The early injected genomic region determines sensitivity to Type I restriction-modification defence against Autographiviridae phages

Bacteriophages must evade bacterial defences to establish successful infections. Type I restriction-modification (RM) systems recognize specific DNA motifs and degrade unmethylated foreign DNA, restricting phage replication. In this study, we detected that Marinomonas mediterranea MMB-2 uses a Type I RM system (Mme2I) to protect against several new phages in the Murciavirus genus within the Autographiviridae family. Whole-genome sequencing and methylation analysis revealed a DNA sequence motif methylated in M. mediterranea MMB-2, which is also present in the phages. Phages lacking the motif within the leading, first injected, region of their genomes, either natural isolates or escape mutants of sensitive phages, successfully infect M. mediterranea MMB-2, despite the presence of the recognition motif elsewhere in their genomes. These results highlight the importance of considering RM motif locations when predicting avoidance of restriction sites as escape mechanisms from RM systems. Additionally, our findings indicate an important role for RM systems in specifically influencing the organization of the leading injected regions of phage genomes, which are highly variable and often encode diverse anti-defence systems.