RT Journal Article SR Electronic T1 Independent Domestication of a Tailed Bacteriophage into a Killing Complex in Pseudomonas JF bioRxiv FD Cold Spring Harbor Laboratory SP 011486 DO 10.1101/011486 A1 Kevin L. Hockett A1 Tanya Renner A1 David A. Baltrus YR 2014 UL http://biorxiv.org/content/early/2014/11/17/011486.abstract AB Competition between microbes for limiting resources is widespread in nature. The strength of competition is often positively correlated with relatedness between microbes (intraspecific) as overlapping metabolism negate opportunities for niche partitioning. Bacteria have evolved numerous protein-based systems, collectively referred to as bacteriocins, that provide a fitness advantage during direct competition because they specifically kill strains or species closely related to the producer. This includes small, posttranslationally modified peptides, large, unmodified proteins, and domesticated tailed bacteriophages. In this work we sought to characterize bacteriocin genetic complements and killing spectra across the phylogenetic breadth of Pseudomonas syringae, an important phytopathogen. In characterizing the killing spectra for the model strain P. syringae B728a, we discovered its activity could not be explained by the presence of predicted bacteriocins. Using a reverse genetic approach, whereby we identified candidate bactericidal factors based on the presence of SOS-response transcriptional regulators, we found that the killing activity is derived from a prophage region. Despite this region being described nearly a decade ago, and numerous comparative genomic studies aimed at understanding evolution across this species, the ecological role of this region has remained elusive. This region does not encode an active prophage (i.e. one that will give rise to a replicative bacteriophage), but rather 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 synteny and molecular function. Multiple lines of evidence, including genomic alignment, amino acid percent sequence identity, and phylogenetic inference all support the conclusion of the R-type syringacin being derived independently of the R-type pyocin. Moreover, we demonstrate that this region is conserved, though not strictly syntenic, among several other Pseudomonas species, including P. fluorescens, P. protegens, P. chlororaphis, and P. putida, and thus is likely important for intermicrobial interactions throughout this important genus.