60Co-γ射线处理稻草秸秆对其纤维质酶解效果的影响

通过60Co-γ射线处理干稻草秸秆以及提取的稻草粗纤维,研究辐照预处理后的稻草秸秆酶降解效果。采用DNS法和硫酸-苯酚法分别测定处理样品中水溶性还原糖和总糖的含量;通过电子显微镜扫描观测辐照处理对稻草秸秆纤维组织结构的影响。结果表明:采用1 000 kGy~1 500 kGy的辐照剂量处理稻草秸秆,能有效破坏稻草的纤维组织结构,特别是稻草表面硅晶结构和纤维结构,随着辐射剂量的加大破坏程度增强,稻草水溶性还原糖和总糖含量显著增加。辐照与酶复合处理稻草秸秆能极显著地提高稻草秸秆纤维的转化率,稻草秸秆降解的水溶性还原糖含量达到21.44%,总糖含量达75.85%。辐照处理对木质素降解无明显影响。     

白腐菌及黑曲霉所产的纤维素复合酶对稻草秸秆的生物降解

研究了白腐菌及纤维素复合酶对稻草秸秆的协同生物降解。结果表明,利用黄孢原毛平革菌固态发酵稻草秸秆的过程中,LiP和MnP的最大活力可以达到28.3U/g和12.6U/g,同时,秸秆中的木质素能被有效降解,但纤维素、半纤维素降解率较低。添加黑曲霉所产的纤维素复合酶能有效地促进秸秆腐熟程度。在接入白腐菌培养10天后,每克稻草添加3 IU纤维素酶液并酶解48h可以使稻草秸秆中纤维素降解53.8%,半纤维素降解57.8%,木质素降解44.5%,干物质损失46.3%。此时细胞壁出现大范围破损,整个组织变得松散,秸秆完全腐熟。     

不同培养料和发酵次数栽培巴氏菇比较

分别以玉米秸秆和稻草为培养料栽培巴氏菇,对菌丝生长性状进行对比;同时,在我国传统发酵栽培方法的基础上,将三次发酵法与二次发酵法进行了对比。试验结果表明:利用玉米秸秆栽培的巴氏菇在发菌速度及子实体质量和产量上均优于稻草;培养料经过3次发酵更适宜巴氏菇生长。经过3次发酵的玉米秸秆培养料栽培的巴氏菇产量和生物学效率分别为7.7 kg/m2和27.5%,子实体粗蛋白含量44.89%,可溶性糖含量44.01%,18种氨基酸总量31.70%,明显高于2次发酵的玉米秸秆培养料及2次、3次发酵的稻草培养料。     

木质素降解菌的筛选及混合菌发酵降解秸秆的研究

农作物秸秆是农业生产的副产品，也是一项重要的生物资源。由于其成分结构的特殊性所导致的难降解问题，一直成为了转化利用秸秆的难题。目前，利用混合菌将秸秆纤维素转化为蛋白质、乙醇、乙酸、乳酸等研究已逐渐为人们所重视。本文通过马铃薯琼脂平板培养、马铃薯液体摇瓶培养和稻草秸秆固态发酵，从6株常见的食用白腐菌中筛选出了生长优势较强、产漆酶酶活高的平菇HF。为了让秸秆得到更好的降解和利用，采用平菇和康氏木霉二步混合发酵法；通过不同的组合方式，发现H6-T10组合得出的降解效果最好，其木质素降解率达到44.77%，纤维素降解率达到41.48%。     

外源微生物及辅料对秸秆降解效果的影响

研究加入外源微生物及添加辅料对秸秆降解率的影响。通过秸杆固体培养进行了降解试验,结果显示,加入外源微生物后纤维素降解率明显提高,嗜热侧孢霉可提高34.76%,放线菌可提高18.99%。通过在秸秆中加入辅料香菇菌糠,培养后秸秆的纤维素含量由原来的32.11%降至14.19%,降解率达55.81%。加入外源微生物的秸秆降解过程具有升温快、温度高及高温维持时间长等优点。加入微生物的秸秆降解高温维持8 d,对照为6 d。秸秆降解过程中的最高温度分别为63℃和58℃。为下一步外源微生物的进一步研究及菌糠的大量利用提供参考。     

微生物菌群协同提高水稻秸秆转化机制的解析

单一微生物降解水稻秸秆效果不明显,多种微生物组合在一起的微生物菌群能够有效降解水稻秸秆,是当前降解秸秆类废物的首要选择。【目的】探究微生物菌群比单一菌株转化秸秆效率提高的种间协作机制,为改善秸秆类物质的生物降解过程提供理论参考。【方法】通过菌种组合,以水稻秸秆减重率为指标人工构建出降解效果优于单菌培养的微生物群体组合,利用分子生物学方法对实验菌株进行鉴定,结合纤维素酶活性、发酵产物GC-MS分析等指标得出水稻秸秆降解时微生物群体的种间协作机制。【结果】菌株B (Bacillus cereus)在30℃培养8 d水稻秸秆降解率为50.9%,菌株B与菌株D_2(Bacillus amyloliquefaciens)、W_1(Ochrobactrum intermedium)、G_1降解(Bacillus licheniformis)组合构成4株菌BD_2W_1G_1的复合菌群,在30℃培养8 d水稻秸秆降解率为73.3%,比B单菌株分解能力提高22.4%。发酵产物分析结果表明,菌株B单独培养产生大量酸、酚等物质。B+D_2联合培养,发酵液内酸类相对减少87.4%,酚类相对减少61.9%(十五烷酸、正十六烷酸、2,4二叔丁基酚和6-叔丁基对甲酚减少明显),水稻秸秆降解率为64.6%。当B+D_2+W_1联合培养,发酵液内酚类进一步减少15.7%(6-叔丁基对甲酚减少明显),水稻秸秆降解率为71.0%。当B+D_2+W_1+G_1联合培养,酚类继续减少10.7%,水稻秸秆降解率为73.3%。【结论】十五烷酸、正十六烷酸、2,4二叔丁基酚和6-叔丁基对甲酚等酸、酚类物质会抑制菌株B分解水稻秸秆的效率,菌株D_2、W_1、G_1能够减少包括4种物质在内的酸、酚类含量(酸类共减少82.9%,酚类共减少88.2%),来提高分解效率(共提升22.4%的分解效果)。水稻秸秆成分复杂,具有不同功能的菌种组合成复合菌剂,减少反馈抑制形成代谢互补,能有效提高水稻秸秆生物降解效果。     

平菇(Pleurotus ostreatus)对稻草中木质素的生物降解及降解产物分析

变色圈试验证明平菇可以选择性优先降解稻草中的木质素,培养15d后,平菇对稻草中的木质素降解率为17.86%,对综纤维素降解率为2.44%,选择性指数为9.79。生料栽培平菇后,稻草中的木质素被降解50.24%。用气—质色谱(GC/MS)和红外光谱(IR)对木质素降解产物分析结果表明,平菇对稻草中木质素的降解效果十分明显,降解产物中检测出了大量含有苯环的小分子,证明木质素聚合体的降解首先发生在单体的侧链及单体间的连键上,发生Cα-Cβ、β-O-4等断裂,形成了单体。在进一步的降解过程中,平菇表现了其自身特有的降解机制,取代苯环单体上的甲氧基为甲基,而后发生苯环的开裂,这与报道的白腐菌降解过程有所不同。红外光谱分析中,平菇对木质素的降解明显,降解产物中含有很多木质素单体所特有的基团,如紫丁香基、愈创木基等,说明木质素的降解首先发生的是侧链的氧化反应。     

纤维素高效降解菌YN1的筛选及其降解特性

为了获得降解天然纤维素的微生物菌株,并用于农田秸秆腐熟及竹林地稻壳促腐。从牛羊粪堆肥中筛选出一株纤维素降解菌YN1,对其进行了形态和系统发育分析;测定了YN1的液、固体发酵酶活;进行了YN1对纤维素的失重测定;对YN1在纤维素表面上的定殖及其对纤维素的降解进行了电镜观察。经菌株形态分析和ITS基因序列分析,将YN1鉴定为曲霉(Aspergillussp.);在YN1菌株的液体发酵培养第3天,内切酶、外切酶、β-糖苷酶和总纤维素酶活性都达到最大值,分别为95.7、14.6、20.5和26.6U/mL,固体发酵培养第5d各酶活均达到峰值,依次为1192.2、100.6、136.9和210.7U/g;在失重测定中,YN1在7d内可降解41.87%的秸秆,31.59%的稻壳;在扫描电镜下可明显观察到YN1对滤纸、秸秆和稻壳的降解。YN1可有效降解天然纤维素,对农田秸秆腐熟及竹林地稻壳促腐具有较好的应用前景。     

表达广谱抗真菌蛋白转基因水稻秸秆的化学成分与纤维素结构

为了给表达广谱抗真菌蛋白转基因水稻的安全性评估提供基础数据,本文以表达广谱抗真菌蛋白转基因水稻转品1和转品8及非转基因七丝软粘（对照）为试材,对其秸秆化学成分进行分析,同时,采用傅立叶变换红外光谱（FTIR）和X 射线衍射（XRD）方法观察秸秆中不同部位纤维素结构的变化情况。研究结果显示：（1）转基因水稻转品1和转品8与对照在秸秆相同部位的化学成分含量不存在显著差异;（2）转基因水稻转品1和转品8及对照在秸秆相同部位纤维素的红外吸收峰形状基本一致,且品种间的吸收峰强度和结晶指数(O′KI和N〖KG-*2〗·〖KG-*4〗O′KI)也无显著差异;（3）转品1和转品8秸秆的X 射线衍射图与对照相似,且结晶度(CrI)与对照无显著差异。综上所述,广谱抗真菌基因的导入不会对水稻的化学成分、纤维素结构及晶体结构产生明显影响。     

木质纤维素的定量测定及降解规律的初步研究

为了准确地测定稻草及其发酵物中纤维素、半纤维素、木质素的含量,通过差重法进行定量测定,并以此评价白腐菌株Pleurotus sapidus对稻草秸秆的降解状况,结果表明：利用差重法测定稻草发酵物中纤维素、半纤维索、木质素的百分含量是可行的,并能很好地评价白腐菌对稻草的降解规律,即降解过程中纤维素、半纤维素、本质素在前20d降解的很快,之后降解减缓,在50d内,纤维素被降解34．02％,半纤维素被降解56．29％,木质素被降解61．65％。     

Isolation and characterization of cellulose nanofibrils from wheat straw using steam explosion coupled with high shear homogenization

Cellulose nanofibrils of diameter 10–50 nm were obtained from wheat straw using alkali steam explosion coupled with high shear homogenization. High shear results in shearing of the fiber agglomerates resulting in uniformly dispersed nanofibrils. The chemical composition of fibers at different stages were analyzed according to the ASTM standards and showed increase in α-cellulose content and decrease in lignin and hemicellulose. Structural analysis of steam exploded fibers was carried out by Fourier Transform Infrared (FT-IR) spectroscopy and X-ray diffraction (XRD). Thermal stability was higher for cellulose nanofibrils as compared to wheat straw and chemically treated fibers. The fiber diameter distribution was obtained using image analysis software. Characterization of the fibers by AFM, TEM, and SEM showed that fiber diameter decreases with treatment and final nanofibril size was 10–15 nm. FT-IR, XRD, and TGA studies confirmed the removal of hemicellulose and lignin during the chemical treatment process.     

Effect of low initial C/N ratio on aerobic composting of swine manure with rice straw

Two pilot composting experiments were conducted to investigate the effect of low initial C/N ratio on the composting of swine manure with rice straw by measuring physical and chemical parameters. The results showed that the thermophilic duration of bin 1 and bin 2 was long enough to satisfy the sanitary standard, and swine manure could reach maturity. Bin 1 containing larger amount of swine manure and less amount of rice straw showed a higher nitrogen loss (8%), shorter thermophilic phase, and longer maturity time (about 2 weeks) than bin 2. However, economical analysis showed a lower initial C/N ratio (20) could reduce 172 kg rice straw per ton fresh swine manure than a higher C/N ratio (25), and more swine manure could also be treated. Therefore, a low initial C/N ratio (20) could be suggested in the composting of swine manure with rice straw.     

Comparison between solid-state and powder-state alkali pretreatment on saccharification and fermentation for bioethanol production from rice straw

The efficacy of different concentrations of NaOH (0.25%, 0.50%, 0.75%, and 1.00%) for the pretreatment of rice straw in solid and powder state in enzymatic saccharification and fermentation for the production of bioethanol was evaluated. A greater amount of biomass was recovered through solid-state pretreatment (3.74 g) from 5 g of rice straw. The highest increase in the volume of rice straw powder as a result of swelling was observed with 1.00% NaOH pretreatment (48.07%), which was statistically identical to 0.75% NaOH pretreatment (32.31%). The surface of rice straw was disrupted by the 0.75% NaOH and 1.00% NaOH pretreated samples as observed using field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). In Fourier-transform infrared (FT-IR) spectra, absorbance of hydroxyl groups at 1,050 cm^?1 due to the OH group of lignin was gradually decreased with the increase of NaOH concentration. The greatest amounts of glucose and ethanol were obtained in 1.00% NaOH solid-state pretreated and powder-state hydrolyzed samples (0.804 g g^?1 and 0.379 g g^?1, respectively), which was statistically similar to the use of 0.75% NaOH (0.763 g g^?1 and 0.358 g g^?1, respectively). Thus, solid-state pretreatment with 0.75% NaOH and powder-state hydrolysis appear to be suitable for fermentation and bioethanol production from rice straw.     

Improved enzymatic hydrolysis yield of rice straw using electron beam irradiation pretreatment

Rice straw was irradiated using an electron beam at currents and then hydrolyzed with cellulase and beta-glucosidase to produce glucose. The pretreatment by electron beam irradiation (EBI) was found to significantly increase the enzyme digestibility of rice straw. Specifically, when rice straw that was pretreated by EBI at 80 kGy at 0.12 mA and 1 MeV was hydrolyzed with 60 FPU of cellulase and 30 CBU of beta-glucosidase, the glucose yield after 132 h of hydrolysis was 52.1% of theoretical maximum. This value was significantly higher than the 22.6% that was obtained when untreated rice straw was used. In addition, SEM analysis of pretreated rice straw revealed that EBI caused apparent damage to the surface of the rice straw. Furthermore, EBI pretreatment was found to increase the crystalline portion of the rice straw. Finally, the crystallinity and enzyme digestibility were found to be strongly correlated between rice straw samples that were pretreated by EBI under different conditions.     

Use of molecular-genetically bred Coprinus cinereus strains for an efficient isolation of cellulose from rice straw

Molecular-bred Coprinus cinereus monokaryotic strains with high lignin- and xylan-degrading activities were mixed-cultured at 27 degrees C in the liquid medium containing 0.5% (w/v) cut rice straw and 0.025% MnCl2. After 3 weeks, the culture supernatant was extensively treated with crude cellulase, showing the presence in it of 9.3% of the total cellulose of rice straw. When rice straw treated with 0.1 N NaOH or cultured with Ganoderma applanatum were used, the recoveries of the cellulose increased up to 29%. The same experiments were done by using a non-bred control strain, showing the recoveries of the cellulose from the treated or cultured rice straw to be 8%.     

Impact of tillage practices on soil bacterial diversity and composition under the tobacco-rice rotation in China

Tobacco-rice rotation is a common farming system in south China, and many tillage practices such as straw mulching, dolomite dust, and quicklime application have been adopted to improve crop production. These agricultural management practices alter soil physical and chemical properties and affect microbial life environment and community composition. In this research, six tillage practices including no tobacco and rice straw mulching (CK), tobacco and rice straw mulching (TrSr), rice straw returning fire (TrSc), tobacco and rice straw mulching with dolomite dust (TSD), rice straw returning fire and quicklime (TSQ), and rice straw returning fire, quicklime and reduced fertilizer (TSQf) were conducted to detect changes in soil bacterial diversity and composition using Illumina sequencing. The results showed that the total number of operational taxonomic units (OTUs) from the six treatments was 2030, and the number of mutual OTUs among all samples was 550. The TrSc treatment had the highest diversity and richness, while TSQf had the lowest. Soil physio-chemical properties and microbial diversity can influence each other. Proteobacteria and Actinobacteria had the greatest proportion in all treatments. The abundance of Nitrospirae was the highest in the TrSc treatment. The TSQf treatment had the highest abundance of Firmicutes. The abundance of Nitrospira in the TrSc treatment was 2.29-fold over CK. Streptomyces affiliated with Firmicutes improved by 37.33% in TSQf compared to TSQ. TSQf treatment was considered to be the most important factor in determining the relative abundance at the genus level.     

Effect of steam explosion on biodegradation of lignin in wheat straw

The effect of steam explosion pretreatment on biodegradation of lignin in wheat straw was studied in this paper. Through experiments and analysis, 0.8MPa operation pressure and 1:20 wheat straw to water ratio are optimum for destroying lignin and the maximum of lignin loss rate is 19.94%. After steam explosion pretreatment, the wheat straw was retted by Trametes versicolor for 40 days. Biodegradation rate of lignin was tested and the maximum of 55.40% lignin loss rate was found on day 30. During the whole process of both steam explosion pretreatment and biodegradation, 75.34% lignin was degraded, without steam explosion the biodegradation of raw material the degradation rate of lignin was 31.23% only. FT-IR spectroscopy, TGA and SEM were used for further validating the results of biodegradation.     

Methane production from rice straw pretreated by a mixture of acetic–propionic acid

Rice straw was treated with a mixed solution of acetic acid and propionic acid to enhance its biodegradability. The effect of acid concentration, pretreatment time, and the ratio of solid to liquid on the delignification performance of rice straw were investigated. It was found that the optimal conditions for hydrolysis were 0.75 mol/L acid concentration, 2 h pretreatment time and 1:20 solid to liquid ratio. Batch methane fermentation of untreated rice straw, pretreated rice straw, and the hydrolysates (the liquid fraction) of pretreatment were conducted at 35 °C for 30 days, and the results indicated that methane production of rice straw can be enhanced by dilute organic acid pretreatment. Moreover, most of the acid in hydrolysates can also be converted into methane gas.     

应用16S rDNA克隆文库技术研究长期稻草还田对水稻土细菌多样性的影响

利用中国科学院桃源农业生态试验站施肥制度长期定位试验田对照(CK)和稻草还田(OM)施肥处理的土壤样品,应用16S rDNA克隆文库技术直接提取土壤微生物总DNA,分别构建细菌16S rDNA克隆文库,并进行序列测定和分析。结果表明,与对照(CK)相比,稻草还田(OM)后土壤细菌群落结构发生了显著改变,土壤细菌多样性和均匀度均有所降低。对照(CK)和稻草还田(OM)两个施肥处理的优势种群均为变形菌,酸杆菌次之;稻草还田减少了变形菌、疣微菌、绿弯菌和绿菌的分布,而增加了硝化螺旋菌的分布。16S rDNA系统发育分析则表明,稻草还田对酸杆菌群落结构影响最大,其次是疣微菌和δ-变形菌。     

稀酸和稀碱预处理对四种不同生物质资源制备还原糖的影响

本论文探讨了不同浓度的稀H_2SO_4和稀NaOH预处理对大豆秸秆、水稻秸秆、象草和狼尾草四种不同生物质酶解制备还原糖的影响。结果表明,大豆秸秆、水稻秸秆、象草和狼尾草具有较高的纤维素和半纤维素含量,是制备还原糖的理想原料。与稀H_2SO_4预处理相比,经稀NaOH预处理后的样品表现出较好的酶解性能。通过使用4%的NaOH对大豆秸秆和狼尾草进行预处理,还原糖产量分别为145.8 mg/mL和319.2 mg/mL。此外,以1%NaOH预处理后的水稻秸秆和象草为原料,可以分别获得385.2 mg/mL和231.6 mg/mL还原糖产量。