Phages Mediate Bacterial Self-Recognition

Summary: Cells are social, and self-recognition is a conserved aspect of group behavior where cells assist kin and antagonize non-kin. However, the role of phage in self-recognition is unexplored. Here we find that a demarcation line is formed between different swimming Escherichia coli strains but not between identical clones; hence, motile cells discriminate between self and non-self. The basis for this self-recognition is a 49 kb, T1-type, lytic phage of the family Siphoviridae (named here SW1) that controls formation of the demarcation line by utilizing one of the host’s cryptic prophage proteins, YfdM of CPS-53, to propagate. Critically, SW1 provides a conditional benefit to E. coli K-12 compared with the identical strain that lacks the phage. A demarcation line is also formed when strains harbor either the lysogenic phage ϕ80 or lambda and encounter siblings that lack the lysogen. In summary, bacteria can use phage to distinguish siblings that lack phage. : While bacteria are foraging, it is beneficial for them to distinguish themselves from related strains. Here, Song et al. show that a lytic phage that infects Escherichia coli may be used to preferentially lyse cells that are not infected so that the infected cells outcompete their virus-free rivals. Keywords: lytic phage, lysogenic phage, cryptic prophage, self-recognition, swimming, lysi