饲料糖源和糖水平对卵形鲳鲹肠道微生物群落构建和演替的影响

Carbohydrate is the main metabolism energy in fish feed. Fish especially the carnivorous fish have a relatively low ability to utilize carbohydrate compared with the terrestrial animals. However, the reasons were not clear and further studies are needed to reach a substantial understanding. The intestinal microbiota plays an important role in the process of nutrients digestion and absorption. The bacterial flora of the gastrointestinal tract in general, represents a diversified enzymatic potential, and it seems logical to think that the enzymatic mass lodged in the digestive tract might interfere in a considerable way with a major part of the metabolism of the host animal. Till now considerable information is available concerning the intestinal microflora of terrestrial animals and the role of these intestinal microflora in digestion, very little information is available concerning the bacterial population in the gastrointestinal tract of fish. Since the intestinal microbiota populations grow upon the food absorbed by the host animal,it is reasonable that the microbiota community structural characteristics may affected by dietary nutrients.However, the effects of dietary carbohydrate sources and contents on the intestinal microbiota community were unknown. Whether intestinal microbiota community would adaptively response to the dietary carbohydrate was not clear. In a previous experiment, it was observed that the dominant species and total number of microoganisms of the intestinal microbiota in the gut of Trachinotus ovatus were significantly different between the fish fed with trash fish and those fed with artificial feed with a high content of carbohydrate. This indicated that the dietary carbohydrate may exerted an affect on the intestinal microbiota community characteristics. Based on these findings, we hypothesis that the intestinal microbiota of T. ovatus could adaptively response to variation of dietary carbohydrate sources and/or contents. However, in-depth studies were need to testify the hypothesis. This project aimed to investigate the intestinal microbiota community characteristics e.g. the shift in dominant species biodiversity of T. ovatus in various growing stage by using fish nutrition and molecular microbial ecological methods. And establish an relationship between the variations of intestinal microbiota and dietary carbohydrate sources and/or contents. Illuminate the role of dietary carbohydrates in the constructing and maintaining of intestinal microbiota comminity. This study aimed to provide knowledge which is helpful to understanding why the carnivorous fish can not utilize dietary carbohydrate efficiently. This is may be an important basis for targeting manipulation of the microbial composition and enhance the utilization of dietary carbohydrates.

鱼类尤其是肉食性鱼类对糖类利用能力低的原因及解决办法是动物营养与饲料研究的重要科学和产业问题。肠道微生物在鱼类消化吸收过程中具有重要作用，它们直接或间接利用鱼类所摄取的营养物质，因而其群落结构也可能会受到宿主食物的影响。我们在前期研究发现摄食不同糖含量食物时，卵形鲳鲹肠道微生物的数量和优势种均发生了改变。在此基础上，本项目提出肠道微生物群落结构能够对饲料糖类产生适应性变化的假说。拟以典型肉食性鱼类-卵形鲳鲹为对象，饲喂不同糖源和糖水平的饲料，运用动物营养学和微生物分子生态学方法，对比分析不同生长发育阶段卵形鲳鲹肠道微生物群落优势种和生物多样性格局等群落结构特征演替规律与糖源和糖水平间的相关性，弄清饲料糖源和糖水平对肠道微生物群落结构的影响，明晰糖在肠道微生物群落构建、演替和相对稳态维持中的作用。旨在从另一个角度思考肉食性鱼类对糖利用能力低的问题，并为寻求改善糖利用的办法提供启发和理论依据。

鱼类尤其是肉食性鱼类对糖类利用能力低的原因及解决办法是动物营养与饲料研究的重要科学和产业问题。本实验研究了不同糖源和糖水平饲料对典型肉食性鱼类--卵形鲳鲹生长性能和肠道微生物群落结构的影响。设计分别以葡萄糖、麦芽糖和小麦淀粉作为糖源，设高、中、低三个水平（分别为10%，20%和30%）。从卵形鲳鲹生长情况，糖代谢和消化酶活性变化，对比分析不同生长阶段卵形鲳鲹肠道微生物群落和生物多样性等群落结构和糖水平间的相关性。旨在从另一个角度思考肉食性鱼类对糖利用能力低的问题，并为寻求改善糖利用的办法提供启发和理论依据。.实验结果显示：卵形鲳鲹摄食含糖源饲料的生长速度低于摄食冰鲜鱼对照组。总体来看卵形鲳鲹对糖类的利用情况是：麦芽糖＞葡萄糖＞小麦淀粉，而麦芽糖水平为20%时生长速度最快。冰鲜鱼组鱼体水分、粗蛋白及灰分含量最高，粗脂肪含量最低。摄食含糖源饲料的卵形鲳鲹体内蓄积脂肪含量较高。葡萄糖激酶不受糖源和水平影响，而己糖激酶、丙酮酸激酶和磷酸果糖激酶均受到影响。糖源和水平对消化酶活性影响显著。对照组的卵形鲳鲹肠道中淀粉酶活性最低。.随着养殖时间的增加至第8周实验结束时，不同处理组的OUT的丰度均有所降低。可见，肠道微生物的丰度并不是随着养殖周期的增长而增加的。在不同生长阶段，肠道微生物主要有Acidobacteria，Actinobacteria，Bacteroidetes，Chloroflexi，Cyanobacteria，Firmicutes，Fusobacteria，Planctomycetes，Proteobacteria，Verrucomicrobia等。不同生长阶段相同糖源和水平肠道微生物的演替规律：10%葡萄糖组不同生长阶段肠道微生物的优势种Pseudomonas_fragi草莓假单胞菌、Bacillus_cereus蜡样芽孢杆菌在第6周最高。同一生长阶段相同糖源不同糖水平肠道微生物演替规律：Acinetobacter_johnsonii约氏不动杆菌随生长时间延长而降低。第2周葡萄糖水平30%时，Bacillus_cereus蜡样芽孢杆菌、Bacillus_flexus弯曲芽胞杆菌最高，而无乳莲球菌则在其他10%和20%组未检出。同一生长阶段相同水平的不同糖源肠道微生物演替规律：粪产碱杆菌仅在10%葡萄糖组检测到。其他组均未检出。