一株保护草鱼肠道和改善水质的枯草芽孢杆菌的分离鉴定及全基因组分析

为研制可降解污染物的高效微生物制剂,本研究从污水中分离到多株可高效降解化学耗氧量(COD)的菌株。通过16S rDNA测序及生理生化分析,鉴定出其中一株为枯草芽孢杆菌,命名为Bacillus subtilis H2。对其进行进化树构建,发现该菌株与B. subtilis strain SCUT09的同源性高达98.8%。细菌最适生长条件探究发现,该菌株的最适生长条件,温度为42°C、pH值为6.5、盐度为1。耐受性实验发现,该菌具有较强的盐度代谢能力和温度及酸碱度胁迫耐受性,可以适应不同的温度和盐度环境。为了探究该菌在水产养殖中的作用,将该菌株进行灌胃草鱼处理后,再利用嗜水气单胞菌攻毒,H.E染色观察草鱼的肠道组织变化。结果显示,灌胃枯草芽孢杆菌处理后,草鱼肠道的完整性得到显著的保护。为了进一步探究该菌株的作用机理,本研究测定了B. subtilis H2的全基因组,结果显示,基因组全长为4 111 243 bp,GC含量为43.46%,编码4 213个基因,其中包含31个核糖体rRNA和87个tRNA基因,编码序列占整个基因组序列的87.67%。比较基因组学分析显示,该菌株和B. subtilis 168全基因组共有基因有3 551个。研究表明,本研究分离出的枯草芽孢杆菌在污水处理和水产养殖中具有重要的应用意义。

Isolation, identification and genome-wide analysis of a strain Bacillus subtilis H2 with the ability to protect Ctenopharyngodon idella gut and improve water quality

To obtain the microbes efficiently degrading pollutants, a new bacterial strain was successfully isolated that has the ability to degrade chemical oxygen demand (COD) from sewage efficiently. According to physiological and biochemical characteristics, and 16S rDNA sequencing phylogenetic analysis, the isolated strain is identified as Bacillus subtilis and named B. subtilis H2. A phylogenetic tree was constructed by comparing the 16S rDNA of the isolated strain and found to have a homology of 98.8% with B. subtilis strain SCUT09. The isolate H2 was found to be highly tolerant to a wide range of temperature, pH, and salinity conditions, however, the optimal growth conditions were at 42 °C, 6.5, and 1, respectively. Further, to explore its application in aquaculture, we investigated the Ctenopharyngodon idella intestine that was administered intragastrically with the B. subtilis H2 for 7 d then challenged with the pathogen Aeromonas hydrophila to observe the intestinal tissue changes of C. idella. B. subtilis H2 showed significant protection against A. hydrophila in the intestinal tract of C. idella. Moreover, to further explore the mechanism of action of this strain, the whole genome of B. subtilis H2 was determined in this study. The genome-wide sequencing of the H2 isolate resulted in 4 111 243 bp with GC content of 43.46%, encoding 4 213 genes that accounted for 87.67% of the gene coding region, including 31 rRNA and 87 tRNA genes. Comparative genomics analysis revealed, there were 3 551 core genes shared by this strain with B. subtilis 168. These results indicated that the isolated Bacillus strain could play significant roles in the treatment of sewage and aquaculture water.