水产学报2025，Vol.49Issue(5)：158-168,11.DOI:10.11964/jfc.20230614036
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
摘要
Abstract
With the exponential expansion of sequenced complete streptococcal genomes,numerous integrative and conjugat-ive 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 hori-zontal 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 Oreochromis niloticus,Lithobates catesbeiana and Lates calcarifer share identical TSPSIs within ICESa2603-like ICEs distributed in the Northern hemisphere aquatic ecosystem.Homology analysis of ICEs indicated that the conserved conjugational transfer backbone of ICESa2603-like ICEs,encoded by human,pig,and fish isolates,is homologous to ConjTn5252 conjugant modules and has the ability to spread across species.The prevalence of ICESa2603-like ICEs in S.agalactiae from Oreochromis niloticus in Guang-dong province was detected by PCR.The rate of ICE-carrying bacteria increased from 78.8％in isolates from 2014 to 2016 to 96.3％isolated from 2020 to 2021,indicating an upward trend.Conjugation experiments verified that ICE Sag 1535 can excise itself from the genome,cyclize,self-transfer,and inserted into the recipient bacterium,Sag 158.The attL,attR,attB,and oriT sites were characterized.After ICE integration into Sag158,the IS30 element was detected between the TSPSI and attR sites.ICESag1535,identified in this study,is a complete ICE element with self-excision and cyclization activities and cross-species conjugal transfer capability.The variable region contains a variety of complex transposons,leading to the formation of multiple horizontal transfer mechanisms and increasing prevalence diversity.Due to the recruitment specialty of IS elements,the variable region of ICEs exhibits open-ended evolution,conferring the host microbe with increased potential for pathogeni-city and dissemination.This research holds significant implications for microbial safety,biological evolution,and genetic resources research.关键词
尼罗罗非鱼/无乳链球菌/ICE_Sag1535_mutT/ConjTn5252/三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Key words
Oreochromis niloticus/Streptococcus agalactiae/ICE_Sag1535_mutT/ConjTn5252 conjugation modules/triplet of site-specific serine integrases/horizontal genes transfer/spread across species/open-ended evolution分类
生物科学引用本文复制引用
车行,卢燕播,王承德,罗敏意,黎果,张德峰,林蠡,赵丽娟..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[J].水产学报,2025,49(5):158-168,11.基金项目
2021省级科技创新战略和乡村振兴战略专项(2021S0082) （2021S0082）
中山市2022年第二批社会公益与基础研究项目(2022B2003) （2022B2003）
广东省现代农业产业技术体系创新团队(2019KJ141) Guangdong Provincial Special Fund For Science and Technology Innovation Strategy and Rural Revitaliza-tion Strategy in 2021(2021S0082) （2019KJ141）
the Second Batch of Social Welfare and Basic Research Fund of Zhongshan in 2022(2022B2003) （2022B2003）
Guangdong Provincial Special Fund for Modern Agriculture Industry Technology Innovation Teams(2019KJ141) （2019KJ141）
