Abstract 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 Dickeya dadantii 3937, can act against environmental bacteria phylogenetically distant from Dickeya spp. Screening 480 soil and rhizosphere isolates from three distinct plant-associated habitats in Poland, we identified nine Pseudomonas spp. strains susceptible to tailocin P2D1. Whole-genome sequencing and phenotype profiling revealed that these isolates spanned multiple clades, including taxa related to P. germanica, P. tensinigenes, and P. parakoreensis. The D. dadantii mutant lacking genes encoding tailocin sheath and tube proteins lost antagonistic activity against Pseudomonas isolates, confirming that tailocins alone mediate the observed killing. Plant tissue assays revealed that six of the P2D1-susceptible strains were non-pathogenic and could mitigate D. dadantii–induced soft rot on potato. In contrast, three isolates related to P. tensinigenes 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 Pseudomonas, 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 in vivo roles remain understudied.
Borowicz et al. (2026) studied this question.