Temperature-dependent pathogenicity of Vibrio alginolyticus in Gracilariopsis lemaneiformis "Baotou" disease

The outbreak of "Baotou" disease in Gracilariopsis lemaneiformis is closely associated with seasonal changes. However, the molecular basis of this seasonal outbreak remains elusive. Here, we demonstrate that elevated seawater temperatures significantly enhance the pathogenicity of Vibrio alginolyticus. The average number of decayed spots on G. lemaneiformis increased from 1.0 per thalli at 21 °C to 2.78 per thalli at 27 °C, correlated with a rise in the relative abundance of the pathogen on the algal surface from 44.2% to 77.2%. Bacterial transcriptome analysis revealed a temperature-dependent quorum sensing (QS) system. Core QS genes-including Opp/Ami and downstream effectors (Opp/Dpp systems)-were consistently downregulated at 21 °C, suggesting that QS serves as a temperature-sensitive virulence accelerator. Concurrently, host transcriptome analysis showed that V. alginolyticus infection systematically suppressed mitochondrial oxidative phosphorylation in G. lemaneiformis, with universal downregulation of electron transport chain complexes I-V and ATP synthase subunits, indicating mitochondrial dysfunction and energy crisis as key host responses. Integrated dual transcriptome analysis elucidated a clear causal chain whereby elevated temperature activates pathogen QS, leading to enhanced virulence, subsequent systemically represses mitochondrial oxidative phosphorylation and induces energy metabolism collapse in G. lemaneiformis and eventual disease outbreak. This study provides an integrated molecular framework for temperature-dependent "Baotou" disease and identifies potential intervention targets for seaweed disease management in the context of global warming.