Closely related and yet special - how SPβ family phages control lysis-lysogeny decisions.

Soon after the discovery of genetic competence in the Gram-positive bacterium Bacillus subtilis, lytic and temperate phages that infect this organism were isolated. For instance, the lytic phage ϕ29 became a model for studying processes such as viral DNA packaging, replication, and transcription. By contrast, only a handful of temperate B. subtilis phages have been comprehensively characterized. However, the discovery of a peptide-based quorum sensing (QS) system in 2017 has brought temperate B. subtilis phages, particularly those of the SPβ family, back into the focus of research. The QS system is used by these phages to modulate lysis-lysogeny decisions. Meanwhile, many key components of the lysis-lysogeny management system have been identified. It turned out that a complex co-adaptation between the B. subtilis host cell and SPβ-like phages occurred during evolution and that a host-encoded toxin-antitoxin system plays a key role in controlling lysis-lysogeny decisions. There are many similarities and many important differences between the two well-studied model phages. Thus, a further comparative analysis of the lysis-lysogeny systems is essential to uncover the fundamental differences between ϕ3T and SPβ. Moreover, we believe that it would be exciting to revive research on temperate B. subtilis phages that are not related to SPβ-family phages.