The coral reef microbiome is central to reef health and resilience. Competitive interactions between opportunistic coral pathogens and other commensal microbes affect the health of coral. Despite great advances over the years in sequencing-based microbial profiling of healthy and diseased coral, the molecular mechanism underlying colonization competition has been much less explored. In this study, by examining the culturable bacteria inhabiting the gastric cavity of healthy Galaxea fascicularis, a scleractinian coral, we found that temperate phages played a major role in mediating colonization competition in the coral microbiota. Specifically, the non-toxigenic Vibrio sp. inhabiting the healthy coral had a much higher colonization capacity than the coral pathogen Vibrio coralliilyticus, yet this advantage was diminished by the latter killing the former. Pathogen-encoded LodAB, which produces hydrogen peroxide, triggers the lytic cycle of prophage in the non-toxicogenic Vibrio sp. Importantly, V. coralliilyticus could outcompete other coral symbiotic bacteria (for example, Endozoicomonas sp.) through LodAB-dependent prophage induction. Overall, we reveal that LodAB can be used by pathogens as an important weapon to gain a competitive advantage over lysogenic competitors when colonizing corals.

珊瑚礁微生物群是珊瑚礁健康和恢复力的核心。机会性珊瑚病原体和其他共生微生物之间的竞争性相互作用会影响珊瑚的健康。尽管多年来在健康和患病珊瑚的基于测序的微生物分析方面取得了很大进展，但对殖民竞争的分子机制的探索却少得多。在这项研究中，通过检查生活在健康的 束状藻（一种石珊瑚）胃腔中的可培养细菌，我们发现温带噬菌体在介导珊瑚微生物群的定殖竞争中起主要作用。具体来说，非产毒弧菌。栖息在健康的珊瑚中的定殖能力比珊瑚病原体高得多Vibriocoralliilyticus，但这种优势因后者杀死前者而减弱。病原体编码的 LodAB 会产生过氧化氢，触发无毒弧菌中的原噬菌体裂解循环。重要的是，V.coralliilyticus可以通过 LodAB 依赖性前噬菌体诱导来胜过其他珊瑚共生细菌（例如，内生单胞菌）。总体而言，我们揭示了 LodAB 可被病原体用作重要武器，从而在殖民珊瑚时获得与溶原性竞争对手相比的竞争优势。