Search Results (2)

Background/Objectives: Aeromonas hydrophila is a significant opportunistic pathogen with a broad host range. It produces a catecholate siderophore, amonabactin, during iron starvation, but the in vivo infection mechanism that involves amonabactin is unclear. This study aims to elucidate the role of amonabactin synthetase G (AmoG) in the pathogenicity of A. hydrophila and its impact on gut barrier function. Methods: ΔAmoG was generated by deleting the AMP-binding domain of AmoG in A. hydrophila CCL1. In vivo infection experiments were conducted to assess the mutant’s iron-chelating ability and pathogenicity. Complementation of ΔAmoG with AmoG (ΔAmoG-C) was performed to confirm the observed phenotypes. Transcriptomic and qRT-PCR analyses were used to investigate gene expression changes in infected fish. Goblet cell counts, tight junction expression, and D-lactic acid and LPS levels were measured to evaluate gut barrier function. Results: ΔAmoG exhibited impaired iron-chelating ability and reduced pathogenicity compared to wild-type CCL1. Complementation with AmoG restored virulence in ΔAmoG-C. Transcriptomic and qRT-PCR analyses revealed an elevated expression of Wnt/β-catenin pathway components and antimicrobial genes in ΔAmoG-infected fish. Further investigation indicated increased goblet cells and an enhanced expression of tight junctions, as well as lower D-lactic acid and LPS levels, in ΔAmoG-infected fish. However, gut permeability, bacterial load, and lethality did not significantly differ between CCL1, ΔAmoG, and ΔAmoG-C infections when the Wnt/β-catenin pathway was activated. Conclusions: AmoG plays a crucial role in A. hydrophila pathogenicity by modulating host Wnt/β-catenin signaling and gut mucosal barrier function. This study provides insights into the pathogenesis of A. hydrophila and potential therapeutic targets. Full article

Aeromonas salmonicida subsp. salmonicida (A. salmonicida), a Gram-negative bacterium causing furunculosis in fish, produces the siderophores acinetobactin and amonabactins in order to extract iron from its hosts. While the synthesis and transport of both systems is well understood, the regulation pathways and conditions necessary for the production of each one of these siderophores are not clear. The acinetobactin gene cluster carries a gene (asbI) encoding a putative sigma factor belonging to group 4 σ factors, or, the ExtraCytoplasmic Function (ECF) group. By generating a null asbI mutant, we demonstrate that AsbI is a key regulator that controls acinetobactin acquisition in A. salmonicida, since it directly regulates the expression of the outer membrane transporter gene and other genes necessary for Fe-acinetobactin transport. Furthermore, AsbI regulatory functions are interconnected with other iron-dependent regulators, such as the Fur protein, as well as with other sigma factors in a complex regulatory network. Full article