The genus of Xanthomonas contains many well-known plant pathogens with the ability to infect some of the most important crop plants, thereby causing significant economic damage. Unfortunately, classical pest-control strategies are neither particularly efficient nor sustainable and we are, therefore, in demand of alternatives. Here, we present the isolation and characterization of seven novel phages infecting the plant-pathogenic species Xanthomonas translucens and Xanthomonas campestris. Transmission electron microscopy revealed that all phages show a siphovirion morphology. The analysis of genome sequences and plaque morphologies are in agreement with a lytic lifestyle of the phages making them suitable candidates for biocontrol. Moreover, three of the isolated phages form the new genus “Shirevirus”. All seven phages belong to four distinct clusters underpinning their phylogenetic diversity. Altogether, this study presents the first characterized isolates for the plant pathogen X. translucens and expands the number of available phages for plant biocontrol.

Phenotypic heterogeneity is an acclimation strategy in bacteria to cope with fluctuating environments and host immunity through cellular specialization. In the rhizosphere, how root-associated bacteria respond to plant defense signals and whether plants actively shape colonization through bacterial cell-type decisions, remains poorly understood. Cell type-resolved, spatiotemporal mapping of Bacillus subtilis and Bacillus velezensis colonizing Arabidopsis thaliana roots reveals dynamic transitions between flagellated and matrix-producing cell states. We identify an RBOHD-dependent, spatially heterogeneous oxidative landscape generated by the plant as a key regulator of bacterial cell-state balance. We show that exposure to reactive oxygen species (ROS) not only promotes differentiation into matrix-producing Bacillus cells, but ROS acclimation is also a prerequisite for cell type switching and stable association. Our findings demonstrate that bacterial stress evasion and acclimation to the host’s oxidative landscape are key steps in a host-microbe feedback system enabling stable rhizoplane colonization.

Pathogens resistant to classical control strategies are on the rise and cause significant damage in crop yield production with seeds as one major transmission route. Bacteriophages are specialized viruses of bacteria and their interaction with seeds holds great potential as targeted and sustainable solution to this problem. In this study, we isolated and characterized two novel phages, Athelas and Alfirin, infecting Pseudomonas syringae and Agrobacterium tumefaciens, respectively , and included the recently published phage Pfeifenkraut infecting Xanthomonas translucens . The three phages were tested for their interaction with the seed coat mucilage. Phage binding on Arabidopsis seeds, which exude the mucilage as a polysaccharide-polymer-matrix, was assessed by comparison to seeds with removed mucilage. Two of the three phages were dependant on mucilage for seed binding, and podophage Athelas showed the highest dependency. Further podoviruses of the Autographiviridae obtained from the systematic E. coli (BASEL) phage collection were tested and showed a similar dependency on the mucilage for seed adhesion. Comparative analysis using a set of Arabidopsis seed coat mutants revealed the diffusible cellulose fraction as important component for phage binding. Long-term activity tests revealed a high stability of phages on seed surfaces and phage coating effectively increased the survival rate of plant seedling in the presence of the pathogen. Utilization of non-virulent host strains was further successfully applied to boost the presence of infectious phage particles on seed surfaces. Altogether, our study highlights the high potential of phage-based applications as sustainable biocontrol strategy on the seed level.