Type III Druantia two-component antiphage defense depends on the DruH-DruE interaction for inhibiting viral DNA circularization and replication.

Bacteria have evolved multiple immune systems to resist phage invasion, however, only a small part of the defensive mechanisms have been clearly uncovered. In this study, we report a type III Druantia two-component defense system, DruH-DruE, identified from Mycolicibacterium smegmatis (M. smegmatis). The DruH-DruE prevents phage DNA circularization and replication. DruE can be replaced from the defense system by either homolog in M. tuberculosis or M. smegmatis. The physical interaction between these two components is essential for fighting against phage infection. Mutations in the interaction sites led to the loss of phage-defending function of the system. The broad-spectrum antiphage ability of the defense system could be activated by the minor tail protein Gp25 of phage A10ZJ24. This study fills a major gap in current knowledge of antiphage mechanism of type III Druantia defense system, expanding our understanding of the immune mechanisms in prokaryotic cells.