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Two functional type VI secretion systems in avian pathogenic Escherichia coli are involved in different pathogenic
Jiale Ma1, Yinli Bao1, Min Sun1
1College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China Key Lab of Animal Bacteriology, Ministry of Agriculture, Nanjing, China.
Infection and Immunity
|July 2, 2014
Summary
Avian pathogenic Escherichia coli (APEC) possesses two Type VI secretion systems (T6SSs). T6SS1 significantly impacts APEC pathogenesis, while T6SS2 specifically contributes to cerebral infections, demonstrating distinct roles in bacterial virulence.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- Type VI secretion systems (T6SSs) are crucial virulence factors in Gram-negative bacteria.
- The VgrG protein is a key component of T6SSs, with its N-terminal domain homologous to phage T4 gp27, involved in host specificity.
- Avian pathogenic Escherichia coli (APEC) harbors T6SSs that contribute to its pathogenicity.
Purpose of the Study:
- To investigate the roles of two distinct T6SS loci in the pathogenesis of APEC strain TW-XM.
- To determine the specific contributions of T6SS1 and T6SS2 to APEC virulence, adherence, invasion, and biofilm formation.
- To elucidate the function of VgrG-TSS2 in host cell interaction.
Main Methods:
- Genomic analysis to identify T6SS loci in APEC TW-XM.
- Construction of deletion mutants by removing clpV clusters and vgrG genes from T6SS loci.
- In vitro assays for bacterial adherence, invasion, and biofilm formation.
- In vivo infection models in ducks and mice to assess pathogenicity.
- Cell binding assays using VgrG-TSS2 and different cell lines (bEnd.3, DF-1).
Main Results:
- T6SS1 mutants exhibited significantly reduced adherence, invasion, pathogenicity, biofilm formation, and competitive advantage.
- TSS2 mutants showed decreased adherence and invasion specifically in mouse brain microvascular endothelial cells (BMECs) and duck brain tissue.
- VgrG-TSS2 demonstrated specific binding to BMEC surfaces but not to chicken embryo fibroblasts (DF-1 cells).
Conclusions:
- T6SS1 plays a broad role in APEC systemic infection and virulence.
- VgrG-TSS2 is specifically involved in cerebral infections, highlighting its role in targeting brain tissue.
- The distinct functions of T6SS1 and VgrG-TSS2 underscore their specialized contributions to APEC pathogenesis.
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