鱼源无乳链球菌整合性接合元件ICESag1535的生物信息特征,剪切、环化活性与流行现状  

Bioinformatic characteristics,excision/cyclization activities and prevalence of an ICE element,ICESag1535,in Streptococcus agalactiae isolated from fish

作　　者：车行 卢燕播 王承德 罗敏意 黎果 张德峰[4] 林蠡 赵丽娟 CHE Hang;LU Yanbo;WANG Chengde;LUO Minyi;LI Guo;ZHANG Defeng;LIN Li;ZHAO Lijuan(College of Animal Science and Technology,Zhongkai University of Agriculture and Engineering,Guangzhou 510225,China;Agricultural Service Center of Xiaolan Town,Zhongshan 510230,China;Bailian Aquatic Seedling Co.,Ltd.of Gaozhou City,Maoming 525200,China;Pearl River Fisheries Research Institute,Chinese Academy of Fishery Sciences,Guangzhou 510380,China)

机构地区：[1]仲恺农业工程学院动物科技学院,广东广州510225 [2]中山市小榄镇农业服务中心,广东中山510230 [3]高州市百联水产种苗有限公司,广东茂名525200 [4]中国水产科学研究院珠江水产研究所,广东广州510380

出　　处：《水产学报》2025年第5期158-168,共11页Journal of Fisheries of China

基　　金：2021省级科技创新战略和乡村振兴战略专项(2021S0082);中山市2022年第二批社会公益与基础研究项目(2022B2003);广东省现代农业产业技术体系创新团队(2019KJ141)。

摘　　要：[目的]揭示水生动物源链球菌ICEs分子生物学特点、水平转移能力、ICEs流行现状,预测ICEs水平扩散的受体范围及对病原菌致病的影响。[方法]在NCBI数据库中检索ICEs特征元件,使用生物信息学方法对基因组进行分析,并鉴定ICE的结构特征、主要元件功能,利用分子生物学技术验证ICE在微生物间的水平转移能力并调查流行情况。[结果]筛选出尼罗罗非鱼无乳链球菌WC1535基因组中存在一个完整的ICE位于mutT基因内,命名为ICESag1535 mutT(简称ICESag1535)。ICESag1535全长约74.1 kb,编码73个蛋白基因,核心转移元件由ConjTn5252超家族的25个移动基因组成,属于类ICESa2603型ICEs。ICESag1535核心区包含5个外源基因插入热点区(HS),可变区(VR)含有7个转座插入元件(IS),形成3个复合型转座子,HS和VR可划分为7个主要功能区,分别与ICE的稳定、接合偶联、物质跨膜运输、应激调控、细菌素合成与输出、接合拓展和宿主黏附等功能相关。ICESag1535的3'-末端是同向串联的3个结构相似的位点特异性丝氨酸重组酶(TSPSI),对TSPSI进行聚类分析发现,尼罗罗非鱼、美洲牛蛙和尖吻鲈分离菌株编码的TSPSI几乎完全相同,都位于类ICESa2603型ICEs内,病原菌分布覆盖北半球水域。对不同来源ICEs同源性分析,发现人、猪、鱼分离菌株携带的类ICESa2603型ICEs,其接合模式皆为ConjTn5252型,可跨种扩散。调查类ICESa2603型ICEs的流行情况,2014—2016年分离的链球菌中携带比例为78.8%,而2020—2021年分离菌株的携带率为96.3%,呈上升趋势。验证ICESag1535的水平转移能力,检测到ICESag1535从WC1535基因组自我剪切,形成环化中间体,然后插入在人链球菌Sag158基因组mutT内,鉴定了转移过程中attL、attR、attB、oriT的位点特征;ICE整合入Sag158后,在TSPSI与attR位点之间检测到IS30插入元件。[结论]本研究鉴定的ICESag1535是具备自我切除和环化活性的完整ICE,可跨种扩With the exponential expansion of sequenced complete streptococcal genomes,numerous integrative and conjugative elements(ICEs)have been identified.However,the characteristics of ICEs in Streptococci spp.of aquatic animal origin remain enigmatic.This study aims to analyze the bioinformatic characteristics of ICEs originating from aquatic animals,verify their horizontal transfer capabilities,investigate the prevalence in bacteria,predict their microbial host distribution for horizontal diffusion,and detect their contributions to pathogenicity of host bacteria.Integrated genomic approaches were employed to systematically characterize the structural-functional attributes and epidemiological distribution of ICEs,complemented by in vitro functional assays to validate their horizontal gene transfer capacity and molecular mechanisms.A complete ICE element was identified in strain WC1535 isolated from Oreochromis niloticus,named ICE_Sag1535_mutT(abbreviation as ICESag1535).The bioinformatic characteristics of ICEs were analyzed,including their conjugation modules,recombinase com-position,variable region function,and ICE homology.ICESag1535 belongs to the ICESa2603 family-like ICEs,with a length of approximately 74.1 kb,encoding 73 genes.It contains 25 core mobile genes of the ConjTn5252 superfamily that form the back-bone of conjugant modules.The conserved backbone region of ICESag1535 includes 5 foreign gene insertion hotspots(HS),and a variable region(VR)containing 7 transposable insertion elements(IS),forming 3 complex transposons.These HS and VR can be divided into 7 major functional regions involved in the ICE functions,such as regulation of ICE stability,conjuga-tion coupling,material transmembrane transportation,stress regulation,bacteriocin synthesis and export,integrative and con-jugative evolution,host adhesion.Additionally,the 3'-terminal of ICESag1535 consists of three structurally similar tandem site-specific serine integrases(TSPSI).Cluster analysis of TSPSI revealed that S.agalactiae isolated from Oreochrom

关 键 词：尼罗罗非鱼 无乳链球菌 ICE_Sag1535_mutT Conj_(Tn5252) 三串联位点特异性丝氨酸重组酶 水平基因转移 跨种扩散 开放式进化 

分 类 号：Q933[生物学—微生物学] S917.1[农业科学—水产科学]