Modern agriculture is expected to face an increasing global demand for food while also needing to comply with higher sustainability standards. Therefore, control of crop pathogens requires new, green alternatives to current methods. Potatoes are susceptible to several bacterial diseases, with infections by soft rot Enterobacteriaceae (SRE) being a significant contributor to the major annual losses. As there are currently no efficient ways of combating SRE, we sought to develop an approach that could easily be incorporated into the potato production pipeline. To this end, 46 phages infecting the emerging potato pathogen Dickeya solani were isolated and thoroughly characterized. The 46 isolated phages were grouped into three different groups based on DNA similarity, representing two distinct clusters and a singleton. One cluster showed similarity to phages previously used to successfully treat soft rot in potatoes, whereas the remaining phages were novel and showed only very limited similarity to previously isolated phages. We selected six diverse phages in order to create the hereto most complex phage cocktail against SRE. The cocktail was applied in a proof-of-principle experiment to treat soft rot in potatoes under simulated storage conditions. We show that the phage cocktail was able to significantly reduce the incidence of soft rot as well as disease severity after 5 days of storage post-infection with Dickeya solani. This confirms results from previous studies that phages represent promising biocontrol agents against SRE infection in potato.

The phyllosphere microbiome plays an important role in plant fitness. Recently, bacteriophages have been shown to play a role in shaping the bacterial community composition of the phyllosphere. However, no studies on the diversity and abundance of phyllosphere bacteriophage communities have been carried out until now. In this study, we extracted, sequenced, and characterized the dsDNA and ssDNA viral community from a phyllosphere for the first time. We sampled leaves from winter wheat (Triticum aestivum), where we identified a total of 876 virus operational taxonomic units (vOTUs), mostly predicted to be bacteriophages with a lytic lifestyle. Remarkably, 848 of these vOTUs corresponded to new viral species, and we estimated a minimum of 2.0 × 10⁶ viral particles per leaf. These results suggest that the wheat phyllosphere harbors a large and active community of novel bacterial viruses. Phylloviruses have potential applications as biocontrol agents against phytopathogenic bacteria or as microbiome modulators to increase plant growth-promoting bacteria.

Lactobacillus plantarum is a bacterium with probiotic properties and promising applications in the food industry and agriculture. So far, bacteriophages of this bacterium have been moderately addressed. We examined the diversity of five new L. plantarum phages via whole genome shotgun sequencing and in silico protein predictions. Moreover, we looked into their phylogeny and their potential genomic similarities to other complete phage genome records through extensive nucleotide and protein comparisons. These analyses revealed a high degree of similarity among the five phages, which extended to the vast majority of predicted virion-associated proteins. Based on these, we selected one of the phages as a representative and performed transmission electron microscopy and structural protein sequencing tests. Overall, the results suggested that the five phages belong to the family Myoviridae, they have a long genome of 137,973–141,344 bp, a G/C content of 36.3–36.6% that is quite distinct from their host’s, and surprisingly, 7 to 15 tRNAs. Only an average 41/174 of their predicted genes were assigned a function. The comparative analyses unraveled considerable genetic diversity for the five L. plantarum phages in this study. Hence, the new genus “Semelevirus” was proposed, comprising exclusively of the five phages. This novel lineage of Lactobacillus phages provides further insight into the genetic heterogeneity of phages infecting Lactobacillus sp. The five new Lactobacillus phages have potential value for the development of more robust starters through, for example, the selection of mutants insensitive to phage infections. The five phages could also form part of phage cocktails, which producers would apply in different stages of L. plantarum fermentations in order to create a range of organoleptic outputs.

Background: Bacterial soft rot caused by members of the soft rot Pectobacteriaceae afflicts plant production of both vegetable and ornamental crops. Recent outbreaks highlight Dickeya sp. in the etiology of this disease in potatoes. Since there is a lack of control strategies for these diseases, alternative approaches have been suggested, including the use of biological control mediated by bacteriophages (phages). However, phages infecting many of these members are still undiscovered or poorly described. Materials and Methods: Two phages targeting Dickeya dadantii subsp. dadantii (NCPPB 4097) were isolated from household organic waste and purified. They were then further characterized using whole-genome sequencing and comparative genomics, transmission electron microscopy, latent period and burst size. Results: Dickeya phage Sucellus displayed Siphovirus morphology and had a genome of 39,826 bp with very limited similarity to any previously described phages. Dickeya phage Amaethon had a Podovirus morphology with a genome comprising 41,436 bp and limited similarity to phages in the Kafuna genus. The phages exhibited burst sizes of app. 94 and 240 virions per cell with latent periods of 91 and 86 minutes for Sucellus and Amaethon, respectively. While both phages had similar adsorption efficiencies and latent periods, the rise periods for the two phages diverged markedly, highlighting an odd growth pattern. Conclusions: Together, the two phages isolated here expand the known diversity of phages infecting the important plant pathogen D. dadantii . As they both share limited similarity to previously described groups of phages, they likely constitute novel genera within their respective groups.

Lactobacillus plantarum is a bacterium with promising applications to the food industry and agriculture and probiotic properties. So far, bacteriophages of this bacterium have been moderately addressed. We examined the diversity of five new L. plantarum phages via whole genome shotgun sequencing and in silico protein predictions. Moreover, we looked into their phylogeny and their potential genomic similarities to other complete phage genome records through extensive nucleotide and protein comparisons. These analyses revealed a high degree of similarity among the five phages, which extended to the vast majority of predicted virion-associated proteins. Based on these, we selected one of the phages as a representative and performed transmission electron microscopy and structural protein sequencing tests. Overall, the results suggested that the five phages belong to the family Myoviridae, they have a long genome of 137.973-141.344 bp, a G/C content of 36,3-36,6% that is quite distinct from their host’s, and, surprisingly, seven to 15 tRNAs. Only an average 41/174 of their predicted genes were assigned a function. The comparative analyses unraveled considerable genetic diversity for the five L. plantarum phages of this study. Hence, the new genus “Semelevirus” was proposed, which comprises exclusively the five phages. This novel lineage of Lactobacillus phages provides further insight into the genetic heterogeneity of phages infecting Lactobacillus sp.. The five new Lactobacillus phages have a potential value for the development of more robust starters through, for example, the selection of mutants insensitive to phage infections. The five phages could also form part of phage cocktails, which producers would apply in different stages of L. plantarum fermentations in order to create a range of organoleptic outputs.

Pectobacterium carotovorum is the causative agent of bacterial soft rot on various plant species. The use of phages for plant disease control have gained increased awareness over the past years. We here describe the isolation and characterization of Pectobacterium phage Jarilo, representing a novel genus of bacteriophages within the subfamily Autographivirinae . Jarilo possesses a double-stranded DNA genome of 40557 bp with a G+C% content of 50.08% and 50 predicted open reading frames (ORFs). Gene synteny and products seem to be somewhat conserved between Pectobacterium phage Jarilo and Enterobacteria phage T7, but limited nucleotide similarity is found between Jarilo and other phages within the subfamily Autographivirinae. We propose Pectobacterium phage Jarilo as the first member of a new genus of bacteriophages within the subfamily Autographivirinae.