尼罗罗非鱼肠道及养殖环境中菌群结构与链球菌病的相关性

为研究尼罗罗非鱼肠道和池塘养殖环境中菌群结构变化与链球菌病暴发的相关性,实验采用16S r DNA高通量测序方法对比分析发病和健康池塘水体、底泥和尼罗罗非鱼肠道菌群的结构特征。结果显示,底泥中微生物多样性最高,水体和肠道中微生物多样性次之;肠道菌群与水体中菌群的相似性较高,而与底泥中菌群相似性较低;发病组的尼罗罗非鱼肠道和池塘底泥中微生物的多样性均低于健康组,而发病组池塘水体中微生物多样性高于健康组。OTU聚类分析发现,发病与健康尼罗罗非鱼肠道微生物差异极显著,大部分健康尼罗罗非鱼肠道微生物样品单独聚为一支。菌群结构组成分析结果表明,虽然发病组和健康组水体或底泥中优势菌群结构组成的差异较小,但在非优势菌群中存在一定差异,发病组水体中变形菌门和梭杆菌门的比例显著高于健康组水体,疣微菌门和浮霉菌门的丰度显著低于健康组水体;发病组池塘底泥中厌氧粘细菌属、甲烷丝菌属和枝芽孢菌属等具有降解有机质和生态修复功能,菌群的丰度显著低于健康组底泥,而具有致病能力的曼氏杆菌属丰度却显著高于健康组底泥。发病组尼罗罗非鱼肠道菌群中链球菌属、分枝杆菌属和曼氏杆菌属等致病菌群的丰度显著高于健康组尼罗罗非鱼肠道,而乳球菌属、鲸杆菌属和红球菌属等益生菌的丰度显著低于健康尼罗罗非鱼肠道。无乳链球菌普遍存在于发病和健康养殖环境,以及尼罗罗非鱼肠道中,无乳链球菌的丰度在发病和健康养殖环境之间无显著差异,但其在发病尼罗罗非鱼肠道中的丰度要显著高于健康组。研究表明,尼罗罗非鱼链球菌病发病池塘水体和底泥中有益菌丰度降低和致病菌丰度的升高反映其养殖环境出现恶化,尼罗罗非鱼链球菌病的暴发与肠道微生态平衡破坏后无乳链球菌丰度增加密切相关,但肠道中无乳链球菌丰度的剧增与养殖水体和底泥中该病原菌的丰度水平之间并无直接关联。

Correlation between microflora structure in intestinal tract and aquaculture environment of tilapia (Oreochromis niloticus) and streptococcicosis

In order to study the correlation between microbial composition of intestinal tract and aquaculture environment of Oreochromis niloticus and streptococcicosis, 16S rDNA high-throughput sequencing method was used to analyze the microflora structure of intestinal tract of healthy and diseased O. niloticus and that of their pond water and sediment. The results showed that the microbial diversity of sediment was higher than that of pond water and O. niloticus intestinal tract. The microbial composition of O. niloticus intestinal tract was more similar to pond water than to sediment. The microbial diversity of O. niloticus intestinal tract and sediment in the disease group was lower than that in the healthy group, while the microbial diversity of pond water in the disease group was higher compared with the healthy group. The OTU cluster analysis revealed that significant difference only existed in intestinal microorganism between the disease group and the health group. The majority of healthy intestinal samples were clustered together. The microflora structure analysis showed that the dominant bacteria of pond water and sediment in the healthy group and the disease group were similar. The abundance of proteobacteria and fusobacteria was far higher in the disease group of pond water, while the abundance of verrucomicrobia and planctomycetes was obviously lower compared with the healthy group of pond water. The abundance of flora with the function of organic degradation and ecologic restoration (such as Anaeromyxobacter, Methanosaeta and Virgibacillus) was far lower in the sediment of disease group, while the abundance of pathogenic bacteria (such as Mannheimia) was higher compared with the sediment of healthy group. The abundance of pathogenic bacteria (such as Streptococcus, Mycobacterium and Mannheimia) in intestinal tract of disease group was higher, while the abundance of probiotics (such as Lactococcus, Cetobacterium and Rhodococcus) was lower compared with intestinal tract of healthy group. Streptococcus agalactiae was detected not only in aquaculture environment and intestinal tract of the disease group but also in those of the healthy group. The abundance of S. agalactiae in intestinal tract of the disease group was significantly higher than that in the healthy group, while there was no significant difference between the disease group and the health group either for pond water or sediment. In conclusion, the variation of the abundance of pathogenic bacteria and probiotics in pond water and sediment revealed that the aquaculture environment of the diseased pond was deteriorated. The outbreak of streptococcicosis was closely related to the rapidly increased abundance of S. agalactiae in the intestinal tract of O. niloticus after its microecological balance had been destroyed. The increased abundance of S. agalactiae in the intestinal tract of infected O. niloticus had no direct link with its abundance in pond water or sediment.