Independent Co-option of a Tailed Bacteriophage into a Killing Complex in Pseudomonas

Competition between microbes is widespread in nature, especially among those that are closely related. To combat competitors, bacteria have evolved numerous protein-based systems (bacteriocins) that kill strains closely related to the producer. In characterizing the bacteriocin complement and killing spectra for the model strain P. syringae B728a, we discovered its activity was not linked to any predicted bacteriocin, but is derived from a prophage. Instead of encoding an active prophage, this region encodes a bacteriophage-derived bacteriocin, termed an R-type syringacin. The R-type syringacin is striking in its convergence with the well-studied R-type pyocin of P. aeruginosa in both chromosomal synteny and molecular function. Genomic alignment, amino acid percent sequence identity, and phylogenetic inference all support a scenario where the R-type syringacin has been co-opted independently of the R-type pyocin. Moreover, the presence of this region is conserved among several other Pseudomonas species, and thus is likely important for intermicrobial interactions throughout this important genus.