Beyond kin killing: <i>Dickeya</i> -derived phage-tail-like bacteriocin P2D1 targets phylogenetically distant <i>Pseudomonas</i> spp.

Tailocins, phage-tail-derived bacteriocins, are increasingly recognized as potent mediators of microbial antagonism, yet their ecological scope beyond kin-targeting remains poorly understood. Here, we investigated whether P2D1, a tailocin produced by the plant pathogen <i>Dickeya dadantii</i> 3937, can act against environmental bacteria phylogenetically distant from <i>Dickeya</i> spp. Screening 480 soil and rhizosphere isolates from three distinct plant-associated habitats in Poland, we identified nine <i>Pseudomonas</i> spp. strains susceptible to tailocin P2D1. Whole-genome sequencing and phenotype profiling revealed that these isolates spanned multiple clades, including taxa related to <i>P. germanica</i>, <i>P. tensinigenes</i>, and <i>P. parakoreensis</i>. The <i>D. dadantii</i> mutant lacking genes encoding tailocin sheath and tube proteins lost antagonistic activity against <i>Pseudomonas</i> isolates, confirming that tailocins alone mediate the observed killing. Plant tissue assays revealed that six of the P2D1-susceptible strains were nonpathogenic and could mitigate <i>D. dadantii</i>-induced soft rot on potato. In contrast, three isolates related to <i>P. tensinigenes</i> were able to cause rot on their own under permissive conditions. Together, these findings demonstrate that P2D1 tailocin extends its activity to ecologically co-occurring but taxonomically distant <i>Pseudomonas</i>, suggesting that conserved receptors underline cross-genus targeting. More broadly, our results add to the limited evidence for tailocin activity beyond kin killing and therefore challenge the prevailing paradigm of kin-restricted tailocin specificity. They further suggest that tailocins may influence microbial community assembly across taxonomic boundaries, while their <i>in vivo</i> roles remain understudied.