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中国作为农业大国之一,具有丰富的秸秆资源。据统计,中国秸秆年生产量达8.65 亿t,但每年有1 亿t秸秆废置,造成资源浪费和环境污染[1]。秸秆主要成分为木质纤维素,其特殊的“纤维素-半纤维素-木质素”三维网络结构在自然状态下难以降解,严重限制了秸秆资源利用[2]。随着技术不断发展,目前已开发出多种秸秆处理方法,如高温热解、蒸汽爆破、酸碱处理等[3]。微生物降解法以成本低、耗能小、环境友好等优点受到广泛关注[4]。相较于细菌和放线菌,真菌能产生更多种类的酶,如纤维素酶、木聚糖酶、果胶酶、过氧化物酶、糖苷酶等来协同降解木质纤维素[5−7],成为当前研究热点。目前,已开发的秸秆降解真菌主要有黄孢原毛平革菌Phanerochaete chrysosporium、黑曲霉Aspergillus niger、草酸青霉Penicillium oxalicu、糙皮侧耳Pleurotus ostreatus等[8−11],但部分真菌仍存在降解周期长、生长条件严格、降解不稳定等缺点[12],难以实现产业化,因此,仍需进一步挖掘高效稳定的木质纤维素降解真菌。
白蚁是自然界中高效的木质纤维素分解者,其特殊的白蚁-共生菌降解系统可消化植物中74%~99%的纤维素和65%~87%的半纤维素[13],降解效率为瘤胃动物的3倍以上[14]。有研究表明:白蚁的共生真菌具有较强的木质纤维素降解能力,如王成盼等[15]研究发现:黑翅土白蚁Odontotermes formosanus菌圃共生真菌蚁巢伞Termitomyces在固体发酵条件下可降解木质食料中20.98%的纤维素、31.89%的半纤维素和11.68%的木质素。SIJINAMANOJ等[16]从胖身土白蚁O. obesus菌圃和肠道中分离得到红绶曲霉A. nomius和哈茨木霉Trichoderma harzianum,分别使不同农业废弃物纤维素降低10.83%~15.53%和8.50%~36.30%。
为进一步挖掘白蚁共生真菌在秸秆资源利用上的应用潜力,本研究从黑翅土白蚁肠道中分离筛选木质纤维素降解真菌,挖掘高效降解水稻Oryza sativa秸秆的真菌菌种资源,为秸秆生物降解产业化提供理论基础。
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本研究共从黑翅土白蚁肠道中分离出6株真菌,分别记为FU-1~FU-6。经刚果红染色后筛选出FU-1、FU-2、FU-4和FU-6共4株产生明显透明圈的真菌,其菌落形态与透明圈形态如图1所示,其中产生透明圈初步表明其能将纤维素降解为多聚糖类物质,具有潜在的木质纤维素降解活性[18]。
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对4株具备木质纤维素降解活性的真菌进行分子生物学鉴定,其中FU-1、FU-2属于篮状菌属Talaromyces,分别鉴定为安拉阿巴德篮状菌T. allahabadensis和刺孢篮状菌T. aculeatus。FU-4属于曲霉属Aspergillus,鉴定为黑曲霉A. niger。FU-6属于多年卧孔菌属Perenniporia,鉴定为灰孔多年卧孔菌P. tephropora(表1)。
表 1 4株真菌鉴定结果
Table 1. Identification results of four fungal strains
菌株编号 GenBank
登记号相似菌种
(GenBank登记号)相似度/
%FU-1 OQ804643 Talaromyces allahabadensis
(MH727608)100.00 FU-2 OQ804660 T. aculeatus (HQ392496) 100.00 FU-4 OQ804669 Aspergillus niger
(MG228418)100.00 FU-6 OQ804677 Perenniporia tephropora
(MW077095)99.84 -
图2结果表明:黑曲霉的内切葡聚糖酶和外切葡聚糖酶活性显著高于其他真菌(P<0.05),分别达4.361和1.893 μkat·L−1,表明其具有较强的纤维素链切割和末端水解能力。安拉阿巴德篮状菌的β-葡萄糖苷酶活性显著高于其他真菌(P<0.05),达11.133 μkat·L−1,说明具有较强的纤维二糖水解能力。
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将筛选得到的4株真菌两两组合对峙,发现安拉阿巴德篮状菌与刺孢篮状菌(图3A)、刺孢篮状菌与黑曲霉(图3B)和刺孢篮状菌与灰孔多年卧孔菌(图3C)菌落之间产生抑菌圈,表现出相互拮抗。而安拉阿巴德篮状菌与黑曲霉(图3D)、安拉阿巴德篮状菌与灰孔多年卧孔菌(图3E)和黑曲霉与灰孔多年卧孔菌(图3F)菌落之间可接触生长,具备共生协作降解木质纤维素的潜能。
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单独降解时,4株真菌均表现出一定降解能力(表2),其中刺孢篮状菌和黑曲霉具有显著较高的纤维素降解率,分别达38.49%和40.72%,灰孔多年卧孔菌具有极高的半纤维素降解率,达59.77%,同时这3种真菌的木质素降解率也达到最高水平。组合降解时,部分真菌组合表现出更强的降解能力,其中当黑曲霉与灰孔多年卧孔菌“强强联合”后,其干物质降解率和纤维素降解率进一步提高,达38.27%和62.59%,同时半纤维素降解率仍保持较高水平,达51.75%。尽管其木质素降解率有所降低,但综合来看,该真菌组合表现出最强的水稻秸秆降解能力,具有潜在的开发价值。
表 2 水稻秸秆干物质与木质纤维素组分的降解率
Table 2. Dry matter and lignocellulose components degradation rates of rice straw
处理组 干物质降解率/% 纤维素降解率/% 半纤维素降解率/% 木质素降解率/% 安拉阿巴德篮状菌 26.38±0.33 e 27.86±0.49 e 19.44±2.05 d 13.06±2.56 c 刺孢篮状菌 33.79±1.16 bc 38.49±0.93 c 21.75±2.20 d 28.96±2.79 a 黑曲霉 32.18±0.13 cd 40.72±1.71 bc 30.45±1.40 c 26.87±2.13 a 灰孔多年卧孔菌 36.61±1.02 ab 33.96±0.67 d 59.77±0.90 a 29.66±1.91 a 安拉阿巴德篮状菌 + 黑曲霉 33.66±1.07 bc 39.91±2.99 bc 33.68±2.34 c 24.38±1.36 ab 安拉阿巴德篮状菌 + 灰孔多年卧孔菌 29.21±1.57 de 45.60±2.98 b 50.41±1.94 b 14.69±2.33 c 黑曲霉 + 灰孔多年卧孔菌 38.27±1.32 a 62.59±0.70 a 51.75±2.56 b 17.39±0.36 bc 说明:数值为平均值±标准差。同列不同小写字母表示不同处理组的降解率之间差异显著(P<0.05)。 -
经黑曲霉与灰孔多年卧孔菌组合降解后,水稻秸秆部分红外吸收峰明显下降(图4),其中3 400 cm−1附近吸收峰与—OH伸缩振动相关[19],说明秸秆部分氢键被破坏,分子间作用力减弱;1 460 cm−1附近吸收峰与半纤维素中亚甲基(CH2)弯曲振动相关[19],表明真菌组合能有效破坏半纤维素结构;1 370和1 315 cm−1附近吸收峰分别与纤维素中CH2摇摆振动和C—H弯曲振动相关[20],证明真菌组合具有一定的纤维素分解能力;1 235 cm−1附近吸收峰与半纤维素-木质素复合物中O=C—C伸缩振动相关[19],说明部分复合结构被瓦解,半纤维素与木质素发生分离;1 160 cm−1附近吸收峰与碳链中C—O—C伸缩振动相关[19],表明在酶作用下,秸秆中部分碳链结构被破坏,分子聚合度下降。
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经黑曲霉与灰孔多年卧孔菌组合降解后,水稻秸秆纤维素非结晶区衍射峰(2θ = 18.0°)明显下降,纤维素结晶区衍射峰(2θ = 22.5°)无明显变化,水稻秸秆纤维素结晶度由22.44%上升至32.53%(图5)。说明相较于纤维素结晶区,真菌组合分泌的纤维素酶能够更容易分解纤维素非结晶区。但随着纤维素结晶度不断升高,纤维素整体晶体结构变为更加紧凑,推测对于进一步降解利用纤维素产生一定阻碍作用[20]。
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通过扫描电镜观察(图6),发现黑曲霉与灰孔多年卧孔菌组合降解后水稻秸秆表面由紧密光滑变为粗糙隆起,纤维结构崩解断裂,结构蓬松化,并产生大量孔隙和碎片,推测真菌菌丝可能通过孔隙深入秸秆内部,在内外双重降解下加速破坏秸秆结构。
Biodegradation of rice straw by symbiotic fungi of Odontotermes formosanus
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摘要:
目的 挖掘黑翅土白蚁Odontotermes formosanus共生真菌在秸秆资源利用上的应用潜力,为实现秸秆生物降解产业化补充菌种资源并提供理论依据。 方法 以羧甲基纤维素钠(CMC-Na)平板为分离培养基,采用刚果红染色法筛选,从黑翅土白蚁肠道中分离筛选具有木质纤维素降解活性的真菌,并测定纤维素酶活性。在液态发酵条件下,评估不同真菌以及真菌组合对水稻Oryza sativa秸秆的降解效果,利用傅立叶红外光谱、X射线晶体衍射和扫描电镜分析降解前后水稻秸秆的理化性质。 结果 从黑翅土白蚁肠道中共分离到4种具有木质纤维素降解活性的真菌,经鉴定分别为安拉阿巴德篮状菌Talaromyces allahabadensis、刺孢篮状菌T. aculeatus、黑曲霉Aspergillus niger和灰孔多年卧孔菌Perenniporia tephropora。纤维素酶活结果显示:黑曲霉的内切葡聚糖酶和外切葡聚糖酶活性最高,安拉阿巴德篮状菌的β-葡萄糖苷酶活性最高。水稻秸秆降解试验表明:黑曲霉与灰孔多年卧孔菌双菌组合具有最强的秸秆降解能力,20 d内可降解秸秆中38.27%的干物质、62.59%的纤维素和51.75%的半纤维素。降解后水稻秸秆内部化学键和分子间作用力被破坏,结晶度由22.44%上升至32.53%,秸秆表面崩解碎裂,结构蓬松化。 结论 从黑翅土白蚁肠道分离得到的黑曲霉和灰孔多年卧孔菌在组合降解水稻秸秆时表现出极强的降解能力,在秸秆生物降解产业化上具有潜在的开发价值。图6表2参30 Abstract:Objective This study aims to explore the application potential of symbiotic fungi of Odontotermes formosanus in the utilization of straw resources, so as to provide a theoretical basis for the industrialization of straw biodegradation and supplement strain resources. Method Using CMC-Na plate as isolation medium and Congo red staining method for screening, the fungi with lignocellulose degrading activity were isolated and screened from the gut of O. formosanus and cellulase activities were measured. The degradation effect of different fungi and fungal combinations on Oryza sativa (rice) straw was evaluated under liquid fermentation. The physicochemical properties of rice straw before and after degradation were analyzed using FTIR, XRD and SEM. Result 4 fungi with lignocellulose degrading activity were isolated from the gut of O. formosanus, identified as Talaromyces allahabadensis, T. aculeatus, Aspergillus niger and Perenniporia tephropora. Cellulase activity results showed that A. niger had the highest activity of endoglucanase and exoglucanase, while T. allahabadensis had the highest activity of β-glucosidase. The rice straw degradation test showed that the combination of A. niger and P. tephropora had the strongest straw degradation ability. Within 20 days, 38.27% of dry matter, 62.59% of cellulose and 51.75% of hemicellulose in rice straw could be degraded. After degradation, the internal chemical bonds and intermolecular forces in rice straw were destroyed, and crystallinity increased from 22.44% to 32.52%. The straw surface disintegrated and smashed, and the structure became fluffy. Conclusion A. niger and P. tephropora isolated from the gut of O. formosanus show strong degradation ability in the combined degradation of rice straw, and have potential development value in the industrialization of straw biodegradation. [Ch, 6 fig. 2 tab. 30 ref.] -
Key words:
- Odontotermes formosanus /
- symbiotic fungus /
- cellulase /
- utilization of straw resources
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表 1 4株真菌鉴定结果
Table 1. Identification results of four fungal strains
菌株编号 GenBank
登记号相似菌种
(GenBank登记号)相似度/
%FU-1 OQ804643 Talaromyces allahabadensis
(MH727608)100.00 FU-2 OQ804660 T. aculeatus (HQ392496) 100.00 FU-4 OQ804669 Aspergillus niger
(MG228418)100.00 FU-6 OQ804677 Perenniporia tephropora
(MW077095)99.84 表 2 水稻秸秆干物质与木质纤维素组分的降解率
Table 2. Dry matter and lignocellulose components degradation rates of rice straw
处理组 干物质降解率/% 纤维素降解率/% 半纤维素降解率/% 木质素降解率/% 安拉阿巴德篮状菌 26.38±0.33 e 27.86±0.49 e 19.44±2.05 d 13.06±2.56 c 刺孢篮状菌 33.79±1.16 bc 38.49±0.93 c 21.75±2.20 d 28.96±2.79 a 黑曲霉 32.18±0.13 cd 40.72±1.71 bc 30.45±1.40 c 26.87±2.13 a 灰孔多年卧孔菌 36.61±1.02 ab 33.96±0.67 d 59.77±0.90 a 29.66±1.91 a 安拉阿巴德篮状菌 + 黑曲霉 33.66±1.07 bc 39.91±2.99 bc 33.68±2.34 c 24.38±1.36 ab 安拉阿巴德篮状菌 + 灰孔多年卧孔菌 29.21±1.57 de 45.60±2.98 b 50.41±1.94 b 14.69±2.33 c 黑曲霉 + 灰孔多年卧孔菌 38.27±1.32 a 62.59±0.70 a 51.75±2.56 b 17.39±0.36 bc 说明:数值为平均值±标准差。同列不同小写字母表示不同处理组的降解率之间差异显著(P<0.05)。 -
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