SXT/R391元件在华南沿海溶藻弧菌中的分布、分子特征及水平转移能力研究

SXT/R391 is one family of integrative and conjugative elements (ICEs), which was first discovered in a clinical O139 Vibrio cholerae strain in 1990s. SXT/R391 elements have high transfer frequency and potentially wide host range, which may rapidly expand antibiotic resistance genes and aggravate epidemic diseases. In 2012, we first reported that SXT/R391 ICEs were widely distributed in environmental V. alginolyticus isolates. SXT/R391 ICEs have the potential to speed up their spread due to V. alginolyticus as their host. In present study, the distributions of SXT/R391 in V. alginolyticus isolated from coastal regions of South China will be investigated followed by the analysis of SXT/R391 structure, the functions, and the phylogeny. The horizontal transfer ability of SXT/R391 was also analyzed under the normal conditions and the conditions of simulative environmental selective pressure. These works will help us to estimate the diffusion hazard of SXT/R391 when carried by V. alginolyticus and to understand the impact of human activities on the spread of this ICE element. The research has important theoretical significances on the study on horizontal gene transfers and drug resistance genes, and at the same time it is aimed to arouse social attentions to the problems caused by bacterial antibiotic resistance and to learn the roles that marine bacteria play in the spread of antibiotic resistance genes. The research also has important significances to guide the usage of antibiotics in clinical science and farming industries.

SXT/R391是一类首先在O139霍乱弧菌发现的位于细菌染色体的整合性结合元件，具有潜在的广泛宿主范围，SXT/R391水平转移很可能造成耐药基因的迅速扩散，加剧疫病流行风险。2012年我们第一次报道溶藻弧菌中广泛存在SXT/R391元件。本项目拟调查SXT/R391在华南沿海溶藻弧菌中的分布；分析溶藻弧菌SXT/R391元件结构和功能；分析溶藻弧菌SXT/R391元件种系发生；研究溶藻弧菌SXT/R391在正常条件下及人工模拟环境选择压力条件下的水平转移能力，进而评估溶藻弧菌作为SXT/R391宿主菌可能带来的SXT/R391扩散风险以及人类活动对于SXT/R391传播的影响。本项目对于微生物基因水平转移、微生物耐药基因研究具有重要理论意义；本项目研究也旨在了解海洋细菌在耐药基因传播中扮演的角色并唤起社会对细菌耐药问题的重视；项目对于指导临床及养殖业抗生素用药也具有重要意义。

SXT/R391是一类首先在O139霍乱弧菌发现的位于细菌染色体上的整合性结合元件，具有广泛宿主范围，SXT/R391水平转移很可能造成耐药基因的迅速扩散，加剧疫病流行风险。本项目中，我们主要研究SXT/R391 元件在华南沿海溶藻弧菌中的分布、全序列特征、种系发生关系，研究溶藻弧菌 SXT/R391基因功能及 SXT/R391 水平转移能力。结果发现环境溶藻弧菌中广泛存在SXT/R391元件，SXT/R391的携带率为8.9%，获得了5株溶藻弧菌的6个ICE序列，发现其中3个属于典型的SXT/R391家族的成员，3个为非典型的SXT/R391元件，ICE包括保守区和可变区，可变区基因编码大量细菌对环境适应功能的蛋白。类似于其它SXT/R391成员，所有的6个ICE都具有bet/exo基因，发现bet/exo基因具有类似于λ噬菌体的重组功能，利用bet/exo基因成功实现了大肠杆菌和霍乱弧菌靶基因的重组和替换，表明bet/exo可能被开发成细菌遗传改造的工具。溶藻弧菌A056的二个ICE具有差异显著的转移能力，二个ICE共同存在时，二者的转移频率会增加，一个ICE进入受体菌会降低另一个ICE进入同一受体菌的机率。setR是ICE进入排斥的主因。萘啶酸以及诺氟沙星处理会显著增加细菌中ICE的转移频率，但卡那霉素处理对细菌中ICE的转移频率没有影响，表明环境中某些抗生素的选择压力不仅造成耐药基因盒的扩散，也会对细菌的其它基因水平转移产生影响。

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