Mechanism of Pseudomonas plecoglossicida T6SS effector vgrG1a in disrupting hepatic immunometabolic homeostasis in large yellow croaker.

Pseudomonas plecoglossicida, a significant pathogen of large yellow croaker (Larimichthys crocea), employs its Type VI secretion system (T6SS1) as a key virulence determinant. However, the role of the T6SS1 spike protein, VgrG1a, in pathogenesis remains poorly understood. This study elucidates the critical function of vgrG1a in disrupting hepatic immunometabolic homeostasis by constructing a vgrG1a deletion mutant (ΔvgrG1a). We found that the ΔvgrG1a strain exhibited markedly attenuated virulence, increasing host survival by 40 % compared to wild-type challenge. Histopathological and ultrastructural analyses revealed that vgrG1a deletion significantly alleviated hepatic vacuolar degeneration, inflammatory infiltration, glycogen depletion, and mitochondrial damage. Physio-biochemical assays demonstrated that the metabolic disturbances in ATP synthase activity, NAD+/NADH ratio, and glutathione content were considerably milder in the ΔvgrG1a-infected group. Proteomic and qRT-PCR analyses indicated that vgrG1a activates a robust pro-inflammatory cytokine storm via the Toll-like receptor 2 (TLR2) and nucleotide-binding oligomerization domain-containing protein 2 (NOD2) signaling pathways. Concurrently, it potently suppressed the AMPK signaling pathway and the expression of key metabolic genes involved in gluconeogenesis (Pck1) and fatty acid β-oxidation (Acaa2). Our findings demonstrate that vgrG1a, as a key T6SS1 component, drives hepatic immunometabolic dysregulation by coordinately activating innate immune responses and inhibiting AMPK-mediated energy metabolism, providing novel insights into the pathogenesis of microbes.