The porin MspA is a phage-specific determinant of mycobacteriophage infection

Mycobacteriophages, which are used as treatments for mycobacterial infections, face limitations due to their wide host ranges. The bacterial factors that influence successful infection are not well understood. Previous research has primarily focused on cell envelope lipids and glycolipids as determinants of susceptibility. However, a recent study has identified a new factor that may play a crucial role in phage infection.

Using a genome-wide CRISPRi screen in Mycobacterium smegmatis, researchers identified the outer membrane porin genes mspA and mspC as potential determinants of phage infection. These genes showed a strong enrichment in susceptibility to a specific bacteriophage, BP{Delta}33HTH HRM10. Deletion of either mspA or mspC led to reduced plaque formation and smaller, more turbid plaques upon phage challenge. The loss of mspA, the major outer membrane porin of M. smegmatis, resulted in the most significant phenotypic changes.

Further investigation revealed that 11 out of 25 tested mycobacteriophages showed a more than tenfold reduction in titer or loss of discrete plaque formation on {Delta}mspA, compared to unaffected phages. These findings suggest that outer membrane porins, such as mspA and mspC, are phage-dependent determinants of mycobacterial susceptibility. This discovery adds a new layer of specificity to the understanding of phage infection beyond the previously identified cell envelope lipids and glycolipids.