草食性鱼类消化道微生物在纤维素分解与转化中的作用

There are no cellulase-specific genes in the genomes of herbivorous vertebrate, but all herbivorous vertebrates can digest cellulose with the help of their digestive tract microbiome (second genome). Therefore, the functions that played by the digestive tract microbiota are especially important for the hosts regarding the cellulose metabolism. However, how the digestive tract microbiota regulate the cellulose metabolism of fish are rarely studied and the mechanism kept unknown. Regard the grass carp and blunt-snout bream as main research objects, the present project intends to study the microbial metabolism of cellulose in the harbivorous fishs, the important cultured freshwater fishes in China. Firstly, we will collect fish samples from different habitats and construct the metabolic network of digestive tract microbiota by combining the results of metagenomic sequencing, DNA microarry analyses and metabolic products detecting. Special attention will be paid in analyzing the cellulolytic microorganisms and functional genes in the digestive tract of herbivorous fishes, and finally construct a artificial neural network regarding feeding, habitats, cellulolytic microorganisms and functional genes. Then, we will locate the cellulolytic microorganisms and genes into respective reactions of cellulosic metabolic pathways for further analysis to confirm their functions in cellulose hydrolysis. The present project will not only enrich our knowledge about the digestive tract microbiota but also have practical applicability in the farming of herbivorous fishes.

草食性脊椎动物基因组中虽然没有纤维素水解酶基因，但都可通过消化道微生物组（第二基因组）来实现对纤维素的消化吸收。因此，消化道微生物在纤维素分解利用中的功能一直广受关注，但鱼类方面还鲜见报道。本项目拟以我国重要的淡水草食性鱼类--草鱼、团头鲂为主要研究对象，结合宏基因组测序、功能基因微阵列分析和代谢产物检测结果构建消化道微生物参与的代谢通路，并着重解析与纤维素相关的消化道微生物类群及其在纤维素分解中的功能，进而构建草食性鱼类摄食、生活环境、纤维素水解微生物和相关功能基因的人工神经网络。结合传统的微生物培养技术对目标微生物在草食性鱼类纤维素降解和转化中的作用加以检验和验证，并将筛选得到的微生物类群定位到纤维素代谢通路的不同反应上，以揭示它们在草食性鱼类纤维素消化吸收方面的具体功能及调控机制。本项研究不但能够丰富我们对消化道微生态系统结构与功能的认识，在草食性鱼类养殖业中也将具有应用价值。

消化道微生物可以协助宿主降解纤维素，相关研究鱼类方面未见系统报道。本项目开展过程中，以草鱼、团头鲂消化道微生物为主要研究对象，采用宏基因组测序、功能基因微阵列分析和代谢产物检测相结合，发现草食性鱼类（草鱼和团头鲂）消化道微生物群落没有显著差异，碳水化合物和氨基酸代谢是草食性鱼类消化道微生物主要的代谢通路，且代谢作用及强度可以被投喂食物显著性影响；另外，对比研究草食性和肉食性鱼类肠道微生物群落形成机制和演替规律差异，利用岛屿生态理论深度解析草鱼消化道内微生物传播模式，发现宿主肠道环境选择作用导致了鱼类消化道微生物的演替。然而，微生物群落的聚类以及控制微生物群落演替的这一决定性过程随鱼类发育逐渐不明显。项目研究结果极大地巩固了我们对于鱼类消化道系统中群落阶段性演替的认识，为未来发展草食性鱼类生态养殖提供重要理论参考。

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