木聚糖的提取分离和应用研究进展

木聚糖是自然界中除纤维素外含量最丰富的一种聚糖，而木质纤维素中半纤维素、纤维素和木质素3大组分构成的复杂结构是获得木聚糖的主要障碍。本文结合最新研究成果着重阐述从木质纤维素中制备木聚糖的主要方法及分离纯化策略，介绍木聚糖在食品、医药、材料等领域的应用，并对木聚糖未来的研究发展方向进行展望。     

酸性阳离子交换树脂催化降解木质纤维素制备可还原糖

 为研究木质纤维素中不同组分的降解规律,以自制强酸性阳离子交换树脂为催化剂,对秸秆、蒸汽爆破预处理秸秆和微晶纤维素(MCC)进行降解处理研究。考查了催化剂用量、反应温度、反应时间等对秸秆降解反应的影响,比较了纤维素和半纤维素降解效果。研究结果表明,在微波加热条件下,以离子液体[Amim]Cl 为溶剂时,当催化剂与木质纤维素质量比为1∶1、反应温度为140~160℃、反应时间为20~40 min 时,总还原糖收率最高可达92%且半纤维素较纤维素易于降解,在140℃反应30 min,木糖收率最高为47.3%,在160℃反应40 min,葡萄糖收率最高可达45.8%。比较木屑、蒸汽爆破预处理的木屑和微晶纤维素催化降解情况,结果表明,酸性阳离子交换树脂对它们均具有有效的催化效果,其中微晶纤维素降解效果最好。     

Evolution of species interactions in a biofilm community

Biofilms are spatially structured communities of microbes whose function is dependent on a complex web of symbiotic interactions. Localized interactions within these assemblages are predicted to affect the coexistence of the component species, community structure and function, but there have been few explicit empirical analyses of the evolution of interactions. Here we show, with the use of a two-species community, that selection in a spatially structured environment leads to the evolution of an exploitative interaction. Simple mutations in the genome of one species caused it to adapt to the presence of the other, forming an intimate and specialized association. The derived community was more stable and more productive than the ancestral community. Our results show that evolution in a spatially structured environment can stabilize interactions between species, provoke marked changes in their symbiotic nature and affect community function.     

仁扇舟蛾幼虫肠道可培养细菌群落结构分析

【目的】了解仁扇舟蛾(Clostera restitura)肠道共生细菌的主要类群及其群落结构特征,明确仁扇舟蛾幼虫前、中和后肠可培养细菌的种类及群落结构组成,为进一步研究特异功能细菌的生理生化特征和功能提供基础。【方法】选取仁扇舟蛾5龄幼虫进行肠道解剖,分离前、中和后肠不同肠段,研磨稀释10^-1~10^-6,分别涂布于NA和LB固体培养基上,每个处理重复3次,28 ℃培养72 h。后对前、中和后肠可培养细菌进行分离纯化培养,提取细菌基因组DNA,利用 16S rDNA 基因序列分析和PCR扩增技术,获得细菌基因组序列,后与NCBI GenBank数据库进行Blast同源性比对,参考序列相似度98%以上近缘序列的物种信息,结合菌落形态特征和生理生化特性鉴定细菌种类,利用MEGA 7.0软件,采用邻接法(Neighbor-Joining)构建系统进化树。【结果】从仁扇舟蛾5龄幼虫的前、中和后肠中共分离获得22株可培养细菌,分属于变形菌门(Proteobacteria)、厚壁菌门(Firmicutes)和放线菌门(Actinobacteria),共13个属,22个种。其中:假单胞菌属(Pseudomonas)4株,罗尔斯通菌属(Ralstonia)3株,芽孢杆菌属(Bacillus)3株,嗜麦芽寡养单胞菌属(Stenotrophomonas)2株,气球菌属(Aerococcus)2株,其余微小杆菌属(Exiguobacterium)、微球菌属(Micrococcus)、短小杆菌属(Curtobacterium)、伯克氏菌属(Burkholderia)、类芽孢杆菌属(Paenibacillus)、节杆菌属(Arthrobacter)、短状杆菌属(Brachybacterium)和两面神菌属(Janibacter)各1株。细菌的种类存在差异,前、中和后肠不同肠段的细菌种类分别为5、10和7种。3个肠段共有的细菌种类是皮氏罗尔斯菌(Ralstonia pickettii)和斯氏假单胞菌(Pseudomonas stutzeri)。【结论】仁扇舟蛾5龄幼虫肠道的可培养细菌种类较为丰富,其中以变形菌门和厚壁菌门为优势菌群。不同肠段中可培养细菌的多样性和群落结构存在差异,其中以中肠可培养细菌种类较为丰富。此次从仁扇舟蛾肠道中分离到与单宁降解相关的细菌,分析表明仁扇舟蛾肠道菌群与宿主的取食习性有关,肠道细菌可能在克服植物次生代谢物质的化学防御上发挥作用。     

含铀凋落物腐解前后微生物群落结构特征及多样性分析

采集含铀凋落物腐解前后土壤样本,通过Illumina Miseq高通量测序技术研究腐解前后土壤微生物的多样性及群落结构,解析含铀凋落物腐解前后土壤微生物群落结构特征及其变化规律,为发掘潜在含铀生物质降解菌种提供理论基础。通过高通量测序,分别获得158 781条细菌和242 198条真菌的有效序列,菌群Alpha分析显示,腐解后细菌的多样性和丰富度增加,真菌的多样性和丰富度减少。通过微生物群落结构解析,发现腐解前后门水平上始终存在的优势菌群,细菌中为绿弯菌门(Chloroflexi)、放线菌门(Actinobacteria)、酸杆菌门(Acidobacteria)和变形菌门(Proteobacteria);真菌中为子囊菌门(Ascomycota)、担子菌门(Basidiomycota)、unclassified_Fungi和被孢囊门(Mortierellomycota)。结果表明,含铀凋落物腐解后,凋落物内的铀被释放到土壤中,改变了土壤微生物群落结构。腐解后土壤中可识别的优势菌群功能主要集中在对纤维素、半纤维素、木质素的降解和铀的浸出。热酸菌属(Acidothermus)和软盘菌属(Mollisia)可能是降解凋落物和浸出铀较好的微生物组合。     

Protein delivery into eukaryotic cells by type III secretion machines

Bacteria that have sustained long-standing close associations with eukaryotic hosts have evolved specific adaptations to survive and replicate in this environment. Perhaps one of the most remarkable of those adaptations is the type III secretion system (T3SS)--a bacterial organelle that has specifically evolved to deliver bacterial proteins into eukaryotic cells. Although originally identified in a handful of pathogenic bacteria, T3SSs are encoded by a large number of bacterial species that are symbiotic or pathogenic for humans, other animals including insects or nematodes, and plants. The study of these systems is leading to unique insights into not only organelle assembly and protein secretion but also mechanisms of symbiosis and pathogenesis.     

木质纤维素水解制化学品的研究进展

 木质纤维素是地球上最为丰富的可再生资源,对其进行研究和利用可以有效缓解对化石能源的依赖。木质纤维素的结构较为复杂,因此木质纤维素水解技术是木质纤维素转化过程中的关键。本文介绍了木质纤维素水解产糖技术存在的问题,对比了木质纤维素水解产糖主要方法的优缺点,概述了国内外最近的利用木质纤维素水解方法制备多元醇类化学品、能源化学品、新平台化学品的研究进展。针对木质纤维素的水解难题及木质纤维素水解制化学品的发展方向提出了展望。     

Insights on cellulose hydrolysis in the porous structure of biomass particles using the lattice Boltzmann method

Lignocellulose biomass has been recognized as one of the most promising sources of low-cost and renewable biofuels, and its conversion into alternative fuels and valuable platform molecules has attracted widespread attention. The porous solid residue from lignocellulose biomass, which was pretreated by steam-stripping, is catalyzed by dilute sulfuric acid to form levulinic acid (LA). The process includes porous media diffusion, multicomponent reactive transport, liquid-solid interface reaction, and cellulose dissolution. Understanding the interactions between these complex physicochemical processes is the basis for optimizing the performance of the hydrolysis reaction. In this study, a porous reaction transport model based on the lattice Boltzmann method (LBM) was established to simulate the conversion of cellulose to LA which was catalyzed by dilute acid. The simulation results were compared with the existing experimental results to verify the accuracy of the model. The simulation results showed that temperature has a significant effect on hydrolysis and the highest carbon yield was obtained at 180 °C. Without considering the lignin reaction, the higher the sulfuric acid concentration, the better is the hydrolysis efficiency in the range of 4% – 8%. The influence of cellulose content and steam-stripping the residue porosity on the dissolution rate of cellulose was also evaluated. The average dissolution rate of cellulose is the highest within 75 min, when the porosity is 0.7 and the cellulose content is 50%.     

生物质三组分热解反应及动力学的比较

采用热重分析法考察了生物质中三种主要成分纤维素、半纤维素和木质素的热解反应行为,以Coats-Redfern积分法对实验数据进行动力学解析,建立了该三组分热解反应的动力学模型。结果表明,分子结构上的不同使得该三组分的热解特性存在明显差异;在所考察的温区内纤维素的失重量约为86%,半纤维素模型化合物木聚糖的失重量为69%左右,而木质素的失重量仅为51%;热解反应深度按照纤维素、木聚糖和木质素的顺序依次降低;木质素和木聚糖的热解反应均可以用两个分段二级动力学方程来描述,但纤维素在低温区和高温区分别遵循一级和二级动力学规律。     

室内饲养松墨天牛幼虫不同肠段细菌的群落结构及功能分析

【目的】了解室内饲养松墨天牛(Monochamus alternatus)幼虫前、中、后肠段细菌的群落结构,比较不同肠段之间菌群多样性和优势菌群的差异,为揭示肠道细菌在松墨天牛获取营养、克服寄主植物化学防御的机理提供参考。【方法】分别提取室内饲养的松墨天牛4龄幼虫前、中、后肠各3组样本(每组5个前肠、5个中肠、5个后肠)的肠道DNA。利用Illumina HiSeq技术对松墨天牛幼虫肠道细菌的16S rDNA V3-V4区序列进行文库构建和高通量测序。原始序列使用Trimmomatic软件和FLASH软件分别进行质控和拼接。利用USEARCH软件对序列进行操作分类单元(OTUs)聚类,统计OTUs数量并绘制Venn图。在门和属分类水平上统计各样本的群落组成及物种丰度情况。通过Alpha多样性和Beta多样性分析反映不同样本的菌群多样性和相似性。采用PICRUSt软件预测松墨天牛幼虫肠道细菌映射到KEGG数据库上的功能,探究不同肠段细菌群落发挥的潜在功能。【结果】共获得643 404条高质量序列,在97% 相似度下将其聚类为1 614个操作分类单元(OTUs),共注释到35门、63纲、137目、250科、554属和844种。前肠OTUs最少,后肠OTUs最多,每个肠段的OTUs组成上既有相似性,也存在差异性。变形菌门(Proteobacteria)为3个肠段中最优势门;葡糖杆菌属(Gluconobacter)为前肠中最优势属,沙雷氏菌属(Serratia)为中肠的最优势属,葡糖杆菌属和沙雷氏菌属同为后肠的最优势属。Alpha多样性显示中、后肠群落多样性更丰富;Beta多样性分析表明,3个肠段的细菌群落组成存在差异,但中肠与后肠的群落组成较相近。功能预测表明,整个肠道菌群中代谢功能丰度最高,其中以糖类代谢和氨基酸代谢为主,这些功能集中在中、后肠。【结论】本实验中菌群功能是基于PICRUSt软件预测的结果,松墨天牛幼虫室内种群的前、中、后肠的细菌群落结构及不同肠段细菌的潜在功能存在差异,是由于不同肠段内的理化性质差异及其在消化中发挥的不同功能所致。肠道细菌与松墨天牛幼虫形成一个共生功能体,菌群在协助幼虫代谢物质、获取营养以及克服寄主植物化学防御方面发挥着重要作用。     

微山湖养殖区与非养殖区细菌多样性的研究与比较

细菌群落结构对湖泊生态系统的物质循环和能量流动起着非常重要的作用,所以微山湖湖泊生态环境中的细菌群落多样性的分析为通过细菌的环境修复功能改善微山湖的生态环境奠定了理论基础.采用了DGGE和16SrDNA建库相结合的方法对微山湖养殖区与非养殖区及其沉积物细菌群落结构进行了研究,并对养殖区和非养殖区细菌的群落结构进行比较.研究的结果表明,养殖区与非养殖区的细菌群落结构存在较大差异,养殖区的细菌种类明显比非养殖区的细菌种类多,养殖区主要分布为:变形菌门(Proteobacteria)、疣微菌门(Verrucomicrobia)、绿弯菌门(Chloroflexi)、酸杆菌门(Acidobacteria)、螺旋体门(Spirochaetes)、绿菌门(Chlorobi)、拟杆菌门(Bacteroidetes).其中β-变形菌纲(Betaproteobacteria)为主要优势菌群.非养殖区主要分布为:变形菌门(Proteobacteria)、疣微菌门(Verrucomicrobia)、拟杆菌门(Bacteroidetes),其中β-变形菌纲(Betaproteobacteria)和δ-变形菌纲(Deltaproteobacteria)种类最为丰富.     

外加菌剂治理含异辛醇废水中菌群组成分析

由外加菌剂对含异辛醇废水处理的实验证明,人工添加的菌剂对废水中异辛醇的降解效果良好.微生物在降解有机物的过程中,不仅会利用污染物中的碳源和氮源,而且会和环境中的化学物质共同形成一个代谢相对稳定的微生态系统.通过对细菌16SrDNAV3可变区序列聚合酶链式反应扩增、变化浓度梯度凝胶电泳等细菌种类的研究,发现微生态中的细菌种类随污水浓度的变化并非呈单一递减的趋势,在一定的浓度条件下,会出现某类微生物优势群体;同时结合气相色谱分析,跟踪观察了异辛醇的降解过程,分析结果表明,降解的中间产物主要为乙醇.     

新型木质纤维素气凝胶的制备、表征及疏水吸油性能

 为制备一种新型的木质纤维素气凝胶,采用化学预处理、溶解再生与冷冻干燥相结合的方法,对废弃的麦秸杆进行提纯、溶解、置换和干燥,并采用绿色、无毒、低廉的氢氧化钠/聚乙二醇溶液作为纤维素溶剂。采用扫描电镜（SEM）、BET 比表面积分析、X 射线衍射仪（XRD）、傅里叶变换红外光谱仪（FTIR）和热重分析仪（TGA）,对制备的新型木质纤维素气凝胶的微观形貌、比表面积与孔径分布、晶型结构、化学结构及热稳定性进行表征。结果表明,制备的新型木质纤维素气凝胶具有连续、层叠的三维网状结构,比表面积为99.17 m²/g,总孔容为0.45 cm³/g;纤维素气凝胶的晶型由纤维素I 型转变为纤维素Ⅱ 型,结晶度为72.3%,相对于原料提高了23.4%,热稳定性也略微升高;并利用三甲基氯硅烷（TMCS）进行疏水改性,制备出了具有疏水性能的纤维素气凝胶。提供了一种新的制备木质纤维素气凝胶的有效溶剂,且具有高吸附性能、高承重能力、高结晶度的纤维素气凝胶是一种具有较大应用潜力的新型功能材料。     

纤维微菌XM-8木聚糖酶基因克隆及酶学性质

【目的】为获得可应用于木聚糖水解的酶资源,希望通过筛选分离得到能够水解木聚糖的木聚糖酶产生菌,克隆表达木聚糖酶基因并研究其酶学性质。【方法】从环境中筛选分离出可水解木聚糖的菌株,利用16SrDNA对其进行分子鉴定。扩增其木聚糖酶基因,以pET22b(+)为表达载体,构建共表达重组质粒,转化Escherichia coli BL21(DE3)进行异源表达,并对重组酶进行酶学性质研究。【结果】经16SrDNA鉴定该菌株为纤维微菌。通过PCR成功克隆到该菌的木聚糖酶基因(xyn-8a),并构建共表达质粒pET22b-xyn-8a,实现木聚糖酶Xyn-8a的活性表达。酶学性质研究表明Xyn-8a最适反应温度为60℃,最适反应pH值为6.0,只对木聚糖底物有活性;HPLC分析其水解产物以木二糖为主,还有少量的木糖和木三糖。【结论】XYN-8A在pH值为6的条件下具有较高活力,且可以催化水解反应,在生产低聚木糖方面具有一定的应用价值。     

上海师范大学奉贤校区内植物与鸟类共生关系探究

上海师范大学奉贤校区具有林地、水域、芦苇地、林水混合区等多种生境,其丰富的植被与鸟类是校园生态系统的重要组成因子.本研究通过样点法和样线法,统计到校内45种植物及42种鸟类,发现植物对鸟类具有取食果实、繁殖寄巢、停栖休息、遮挡隐蔽等功能,而鸟类对植物而言具有传播种子等作用,因此校园植物和鸟类存在多种共生关系,其中主要包括互利共生、偏性共生和无关共生等.调查结果还表明,多种生境中,林水混合生境具有更高的物种多样性.该研究发现的植物与鸟类的共生关系,为未来城市绿地服务于保护生物多样性的功能优化提供了科学依据.     

The contribution of species richness and composition to bacterial services

Bacterial communities provide important services. They break down pollutants, municipal waste and ingested food, and they are the primary means by which organic matter is recycled to plants and other autotrophs. However, the processes that determine the rate at which these services are supplied are only starting to be identified. Biodiversity influences the way in which ecosystems function, but the form of the relationship between bacterial biodiversity and functioning remains poorly understood. Here we describe a manipulative experiment that measured how biodiversity affects the functioning of communities containing up to 72 bacterial species constructed from a collection of naturally occurring culturable bacteria. The experimental design allowed us to manipulate large numbers of bacterial species selected at random from those that were culturable. We demonstrate that there is a decelerating relationship between community respiration and increasing bacterial diversity. We also show that both synergistic interactions among bacterial species and the composition of the bacterial community are important in determining the level of ecosystem functioning.     

木质纤维素降解酶系的基础和技术研究进展

山东大学微生物学科从事纤维素降解研究已有五十多年的历史。在木质纤维素微生物降解机理研究的基础上,从自然界中筛选到一株能高效降解植物纤维类生物质的斜卧青霉菌株,并获得该菌的多株抗降解物阻遏纤维素酶高产突变菌株。最近,已完成了对多株斜卧青霉菌株的全基因组测序,正在利用系统生物学技术深入探讨其酶系组成和酶合成调控机理。选育出的高产突变株,已用于规模化生产工业用酶,并开发出玉米芯生物炼制生产纤维素乙醇技术。     

A plant receptor-like kinase required for both bacterial and fungal symbiosis

Most higher plant species can enter a root symbiosis with arbuscular mycorrhizal fungi, in which plant carbon is traded for fungal phosphate. This is an ancient symbiosis, which has been detected in fossils of early land plants. In contrast, the nitrogen-fixing root nodule symbioses of plants with bacteria evolved more recently, and are phylogenetically restricted to the rosid I clade of plants. Both symbioses rely on partially overlapping genetic programmes. We have identified the molecular basis for this convergence by cloning orthologous SYMRK ('symbiosis receptor-like kinase') genes from Lotus and pea, which are required for both fungal and bacterial recognition. SYMRK is predicted to have a signal peptide, an extracellular domain comprising leucine-rich repeats, a transmembrane and an intracellular protein kinase domain. Lotus SYMRK is required for a symbiotic signal transduction pathway leading from the perception of microbial signal molecules to rapid symbiosis-related gene activation. The perception of symbiotic fungi and bacteria is mediated by at least one common signalling component, which could have been recruited during the evolution of root nodule symbioses from the already existing arbuscular mycorrhiza symbiosis.     

调控酶解底物初始pH制备低聚木糖

研究在木聚糖酶定向酶解纯木聚糖及木聚糖碱抽提液制备功能性低聚木糖时,酸和缓冲溶液调控底物的初始ｐＨ对低聚木糖的影响。结果表明,木聚糖酶在ｐＨ５．０左右的活力最高;酸调控纯木聚糖底物的低聚木糖得率低于缓冲溶液调控的低聚木糖得率,但两者相关不大;而当底物为木聚糖碱抽提液是,由于木素的存在,两种调控方式的低聚木糖得率相差较大,酶解液出现浑浊状态;酸调控纯木聚糖,木聚糖碱抽提液时,低聚木糖得率最高的初始ｐ     

超声波预处理下的稀酸-球磨系统降解桦木木屑

为研究木质纤维素水解技术,利用超声波结合稀酸球磨系统的方法降解桦木木屑.在pH=5的柠檬酸中处理36小时后,桦木木屑的还原性糖产率为130mg/g wood,主要的单糖组分为木糖、葡萄糖和甘露糖.利用X-射线衍射仪和紫外扫描仪对于球磨前后木屑的晶体结构和化学键变化进行表征,结果显示:稀酸球磨系统可以在常温常压下较好地水解木屑的木质纤维素.其中木质纤维素的结晶度明显降低,产生更多的不定形态纤维素,并且木质素部分被破坏,说明超声波预处理过程提高了纤维对化学试剂的可及性,促进木屑的糖化水解.