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Temperate viruses can become dormant in their host cells, a process called lysogeny. In every infection, such viruses need to decide between the lytic and the lysogenic cycles, i.e., whether to replicate and lyse their host or to lysogenize and keep the host viable. Here we show that viruses (phages) of the spBeta group use a small-molecule communication system to coordinate lysis-lysogeny decisions. During infection of its Bacillus host cell, the phage produces a 6aa communication peptide that is released to the medium. In subsequent infections, progeny phages measure the concentration of this peptide and lysogenize if the concentration is sufficiently high. We found that different phages encode different versions of the communication peptide, demonstrating a phage-specific peptide communication code for lysogeny decisions. We termed this communication system the “arbitrium” system, and further show that it is encoded by 3 phage genes: aimP, producing the peptide, aimR, the intracellular peptide receptor, and aimX, a negative regulator of lysogeny. The arbitrium system enables an offspring phage to communicate with its predecessors, i.e., to estimate the amount of recent prior infections and hence decide whether to employ the lytic or lysogenic cycle.

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Highlightsd Retrons are preferentially located in defense islands d Retrons, together with their effector genes, protect bacteria from phages d Protection from phage is mediated by abortive infection

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