Temperate ϕH20-like phages are repeatedly identified at geographically distinct areas as free phage particles or as prophages of the fish pathogen Vibrio anguillarum. We studied mutants of a lysogenic isolate of V. anguillarum locked in the quorum-sensing regulatory modes of low (ΔvanT) and high (ΔvanO) cell densities by in-frame deletion of key regulators of the quorum-sensing pathway. Remarkably, we find that induction of the H20-like prophage is controlled by the quorum-sensing state of the host, with an eightfold increase in phage particles per cell in high-cell-density cultures of the quorum-sensing-deficient ΔvanT mutant. Comparative studies with prophage-free strains show that biofilm formation is promoted at low cell density and that the H20-like prophage stimulates this behavior. In contrast, the high-cell-density state is associated with reduced prophage induction, increased proteolytic activity, and repression of biofilm. The proteolytic activity may dually function to disperse the biofilm and as a quorum-sensing-mediated antiphage strategy. We demonstrate an intertwined regulation of phage-host interactions and biofilm formation, which is orchestrated by host quorum-sensing signaling, suggesting that increased lysogeny at high cell density is not solely a strategy for phages to piggy-back the successful bacterial hosts but is also a host strategy evolved to take control of the lysis-lysogeny switch to promote host fitness.

温带 phiH20 类噬菌体在不同地理区域被反复鉴定为游离噬菌体颗粒或鱼类病原体鳗弧菌的原噬菌体。我们研究了鳗鱼溶源分离株的突变体，通过框内删除群体感应途径的关键调节因子，锁定在低（Δ vanT）和高（Δ vanO ）细胞密度的群体感应调节模式中。值得注意的是，我们发现 H20 样原噬菌体的诱导是由宿主的群体感应状态控制的，在群体感应缺陷的 Δ vanT 突变体的高细胞密度培养物中，每个细胞的噬菌体颗粒增加了八倍。与无原噬菌体菌株的比较研究表明，低细胞密度下会促进生物膜形成，并且 H20 样原噬菌体会刺激这种行为。相反，高细胞密度状态与原噬菌体诱导减少、蛋白水解活性增加和生物膜抑制相关。蛋白水解活性可能具有分散生物膜和作为群体感应介导的抗噬菌体策略的双重功能。我们证明了噬菌体-宿主相互作用和生物膜形成的相互交织的调节，这是由宿主群体感应信号精心策划的，这表明高细胞密度下增加的溶源性不仅是噬菌体搭载成功的细菌宿主的一种策略，而且也是一种策略。宿主策略进化为控制裂解-溶源开关以促进宿主适应性。