title: A quorum sensing-based in vivo expression system and its application in multivalent bacterial vaccine.
abstract: BACKGROUND
  Delivery of antigens by live bacterial carriers can elicit effective humoral and cellular responses and may be an attractive strategy for live bacterial vaccine production through introduction of a vector that expresses an exogenous protective antigen. To overcome the instability and metabolic burden associated with plasmid introduction, alternative strategies, such as the use of in vivo-inducible promoters, have been proposed. However, screening an ideal in vivo-activated promoter with high efficiency and low leak expression in a particular strain poses great challenges to many researchers.
  
  
  RESULTS
  In this work, we constructed an in vivo antigen-expressing vector suitable for Edwardsiella tarda, an enteric Gram-negative invasive intracellular pathogen of both animals and humans. By combining quorum sensing genes from Vibrio fischeri with iron uptake regulons, a synthetic binary regulation system (ironQS) for E. tarda was designed. In vitro expression assay demonstrated that the ironQS system is only initiated in the absence of Fe2+ in the medium when the cell density reaches its threshold. The ironQS system was further confirmed in vivo to present an in vivo-triggered and cell density-dependent expression pattern in larvae and adult zebrafish. A recombinant E. tarda vector vaccine candidate WED(ironQS-G) was established by introducing gapA34, which encodes the protective antigen glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from the fish pathogen Aeromonas hydrophila LSA34 into ironQS system, and the immune protection afforded by this vaccine was assessed in turbot (Scophtalmus maximus). Most of the vaccinated fish survived under the challenge with A. hydrophila LSA34 (RPS=67.0%) or E. tarda EIB202 (RPS=72.3%).
  
  
  CONCLUSIONS
  Quorum sensing system has been extensively used in various gene structures in synthetic biology as a well-functioning and population-dependent gene circuit. In this work, the in vivo expression system, ironQS, maintained the high expression efficiency of the quorum sensing circuit and achieved excellent expression regulation of the Fur box. The ironQS system has great potential in applications requiring in vivo protein expression, such as vector vaccines. Considering its high compatibility, ironQS system could function as a universal expression platform for a variety of bacterial hosts.
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, China. chutenglab@163.com.
authors.forename: Teng
authors.initials: T
authors.lastname: Chu
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, China. nichunshan_2005@163.com.
authors.forename: Chunshan
authors.initials: C
authors.lastname: Ni
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, China. ziling914@hotmail.com.
authors.forename: Lingzhi
authors.initials: L
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, China. oaiwqiyao@ecust.edu.cn.
authors.forename: Qiyao
authors.initials: Q
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, China. jfxiao@ecust.edu.cn.
authors.forename: Jingfan
authors.initials: J
authors.lastname: Xiao
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, China. yxzhang@ecust.edu.cn.|Shanghai Collaborative Innovation Center for Biomanufacturing, Shanghai, 200237, China. yxzhang@ecust.edu.cn.
authors.forename: Yuanxing
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, China. qinliu@ecust.edu.cn.|Shanghai Collaborative Innovation Center for Biomanufacturing, Shanghai, 200237, China. qinliu@ecust.edu.cn.
authors.forename: Qin
authors.initials: Q
authors.lastname: Liu
mesh_terms: D016980:Aeromonas hydrophila / Q000235:genetics / Q000276:immunology; D048908:Aliivibrio fischeri / Q000235:genetics / Q000276:immunology; D000818:Animals; D000942:Antigens, Bacterial / Q000235:genetics / Q000276:immunology*; D001428:Bacterial Vaccines / Q000235:genetics / Q000276:immunology*; D020609:Edwardsiella tarda / Q000235:genetics / Q000276:immunology*; D005393:Fish Diseases / Q000276:immunology / Q000401:mortality / Q000469:parasitology; D005412:Flatfishes / Q000276:immunology / Q000469:parasitology; D015870:Gene Expression / Q000187:drug effects / Q000276:immunology; D005822:Genetic Vectors / Q000235:genetics / Q000276:immunology; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000235:genetics / Q000276:immunology*; D007501:Iron / Q000494:pharmacology; D007814:Larva / Q000276:immunology; D011401:Promoter Regions, Genetic / Q000235:genetics / Q000276:immunology; D053038:Quorum Sensing / Q000235:genetics / Q000276:immunology*; D015203:Reproducibility of Results; D015996:Survival Rate; D014611:Vaccination / Q000379:methods; D015027:Zebrafish / Q000276:immunology
chemical_list: D000942:Antigens, Bacterial; D001428:Bacterial Vaccines; D007501:Iron; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases