to the melting temperature or glass transition temperature of plastics, thermophilic reactions can offer an alternative direction to conventional plastic biodegradation strategies.     

评论：塑料结合模块促进聚对苯二甲酸乙二醇酯的酶法降解

塑料的大量生产和无节制的使用已造成严重的环境污染。为了减少塑料废物对环境的影响,近年来塑料酶法降解已成为国内外研究者关注的热点。例如,通过蛋白质工程策略提高塑料降解酶催化活性和热稳定性,进一步提高酶法降解的效率。另外,通过融合酶策略将塑料结合模块与塑料降解酶融合,也可以促进塑料降解。近期发表在期刊Chem Catalysis的一项研究表明,采用碳水化合物结合模块融合策略可以在低浓度(<10 wt%)的底物聚对苯二甲酸乙二醇酯[poly(ethylene terephthalate),PET]中提高塑料降解酶的活性。但是在高浓度底物(10 wt%−20 wt%)中,该策略无法提高PET的酶法降解。该项研究对于采用塑料结合模块促进酶法降解塑料具有重要的指导意义。