Viral Infection Plays a Role in Bacterial Self-Recognition

Cells are social. A critical aspect of group behavior is self-recognition, as cells assist kin and antagonize non-kin in foraging for food and forming biofilms. In a study published last week in Cell Reports, scientists discovered that cells can distinguish themselves from closely related competitors through the use of a virus, and the harboring of phage in bacterial genomes benefits host cells when facing competitors in the environment.

The researchers found that a boundary (demarcation line) was formed due to phage lysis between different swimming E. coli strains but not between identical clones; hence, motile bacterial cells discriminated between self and non-self. The basis for this self-recognition is a T1-type lytic phage of the family Siphoviridae (named SW1) that controls the formation of the demarcation line by utilizing one of the host’s cryptic prophage proteins, YfdM of CPS-53, to propagate.

SW1 provides a conditional benefit to E. coli compared to the identical strain that lacks the phage. Additionally, a demarcation line also forms when E. coli strains harbor either the lysogenic phage φ80 or lambda and encounter siblings that lack the lysogen. Thus, the relationship between a virus and its cellular host should be re-evaluated, since a viral infection is sometimes beneficial.

Image: Demarcation lines (shown by red arrows) developed between cells of self and of non-self. Image courtesy of WANG Xiaoxue.