A Plasmid With Conserved Phage Genes Helps Defend Against the Invasion of Transferable DNA Elements at the Cost of Reduced Virulence.

exhibits extensive phenotypic and genetic diversity. Higher plasmid loads in the cell were supposed to play an key role in its genome diversity. Although some plasmids are widely distributed in populations, they are poorly recognized. A plasmid named p2 in strain was predicted to be an intact prophage like phage SSU5. However, our study showed that p2 was specifically packaged into membrane vesicles (MVs) rather than phage particles triggered by mitomycin C and subinhibitory concentrations of antibiotics. p2-minus mutant Δ did not affect MV production. Compared with , the capacity of plasmid uptake and the amount of phage burst of Δ were improved. Moreover, virulence of Δ also increased. Our results indicated that p2 could contribute to the host defense against the invasion of transferable DNA elements at the cost of reduced virulence. Further study on the mechanism will help us understand how it provides adaptive phenotypes to host evolution.