title: The Type VI Secretion System Modulates Flagellar Gene Expression and Secretion in Citrobacter freundii and Contributes to Adhesion and Cytotoxicity to Host Cells.
abstract: The type VI secretion system (T6SS) as a virulence factor-releasing system contributes to virulence development of various pathogens and is often activated upon contact with target cells. Citrobacter freundii strain CF74 has a complete T6SS genomic island (GI) that contains clpV, hcp-2, and vgr T6SS genes. We constructed clpV, hcp-2, vgr, and T6SS GI deletion mutants in CF74 and analyzed their effects on the transcriptome overall and, specifically, on the flagellar system at the levels of transcription and translation. Deletion of the T6SS GI affected the transcription of 84 genes, with 15 and 69 genes exhibiting higher and lower levels of transcription, respectively. Members of the cell motility class of downregulated genes of the CF74ΔT6SS mutant were mainly flagellar genes, including effector proteins, chaperones, and regulators. Moreover, the production and secretion of FliC were also decreased in clpV, hcp-2, vgr, or T6SS GI deletion mutants in CF74 and were restored upon complementation. In swimming motility assays, the mutant strains were found to be less motile than the wild type, and motility was restored by complementation. The mutant strains were defective in adhesion to HEp-2 cells and were restored partially upon complementation. Further, the CF74ΔT6SS, CF74ΔclpV, and CF74Δhcp-2 mutants induced lower cytotoxicity to HEp-2 cells than the wild type. These results suggested that the T6SS GI in CF74 regulates the flagellar system, enhances motility, is involved in adherence to host cells, and induces cytotoxicity to host cells. Thus, the T6SS plays a wide-ranging role in C. freundii.
authors: State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, China Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Hangzhou, Zhejiang Province, China.
authors: Liyun
authors: L
authors: Liu
authors: Key Laboratory of Cell Proliferation and Regulation of Ministry of Education, Beijing Normal University, Beijing, China Universities of Confederated Institute for Proteomics, Beijing, China.
authors: Shuai
authors: S
authors: Hao
authors: School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, New South Wales, Australia.
authors: Ruiting
authors: R
authors: Lan
authors: Key Laboratory of Cell Proliferation and Regulation of Ministry of Education, Beijing Normal University, Beijing, China Universities of Confederated Institute for Proteomics, Beijing, China.
authors: Guangxia
authors: G
authors: Wang
authors: State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, China Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Hangzhou, Zhejiang Province, China.
authors: Di
authors: D
authors: Xiao
authors: State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, China Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Hangzhou, Zhejiang Province, China.
authors: Hui
authors: H
authors: Sun
authors: State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, China Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Hangzhou, Zhejiang Province, China xujianguo@icdc.cn.
authors: Jianguo
authors: J
authors: Xu
mesh_terms: D001422:Bacterial Adhesion; D058947:Bacterial Secretion Systems; D001427:Bacterial Toxins / Q000378:metabolism*; D016971:Citrobacter freundii / Q000235:genetics / Q000502:physiology*; D005407:Flagella / Q000502:physiology*; D005408:Flagellin / Q000096:biosynthesis; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D053263:Gene Regulatory Networks; D005816:Genetic Complementation Test; D044404:Genomic Islands; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000382:microbiology; D006801:Humans; D008124:Locomotion; D014176:Protein Biosynthesis; D014158:Transcription, Genetic; D037521:Virulence Factors / Q000378:metabolism
chemical_list: D058947:Bacterial Secretion Systems; D001427:Bacterial Toxins; D037521:Virulence Factors; D005408:Flagellin