The role of benzoate in anaerobic degradation of terephthalate

The effects of acetate, benzoate, and periods without substrate on the anaerobic degradation of terephthalate (1, 4-benzene-dicarboxylate) by a syntrophic methanogenic culture were studied. The culture had been enriched on terephthalate and was capable of benzoate degradation without a lag phase. When incubated with a mixture of benzoate and terephthalate, subsequent degradation with preference for benzoate was observed. Both benzoate and acetate inhibited the anaerobic degradation of terephthalate. The observed inhibition is partially irreversible, resulting in a decrease (or even a complete loss) of the terephthalate-degrading activity after complete degradation of benzoate or acetate. Irreversible inhibition was characteristic for terephthalate degradation only because the inhibition of benzoate degradation by acetate could well be described by reversible noncompetitive product inhibition. Terephthalate degradation was furthermore irreversibly inhibited by periods without substrate of only a few hours. The inhibition of terephthalate degradation due to periods without substrate could be overcome through incubation of the culture with a mixture of benzoate and terephthalate. In this case no influence of a period without substrate was observed. Based on these observations it is postulated that decarboxylation of terephthalate, resulting in the formation of benzoate, is strictly dependent on the concomitant fermentation of benzoate. In the presence of higher concentrations of benzoate, however, benzoate is the favored substrate over terephthalate, and the culture loses its ability to degrade terephthalate. In order to overcome the inhibition of terephthalate degradation by benzoate and acetate, a two-stage reactor system is suggested for the treatment of wastewater generated during terephthalic acid production.     

Identification and isolation of anaerobic, syntrophic phthalate isomer-degrading microbes from methanogenic sludges treating wastewater from terephthalate manufacturing

The microbial populations responsible for anaerobic degradation of phthalate isomers were investigated by enrichment and isolation of those microbes from anaerobic sludge treating wastewater from the manufacturing of terephthalic acid. Primary enrichments were made with each of three phthalate isomers (ortho-, iso-, and terephthalate) as the sole energy source at 37 degrees C with two sources of anaerobic sludge (both had been used to treat wastewater containing high concentrations of phthalate isomers) as the inoculum. Six methanogenic enrichment cultures were obtained which not only degraded the isomer used for the enrichment but also had the potential to degrade part of other phthalate isomers as well as benzoate with concomitant production of methane, presumably involving strictly syntrophic substrate degradation. Our 16S rRNA gene-cloning analysis combined with fluorescence in situ hybridization revealed that the predominant bacteria in the enrichment cultures were affiliated with a recently recognized non-sulfate-reducing subcluster (subcluster Ih) in the group 'Desulfotomaculum lineage I' or a clone cluster (group TA) in the class delta-PROTEOBACTERIA: Several attempts were made to isolate these microbes, resulting in the isolation of a terephthalate-degrading bacterium, designated strain JT, in pure culture. A coculture of the strain with the hydrogenotrophic methanogen Methanospirillum hungatei converted terephthalate to acetate and methane within 3 months of incubation, whereas strain JT could not degrade terephthalate in pure culture. During the degradation of terephthalate, a small amount of benzoate was transiently accumulated as an intermediate, indicative of decarboxylation of terephthalate to benzoate as the initial step of the degradation. 16S rRNA gene sequence analysis revealed that the strain was a member of subcluster Ih of the group 'Desulfotomaculum lineage I', but it was only distantly related to other known species.     

High rate treatment of terephthalic acid production wastewater in a two-stage anaerobic bioreactor

The feasibility was studied of anaerobic treatment of wastewater generated during purified terephthalic acid (PTA) production in two-stage upflow anaerobic sludge blanket (UASB) reactor system. The artificial influent of the system contained the main organic substrates of PTA-wastewater: acetate, benzoate, and terephthalate. Three parallel operated reactors were used for the second stage, and seeded with a suspended terephthalate degrading culture, with and without additional methanogenic granular sludge (two different types). The first stage UASB-reactor was seeded with methanogenic granular sludge. Reactors were operated at 37 degrees C and pH 7. During the first 300 days of operation a clear distinction between the biomass grown in both reactor stages was obtained. In the first stage, acetate and benzoate were degraded at a volumetric loading rate of 40 g-COD/L . day at a COD-removal efficiency of 95% within the first 25 days of operation. No degradation of terephthalate was obtained in the first stage during the first 300 days of operation despite operation of the reactor at a decreased volumetric loading rate with acetate and benzoate of 9 g-COD/L . day from day 150. Batch incubation of biomass from the reactor with terephthalate showed that the lag-phase prior to terephthalate degradation remained largely unchanged, indicating that no net growth of terephthalate degrading biomass occurred in the first stage reactor. From day 300, however, terephthalate degradation was observed in the first stage, and the biomass in this reactor could successfully be enriched with terephthalate degrading biomass, resulting in terephthalate removal capacities of 15 g-COD/L . day. Even though no single reason could be identified why (suddenly) terephthalate degradation was obtained after such a long period of operation, it is suggested that the solid retention time as well the prevailing reactor concentrations acetate and benzoate may have played an important role. From day 1 of operation, terephthalate was degraded in the second stage. In presence of methanogenic granular biomass, high terephthalate removal capacities were obtained in these reactors (15 g-COD/L . day) after approximately 125 days of operation. From the results obtained it is concluded that terephthalate degradation is the bottleneck during anaerobic treatment of PTA-wastewater. Pre-removal of acetate and benzoate in staged bioreactor reduces the lag-phase prior to terephthalate degradation in latter stages, and enables high rate treatment of PTA-wastewater.     

Comparative molecular docking and molecular-dynamic simulation of wild-type- and mutant carboxylesterase with BTA-hydrolase for enhanced binding to plastic

According to the literature review, microbial degradation of polyethylene terephthalate by PETases has been detected effective and eco-friendly. However, the number of microorganisms capable of such feats is limited with some undesirable bioprospecting results. BTA-hydrolase has been already reported capable of degrading polyethylene terephthalate. Therefore, mutation by in silico site-directed mutagenesis means to introduce current isomer of PETase for polyethylene terephthalate degradative capability as a better approach to resolve this issue. This study aimed to use in silico site-directed mutagenesis to convert a carboxylesterase from Archaeoglobus fulgidus to BTA-hydrolase from Thermobifida fusca by replacing six amino acids in specific locations. This work was followed by molecular docking analysis with polyethylene terephthalate and polypropylene to compare their interactions. The best-docked enzyme-substrate complex was further subjected to molecular dynamics simulation to gauge the binding quality of the BTA-hydrolase, wild-type and mutant-carboxylesterase with only polyethylene terephthalate as a substrate. Results of molecular docking revealed lowest binding energy for the wild-type carboxylesterase-polypropylene complex (-7.5 kcal/mol). The root-mean-square deviation value was observed stable for BTA-hydrolase. Meanwhile, root-mean-square fluctuation was assessed with higher fluctuation for the mutated residue Lys178. Consequently, the Rg value for BTA-hydrolase-ligand complex (～1.68 nm) was the lowest compared to the mutant and wild-type carboxylesterase. The collective data conveyed that mutations imparted a minimal change in the ability of the mutant carboxylesterase to bind to polyethylene terephthalate.     

Anaerobic biodegradability of phthalic acid isomers and related compounds

All three phthalic acid isomers ( ortho, meta and para benzene dicarboxylic acid) are produced in massive amounts, and used in the chemical industry as plasticizers or for the production of polyester. Wastestreams generated during the production of phthalate isomers generally contain high concentrations of aromatic acids. To study the potential biodegradability of these primarily anthropogenic compounds in anaerobic bioreactors, biodegradability studies were performed. Compounds tested were benzoate, ortho-phthalate, isophthalate, terephthalate, dimethyl phthalate, dimethyl terephthalate, para-toluate and para-xylene. Seed materials tested were two types of granular sludge and digested sewage sludge. It was found that all phthalate isomers and their corresponding dimethyl-esters, could be completely mineralized by all seed materials studied. Lag phases required for 50% degradation of these compounds, ranged from 17 to 156 days. The observed degradation curves could be explained by growth of an initially small amount of organisms in the inoculum with the specific ability to degrade one phthalate isomer. The observed order in the length of the lag phases for the phthalate isomers is: phthalate < terephthalate < isophthalate. This order appears to be related to the environmental abundancy of the different phthalate isomers. The initial step in the degradation pathway of both dimethyl phthalate esters was hydrolysis of the ester sidechain, resulting in the formation of the corresponding mono-methyl-phthalate isomer and phthalate isomer. The rate limiting step in mineralization of both dimethyl phthalate and dimethyl terephthalate was found to be fermentation of the phthalate isomer. Para-toluate was degraded only by digested sewage sludge after a lag phase of 425 days. The observed degradation rates of this compound were very low. No mineralization of para-xylene was observed. In general, the differences in the lag phases between different seed materials were relatively small. These results indicate that the time needed for the start-up of anaerobic bioreactors treating wastewaters containing phthalic acid isomers, depends little on the microbial composition of the seed material applied, but may take several months.     

High-rate treatment of terephthalate in anaerobic hybrid reactors.

The anaerobic degradation of terephthalate as sole substrate was studied in three anaerobic upflow reactors. Initially, the reactors were operated as upflow anaerobic sludge bed (UASB) reactors and seeded with suspended methanogenic biomass obtained from a full-scale down-flow fixed film reactor, treating wastewater generated during production of purified terephthalic acid. The reactors were operated at 30, 37, and 55 degrees C. The terephthalate removal capacities remained low in all three reactors (<4 mmolxL-1xday-1, or 1 g of chemical oxygen demand (COD)xL-1xday-1) due to limitations in biomass retention. Batch experiments with biomass from the UASB reactors revealed that, within the mesophilic temperature range, optimal terephthalate degradation is obtained at 37 degrees C. No thermophilic terephthalate-degrading culture could be obtained in either continuous or batch cultures. To enhance biomass retention, the reactors were modified to anaerobic hybrid reactors by introduction of two types of reticulated polyurethane (PUR) foam particles. The hybrid reactors were operated at 37 degrees C and seeded with a mixture of biomass from the UASB reactors operated at 30 and 37 degrees C. After a lag period of approximately 80 days, the terephthalate conversion capacity of the hybrid reactors increased exponentially at a specific rate of approximately 0.06 day-1, and high removal rates were obtained (40-70 mmolxL-1xday-1, or 10-17 g of CODxL-1xday-1) at hydraulic retention times between 5 and 8 h. These high removal capacities could be attributed to enhanced biomass retention by the development of biofilms on the PUR carrier material as well as the formation of granular biomass. Biomass balances over the hybrid reactors suggested that either bacterial decay or selective wash-out of the terephthalate fermenting biomass played an important role in the capacity limitations of the systems. The presented results suggest that terephthalate can be degraded at high volumetric rates if sufficiently long sludge ages can be maintained, and the reactor pH and temperature are close to their optima.     

A dual enzyme system composed of a polyester hydrolase and a carboxylesterase enhances the biocatalytic degradation of polyethylene terephthalate films

TfCut2 from Thermobifida fusca KW3 and the metagenome‐derived LC‐cutinase are bacterial polyester hydrolases capable of efficiently degrading polyethylene terephthalate (PET) films. Since the enzymatic PET hydrolysis is inhibited by the degradation intermediate mono‐(2‐hydroxyethyl) terephthalate (MHET), a dual enzyme system consisting of a polyester hydrolase and the immobilized carboxylesterase TfCa from Thermobifida fusca KW3 was employed for the hydrolysis of PET films at 60°C. HPLC analysis of the reaction products obtained after 24 h of hydrolysis showed an increased amount of soluble products with a lower proportion of MHET in the presence of the immobilized TfCa. The results indicated a continuous hydrolysis of the inhibitory MHET by the immobilized TfCa and demonstrated its advantage as a second biocatalyst in combination with a polyester hydrolase for an efficient degradation oft PET films. The dual enzyme system with LC‐cutinase produced a 2.4‐fold higher amount of degradation products compared to TfCut2 after a reaction time of 24 h confirming the superior activity of his polyester hydrolase against PET films.     

Metabolism of dimethylterephthalate byAspergillus niger

Aspergillus niger (AG-1) metabolized dimethylterephthalate through monomethylterephthalate, terephthalate and protocatechuate. Degradation of dimethylterephthalate was followed by extraction of residual dimethylterephthalate from the spent medium. The quantitative UV analysis showed that 58% of the dimethylterephthalate supplement was taken up in 144 h. The metabolites were isolated from resting cell cultures. Thin layer chromatography analysis of the extract revealed the presence of two intermediates, monomethylterephthalate and terephthalate. Use of an inhibitor in resting cell culture experiment demonstrated the accumulation of protocatechuate. The time course of protocatechuate accumulation was also studied. Metabolites were identified by employing various physicochemical methods. Enzyme studies using cell-free extracts exhibited dimethylterephthalate esterase and protocatechuate dioxygenase activities. Protocatechuate was oxidized by themeta cleavage pathway. A tentative pathway for the degradation of DMTP has been proposed inA. niger.Abbreviations A. niger Aspergillus niger (AG1) - DMSO dimethyl sulfoxide - DMTP dimethylterephthalate - MMTP monomethylterephthalate - MS mass spectra - NMR nuclear magnetic resonance spectra - PCA protocatechuate - TLC thin layer chromatography - TP terephthalate - UV ultra violet spectra     

聚对苯二甲酸乙二醇酯(PET)降解酶的研究进展

聚对苯二甲酸乙二醇酯(Polyethylene terephthalate,PET)因其优越的物理化学性质,在各个领域尤其在包装产业得到了广泛的应用.然而,由于使用后的PET处置不当,对生态环境造成了严重威胁.目前生物降解尤其是酶促降解已成为极具可行性且环境友好的PET处理方式.本文集中梳理和总结了近年来已报道的PET...     

一株嗜热聚对苯二甲酸乙二醇酯降解菌的分离及其降解特性解析北大核心

【目的】大量聚对苯二甲酸乙二醇酯(polyethylene terephthalate,PET)塑料作为废弃物被丢弃,严重危害生态健康。针对嗜热PET降解菌缺乏这一情况,本研究旨在获得能够降解PET的嗜热菌,并阐述其降解机制。【方法】采集云南腾冲热泉中的废弃PET瓶,分析其表面生物膜的微生物群落多样性,从中筛选能够以PET为营养源生长的嗜热菌,并基于16S rRNA基因序列加以鉴定;以菌株的定殖能力与生长曲线为指标,优选出降解能力较强的降解菌,并测定其最适pH、温度和NaCl浓度;降解能力较强的降解菌分别作用于PET及PET中间体双(羟乙基)对苯二甲酸酯[bis(hydroxyethyl)terephthalate,BHET]和对苯二甲酸单(2-羟乙基)酯[mono(2-hydroxyethyl)terephthalate,MHET],测定产物生成量与降解率;通过观察PET膜表面微观结构、活菌数、酯酶活性等探究降解菌与PET的互作过程。【结果】废弃PET瓶表面生物膜中的微生物群落多样性低;从生物膜中筛选出5株能够以PET为营养源生长的嗜热菌;其中,菌株JQ3以PET为唯一碳源生长最佳,作为降解能力较强的降解菌,被鉴定为嗜热淀粉芽孢杆菌(Bacillus thermoamylovorans),其最适生长pH为7.0、最适生长温度为50℃、最适生长NaCl浓度为0.5%;菌株JQ3以0.043 mg PET/d的速率降解PET,对苯二甲酸(terephthalic acid,TPA)产量在第7天达到峰值45.2 mmol/L;菌株JQ3对PET中间体降解效率显著,6 h可降解85.9%的BHET,60 h可降解50.1%的MHET。菌株JQ3能够定殖于PET表面并形成生物膜,侵蚀PET并造成开裂和剥落。【结论】B.thermoamylovorans JQ3作为一株嗜热PET降解菌,能够高温(60℃)降解PET及其中间体,为实现PET的有效降解提供了新策略。     

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。     

Microbial degradation of disodium terephthalate by alkaliphilic Dietzia sp. strain GS-1

An alkaliphilic Dietzia sp., strain GS-1, which degraded disodium terephthalate (DT), was isolated from soil. Strain GS-1 degraded 19.3 mM of DT in 168 h at pH 10. The maximum degradation velocity was 0.46 mM/h. The resting cells efficiently degraded 28.7 mM of DT in 51 h at 28 degrees C and pH 10. The degradation velocity was 0.41 mM/(h g-wet cell).     

Hydrolysis of PET and bis-(benzoyloxyethyl) terephthalate with a new polyesterase from Penicillium citrinum

A polyethylene terephthalate (PET) model substrate, bis-(benzoyloxyethyl)terephthalate (3PET), was used to screen for micro-organisms producing enzymes hydrolyzing PET. From this screen, a strain growing on 3PET was isolated and identified as Penicillium citrinum. The polyesterase responsible for 3PET and PET hydrolysis was purified to electrophoretic homogeneity. The polyesterase had a molecular weight of 14.1 kDa, and the K_m and K_cat values on 4-nitrophenyl butyrate were 0.57 mM and 0.21 s^-1, respectively. Highest enzyme activities were obtained when P. citrinum was grown on a medium containing cutin, which was hydrolyzed by the polyesterase. Surface hydrolysis of PET with the enzyme lead to an increase in hydrophilicity based on rising height (+5.1 cm) and drop dissipation measurements (55 s). Both from PET and 3PET bis-(2-hydroxyethyl)terephthalate and mono-(2-hydroxyethyl)terephthalate were released, while only low amounts of terephthalic acid were liberated.     

Microbial degradation of aliphatic and aliphatic-aromatic co-polyesters

Biodegradable plastics (BPs) have attracted much attention since more than a decade because they can easily be degraded by microorganisms in the environment. The development of aliphatic-aromatic co-polyesters has combined excellent mechanical properties with biodegradability and an ideal replacement for the conventional nondegradable thermoplastics. The microorganisms degrading these polyesters are widely distributed in various environments. Although various aliphatic, aromatic, and aliphatic-aromatic co-polyester-degrading microorganisms and their enzymes have been studied and characterized, there are still many groups of microorganisms and enzymes with varying properties awaiting various applications. In this review, we have reported some new microorganisms and their enzymes which could degrade various aliphatic, aromatic, as well as aliphatic-aromatic co-polyesters like poly(butylene succinate) (PBS), poly(butylene succinate)-co-(butylene adipate) (PBSA), poly(ε-caprolactone) (PCL), poly(ethylene succinate) (PES), poly(l-lactic acid) (PLA), poly(3-hydroxybutyrate) and poly(3-hydoxybutyrate-co-3-hydroxyvalterate) (PHB/PHBV), poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(butylene adipate-co-terephthalate (PBAT), poly(butylene succinate-co-terephthalate) (PBST), and poly(butylene succinate/terephthalate/isophthalate)-co-(lactate) (PBSTIL). The mechanism of degradation of aliphatic as well as aliphatic-aromatic co-polyesters has also been discussed. The degradation ability of microorganisms against various polyesters might be useful for the treatment and recycling of biodegradable wastes or bioremediation of the polyester-contaminated environments.     

角质酶在生物可降解聚酯聚己二酸/对苯二甲酸丁二醇酯降解中的应用

随着废弃塑料带来的环境污染越来越严重,生物可降解聚酯已成为大众关注的焦点。聚己二酸/对苯二甲酸丁二醇酯[poly(butylene adipate-co-terephthalate),PBAT]是脂肪族和芳香族共聚形成的生物可降解聚酯,兼具两者的优异性能。针对PBAT在自然条件下对降解环境要求严格且降解周期长的不足之处,本研究探究了角质酶在PBAT降解中的应用和对苯二甲酸-丁二醇酯(butylene terephthalate,BT)含量对PBAT生物降解性的影响,以实现对PBAT降解速率的提升。选取5种不同来源的聚酯降解酶对PBAT进行降解应用并比较出降解效果最优的酶,并测定了含有不同BT含量的PBAT聚酯的降解效率。结果表明,角质酶ICCG为降解效果最好的酶,且BT含量越高PBAT的降解率越低。此外,还确定了角质酶ICCG对高BT含量的PBAT(H)降解的最适温度、最适缓冲液类型、最适pH、最适E/S(enzyme to substrate)和最适底物浓度比分别为75℃、Tris-HCl、9.0、0.4%和1.0%。本研究结果可为角质酶在PBAT降解中的应用提供一定的理论依据和实验...     

Influences of organic loading disturbances on the performance of anaerobic filter process to treat purified terephthalic acid wastewater

A lab-scale anaerobic filter process was operated for the treatment of purified terephthalic acid (PTA) wastewater, and the influences of organic loading disturbances on the process performance were investigated. After about 15 month operation, the COD removal efficiency was maintained at 79% under the volumetric loading rate of 5.05 kg-COD/m³/d and the hydraulic retention time (HRT) of 50 h. Interestingly, this performance could be further enhanced over 85% by applying a step-increase/decrease of the HRT, which was mainly due to the increased p-toluate degradation. In the shock loading tests of four major pollutants (benzoate, acetate, terephthalate and p-toluate), it was found that the overall process performance was adversely affected by all the shock loadings, indicating that the syntrophic microbial consortium involved in the PTA wastewater treatment is highly sensitive to the organic loading disturbances. The complex inhibition effects of the benzoate and acetate on the terephthalate and p-toluate degradations were mainly responsible for this sensitivity.     

Degradation of Dimethyl Isophthalate by Viarovorax paradoxus Strain T4 Isolated from Deep-Ocean Sediment of the South China Sea

Viarovorax paradoxusT4 strain was isolated from deep-ocean sediment and demonstrated to be able to degrade dimethyl isophthalate (DMI). When DMI was utilized as the sole source of carbon and energy, it was transformed by hydrolysis initially, forming monomethyl isophthalate (MMI) and isophthalate acid (IA) as degradation intermediates. DMI and MMI were completely transformed to MMI and IA in about 100 h, respectively. Degradation of IA was completed in about 55 h. Analysis of total organic carbon in the culture medium confirmed that more than 80% of the substrate carbon was mineralized. Bacterial esterase induced by a range of substrates could be assessed using p-nitrophenyl acetate as the common substrate using crude enzyme preparation. The decreasing trend of K _m values derived from the Michaelis–Menten equation was dimethyl phthalate (DMP) > monomethyl phthalate (MMP) > dimethyl terephthalate (DMT) > Liver esterase > DMI > MMI > monomethyl terephthalate (MMT), indicating that higher K _m values were obtained by di-esters than mono-ester and the esters induced by terephthalate esters showed the highest activity. This investigation suggests that biochemical pathways for phthalate esters share many common characteristics and the esterases induced by different substrates are highly specific.     

Hydrolysis of PET and bis-(benzoyloxyethyl) terephthalate with a new polyesterase from Penicillium citrinum

A polyethylene terephthalate (PET) model substrate, bis-(benzoyloxyethyl)terephthalate (3PET), was used to screen for micro-organisms producing enzymes hydrolyzing PET. From this screen, a strain growing on 3PET was isolated and identified as Penicillium citrinum. The polyesterase responsible for 3PET and PET hydrolysis was purified to electrophoretic homogeneity. The polyesterase had a molecular weight of 14.1 kDa, and the K_m and K_cat values on 4-nitrophenyl butyrate were 0.57?mM and 0.21?s^?1, respectively. Highest enzyme activities were obtained when P. citrinum was grown on a medium containing cutin, which was hydrolyzed by the polyesterase. Surface hydrolysis of PET with the enzyme lead to an increase in hydrophilicity based on rising height (+5.1?cm) and drop dissipation measurements (55?s). Both from PET and 3PET bis-(2-hydroxyethyl)terephthalate and mono-(2-hydroxyethyl)terephthalate were released, while only low amounts of terephthalic acid were liberated.     

聚对苯二甲酸乙二醇酯降解酶的研究进展

聚对苯二甲酸乙二醇酯(Polyethylene terephthalate,PET)因其良好的耐用性和可塑性,已在世界范围内的工业领域和日常生活中得到广泛应用。目前自然环境中大量PET使用废弃物的积累和迁移给全球生态系统带来了严重负担,因此PET的降解问题已成为全球性的热点问题。微生物酶降解法目前被认为是一种理想绿色PET降解方法,有希望应用于大规模降解PET废弃物降解处理。传统的PET降解酶主要包括脂肪酶、酯酶和角质酶等,但这些酶的PET降解活性相对不高。近期科学家从Ideonella sakaiensis细菌中分离了一种新型水解酶PETase,能够特异性高效降解PET。本文从结构生物学角度对多种PET降解酶进行梳理,重点总结了新近发现的PETase催化机制,为发展改造更有效的PET降解酶提供理论依据。     

A computer-assisted microscopic analysis of bone tissue developed inside a polyactive polymer implanted into an equine articular surface

One of the most promising applications for the restoration of small or moderately sized focal articular lesions is mosaicplasty (MP). Although recurrent hemarthrosis is a rare complication after MP, recently, various strategies have been designed to find an effective filling material to prevent postoperative bleeding from the donor site. The porous biodegradable polymer Polyactive (PA; a polyethylene glycol terephthalate - polybutylene terephthalate copolymer) represents a promising solution in this respect. A histological evaluation of the longterm PA-filled donor sites obtained from 10 experimental horses was performed. In this study, attention was primarily focused on the bone tissue developed in the plug. A computer-assisted image analysis and quantitative polarized light microscopic measurements of decalcified, longitudinally sectioned, dimethylmethylene blue (DMMB)- and picrosirius red (PS) stained sections revealed that the coverage area of the bone trabecules in the PA-filled donor tunnels was substantially (25%) enlarged compared to the neighboring cancellous bone. For this quantification, identical ROIs (regions of interest) were used and compared. The birefringence retardation values were also measured with a polarized light microscope using monochromatic light. Identical retardation values could be recorded from the bone trabeculae developed in the PA and in the neighboring bone, which indicates that the collagen orientation pattern does not differ significantly among these bone trabecules. Based on our new data, we speculate that PA promotes bone formation, and some of the currently identified degradation products of PA may enhance osteo-conduction and osteoinduction inside the donor canal.