基于转录组和加权基因共表达网络的广叶绣球菌木质纤维素降解特性分析

【目的】分析广叶绣球菌（Sparassis latifolia）在不同木质纤维素诱导条件下基因表达差异，为广叶绣球菌木质纤维素降解关键基因和分子机制研究提供参考。【方法】以松木、杉木、甘蔗渣和天然堆积发酵后的杉木和发酵后的甘蔗渣为碳源，在液体培养条件下培养诱导广叶绣球菌，对其转录组进行测序研究，并对不同木质纤维素诱导样本进行加权基因共表达网络分析（weighted gene co-expression network analysis，WGCNA）。【结果】杉木培养与松木培养比较组差异表达基因最少（20个），蔗渣培养与松木培养比较组差异表达基因最多（486个）。基因本体（gene ontology，GO）富集分析结果表明，差异表达基因主要涉及氧化还原酶活性、单加氧酶活性和铁离子结合活性等，京都基因和基因组百科全书（Kyoto encyclopedia of genes and genomes，KEGG）通路富集分析结果表明，差异表达基因主要涉及戊糖和葡萄糖醛酸转换、甲烷代谢和乙醛酸盐和二羧酸盐代谢等通路。发酵甘蔗渣为碳源培养时，纤维素和半纤维素降解相关的糖苷水解酶基因表达量总体上较高，而未发酵的松木、杉木和甘蔗渣为碳源培养时木质素降解或修饰相关的碳水化合物辅助酶基因表达量总体上较高。利用WGCNA共鉴定出10个共表达模块，其中green模块与未发酵蔗渣诱导显著正相关，blue模块与发酵甘蔗渣诱导显著正相关，magenta和turquoise模块与发酵杉木诱导显著正相关。GO富集分析结果表明，turquoise模块内基因显著富集到尿素跨膜转运子活性、甲基转移酶活性和单加酶活性等，blue模块基因显著富集到水解酶活性和β-甘露糖苷酶活性。KEGG通路富集分析结果表明，blue模块内基因显著富集的通路有半乳糖代谢、果糖和甘露糖代谢、苯丙氨酸代谢、精氨酸和脯氨酸代谢等。通过构建互作网络图挖掘到12个核心基因，其可能参与了基质降解及相关基因的表达调控。【结论】不同木质纤维素类型显著影响了广叶绣球菌木质纤维素降解基因的差异表达轮廓，这种差异反映了广叶绣球菌对不同木质纤维素特异的降解策略。     

一株木质纤维素降解菌的筛选及其全基因组分析北大核心CSCD

【目的】筛选和鉴定有木质纤维素降解能力的1株细菌,测定其相关酶活力并进行全基因组分析,为构建木质纤维素降解工程菌提供依据。【方法】采用3种木质素类似物(天青-B;酚红;愈创木酚)的脱色/染色法,从腐木和被枝叶覆盖的土壤中分离和筛选出1株具有较强木质纤维素降解能力的细菌。通过16S r RNA基因和全基因组序列分析对该菌进行种属鉴定。使用紫外分光光度法测定其锰过氧化物酶(Mn P)、漆酶(Lac)、羧甲基纤维素酶(CMCase)以及滤纸酶(FPA)活力,了解该菌相关酶活力大小在一定时间内的变化趋势。使用Illumina Miseq和454 GS Junior测序平台获取该菌的全基因组序列,将其全基因组序列经过注释的基因蛋白质序列提交COG和KEGG数据库进行BLASTp比对分析,确定该菌潜在的重要酶类和代谢途径,并对部分注释基因进行定量RT-PCR验证。【结果】筛选得到1株优势菌株S12,该菌经鉴定后命名为解鸟氨酸拉乌尔菌(Raoultella ornithinolytica)。在液体CMC-Na培养基中发酵28 h,菌体生长达到稳定期,纤维素降解相关酶活力也在此时达到峰值。生物信息学分析结果表明,菌株S12具有木质素降解通路中重要酶类的编码基因,如过氧化物酶、Fe-Mn型超氧化物歧化酶、邻苯二酚1,2-双加氧酶和原儿茶酸-3,4-双加氧酶等,这些基因在以碱性木质素为碳源的培养条件下表达量不同程度地高于以葡萄糖为碳源的培养条件。另外,菌株S12具备完整的纤维素降解和乙醇生成通路。【结论】本研究首次揭示了Raoultella ornithinolytica S12具备有效的木质纤维素降解性能,这对于推动木质纤维素应用产业的发展具有重要意义。     

联苯培养条件下红球菌R04转录表达和苯甲酸代谢途径解析

摘要:【目的】研究不同碳源,特别是联苯条件下红球菌的细胞转录应答,以挖掘与多氯联苯(PCBs)转运、代谢及其调控相关的基因,为进一步全面理解PCB微生物降解的分子机制奠定基础。【方法】以一株多氯联苯降解菌红球菌(Rhodococcus sp.R04)为材料,分别提取不同碳源(乙醇、葡萄糖和联苯)培养条件下菌体的总RNA,反转录合成cDNA。采用高通量测序法分别对这三种样品进行转录组测序,分析测序数据得出全基因组表达模式,并对不同条件下的基因表达进行差示分析,进而对联苯代谢网络和红球菌中其他基因的转录调节和代谢应答反应做出相关性分析。Q-RT-PCR分析不同碳源培养条件下的基因表达情况。【结果】测序结果表明,与葡萄糖和乙醇相比,联苯培养条件下明显上调(log2 Ratio 1)基因个数分别为375和332个。与葡萄糖相比,联苯培养条件下,相关基因上调表达量与Q-RT-PCR实验结果基本一致。功能分类获得细胞组分、分子功能和生物学过程三大类别160多个细小分支的差示表达基因,部分基因参与联苯代谢转录调控、联苯转运、抗氧化应激反应以及信号传导通路系统等多种生理过程。参与联苯上游代谢途径的众多同工酶基因中,只有bphC2和bphD1在联苯中大量上调表达,其余同工酶在联苯中基本量不变或下调表达。转录组注释及差示分析推测,红球菌R04中苯甲酸的代谢主要是通过儿茶酚邻位途径、间位途径以及原儿茶酸途径三条代谢途径完成。【结论】与葡萄糖和乙醇相比,红球菌R04在联苯培养条件下基因表达差异明显,这为我们进一步解析多氯联苯代谢特征和代谢调控提供理论依据。     

球毛壳菌降解天然木质纤维素能力差异及酶系基因分析

目的:以不同植物中分离到的4株内生球毛壳菌NK102、NK103、NK104和NK105为对象,研究不同生态来源球毛壳菌降解木质素和纤维素的能力。方法:首先采用羧甲基纤维素和纤维素刚果红平板检测各菌株的纤维素降解能力,并利用Bavendamm平板反应检测各菌株的木质素降解能力;将4株菌分别培养在以微晶纤维素、杨树叶和木屑为惟一碳源的液体培养基中,通过检测培养液中纤维素酶和漆酶的酶活力,比较各菌株分解利用天然木质纤维素材料的能力,连续培养12 d后检测培养液中次级代谢产物的合成情况;利用已测序的球毛壳菌CBS148.51的基因组信息,寻找编码木质纤维素降解酶类的基因,为球毛壳菌分解利用木质纤维素提供分子生物学依据。结果:NK102、NK103、NK104和NK105在羧甲基纤维素培养基和纤维素刚果红培养基上都能够生长并形成水解圈;Bavendamm平板反应显示4株菌降解木质素的能力由强到弱依次是NK103、NK102、NK105和NK104。4株菌都能分解利用微晶纤维素、杨树叶和木屑,分泌纤维素酶和漆酶,其中NK102在以木屑为碳源的培养基上纤维素酶活力最强,达到0.76 U/mL发酵液,NK103在以杨树叶为碳源的培养基上漆酶活力最强。与此同时,4株菌在发酵培养过程中都能够稳定地合成球毛壳甲素(ChA),ChA产量受到碳源影响,在以杨树叶为碳源的培养基上,NK104的ChA产量最高,可达到14.88 mg/L发酵液。利用已测序的球毛壳菌CBS148.51的基因组信息,寻找到119个编码纤维素半纤维素酶的基因、8个编码漆酶的基因和2个编码锰过氧化物酶的基因,球毛壳菌具有完整的降解纤维素半纤维素的酶体系,在木质纤维素降解真菌的开发过程中具有重要的研究价值。结论:本研究为球毛壳菌木质纤维素降解过程的研究及该菌种的开发利用奠定了基础。     

香菇HMG-box转录因子lelcrp1基因的功能

【目的】研究香菇(Lentinula edodes) HMG-box转录因子LELCRP1 (Lentinula edodes lignocellulase genes regulation protein 1)在木质纤维素降解相关酶基因表达中的功能与作用。【方法】通过double-joint及同源重组方法构建lelcrp1基因RNAi载体,采用根癌农杆菌介导转化的方法转入香菇异核菌株W1菌丝中,筛选得到RNAi转化子,通过Southern杂交检测插入片段在菌株W1基因组中的拷贝数量。采用荧光定量PCR检测RNAi转化子木质纤维素降解酶基因表达水平变化,并在含有3.5μg/mL潮霉素的MYG平板上测定RNAi转化子的菌丝生长速度。【结果】获得了4个lelcrp1基因表达水平与出发菌株W1相比显著下调6–7倍的RNAi转化子。Southern杂交结果显示,lelcrp1基因RNAi片段已成功整合至香菇菌株W1基因组内,并以单拷贝形式存在。对其中2个RNAi转化子的26个木质纤维素降解酶基因表达水平进行分析,发现其中9个纤维素酶基因、1个半纤维素酶基因、2个辅助酶AA9基因和1个锰过氧化物酶基因的表达水平均表现出明显的下调。平板生长试验表明,RNAi转化子菌丝生长速度均显著慢于出发菌株W1。【结论】通过RNAi技术成功抑制了香菇异核菌株中lelcrp1基因表达水平,并导致部分纤维素及木质素酶基因表达水平相应下调,首次发现HMG-box结构域的转录因子能调控木质纤维素降解相关酶基因表达。     

球毛壳菌降解天然木质纤维素能力差异及酶系基因分析简

目的：以不同植物中分离到的4株内生球毛壳菌NK102、NK103、NK104和NK105为对象,研究不同生态来源球毛壳菌降解木质素和纤维素的能力。方法：首先采用羧甲基纤维素和纤维素刚果红平板检测各菌株的纤维素降解能力,并利用Bavendamm平板反应检测各菌株的木质素降解能力;将4株菌分别培养在以微晶纤维素、杨树叶和木屑为惟一碳源的液体培养基中,通过检测培养液中纤维素酶和漆酶的酶活力,比较各菌株分解利用天然木质纤维素材料的能力,连续培养12d后检测培养液中次级代谢产物的合成情况;利用已测序的球毛壳菌CBS148．51的基因组信息,寻找编码木质纤维素降解酶类的基因,为球毛壳菌分解利用木质纤维素提供分子生物学依据。结果：NK102、NK103、NK104和NK105在羧甲基纤维素培养基和纤维素刚果红培养基上都能够生长并形成水解圈;Bavendamm平板反应显示4株菌降解木质素的能力由强到弱依次是NK103、NK102、NK105和NK104。4株菌都能分解利用微晶纤维素、杨树叶和木屑,分泌纤维素酶和漆酶,其中NK102在以木屑为碳源的培养基上纤维素酶活力最强,达到0．76U/mL发酵液,NK103在以杨树叶为碳源的培养基上漆酶活力最强。与此同时,4株菌在发酵培养过程中都能够稳定地合成球毛壳甲素（ChA）,ChA产量受到碳源影响,在以杨树叶为碳源的培养基上,NK104的ChA产量最高,可达到14．88mg/L发酵液。利用已测序的球毛壳菌CBS148．51的基因组信息,寻找到119个编码纤维素半纤维素酶的基因、8个编码漆酶的基因和2个编码锰过氧化物酶的基因,球毛壳菌具有完整的降解纤维素半纤维素的酶体系,在木质纤维素降解真菌的开发过程中具有重要的研究价值。结论：本研究为球毛壳菌木质纤维素降解过程的研究及该菌种的开发利用奠定了基础。     

鸡枞菌转录组分析揭示其对木质纤维素的降解功能

【目的】探究鸡枞菌是否能降解木质纤维素成分,并理解其与共生白蚁之间的共生关系。【方法】本研究是应用新一代高通量测序技术454 GS FLX Titanium对鸡枞菌的转录组进行测序,挖掘鸡枞菌中能参与降解纤维素和木质素等成分的多样性酶系。【结果】八分之一的RUN测序总共得到了82386条表达序列标签,去除引物和载体等序列后,剩余的54410条序列被拼接成3301条contigs以及3193条singletons。根据序列相似性,将这些unigenes与三大蛋白数据库(Nr数据库、SwissProt数据库、CDD数据库)中的蛋白序列进行BLAST比较,发现有2681条基因与其他生物的已知基因有不同程度的相似性。在鸡枞菌的这些转录产物中,有33条编码可能参与降解纤维素或半纤维素的酶基因,其中包括5种纤维素酶以及28种水解半纤维素、淀粉或几丁质等物质的酶类。更重要的是,还发现了4种漆酶以及一种芳基乙醇氧化酶基因,这些都是能有效降解木质素的酶类。这些结果揭示了鸡枞菌中存在漆酶并可能有效降解植物残渣中的酚化合物。【结论】这些基因的发现说明了鸡枞菌能降解木质素,并能与共生白蚁分泌的纤维素酶协同作用有效降解纤维素。     

解糖热解纤维素菌F32降解未预处理秸秆及产纤维素酶特性分析

【目的】明确极端嗜热厌氧木质纤维素降解菌解糖热解纤维素菌F32代谢特征,并分析其产酶特性。【方法】使用细胞计数法绘制菌株的生长曲线,使用离子色谱及气相色谱进行产物和残糖量分析,以DNS法及对硝基苯酚法检测菌株胞外蛋白的酶活性。【结果】解糖热解纤维素菌F32在以葡萄糖、微晶纤维素和未经预处理小麦秸秆为碳源时生长状况优于解糖热解纤维素菌DSM 8903。在以葡萄糖为碳源进行培养时,与菌株DSM 8903相比,菌株F32具有产乳酸较多,而产氢气较少的特点。在以微晶纤维素和未经预处理小麦秸秆为碳源进行培养时,与菌株DSM 8903相比,菌株F32胞外蛋白具有较高的内切纤维素酶活性和木聚糖酶活性。【结论】解糖热解纤维素菌F32表现出较强的木质纤维素降解能力,其与DSM 8903的产物组成及胞外蛋白的酶活性具有明显差异。     

基于转录组分析香菇不同漆酶活性单核菌丝体基因表达

漆酶是香菇生长发育过程中一种重要的木质素降解酶,其活性高低对于香菇木质素降解能力和香菇品质形成具有重要作用。为探讨香菇不同漆酶活性的单核菌丝体基因表达变化,对漆酶活性存在差异的单核菌丝体进行转录组测序分析,共获得15 522个注释基因。GO（gene ontology）分析表明差异基因在氧化还原酶活性节点大量富集,包括参与木质素降解的酶类及55个细胞色素P450基因;KEGG（Kyoto encyclopedia of genes and genomes）分析发现淀粉和蔗糖代谢、戊糖和葡萄糖醛酸相互转化途径中糖苷水解酶、UDPG脱氢酶等基因上调表达。通过搜索转录因子数据筛选到172个差异表达的转录因子,预测了可能与漆酶结合的bZIP、C₂H₂、C₄转录因子家族。由此推测,在漆酶高产单核菌株中木质素降解和碳水化合物代谢的相关基因的表达发生变化,及糖醛酸和磷酸戊糖途径相关基因上调表达,促进了木质素降解产物高效转化成糖、核酸等生物大分子,有助于香菇菌丝体的生长,转录因子在漆酶活性调控中起了重要作用。本研究为深入理解香菇漆酶高产菌株的生理代谢机制提供了重要的基因数据资源。     

纤维素降解菌烟曲霉HZ1的基因组测序及生物信息学分析

【目的】烟曲霉Aspergillus fumigatus作为一类具有纤维素降解能力的真菌,对其基因组的研究,将有利于从A. fumigatus中挖掘和开发利用与纤维素降解相关的酶资源。【方法】利用CMC选择培养基和刚果红染色法从长足大竹象肠道中分离和筛选出纤维素降解菌A. fumigatus HZ1,同时采用Illumina PE150平台进行基因组测序,随后进行了相关的生物信息学分析,此外还利用了DNS法测定了其纤维素酶活。【结果】纤维素降解菌A. fumigatus HZ1基因组大小为27.45 Mb,GC含量为49.43%;通过NR、KOG、GO、Swissprot、eggNOG、KEGG和Pfam数据库注释结果表明基因组包含9473个基因;同时碳水化合物活性酶(CAZyme)注释结果表明基因组含有534个CAZyme基因,并与其他4种A. fumigatus基因组CAZyme分布无显著差异;本研究还鉴定出多种与木质纤维素降解相关的纤维素酶基因、半纤维素酶基因和木质素酶基因;此外纤维素酶活结果表明,在CMC培养基中其酶活呈上升趋势且具有较高活性。【结论】本研究首次对A. fumigatus HZ1基因组进行了测序和分析,探讨了其纤维素降解的遗传基础,并通过酶活验证了其纤维素降解潜力,为该菌的实际应用提供了理论基础。     

Thermophilic anaerobic biodegradation of [C]lignin, [C]cellulose, and [C]lignocellulose preparations

Thermophilic (55 degrees C) anaerobic enrichment cultures were incubated with [C-lignin]lignocellulose, [C-polysaccharide]lignocellulose, and kraft [C]lignin prepared from slash pine, Pinus elliottii, and C-labeled preparations of synthetic lignin and purified cellulose. Significant but low percentages (2 to 4%) of synthetic and natural pine lignin were recovered as labeled methane and carbon dioxide during 60-day incubations, whereas much greater percentages (13 to 23%) of kraft lignin were recovered as gaseous end products. Percentages of label recovered from lignin-labeled substrates as dissolved degradation products were approximately equal to percentages recovered as gaseous end products. High-pressure liquid chromatographic analyses of CuO oxidation products of sound and degraded pine lignin indicated that no substantial chemical modifications of the remaining lignin polymer, such as demethoxylation and dearomatization, occurred during biodegradation. The polysaccharide components of pine lignocellulose and purified cellulose were relatively rapidly mineralized to methane and carbon dioxide; 31 to 37% of the pine polysaccharides and 56 to 63% of the purified cellulose were recovered as labeled gaseous end products. An additional 10 to 20% of the polysaccharide substrates was recovered as dissolved degradation products. Overall, these results indicate that elevated temperatures can greatly enhance rates of anaerobic degradation of lignin and lignified substrates to methane and low-molecular-weight aromatic compounds.     

Thermophilic Anaerobic Biodegradation of [14C]Lignin, [14C]Cellulose, and [14C]Lignocellulose Preparations

Thermophilic (55°C) anaerobic enrichment cultures were incubated with [¹⁴C-lignin]lignocellulose, [¹⁴C-polysaccharide]lignocellulose, and kraft [¹⁴C]lignin prepared from slash pine, Pinus elliottii, and ¹⁴C-labeled preparations of synthetic lignin and purified cellulose. Significant but low percentages (2 to 4%) of synthetic and natural pine lignin were recovered as labeled methane and carbon dioxide during 60-day incubations, whereas much greater percentages (13 to 23%) of kraft lignin were recovered as gaseous end products. Percentages of label recovered from lignin-labeled substrates as dissolved degradation products were approximately equal to percentages recovered as gaseous end products. High-pressure liquid chromatographic analyses of CuO oxidation products of sound and degraded pine lignin indicated that no substantial chemical modifications of the remaining lignin polymer, such as demethoxylation and dearomatization, occurred during biodegradation. The polysaccharide components of pine lignocellulose and purified cellulose were relatively rapidly mineralized to methane and carbon dioxide; 31 to 37% of the pine polysaccharides and 56 to 63% of the purified cellulose were recovered as labeled gaseous end products. An additional 10 to 20% of the polysaccharide substrates was recovered as dissolved degradation products. Overall, these results indicate that elevated temperatures can greatly enhance rates of anaerobic degradation of lignin and lignified substrates to methane and low-molecular-weight aromatic compounds.     

Isolation of a Bacterium Capable of Degrading Peanut Hull Lignin

Thirty-seven bacterial strains capable of degrading peanut hull lignin were isolated by using four types of lignin preparations and hot-water-extracted peanut hulls. One of the isolates, tentatively identified as Arthrobacter sp., was capable of utilizing all four lignin preparations as well as extracted peanut hulls as a sole source of carbon. The bacterium was also capable of degrading specifically labeled [¹⁴C]lignin-labeled lignocellulose and [¹⁴C]cellulose-labeled lignocellulose from the cordgrass Spartina alterniflora and could also degrade [¹⁴C]Kraft lignin from slash pine. After 10 days of incubation with [¹⁴C]cellulose-labeled lignocellulose or [¹⁴C]lignin-labeled lignocellulose from S. alterniflora, the bacterium mineralized 6.5% of the polysaccharide component and 2.9% of the lignin component.     

Preparation, characterization, and microbial degradation of specifically radiolabeled [C]lignocelluloses from marine and freshwater macrophytes

Specifically radiolabeled [C-lignin]lignocelluloses were prepared from the aquatic macrophytes Spartina alterniflora, Juncus roemerianus, Rhizophora mangle, and Carex walteriana by using [C]phenylalanine, [C]tyrosine, and [C]cinnamic acid as precursors. Specifically radiolabeled [C-polysaccharide]lignocelluloses were prepared by using [C]glucose as precursor. The rates of microbial degradation varied among [C-lignin]lignocelluloses labeled with different lignin precursors within the same plant species. To determine the causes of these differential rates, [C-lignin]lignocelluloses were thoroughly characterized for the distribution of radioactivity in nonlignin contaminants and within the lignin macromolecule. In herbaceous plants, significant amounts (8 to 24%) of radioactivity from [C]phenylalanine and [C]tyrosine were found associated with protein, although very little (3%) radioactivity from [C]cinnamic acid was associated with protein. Microbial degradation of radiolabeled protein resulted in overestimation of lignin degradation rates in lignocelluloses derived from herbaceous aquatic plants. Other differences in degradation rates among [C-lignin]lignocelluloses from the same plant species were attributable to differences in the amount of label being associated with ester-linked subunits of peripheral lignin. After acid hydrolysis of [C-polysaccharide]lignocelluloses, radioactivity was detected in several sugars, although most of the radioactivity was distributed between glucose and xylose. After 576 h of incubation with salt marsh sediments, 38% of the polysaccharide component and between 6 and 16% of the lignin component (depending on the precursor) of J. roemerianus lignocellulose was mineralized to CO(2); during the same incubation period, 30% of the polysaccharide component and between 12 and 18% of the lignin component of S. alterniflora lignocellulose was mineralized.     

Decomposition of [C]Lignocelluloses of Spartina alterniflora and a Comparison with Field Experiments

Decomposition of lignocelluloses from Spartina alterniflora in salt-marsh sediments was measured by using C-labeled compounds. Rates of decomposition were fastest in the first 4 days of incubation and declined later. Lignins labeled in side chains were mineralized slightly faster than uniformly labeled lignins; 12% of the [side chain-C]lignin-labeled lignocellulose was mineralized after 816 h of incubation, whereas only 8% of the [U-C]lignin-labeled lignocelluloses were degraded during this period. The carbohydrate moiety within the lignocellulose complex was degraded about four times faster than the lignin moiety; after 816 h of incubation, 29 to 37% of the carbohydrate moiety had been mineralized. Changes in concentration of lignin and cellulose in litter of S. alterniflora were followed over 2 years of decay. Cellulose disappeared from litter more rapidly than lignin; 50% of the initial content of cellulose was lost after 130 days, whereas lignin required 330 to 380 days for 50% loss. The slow loss of lignin compared with other litter components resulted in a progressive enrichment of litter in lignin content. The rates of mineralization of [C]lignocelluloses in marsh sediments were similar to the rates of lignocellulose decomposition in litter on the marsh.     

Effects of pH on Lignin and Cellulose Degradation by Streptomyces viridosporus

Lignocellulose degradation by Streptomyces viridosporus results in the oxidative depolymerization of lignin and the production of a water-soluble lignin polymer, acid-precipitable polymeric lignin (APPL). The effects of the culture pH on lignin and cellulose metabolism and APPL production by S. viridosporus are reported. Dry, ground, hot-water-extracted corn (Zea mays) lignocellulose was autoclaved in 1-liter reagent bottles (5 g per bottle) and inoculated with 50-ml volumes of S. viridosporus cells suspended in buffers of specific pH (pH 6.0 to 9.2 at 0.4 pH unit intervals). Four replicates of inoculated cultures and of uninoculated controls at each pH were incubated as solid-state fermentations at 37°C. After 6 weeks of incubation the percent loss of lignocellulose, lignin, and carbohydrate and the amount of APPL produced were determined for each replicate. Optimal lignocellulose degradation, as shown by substrate weight loss, was observed in the pH range of 8.4 to 8.8. Only minor differences were seen in the Klason lignin, carbohydrate, protein, and ash contents of the APPLS produced by cultures at each pH. The effects of pH on the degradation of a spruce (Picea pungens) [¹⁴C-lignin]lignocellulose and a Douglas fir (Pseudotsuga menziesii) [¹⁴C-glucan]-lignocellulose were also determined at pH values between 6.5 and 9.5 (0.5 pH unit intervals). The incubations were carried out for 3 weeks at 37°C with bubbler-tube cultures. The percentage of initial ¹⁴C recovered as ¹⁴CO₂, ¹⁴C-labeled water-soluble products, and [¹⁴C]APPL was then determined. The mineralization of lignin and cellulose to CO₂ was optimal at pHs 6.5 and 7.0, respectively. However, the optimum for lignin and cellulose solubilization was pH 8.5, which correlated with the pH 8.5 optimum for APPL production. Overall, the data show that, whereas lignin mineralization is optimal at neutral to slightly acidic pHs, lignocellulose degradation with lignin solubilization and APPL production is promoted by alkaline pHs. These findings indicate that lignin-solubilizing actinomycetes may play an important role in the metabolism of lignin in neutral to alkaline soils in which ligninolytic fungi are not highly competitive.     

Decomposition of [14C]Lignocelluloses of Spartina alterniflora and a Comparison with Field Experiments

Decomposition of lignocelluloses from Spartina alterniflora in salt-marsh sediments was measured by using ¹⁴C-labeled compounds. Rates of decomposition were fastest in the first 4 days of incubation and declined later. Lignins labeled in side chains were mineralized slightly faster than uniformly labeled lignins; 12% of the [side chain-¹⁴C]lignin-labeled lignocellulose was mineralized after 816 h of incubation, whereas only 8% of the [U-¹⁴C]lignin-labeled lignocelluloses were degraded during this period. The carbohydrate moiety within the lignocellulose complex was degraded about four times faster than the lignin moiety; after 816 h of incubation, 29 to 37% of the carbohydrate moiety had been mineralized. Changes in concentration of lignin and cellulose in litter of S. alterniflora were followed over 2 years of decay. Cellulose disappeared from litter more rapidly than lignin; 50% of the initial content of cellulose was lost after 130 days, whereas lignin required 330 to 380 days for 50% loss. The slow loss of lignin compared with other litter components resulted in a progressive enrichment of litter in lignin content. The rates of mineralization of [¹⁴C]lignocelluloses in marsh sediments were similar to the rates of lignocellulose decomposition in litter on the marsh.     

巴西蘑菇对木质纤维素的降解与转化*

巴西蘑菇能够降解棉籽壳和麦草两种培养基中木质纤维素复合体中的全部组分,属于白腐真菌;巴西蘑菇降解的有机物质的绝大部分被菌体的呼吸过程消耗掉,其绝对生物学效率较低,仅为4.41%~5.25%;在栽培前期木质素的降解速率大于纤维素和半纤维素,这对纤维素和半纤维素的降解十分有利;非木质纤维素组分主要在菌丝生长阶段被利用,而木质纤维素是子实体生长发育阶段的主要碳源;就整个栽培过程而言,巴西蘑菇生长发育所需要的82.39%~84.50%的碳源来自木质纤维素。     

Anaerobic Biodegradation of the Lignin and Polysaccharide Components of Lignocellulose and Synthetic Lignin by Sediment Microflora

Specifically radiolabeled [¹⁴C-lignin]lignocelluloses and [¹⁴C-polysaccharide]lignocelluloses were prepared from a variety of marine and freshwater wetland plants including a grass, a sedge, a rush, and a hardwood. These [¹⁴C]lignocellulose preparations and synthetic [¹⁴C]lignin were incubated anaerobically with anoxic sediments collected from a salt marsh, a freshwater marsh, and a mangrove swamp. During long-term incubations lasting up to 300 days, the lignin and polysaccharide components of the lignocelluloses were slowly degraded anaerobically to ¹⁴CO₂ and ¹⁴CH₄. Lignocelluloses derived from herbaceous plants were degraded more rapidly than lignocellulose derived from the hardwood. After 294 days, 16.9% of the lignin component and 30.0% of the polysaccharide component of lignocellulose derived from the grass used (Spartina alterniflora) were degraded to gaseous end products. In contrast, after 246 days, only 1.5% of the lignin component and 4.1% of the polysaccharide component of lignocellulose derived from the hardwood used (Rhizophora mangle) were degraded to gaseous end products. Synthetic [¹⁴C]lignin was degraded anaerobically faster than the lignin component of the hardwood lignocellulose; after 276 days, 3.7% of the synthetic lignin was degraded to gaseous end products. Contrary to previous reports, these results demonstrate that lignin and lignified plant tissues are biodegradable in the absence of oxygen. Although lignocelluloses are recalcitrant to anaerobic biodegradation, rates of degradation measured in aquatic sediments are significant and have important implications for the biospheric cycling of carbon from these abundant biopolymers.