牦牛瘤胃厌氧真菌和甲烷菌共培养物降解秸秆功效和机理研究

Yak (Bos grunniens) is a unique ruminant mammal on Qinghai-Tibet Plateau. Due to the special habitat, its rumen has evolved into a natural anaerobic fermenter that degrades lignocellulose efficiently. The co-cultures of anaerobic fungus and methanogen from the rumen of yaks have a great potential to degrade lignocellulose efficiently, however, there are few studies on it, and the specific mechanism of lignocellulose degradation by the rumen fungus-methanogen co-cultures of yaks is still unknown. The present study aims to isolate the single anaerobic fungus indigenously associated methanogen (this is called fungus-methanogen co-culture for short ) from the rumen of yaks, which are grazing in the six areas in Qinghai and three areas in Gansu, further to identify them to reveal the combination types of the fungus-methanogen co-cultures. Then we will determine the effect of co-cultures on the degradation of seven kinds of straw and their products. On this basis, the co-cultures which can degrade straw efficiently will be selected to further study the mechanism of lignocellulose degradation by the fungus-methanogen co-cultures from the aspects of the physical degradation, biodegradation and anaerobic fungus degradation with the incremental effect by methanogen, respectively. This study will provide an important scientific basis for increasing the utilization rate of straw in our country and revealing the mechanism of lignocellulose degradation by the anaerobic fungus-methanogen co-cultures.

牦牛是生活在我国青藏高原的反刍动物种群。由于特殊的生境，其瘤胃已进化成为高效降解木质纤维素的天然厌氧发酵罐。牦牛瘤胃厌氧真菌和甲烷菌共培养物具有高效降解木质纤维素的巨大潜力，但是目前国内外对其研究极为稀少，对于其降解木质纤维素的具体机理仍然不了解。本项目拟首次从世界牦牛之都—中国青海省的6个牦牛主产区和甘肃省的3个牦牛主产区的长年放牧牦牛瘤胃液中分离纯化单个厌氧真菌和与其自然粘附共存的甲烷菌的共培养物，并对其进行鉴定以揭示不同地区牦牛瘤胃厌氧真菌和甲烷菌共培养物的组合类型；进一步研究共培养物降解7种秸秆的功效和产物；在此基础上选择高效降解秸秆的共培养物，分别从其对秸秆的物理降解、生物降解和甲烷菌提高厌氧真菌降解秸秆功效这3方面研究共培养物降解秸秆木质纤维素的具体机理。本项目将为提高我国秸秆利用率，揭示厌氧真菌和甲烷菌共培养物降解木质纤维素的机理提供重要的科学依据。

世界牦牛主要分布在我国青藏高原，主要以放牧为主。牦牛瘤胃内栖息着独特的，复杂多样的大量微生物群落协同代谢高效降解野牧草为牦牛提供生存能量和营养物质。其中牦牛瘤胃厌氧真菌和甲烷菌共培养物发挥着重要的降解木质纤维素的作用。. 本项目研究从青海省和甘肃省放牧牦牛瘤胃中分离出一些高效降解秸秆的厌氧真菌和甲烷菌共培养物，通过分子生物学和形态学鉴定其种属并从中筛选出降解秸秆的最佳高效共培养物—来自青海海南州兴海县的放牧牦牛瘤胃的厌氧真菌和甲烷菌共培养物（N. frontalis + M. gottschalkii）YakQH5。它在5天培养期内分别降解了小麦秸秆、玉米秸秆、水稻秸秆、燕麦秸秆、高粱秸秆、大豆秸秆和芦苇秆的59.0%-68.1%干物质和49.5%-59.7%中性洗涤纤维素产生甲烷3.0-4.6 mmol/g DM和乙酸7.3-8.6 mmol/g DM作为代谢终产物；以玉米秸秆为底物释放阿魏酸达到最高量4.8 mg/g DM，以高粱秸秆为底物释放香豆酸达到最高量11.7 mg/g DM；以小麦秸秆为底物所产木聚糖酶活性达到最高12910 mU/mL，以玉米秸秆为底物所产阿魏酸酯酶活性高达10.5 mU/mL，以高粱秸秆为底物所产香豆酸酯酶活性高达20.5 mU/mL，以芦苇秆为底物所产漆酶活性达到最高60.5 U/mL。来自青海牦牛的N. frontalis+M. gottschalkii共培养物YakQH5代表了一种新的高效木质纤维素生物降解优势组合，比以前已报道的来自反刍动物消化道的厌氧真菌和甲烷共培养物降解秸秆的功效更好。通过将分离出来的一些厌氧真菌的高活性木聚糖酶基因进行扩增、测序和分析，初步阐释了牦牛瘤胃厌氧真菌和甲烷菌共培养物降解秸秆的部分机理。. 高效共培养物（N. frontalis + M. gottschalkii）YakQH5通过厌氧罐扩大培养后获得的高活性木质纤维素降解酶发酵液进一步应用于秸秆黄贮前处理，以及西门塔尔牛和冬季补饲牦牛的秸秆粗饲料中，不但提升了秸秆黄贮感官品质和营养成份，而且提高了西门塔尔牛和冬季牦牛的秸秆粗饲料消化利用率，改善了牛肉品质。研究证明牦牛瘤胃厌氧真菌和甲烷菌共培养物在粗饲料降解中具有独特应用价值和优势。