Factors affecting survival of bacteriophage on tomato leaf surfaces

BglaTNB6, a tailocin produced by a plant-associated nonpathogenic bacterium, prevents rice seed-borne bacterial diseases

Rice seed-borne diseases caused by the bacterial pathogens Burkholderia glumae and B. plantarii pose a major threat to rice production worldwide. To manage these diseases in a sustainable manner, a biocontrol strategy is crucial. In this study, we showed that B. gladioli NB6 (NB6), a nonpathogenic bacterium, strongly protects rice from infection caused by the above-mentioned pathogens. NB6 was isolated from the indica rice cultivar Nona Bokra seedlings, which possesses genetic resistance to B. glumae. We discovered that cell suspensions of NB6 and its culture filtrate suppressed the disease symptoms caused by B. glumae and B. plantarii in rice seedlings, which indicated that NB6 secretes a plant-protective substance extracellularly. Through purification and mass spectrometry analysis of the culture filtrate, combined with transmission electron microscopy and mutant analysis, the substance was identified as a tailocin and named BglaTNB6. Tailocins are bacteriotoxic multiprotein structures morphologically similar to headless phage tails. BglaTNB6 exhibited antibacterial activity against several Burkholderia species, including B. glumae, B. plantarii, and B. gladioli, suggesting it can prevent pathogen infection. Interestingly, BglaTNB6 greatly contributed only to the biocontrol activity of NB6 cell suspensions against B. plantarii, and not against B. glumae. BglaTNB6 was shown to be encoded by a prophage locus lacking genes for phage head proteins, and a B. gladioli strain with the coded BglaTNB6-like locus equipped with phage head proteins failed to prevent rice seedlings from being infected with B. plantarii. These results suggested that BglaTNB6 may enhance the competitiveness of NB6 against a specific range of bacteria. Our study also highlights the potential of tailocin-producing endophytes for managing crop bacterial diseases.

Evaluation of Different Formulations on the Viability of Phages for Use in Agriculture

Bacteriophages have been proposed as biological controllers to protect plants against different bacterial pathogens. In this scenario, one of the main challenges is the low viability of phages in plants and under adverse environmental conditions. This work explores the use of 12 compounds and 14 different formulations to increase the viability of a phage mixture that demonstrated biocontrol capacity against Pseudomonas syringae pv. actinidiae (Psa) in kiwi plants. The results showed that the viability of the phage mixture decreases at 44 °C, at a pH lower than 4, and under UV radiation. However, using excipients such as skim milk, casein, and glutamic acid can prevent the viability loss of the phages under these conditions. Likewise, it was demonstrated that the use of these compounds prolongs the presence of phages in kiwi plants from 48 h to at least 96 h. In addition, it was observed that phages remained stable for seven weeks when stored in powder with skim milk, casein, or sucrose after lyophilization and at 4 °C. Finally, the phages with glutamic acid, sucrose, or skim milk maintained their antimicrobial activity against Psa on kiwi leaves and persisted within kiwi plants when added through roots. This study contributes to overcoming the challenges associated with the use of phages as biological controllers in agriculture.

Exploring the historical roots, advantages and efficacy of phage therapy in plant diseases management

In the drug-resistance era, phage therapy has received considerable attention from worldwide researchers. Phage therapy has been given much attention in public health but is rarely applied to control plant diseases. Herein, we discuss phage therapy as a biocontrol approach against several plant diseases. The emergence of antibiotic resistance in agriculturally important pathogenic bacteria and the toxic nature of different synthetic compounds used to control microbes has driven researchers to rethink the century-old strategy of phage therapy''. Compared to other treatment strategies, phage therapy offers remarkable advantages such as high specificity, less chances of drug resistance, non-harmful nature, and benefit to soil microbial flora. The optimizations and protective formulations of phages are significant accomplishments; however, steps towards a better understanding of the physiologic characteristics of phages need to be preceded to commercialize their use. The future of phage therapy in the context of plant disease management is promising and could play a significant role in sustainable agriculture. Ongoing research will likely affirm the safety of phage therapy, ensuring that it does not harm non-target organisms, including beneficial soil microbes. Phage therapy could become vital in addressing global food security challenges, particularly in regions heavily impacted by plant bacterial diseases. Efforts to create formulations that enhance the stability and shelf-life of phages will be crucial, especially for their use in varied environmental conditions.

Newly isolated Drexlerviridae phage LAPAZ is physically robust and fosters eradication of Klebsiella pneumoniae in combination with meropenem

Due to the spread of multidrug resistance there is a renewed interest in using bacteriophages (briefly: phages) for controlling bacterial pathogens. The objective of this study was the characterization of a newly isolated phage (i.e. phage LAPAZ, vB_KpnD-LAPAZ), its antimicrobial activity against multidrug resistant Klebsiella pneumoniae and potential synergistic interactions with antibiotics. LAPAZ belongs to the family Drexlerviridae (genus: Webervirus) and lysed 30 % of tested strains, whereby four distinct capsular types can be infected. The genome consists of 51,689 bp and encodes 84 ORFs. The latent period is 30 min with an average burst size of 27 PFU/cell. Long-term storage experiments show that LAPAZ is significantly more stable in wastewater compared to laboratory media. A phage titre of 90 % persists up to 30 min at 50 ˚C and entire phage loss was seen only at temperatures > 66 ˚C. Besides stability against UV-C, antibacterial activity in liquid culture medium was consistent at pH values ranging from 4 to 10. Unlike exposure to phage or antibiotic alone, synergistic interactions and a complete bacterial eradication was achieved when combining LAPAZ with meropenem. In addition, synergism with the co-presence of ciprofloxacin was observed and phage resistance emergence could be delayed. Without co-addition of the antibiotic, phage resistant mutants readily emerged and showed a mixed pattern of drug sensitivity alterations. Around 88 % became less sensitive towards ceftazidime, meropenem and gentamicin. Conversely, around 44 % showed decreased resistance levels against ciprofloxacin. Whole genome analysis of a phage-resistant mutant with a 16-fold increased sensitivity towards ciprofloxacin revealed one de novo frameshift mutation leading to a gene fusion affecting two transport proteins belonging to the major facilitator-superfamily (MFS). Apparently, this mutation compromises ciprofloxacin efflux efficiency and further studies are warranted to understand how the non-mutated protein might be involved in phage-host adsorption.

Isolation, characterization and application of noble bacteriophages targeting potato common scab pathogen Streptomyces stelliscabiei

Bacteriophages have emerged as promising alternatives to pesticides for controlling bacterial pathogens in crops. Among these pathogens, Streptomyces stelliscabiei (syn. S. stelliscabiei) is a primary causative agent of potato common scab (PCS), resulting in substantial global economic losses. The traditional management methods for PCS face numerous challenges, highlighting the need for effective and environmentally friendly control strategies. In this study, we successfully isolated three novel bacteriophages, namely Psst1, Psst2, and Psst4, which exhibited a broad host range encompassing seven S. stelliscabiei strains. Morphological analysis revealed their distinct features, including an icosahedral head and a non-contractile tail. These phages demonstrated stability across a broad range of temperatures (20-50°C), pH (pH 3-11), and UV exposure time (80 min). Genome sequencing revealed double-stranded DNA phage with open reading frames encoding genes for phage structure, DNA packaging and replication, host lysis and other essential functions. These phages lacked genes for antibiotic resistance, virulence, and toxicity. Average nucleotide identity, phylogenetic, and comparative genomic analyses classified the three phages as members of the Rimavirus genus, with Psst1 and Psst2 representing novel species. All three phages efficiently lysed S. stelliscabiei in the liquid medium and alleviated scab symptom development and reduced pathogen abundance on potato slices. Furthermore, phage treatments of radish seedlings alleviated the growth inhibition caused by S. stelliscabiei with no disease symptoms. In soil potted experiments, phages significantly reduced disease incidence by 40%. This decrease is attributed to a reduction in pathogen density and the selection of S. stelliscabiei strains with reduced virulence and slower growth rates in natural environments. Our study is the first to report the isolation of three novel phages that infect S. stelliscabiei as a host bacterium. These phages exhibit a broad host range, and demonstrate stability under a variety of environmental conditions. Additionally, they demonstrate biocontrol efficacy against bacterial infections in potato slices, radish seedlings, and potted experiments, underscoring their significant potential as biocontrol agents for the effective management of PCS.

Physicochemical Characterization of Novel Bacteriophages of Pseudomonas syringe from Northwest Iran

Bacterial canker, caused by Pseudomonas syringae, is a devastating disease of stone fruit trees worldwide. The bacterium has a broad host range and a high capacity for adaptation and dissemination, owing to its high mutation rate and horizontal gene transfer. Traditional control methods based on copper compounds and antibiotics have resulted in the development of resistance in the bacterial population. Thus, alternative approaches are needed, such as phage therapy. This study aimed to characterize the physicochemical and biological properties of novel Pseudomonas syringae pv. syringae (Pss)-specific phages isolated from the soils of northwestern Iran. Seventy-five phage isolates were obtained, and their host range was determined against various bacterial pathogens. Five phages exhibiting the highest lytic activity against Pss and a narrow host range were selected for subsequent analysis. The stability of the selected phages was assessed under different conditions such as ultraviolet irradiation, temperature, pH, NaCl concentration, and chloroform exposure. The selected phages demonstrated significant effectiveness in vivo, exerting substantial suppression on the population of Pss. This reduction was observed for both individual phages and when the phages were utilized as a mixture. The findings indicate that phages have the potential to be used as biocontrol agents in agriculture.

Multisite Field Evaluation of Bacteriophages for Fire Blight Management: Incorporation of Ultraviolet Radiation Protectants and Impact on the Apple Flower Microbiome

Fire blight, a disease of pome fruits caused by the bacterium Erwinia amylovora, has become increasingly difficult to manage after the emergence of streptomycin-resistant strains. Alternative antibiotics and copper are available; however, these chemicals have use restrictions in some countries and also can carry risks of phytotoxicity. Therefore, there is growing interest in biological-based management options, with bacteriophage (phages) showing promise, as these naturally occurring pathogens of bacteria are easy to isolate and grow. However, there are several technical challenges regarding the implementation of phage biocontrol in the field, as the viral molecules suffer from ultraviolet radiation (UVR) degradation and can die off rapidly in the absence of the host bacterium. In this work, we assessed the efficacy of Erwinia phages and a commercial phage product for blossom blight control in the field across multiple locations in the eastern United States. In these tests, disease control ranged from 0.0 to 82.7%, and addition of a UVR protectant only resulted in significantly increased disease control in 2 of 12 tests. We also analyzed microbial community population changes in response to phage application. Changes in bacterial community diversity metrics over time were not detected; however, relative abundances of target taxa were temporarily reduced after phage applications, indicating that these phage applications did not have deleterious effects on the flower microbiome. We have demonstrated that biological control of fire blight with phages is achievable, but a better understanding of phage-pathogen dynamics is required to optimize disease control efficacy.

The role of rhizosphere phages in soil health

While the One Health framework has emphasized the importance of soil microbiomes for plant and human health, one of the most diverse and abundant groups-bacterial viruses, i.e. phages-has been mostly neglected. This perspective reviews the significance of phages for plant health in rhizosphere and explores their ecological and evolutionary impacts on soil ecosystems. We first summarize our current understanding of the diversity and ecological roles of phages in soil microbiomes in terms of nutrient cycling, top-down density regulation, and pathogen suppression. We then consider how phages drive bacterial evolution in soils by promoting horizontal gene transfer, encoding auxiliary metabolic genes that increase host bacterial fitness, and selecting for phage-resistant mutants with altered ecology due to trade-offs with pathogen competitiveness and virulence. Finally, we consider challenges and avenues for phage research in soil ecosystems and how to elucidate the significance of phages for microbial ecology and evolution and soil ecosystem functioning in the future. We conclude that similar to bacteria, phages likely play important roles in connecting different One Health compartments, affecting microbiome diversity and functions in soils. From the applied perspective, phages could offer novel approaches to modulate and optimize microbial and microbe-plant interactions to enhance soil health.

Biological characteristics of the bacteriophage LDT325 and its potential application against the plant pathogen Pseudomonas syringae

Bud blight disease caused by Pseudomonas syringae is a major bacterial disease of tea plants in China. Concerns regarding the emergence of bacterial resistance to conventional copper controls have indicated the need to devise new methods of disease biocontrol. Phage-based biocontrol may be a sustainable approach to combat bacterial pathogens. In this study, a P. syringae phage was isolated from soil samples. Based on morphological characteristics, bacteriophage vB_PsS_LDT325 belongs to the Siphoviridae family; it has an icosahedral head with a diameter of 53 ± 1 nm and nonretractable tails measuring 110 ± 1 nm. The latent period and burst size of the phage were 10 min and 17 plaque-forming units (PFU)/cell, respectively. Furthermore, an analysis of the biological traits showed that the optimal multiplicity of infection (MOI) of the phage was 0.01. When the temperature exceeded 60°C, the phage titer began to decrease. The phage exhibited tolerance to a wide range of pH (3-11) and maintained relatively stable pH tolerance. It showed a high tolerance to chloroform, but was sensitive to ultraviolet (UV) light. The effects of phage LDT325 in treating P. syringae infections in vivo were evaluated using a tea plant. Plants were inoculated with 2 × 107 colony-forming units (CFU)/mL P. syringae using the needle-prick method and air-dried. Subsequently, plants were inoculated with 2 × 107 PFU/mL LDT325 phage. Compared with control plants, the bacterial count was reduced by 1 log10/0.5 g after 4 days in potted tea plants inoculated with the phage. These results underscore the phage as a potential antibacterial agent for controlling P. syringae.

First European Erwinia amylovora Lytic Bacteriophage Cocktails Effective in the Host: Characterization and Prospects for Fire Blight Biocontrol

Fire blight, caused by the plant-pathogenic bacterium Erwinia amylovora, is a highly contagious and difficult-to-control disease due to its efficient dissemination and survival and the scarcity of effective control methods. Copper and antibiotics are the most used treatments but pose environmental and human health risks. Bacteriophages (phages) constitute an ecological, safe, and sustainable fire blight control alternative. The goal of this study was to search for specific E. amylovora phages from plant material, soil, and water samples in Mediterranean environments. A collection of phages able to specifically infect and lyse E. amylovora strains was generated from former fire blight-affected orchards in Eastern Spain. Following in vitro characterization, assays in immature fruit revealed that preventively applying some of the phages or their combinations delayed the onset of fire blight symptoms and reduced the disease's severity, suggesting their biocontrol potential in Spain and other countries. The morphological and molecular characterization of the selected E. amylovora phages classified them as members of the class Caudoviricetes (former Myoviridae family) and genus Kolesnikvirus. This study reveals Mediterranean settings as plausible sources of E. amylovora-specific bacteriophages and provides the first effective European phage cocktails in plant material for the development of sustainable fire blight management measures.

Phytopathological management through bacteriophages: enhancing food security amidst climate change

The increasing global population and climate change pose significant challenges to agriculture, particularly in managing plant diseases caused by phytopathogens. Traditional methods, including chemical pesticides and antibiotics, have become less effective due to pathogen resistance and environmental concerns. Phage therapy emerges as a promising alternative, offering a sustainable and precise approach to controlling plant bacterial diseases without harming beneficial soil microorganisms. This review explores the potential of bacteriophages as biocontrol agents, highlighting their specificity, rapid multiplication, and minimal environmental impact. We discuss the historical context, current applications, and prospects of phage therapy in agriculture, emphasizing its role in enhancing crop yield and quality. Additionally, the paper examines the integration of phage therapy with modern agricultural practices and the development phage cocktails and genetically engineered phages to combat resistant pathogens. The findings suggest that phage therapy could revolutionize phytopathological management, contributing to global food security and sustainable agricultural practices.

ONE-SENTENCE SUMMARY

The burden of plant diseases and phage-based phytopathological treatment.

Pan-metagenome reveals the abiotic stress resistome of cigar tobacco phyllosphere microbiome

The important role of microbial associations in mediating plant protection and responses to abiotic stresses has been widely recognized. However, there have been limited studies on the functional profile of the phyllosphere microbiota from tobacco (Nicotiana tabacum), hindering our understanding of the mechanisms underlying stress resilience in this representative and easy-to-cultivate model species from the solanaceous family. To address this knowledge gap, our study employed shotgun metagenomic sequencing for the first time to analyze the genetic catalog and identify putative plant growth promoting bacteria (PGPB) candidates that confer abiotic stress resilience throughout the growth period of cigar tobacco in the phyllosphere. We identified abundant genes from specific bacterial lineages, particularly Pseudomonas, within the cigar tobacco phyllospheric microbiome. These genes were found to confer resilience against a wide range of stressors, including osmotic and drought stress, heavy metal toxicity, temperature perturbation, organic pollutants, oxidative stress, and UV light damage. In addition, we conducted a virome mining analysis on the metagenome to explore the potential roles of viruses in driving microbial adaptation to environmental stresses. Our results identified a total of 3,320 scaffolds predicted to be viral from the cigar tobacco phyllosphere metagenome, with various phages infecting Pseudomonas, Burkholderia, Enterobacteria, Ralstonia, and related viruses. Within the virome, we also annotated genes associated with abiotic stress resilience, such as alkaline phosphatase D (phoD) for nutrient solubilization and glutamate-5-semialdehyde dehydrogenase (proA) for osmolyte synthesis. These findings shed light on the unexplored roles of viruses in facilitating and transferring abiotic stress resilience in the phyllospheric microbiome through beneficial interactions with their hosts. The findings from this study have important implications for agricultural practices, as they offer potential strategies for harnessing the capabilities of the phyllosphere microbiome to enhance stress tolerance in crop plants.

Improved Persistence of Bacteriophage Formulation with Nano N-Acetylcysteine-Zinc Sulfide and Tomato Bacterial Spot Disease Control

Bacteriophages are biocontrol agents used to manage bacterial diseases. They have long been used against plant pathogenic bacteria; however, several factors impede their use as a reliable disease management strategy. Short-lived persistence on plant surfaces under field conditions results mainly from rapid degradation by exposure to ultraviolet (UV) light. Currently, there are no effective commercial formulations that protect phages from UV. The phage ΦXp06-02-1, which lyses strains of the tomato bacterial spot pathogen Xanthomonas perforans, was mixed with different concentrations of the nanomaterial N-acetylcysteine surface-coated manganese-doped zinc sulfide (NAC-ZnS; 3.5 nm). In vitro, NAC-ZnS at 10,000 μg/ml formulated phage, when exposed to UV for 1 min, provided statistically equivalent plaque-forming unit (PFU) recovery as phages that were not exposed to UV. NAC-ZnS had no negative effect on the phage's ability to lyse bacterial cells under in vitro conditions. NAC-ZnS reduced phage degradation over time in comparison with the nontreated control, whereas N-acetylcysteine-zinc oxide (NAC-ZnO) had no effect. In fluorescent light, without UV exposure, NAC-ZnO-formulated phages were more infective than NAC-ZnS-formulated phages. The nanomaterial-phage mixture did not cause any phytotoxicity when applied to tomato plants. Following exposure to sunlight, the NAC-ZnS formulation improved phage persistence in the phyllosphere by 15 times compared with nonformulated phages. NAC-ZnO-formulated phage populations were undetectable within 32 h, whereas NAC-ZnS-formulated phage populations were detected at 103 PFU/g. At 4 h of sunlight exposure, NAC-ZnS-formulated phages at 1,000 μg/ml significantly reduced tomato bacterial spot disease severity by 16.4% compared with nonformulated phages. These results suggest that NAC-ZnS can be used to improve the efficacy of phages for bacterial diseases.

Optimizing the formulation of Erwinia bacteriophages for improved UV stability and adsorption on apple leaves

Fire blight is a bacterial disease that affects plants of the Rosaceae family and causes significant economic losses worldwide. Although antibiotics have been used to control the disease, concerns about their environmental impact and the potential to promote antibiotic resistance have arisen. Bacteriophages are being investigated as an alternative to antibiotics; however, their efficacy can be affected by environmental stresses, such as UV radiation. In this study, we optimized the formulation of Erwinia phages to enhance their stability in the field, focusing on improving their UV stability and adsorption using adjuvants. Our results confirmed that 4.5 % polysorbate 80 and kaolin improve phage stability under UV stress, resulting in an 80 % increase in PFU value and improved UV protection efficacy. Adsorption assays also demonstrated that polysorbate 80 and kaolin improved the absorption efficiency, with phages detected in plant for up to two weeks. These findings demonstrate the effectiveness of the auxiliary formulation of Erwinia bacteriophages against environmental stress.

Xanthomonas euvesicatoria-Specific Bacteriophage BsXeu269p/3 Reduces the Spread of Bacterial Spot Disease in Pepper Plants

The present study was focused on the pathosystem pepper plants (Capsicum annuum L.)-phytopathogenic bacterium X. euvesicatoria (wild strain 269p)-bacteriophage BsXeu269p/3 and the possibility of bacteriophage-mediated biocontrol of the disease. Two new model systems were designed for the monitoring of the effect of the phage treatment on the infectious process in vivo. The spread of the bacteriophage and the pathogen was monitored by qPCR. A new pair of primers for phage detection via qPCR was designed, as well as probes for TaqMan qPCR. The epiphytic bacterial population and the potential bacteriolytic effect of BsXeu269p/3 in vivo was observed by SEM. An aerosol-mediated transmission model system demonstrated that treatment with BsXeu269p/3 reduced the amount of X. euvesicatoria on the leaf surface five-fold. The needle-pricking model system showed a significant reduction of the amount of the pathogen in infectious lesions treated with BsXeu269p/3 (av. 59.7%), compared to the untreated control. We found that the phage titer is 10-fold higher in the infection lesions but it was still discoverable even in the absence of the specific host in the leaves. This is the first report of in vivo assessment of the biocontrol potential of locally isolated phages against BS pathogen X. euvesicatoria in Bulgaria.

Isolation, characterization, and evaluation of putative new bacteriophages for controlling bacterial spot on tomato in Brazil

Bacterial spot is a highly damaging tomato disease caused by members of several species of the genus Xanthomonas. Bacteriophages have been studied for their potential use in the biological control of bacterial diseases. In the current study, bacteriophages were obtained from soil and tomato leaves in commercial fields in Brazil with the aim of obtaining biological control agents against bacterial spot. Phage isolation was carried out by co-cultivation with isolates of Xanthomonas euvesicatoria pv. perforans, which was prevalent in the collection areas. In a host range evaluation, none of the phage isolates was able to induce a lytic cycle in all of the bacterial isolates tested. In in vivo tests, treatment of susceptible bacterial isolates with the corresponding phage prior to application to tomato plants led to a reduction in the severity of the resulting disease. The level of disease control provided by phage application was equal to or greater than that achieved using copper hydroxide. Electron microscopy analysis showed that all of the phages had similar morphology, with head and tail structures similar to those of viruses belonging to the class Caudoviricetes. The presence of short, non-contractile tubular tails strongly suggested that these phages belong to the family Autographiviridae. This was confirmed by phylogenetic analysis, which further revealed that they all belong to the genus Pradovirus. The phages described here are closely related to each other and potentially belong to a new species within the genus. These phages will be evaluated in future studies against other tomato xanthomonad strains to assess their potential as biological control agents.

Biological and Genetic Characterizations of a Novel Lytic ΦFifi106 against Indigenous Erwinia amylovora and Evaluation of the Control of Fire Blight in Apple Plants

Erwinia amylovora is a devastating phytobacterium causing fire blight in the Rosaceae family. In this study, ΦFifi106, isolated from pear orchard soil, was further purified and characterized, and its efficacy for the control of fire blight in apple plants was evaluated. Its genomic analysis revealed that it consisted of 84,405 bp and forty-six functional ORFs, without any genes encoding antibiotic resistance, virulence, and lysogenicity. The phage was classified into the genus Kolesnikvirus of the subfamily Ounavirinae. ΦFifi106 specifically infected indigenous E. amylovora and E. pyrifoliae. The lytic activity of ΦFifi106 was stable under temperature and pH ranges of 4-50 °C and 4-10, as well as the exposure to ultraviolet irradiation for 6 h. ΦFifi106 had a latent period of 20 min and a burst size of 310 ± 30 PFU/infected cell. ΦFifi106 efficiently inhibited E. amylovora YKB 14808 at a multiplicity of infection (MOI) of 0.1 for 16 h. Finally, the pretreatment of ΦFifi106 at an MOI of 1000 efficiently reduced disease incidence to 37.0% and disease severity to 0.4 in M9 apple plants. This study addressed the use of ΦFifi106 as a novel, safe, efficient, and effective alternative to control fire blight in apple plants.

Bacteriophages for the Targeted Control of Foodborne Pathogens

Foodborne illness is exacerbated by novel and emerging pathotypes, persistent contamination, antimicrobial resistance, an ever-changing environment, and the complexity of food production systems. Sporadic and outbreak events of common foodborne pathogens like Shiga toxigenic E. coli (STEC), Salmonella, Campylobacter, and Listeria monocytogenes are increasingly identified. Methods of controlling human infections linked with food products are essential to improve food safety and public health and to avoid economic losses associated with contaminated food product recalls and litigations. Bacteriophages (phages) are an attractive additional weapon in the ongoing search for preventative measures to improve food safety and public health. However, like all other antimicrobial interventions that are being employed in food production systems, phages are not a panacea to all food safety challenges. Therefore, while phage-based biocontrol can be promising in combating foodborne pathogens, their antibacterial spectrum is generally narrower than most antibiotics. The emergence of phage-insensitive single-cell variants and the formulation of effective cocktails are some of the challenges faced by phage-based biocontrol methods. This review examines phage-based applications at critical control points in food production systems with an emphasis on when and where they can be successfully applied at production and processing levels. Shortcomings associated with phage-based control measures are outlined together with strategies that can be applied to improve phage utility for current and future applications in food safety.

Isolation, screening and characterization of phage

Bacterial resistance threatens public health due to a lack of novel antibacterial classes since the 21st century. Bacteriophages, the most ubiquitous microorganism on Earth and natural predators of bacteria, have the potential to save the world from the post-antibiotic era. Therefore, phage isolation and characterization are in high demand to find suitable phages for therapeutic and bacterial control applications. The chapter presents brief guidance supported by recommendations on the isolation of phages, and initial screening of phage antimicrobial efficacy, in addition to, conducting comprehensive characterization addressing morphological, biological, genomic, and taxonomic features.

Isolation of bacteriophages infecting Xanthomonas oryzae pv. oryzae and genomic characterization of novel phage vB_XooS_NR08 for biocontrol of bacterial leaf blight of rice

Bacterial leaf blight (BLB) disease of rice caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most destructive diseases worldwide in rice-growing regions. The Ineffectiveness of chemicals in disease management has increased the interest in phage therapy. In this study, we isolated 19 bacteriophages, infecting Xoo, from a rice field, which belonged to phage families Siphoviridae, Myoviridae, and Podoviridae on the basis of electron microscopy. Among 19 phages, Phage vB_XooS_NR08, a member of the Siphoviridae family, expressed antibacterial activity against all Xoo strains tested and did not lyse X. campestris and other unrelated bacterial hosts. Phage NR08 showed more than 80% viability at a temperature range of 4°C–40°C, pH range of 5–9, and direct exposure to sunlight for 2 h, whereas UV light and chemical agents were highly detrimental. In a one-step growth curve, NR08 has a 40-min latent period, followed by a 30-min burst period with a burst size of 250 particle/bacterium. The genome of NR08 is double-stranded DNA, linear having a size of 98,812 bp with a G + C content of 52.9%. Annotation of the whole-genome sequence indicated that NR08 encodes 142 putative open reading frames (ORFs), including one ORF for tRNA, namely, trna1-GlnTTG. Comparative genome analysis of NR08 showed that it shares maximum similarity with Pseudomonas phage PaMx42 (40% query coverage, 95.39% identity, and acc. Length 43,225) and Xanthomonas phage Samson (40% query coverage, 96.68% identity, and acc. Length 43,314). The average alignment percentage (AP) of NR08 with other Xoophages was only 0.32 to 1.25 since the genome of NR08 (98.8 kb) is almost double of most of the previously reported Xoophages (43–47 kb), thus indicating NR08 a novel Xoophage. In in vitro bacterial challenge assay, NR08 showed bacteriostasis up to 24 h and a 99.95% reduction in bacterial growth in 48 h. In rice pot efficacy trials, single-dose treatment of NR08 showed a significant reduction in disease up to 90.23% and 79.27% on 7 and 21 dpi, respectively. However, treatment using 2% skim milk-supplemented phage preparation was significantly less effective as compared to the neat phage preparation. In summary, this study characterized a novel Xoophage having the potential as a biocontrol agent in the mitigation of BLB in rice.

Transmission characteristics of infectious pathogen-laden aerosols in a negative-pressure operating room

The infectious pathogen-laden aerosols generated by infected patients have a significant impact on the safety of surgical staff in highly clean negative-pressure operating rooms. Understanding the transmission characteristics of infectious pathogen-laden aerosols is therefore essential. Therefore, in this study, we conducted experiments in a full-size negative-pressure operating room, and the Phi-X174 phage was used as a bioaerosol release source to investigate the migration and deposition of bioaerosols. The high-concentration spatial regions and high-concentration deposition surfaces of the bioaerosols in the operating room were determined. The results showed that there was a high concentration of bioaerosols in the vortex region below the medical lamp for extended periods of time. Three surgical staff members close to the patient's surgical site had high bioaerosol concentrations at their facial sampling points, with the highest concentration reaching 16,553 PFU/m³ . At the end of bioaerosol generation, 99.9% of the bioaerosols were discharged within 10 mins. The bioaerosol deposition rates per unit area were high at 1.48%/m², 0.46%/m² and 1.79%/m² for the central control panel, storage cabinet, and door surface, respectively. This research can be used as a scientific reference for controlling bioaerosols and determining key disinfection parts in a negative-pressure operating room.

Phenotypic and Genotypic Characterization of Newly Isolated Xanthomonas euvesicatoria-Specific Bacteriophages and Evaluation of Their Biocontrol Potential

Bacteriophages have greatly engaged the attention of scientists worldwide due to the continuously increasing resistance of phytopathogenic bacteria to commercially used chemical pesticides. However, the knowledge regarding phages is still very insufficient and must be continuously expanded. This paper presents the results of the isolation, characterization, and evaluation of the potential of 11 phage isolates as natural predators of a severe phytopathogenic bacterium-Xanthomonas euvesicatoria. Phages were isolated from the rhizosphere of tomato plants with symptoms of bacterial spot. The plaque morphology of all isolates was determined on a X. euvesicatoria lawn via a plaque assay. Three of the isolates were attributed to the family Myoviridae based on TEM micrographs. All phages showed good long-term viability when stored at 4 °C and -20 °C. Three of the phage isolates possessed high stability at very low pH values. Fifty-five-day persistence in a soil sample without the presence of the specific host and a lack of lytic activity on beneficial rhizosphere bacteria were found for the phage isolate BsXeu269p/3. The complete genome of the same isolate was sequenced and analyzed, and, for the first time in this paper, we report a circular representation of a linear but circularly permuted phage genome among known X. euvesicatoria phage genomes.

Biological and Molecular Characterization of the Lytic Bacteriophage SoKa against Pseudomonas syringae pv. syringae, Causal Agent of Citrus Blast and Black Pit in Tunisia

Pseudomonas syringae pv. syringae (Pss), the causal agent of citrus blast and black pit lesion of lemon fruit, continues to cause serious damage in citrus production in Tunisia. Faced with the rapid emergence of the disease and the inefficiency of conventional control methods, an alternative strategy based on the use of bacteriophages was pursued in this study. The lytic Pss bacteriophage SoKa was isolated from soil collected from Tunisian citrus orchards. Analysis of the host range showed that SoKa was able to lyse seven other Pss strains. Interestingly, Pseudomonas syringae pv. porri, pathogenic to leek, could also be infected by SoKa. The activity of SoKa was maintained at pH values between 2 and 10, at temperatures between −80 and 37 °C; the phage could resist UV radiation at an intensity of 320 nm up to 40 min. Whole genome sequencing revealed that the Pseudomonas phage SoKa is a novel phage that belongs to the Bifseptvirus genus of the Autographiviridae family. The absence of virulence proteins and lysogeny-associated proteins encoded on the phage genome, its anti-biofilm activity, and the significant reduction of tissue necrosis in different fruit bioassays make SoKa potentially suitable for use in phage biocontrol.

Future of Bacterial Disease Management in Crop Production

Bacterial diseases are a constant threat to crop production globally. Current management strategies rely on an array of tactics, including improved cultural practices; application of bactericides, plant activators, and biocontrol agents; and use of resistant varieties when available. However, effective management remains a challenge, as the longevity of deployed tactics is threatened by constantly changing bacterial populations. Increased scrutiny of the impact of pesticides on human and environmental health underscores the need for alternative solutions that are durable, sustainable, accessible to farmers, and environmentally friendly. In this review, we discuss the strengths and shortcomings of existing practices and dissect recent advances that may shape the future of bacterial disease management. We conclude that disease resistance through genome modification may be the most effective arsenal against bacterial diseases. Nonetheless, more research is necessary for developing novel bacterial disease management tactics to meet the food demand of a growing global population.

Xanthomonas hortorum - beyond gardens: Current taxonomy, genomics, and virulence repertoires

TAXONOMY

Bacteria; Phylum Proteobacteria; Class Gammaproteobacteria; Order Lysobacterales (earlier synonym of Xanthomonadales); Family Lysobacteraceae (earlier synonym of Xanthomonadaceae); Genus Xanthomonas; Species X. hortorum; Pathovars: pv. carotae, pv. vitians, pv. hederae, pv. pelargonii, pv. taraxaci, pv. cynarae, and pv. gardneri.

HOST RANGE

Xanthomonas hortorum affects agricultural crops, and horticultural and wild plants. Tomato, carrot, artichoke, lettuce, pelargonium, ivy, and dandelion were originally described as the main natural hosts of the seven separate pathovars. Artificial inoculation experiments also revealed other hosts. The natural and experimental host ranges are expected to be broader than initially assumed. Additionally, several strains, yet to be assigned to a pathovar within X. hortorum, cause diseases on several other plant species such as peony, sweet wormwood, lavender, and oak-leaf hydrangea.

EPIDEMIOLOGY AND CONTROL

X. hortorum pathovars are mainly disseminated by infected seeds (e.g., X. hortorum pvs carotae and vitians) or cuttings (e.g., X. hortorum pv. pelargonii) and can be further dispersed by wind and rain, or mechanically transferred during planting and cultivation. Global trade of plants, seeds, and other propagating material constitutes a major pathway for their introduction and spread into new geographical areas. The propagules of some pathovars (e.g., X. horturum pv. pelargonii) are spread by insect vectors, while those of others can survive in crop residues and soils, and overwinter until the following growing season (e.g., X. hortorum pvs vitians and carotae). Control measures against X. hortorum pathovars are varied and include exclusion strategies (i.e., by using certification programmes and quarantine regulations) to multiple agricultural practices such as the application of phytosanitary products. Copper-based compounds against X. hortorum are used, but the emergence of copper-tolerant strains represents a major threat for their effective management. With the current lack of efficient chemical or biological disease management strategies, host resistance appears promising, but is not without challenges. The intrastrain genetic variability within the same pathovar poses a challenge for breeding cultivars with durable resistance.

USEFUL WEBSITES

https://gd.eppo.int/taxon/XANTGA, https://gd.eppo.int/taxon/XANTCR, https://gd.eppo.int/taxon/XANTPE, https://www.euroxanth.eu, http://www.xanthomonas.org, http://www.xanthomonas.org/dokuwiki.

Isolation and characterization of vB_XciM_LucasX, a new jumbo phage that infects Xanthomonas citri and Xanthomonas fuscans

Citrus canker is one of the main bacterial diseases that affect citrus crops and is caused by Xanthomonas citri which affects all citrus species worldwide. New strategies to control citrus canker are necessary and the use of bacteriophages as biocontrol agent could be an alternative. Phages that infect Xanthomonas species have been studied, such as XacN1, a myovirus that infects X. citri. Here we report the isolation and characterization of a new jumbo phage, vb_XciM_LucasX, which infects X. citri and X. fuscans. Transmission electron microscopy allowed classification of LucasX in the Myoviridae family, which was corroborated by its genomic sequencing, annotation, and proteome clustering. LucasX has a 305,651 bp-long dsDNA genome. ORF prediction and annotation revealed 157 genes encoding putative structural proteins such as capsid and tail related proteins and phage assembly associated proteins, however, for most of the structural proteins it was not possible assign specific functions. Its genome encodes several proteins related to DNA replication and nucleotide metabolism, five putative RNA polymerases, at least one homing endonuclease mobile element, a terminase large subunit (TerL), an endolysin and many proteins classified as beneficial to the host. Proteome clustering and phylogeny analyses showed that LucasX is a new jumbo phage having as its closest neighbor the Xanthomonas jumbo phage Xoo-sp14. LucasX presented a burst size of 40 PFU/infected cell of X. citri 306, was completely inactivated at temperatures above 50°C, presented survival lower than 25% after 80 s of exposition to artificial UV light and had practically no tolerance to concentrations above 2.5 g/L NaCl or 40% ethanol. LucasX presented optimum pH at 7 and a broad range of Xanthomonas hosts, infecting twenty-one of the twenty-three strains tested. Finally, the LucasX yield was dependent on the host strain utilized, resulting one order of magnitude higher in X. fuscans C 752 than in X. citri 306, which points out to the possibility of phage yield improvement, an usual challenge for biocontrol purposes.

Challenges for the application of bacteriophages as effective antibacterial agents in the food industry

Food contamination caused by foodborne pathogens is one of the most important concerns in public health worldwide, and accounts for a significant portion of food loss every year. The emergence of antimicrobial resistant bacteria has turned the attention of researchers back to the potential of bacteriophages as antibacterial agents, and their use has been attempted in various pre-and post-harvest food production settings. The application of phage-based antibacterial products has achieved considerable success but a number of technical, environmental and administrative challenges remain unaddressed. In this review, we summarize the current status of bacteriophage application in the food industry. We discuss the obstacles facing the further development of phage-based antibacterial products from the aspects of technology, environmental safety, and administrative policy. We also advance some possible solutions to these challenges. © 2021 Society of Chemical Industry.

The potential of bacteriophages to control Xanthomonas campestris pv. campestris at different stages of disease development

Xanthomonas campestris pv. campestris (Xcc) is a vascular pathogen that invades the xylem of Brassica crops. Current chemical and antibiotics‐based control measures for this bacterium are unsustainable and inefficient. After establishing a representative collection of Xcc strains, we isolated and characterized bacteriophages from two clades of phages to assess their potential in phage‐based biocontrol. The most promising phages, FoX2 and FoX6, specifically recognize (lipo) polysaccharides, associated with the wxc gene cluster, on the surface of the bacterial cell wall. Next, we determined and optimized the applicability of FoX2 and FoX6 in an array of complementary bioassays, ranging from seed decontamination to irrigation‐ and spray‐based applications. Here, an irrigation‐based application showed promising results. In a final proof‐of‐concept, a CaCl₂‐formulated phage cocktail was shown to control the outbreak of Xcc in the open field. This comprehensive approach illustrates the potential of phage biocontrol of black rot disease in Brassica and serves as a reference for the broader implementation of phage biocontrol in integrated pest management strategies.

Bacteriophages Roam the Wheat Phyllosphere

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.

Potential Solutions Using Bacteriophages against Antimicrobial Resistant Bacteria

Bacteriophages are viruses that specifically infect a bacterial host. They play a great role in the modern biotechnology and antibiotic-resistant microbe era. Since the discovery of phages, their application as a control agent has faced challenges that made antibiotics a better fit for combating pathogenic bacteria. Recently, with the novel sequencing technologies providing new insight into the nature of bacteriophages, their application has a second chance to be used. However, novel challenges need to be addressed to provide proper strategies for their practical application. This review focuses on addressing these challenges by initially introducing the nature of bacteriophages and describing the phage-host-dependent strategies for phage application. We also describe the effect of the long-term application of phages in natural environments and other bacterial communities. Overall, this review gathered crucial information for the future application of phages. We predict the use of phages will not be the only control strategy against pathogenic bacteria. Therefore, more studies must be done for low-risk control methods against antimicrobial-resistant bacteria.

A centenary for bacterial spot of tomato and pepper

DISEASE SYMPTOMS

Symptoms include water-soaked areas surrounded by chlorosis turning into necrotic spots on all aerial parts of plants. On tomato fruits, small, water-soaked, or slightly raised pale-green spots with greenish-white halos are formed, ultimately becoming dark brown and slightly sunken with a scabby or wart-like surface.

HOST RANGE

Main and economically important hosts include different types of tomatoes and peppers. Alternative solanaceous and nonsolanaceous hosts include Datura spp., Hyoscyamus spp., Lycium spp., Nicotiana rustica, Physalis spp., Solanum spp., Amaranthus lividus, Emilia fosbergii, Euphorbia heterophylla, Nicandra physaloides, Physalis pubescens, Sida glomerata, and Solanum americanum.

TAXONOMIC STATUS OF THE PATHOGEN

Domain, Bacteria; phylum, Proteobacteria; class, Gammaproteobacteria; order, Xanthomonadales; family, Xanthomonadaceae; genus, Xanthomonas; species, X. euvesicatoria, X. hortorum, X. vesicatoria.

SYNONYMS (NONPREFERRED SCIENTIFIC NAMES)

Bacterium exitiosum, Bacterium vesicatorium, Phytomonas exitiosa, Phytomonas vesicatoria, Pseudomonas exitiosa, Pseudomonas gardneri, Pseudomonas vesicatoria, Xanthomonas axonopodis pv. vesicatoria, Xanthomonas campestris pv. vesicatoria, Xanthomonas cynarae pv. gardneri, Xanthomonas gardneri, Xanthomonas perforans.

MICROBIOLOGICAL PROPERTIES

Colonies are gram-negative, oxidase-negative, and catalase-positive and have oxidative metabolism. Pale-yellow domed circular colonies of 1-2 mm in diameter grow on general culture media.

DISTRIBUTION

The bacteria are widespread in Africa, Brazil, Canada and the USA, Australia, eastern Europe, and south-east Asia. Occurrence in western Europe is restricted.

PHYTOSANITARY CATEGORIZATION

A2 no. 157, EU Annex designation II/A2.

EPPO CODES

XANTEU, XANTGA, XANTPF, XANTVE.

Bacteriophages as an Alternative Method for Control of Zoonotic and Foodborne Pathogens

The global increase in multidrug-resistant infections caused by various pathogens has raised concerns in human and veterinary medicine. This has renewed interest in the development of alternative methods to antibiotics, including the use of bacteriophages for controlling bacterial infections. The aim of this review is to present potential uses of bacteriophages as an alternative to antibiotics in the control of bacterial infections caused by multidrug-resistant bacteria posing a risk to humans, with particular emphasis on foodborne and zoonotic pathogens. A varied therapeutic and immunomodulatory (activation or suppression) effect of bacteriophages on humoral and cellular immune response mechanisms has been demonstrated. The antibiotic resistance crisis caused by global antimicrobial resistance among bacteria creates a compelling need for alternative safe and selectively effective antibacterial agents. Bacteriophages have many properties indicating their potential suitability as therapeutic and/or prophylactic agents. In many cases, bacteriophages can also be used in food quality control against microorganisms such as Salmonella, Escherichia coli, Listeria, Campylobacter and others. Future research will provide potential alternative solutions using bacteriophages to treat infections caused by multidrug-resistant bacteria.

Efficacy of phage therapy in poultry: a systematic review and meta-analysis

The increasing prevalence of antimicrobial resistant bacteria has sparked a renewed interest in alternative bacterial control methods, including bacteriophage administration. In order to determine the overall efficacy of bacteriophage administration for the reduction of bacterial concentrations in poultry, a systematic literature review and a meta-analysis were conducted. The systematic review included studies in which 1) live chickens were challenged with a known quantity of bacteria; and 2) challenged chickens were administered a known quantity of bacteriophages; and 3) concentrations of the challenge bacteria were measured in tissue/fluid samples from both challenged and unchallenged chickens after phage administration; and 4) either standard deviation or standard error was reported. Results of a meta-analysis of the 12 studies included in this review (total inputs: n = 41; total observations: n = 711) indicated that concentrations of challenge bacteria were significantly lower (P < 0.001) in challenged, phage-treated chickens than in challenged, untreated chickens (effect size = -0.82 log₁₀ cfu/g). Phage treatment effects were significantly greater (P < 0.01) in chickens administered phages via feed than in chickens administered phages via drinking water or aerosol spray. No significant differences were observed between subgroups when data were disaggregated by various other experimental characteristics, though some significant differences were observed across subgroups after further disaggregation by sampling time and animal age. As a whole, findings from the systematic review and meta-analysis indicate that phage administration can significantly lower concentrations of targeted bacteria in chickens and that, in some instances, the effect may be greater in the short-term vs. the long-term and in older vs. younger chickens.

Xanthomonas bacteriophages: a review of their biology and biocontrol applications in agriculture

Phytopathogenic bacteria are economically important because they affect crop yields and threaten the livelihoods of farmers worldwide. The genus Xanthomonas is particularly significant because it is associated with some plant diseases that cause tremendous loss in yields of globally essential crops. Current management practices are ineffective, unsustainable and harmful to natural ecosystems. Bacteriophage (phage) biocontrol for plant disease management has been of particular interest from the early nineteenth century to date. Xanthomonas phage research for plant disease management continues to demonstrate promising results under laboratory and field conditions. AgriPhage has developed phage products for the control of Xanthomonas campestris pv. vesicatoria and Xanthomonas citri subsp. citri. These are causative agents for tomato, pepper spot and speck disease as well as citrus canker disease.

Phage-mediated biocontrol is becoming a viable option because phages occur naturally and are safe for disease control and management. Thorough knowledge of biological characteristics of Xanthomonas phages is vital for developing effective biocontrol products. This review covers Xanthomonas phage research highlighting aspects of their ecology, biology and biocontrol applications.

Fate of enteric viruses during leafy greens (romaine lettuce) production using treated municipal wastewater and AP205 bacteriophage as a surrogate

Water reuse programs are being explored to close the gap between supply and demand for irrigation in agriculture. However, these sources could contain hazardous microbial contaminants, and pose risks to public health. This study aimed to grow and irrigate romaine lettuce with inoculated wastewater effluent to track AP205 bacteriophage prevalence through cultivation and post-harvest storage. AP205 is a bacteriophage and was used as a surrogate for enteric viruses. Low and high dosages (mean ± standard deviation) of AP205 at 4.8 ± 0.4 log PFU/mL and 6.6 ± 0.2 log PFU/mL; respectively, were prepared to examine viral load influence on contamination levels. Foliage, leachate, and soil contamination levels were directly related to AP205 concentrations in the effluent. AP205 concentrations increased throughout cultivation for foliage and leachate, suggesting bacteriophage accumulation. During post-harvest storage (14 day at 4 °C), there was a significant decrease in AP205 concentration on the foliage. Results show that wastewater effluents usage for leafy greens cultivation can pose risks to humans and additional steps are required to safely apply wastewater effluents to soils and crops.

Novel Viruses That Lyse Plant and Human Strains of Kosakonia cowanii

Kosakonia cowanii (syn. Enterobacter cowanii) is a highly competitive bacterium that lives with plant, insect, fish, bird, and human organisms. It is pathogenic on some plants and an opportunistic pathogen of human. Nine novel viruses that lyse plant pathogenic strains and/or human strains of K. cowanii were isolated, sequenced, and characterized. Kc166A is a novel kayfunavirus, Kc261 is a novel bonnellvirus, and Kc318 is a new cronosvirus (all Autographiviridae). Kc237 is a new sortsnevirus, but Kc166B and Kc283 are members of new genera within Podoviridae. Kc304 is a new winklervirus, and Kc263 and Kc305 are new myoviruses. The viruses differ in host specificity, plaque phenotype, and lysis kinetics. Some of them should be suitable also as pathogen control agents.

Efficacy of phage therapy in pigs: systematic review and meta-analysis

Limits on the use and efficacy of various antibiotics coupled with negative consumer perception of the practice have together spurred substantial research into compounds that could reduce the use antibiotics to control bacterial diseases in pigs. Bacteriophages are often among such potential compounds, and various groups have examined the efficacy of bacteriophages or bacteriophage products in limiting transmission or colonization of targeted bacteria. The study presented here provides a systematic review of such studies followed by a meta-analysis of aggregated data produced by each study. The data set was limited to inputs (n = 19; 576 total observations) from studies where: 1) live pigs were inoculated with a known quantity of challenge bacteria; 2) challenged animals were treated with a known quantity of phages; 3) concentrations of the challenge bacteria were measured in different tissues/fluids following phage treatment; and 4) SD (or SE to allow calculation of SD) was reported. Concentrations of challenge bacteria were significantly lower in phage-treated pigs versus challenged but untreated pigs (P < 0.0001; effect size = −1.06 1log₁₀ colony-forming units [CFU]/g). The effect size of phage treatment was significantly greater (P < 0.05) in samples collected 48 to 96 h following phage treatment versus those collected ≤ 24 h following phage treatment. Likewise, effect size of phage treatment was significantly greater in piglets versus market-weight pigs. Across observations, phage treatment effect sizes were greatest (P < 0.01) in fecal samples versus ileal or cecal samples. Taken together, these data indicate that phage treatment can significantly reduce the concentrations of targeted bacteria in pigs; scenarios exist, however, where phage treatment could predictably be more or less effective.

Broad host range bacteriophages found in rhizosphere soil of a healthy tomato plant in Bulgaria

The urgent need of research of new approaches to control bacterial disease on economical important crops, focuses our attention on bacteriophages as alternative biocontrol agents. Thus, the purpose of this paper is to present the isolation and initial characterization of three bacteriophages (SfXv124t/1, 2 and 3) isolated from rhizosphere soil of a healthy tomato plant in Bulgaria that are capable to lyse three phytopathogenic bacteria. The initial characterization includes determination of: their host range, plaque morphology, optimal storage temperature of pure phage lysates, their sensitivity to UV light, thermal inactivation, optimal multiplicity of infection (MOI) and virion morphology. The obtained results showed that one of the phage isolates was capable to lyse wild strains from three phytopathogenic bacterial species: Xanthomonas vesicatoria, Xanthomonas euvesicatoria and Xanthomonas gardneri, and the two remaining phages were active against X. vesicatoria and X. euvesicatoria. On X. vesicatoria lawn, the phages produced the same plaque types that differed only in their size. Storage at 4 °C for 26 days did not lead to decrease in phage titer as opposed to storage at 28 °C followed by decrease to varying degree for all three phages. The results obtained after exposure of the phage lysates to sunlight (UVA + B) and UVC light in separate experiments showed that UVC had a potent phagocidal effect as after 50 min of exposure there were no viable phages in the samples. UVA an UVB had lethal effect for two of the phage isolates and absolutely no lethal effect for the third one as after 50 min of exposure to sunlight there was no decrease in the initial phage titer. Phage isolates were tested for their thermal inactivation after incubation of pure phage lysates at three different temperatures: 55 °C, 75 °C and 95 °C for a period of 10 and 30 min. The most lethal temperature turned out to be 95 °C as after 10 min there were no viable phages in the samples. Phage isolate SfXv124t/1 was the most susceptible as its titer decreased by 1 lg after 10 min of incubation at 55 °C and by another 1 lg after 30 min. The most thermally resistant isolate was SfXv124t/3 as its titer remained stable after 30 min of incubation at 55 °C and decreased only by lg after incubation at 75 °C for 10 min. The optimal MOI for SfXv124t/3 was 0,01 (tested range 0,01–100) with maximal phage titer, reported at the 24^th hour of incubation. TEM micrographs of the same isolates reveals that it belongs to family Podoviridae.

Bacteriophage-Mediated Control of Phytopathogenic Xanthomonads: A Promising Green Solution for the Future

Xanthomonads, members of the family Xanthomonadaceae, are economically important plant pathogenic bacteria responsible for infections of over 400 plant species. Bacteriophage-based biopesticides can provide an environmentally friendly, effective solution to control these bacteria. Bacteriophage-based biocontrol has important advantages over chemical pesticides, and treatment with these biopesticides is a minor intervention into the microflora. However, bacteriophages’ agricultural application has limitations rooted in these viruses’ biological properties as active substances. These disadvantageous features, together with the complicated registration process of bacteriophage-based biopesticides, means that there are few products available on the market. This review summarizes our knowledge of the Xanthomonas-host plant and bacteriophage-host bacterium interaction’s possible influence on bacteriophage-based biocontrol strategies and provides examples of greenhouse and field trials and products readily available in the EU and the USA. It also details the most important advantages and limitations of the agricultural application of bacteriophages. This paper also investigates the legal background and industrial property right issues of bacteriophage-based biopesticides. When appropriately applied, bacteriophages can provide a promising tool against xanthomonads, a possibility that is untapped. Information presented in this review aims to explore the potential of bacteriophage-based biopesticides in the control of xanthomonads in the future.

Kiwifruit bacterial canker: an integrative view focused on biocontrol strategies

Phage-based biocontrol strategies can be an effective alternative to control Psa-induced bacterial canker of kiwifruit. The global production of kiwifruit has been seriously affected by Pseudomonas syringae pv. actinidiae (Psa) over the last decade. Psa damages both Actinidia chinensis var. deliciosa (green kiwifruit) but specially the susceptible Actinidia chinensis var. chinensis (gold kiwifruit), resulting in severe economic losses. Treatments for Psa infections currently available are scarce, involving frequent spraying of the kiwifruit plant orchards with copper products. However, copper products should be avoided since they are highly toxic and lead to the development of bacterial resistance to this metal. Antibiotics are also used in some countries, but bacterial resistance to antibiotics is a serious worldwide problem. Therefore, it is essential to develop new approaches for sustainable agriculture production, avoiding the emergence of resistant Psa bacterial strains. Attempts to develop and establish highly accurate approaches to combat and prevent the occurrence of bacterial canker in kiwifruit plants are currently under study, using specific viruses of bacteria (bacteriophages, or phages) to eliminate the Psa. This review discusses the characteristics of Psa-induced kiwifruit canker, Psa transmission pathways, prevention and control, phage-based biocontrol strategies as a new approach to control Psa in kiwifruit orchards and its advantages over other therapies, together with potential ways to bypass phage inactivation by abiotic factors.

Harnessing the plant microbiome to promote the growth of agricultural crops

The rhizosphere microbiome is composed of diverse microbial organisms, including archaea, viruses, fungi, bacteria as well as eukaryotic microorganisms, which occupy a narrow region of soil directly associated with plant roots. The interactions between these microorganisms and the plant can be commensal, beneficial or pathogenic. These microorganisms can also interact with each other, either competitively or synergistically. Promoting plant growth by harnessing the soil microbiome holds tremendous potential for providing an environmentally friendly solution to the increasing food demands of the world's rapidly growing population, while also helping to alleviate the associated environmental and societal issues of large-scale food production. There recently have been many studies on the disease suppression and plant growth promoting abilities of the rhizosphere microbiome; however, these findings largely have not been translated into the field. Therefore, additional research into the dynamic interactions between crop plants, the rhizosphere microbiome and the environment are necessary to better guide the harnessing of the microbiome to increase crop yield and quality. This review explores the biotic and abiotic interactions that occur within the plant's rhizosphere as well as current agricultural practices, and how these biotic and abiotic factors, as well as human practices, impact the plant microbiome. Additionally, some limitations, safety considerations, and future directions to the study of the plant microbiome are discussed.

Bacteriophage-Mediated Reduction of Bacterial Speck on Tomato Seedlings

Background: One crucial first step in bacteriophage therapy is choosing a phage to apply, which involves screening for effectiveness in a meaningful way. Increasingly, research suggests that in vitro tests of phage-mediated bacterial lysis poorly translate to in planta effectiveness. Materials and Methods: We tested a seedling-based method for rapidly screening phage effectiveness in vivo. In three trials, phages were prophylactically applied to tomato seedlings in sterile conical tubes before flooding with the bacterial pathogen Pseudomonas syringae pv. tomato DC3000. We recorded seedling disease progression and quantified endpoint bacteria and phage densities. Results: Phages replicated in all trials, but reduction of disease symptoms and endpoint P. syringae density varied across trials with different application densities. Conclusions: This resource-efficient method rapidly identified an effective phage and application density to mitigate disease on seedlings. We propose that this method could be used to screen candidate phages before testing in agricultural conditions.

Encapsulation in alginate-polymers improves stability and allows controlled release of the UFV-AREG1 bacteriophage

The bacteriophage UFV-AREG1 was used as a model organism to evaluate the encapsulation via extrusion using different hydrocolloids. Pure alginate [0.75%, 1.0%, 1.5% and 2.0% (m/v)] and mixtures of alginate [0.75% or 1.0% (m/v)] with carrageenan [1.25% (m/v)], chitosan [0.5% (m/v)], or whey protein [1.5% (m/v)] were used to produce bacteriophage-loaded beads. The encapsulating solutions presented flow behavior of non-Newtonian pseudoplastic fluids and the concentration of hydrocolloid did not influence (p > 0.05) the morphology of the beads, except for alginate-chitosan solutions, which presented the higher flow consistency index (K) and the lower flow behavior index (n). The encapsulation efficiency was about 99% and the confocal photomicrography of the encapsulated bacteriophages labeled with fluorescein isothiocyanate showed homogenous distribution of the viral particles within the beads. The phages remained viable in the beads of alginate-whey protein even when submitted to pH 2.5 for 2 h. Beads incubated directly in simulated intestinal fluid (pH 6.8) resulted in a minimal of 50% release of the UFV-AREG1 phages after 5 min, even when previously submitted to the simulated gastric fluid (pH 2.5). Encapsulation enabled phages to remain viable under refrigeration for five months. Encapsulated UFV-AREG1 phages were sensitive to dehydration, suggesting the need for protective agents. In this study, for the first-time bacteriophages were encapsulated in alginate-carrageenan beads, as well as alginate-chitosan as a bead-forming hydrocolloid. In addition, a novel procedure for encapsulating bacteriophages in alginate-whey protein was proposed. The assembled system showed efficiency in the encapsulation of UFV-AREG1 bacteriophages using different hydrocolloids and has potential to be used for the entrapment of a variety of bioactive compounds.

Assessment of toxicity and persistence of Yersinia entomophaga and its Yen-Tc associated toxin

BACKGROUND

The insect-pathogenic bacterium Yersinia entomophaga MH96 is currently under development as a microbial pesticide active against various pasture and crop pests such as the diamondback moth Plutella xylostella and the cotton bollworm Helicoverpa armigeria. To enable nonrestricted field trials of Y. entomophaga MH96, information on the persistence and nontarget effects of the bacterium and its Yen-Tc proteinaceous toxin are required.

RESULTS

The Y. entomophaga Yen-Tc associated toxin was found to have limited persistence on foliage and is inactivated by UV light. The Yen-Tc was rapidly degraded in ovine or bovine rumen fluid or the intestinal fluid of H. armigera. In H. armigera an intestinal protein of >50 kDa was found to cleave the Yen-Tc bond. Assessment of Y. entomophaga persistence on foliage and in soil found that after 42 days the bacterium could not be detected in soil at 20% soil moisture content but persisted for 72 days at 30-40% soil moisture. Nontarget effects of Y. entomophaga towards earthworms found that the bacterium afforded no adverse effects on worm growth or behavior. A summary of historic Yen-Tc and Y. entomophaga persistence and toxicity data is presented.

CONCLUSION

The bacterium Y. entomophaga and its Yen-Tc associated toxin have limited persistence in the environment, with the Yen-Tc being susceptible to UV inactivation and proteolytic degradation, and the bacterium persisting longer in soil of a high moisture content. © 2020 Society of Chemical Industry.

Food-Grade Microscale Dispersion Enhances UV Stability and Antimicrobial Activity of a Model Bacteriophage (T7) for Reducing Bacterial Contamination (Escherichia coli) on the Plant Surface

To reduce the use of conventional chemical pesticides, naturally occurring biopesticides such as bacteriophages have emerged as a promising solution, but effectiveness of these biopesticides can be limited because of their UV and desiccation instability. This study developed a biopolymer formulation to improve the phage stability, enhance the antimicrobial activity of phages, and prevent bacterial contaminations on a leaf surface in the presence of UV-A. The mixture of microscale polydopamine (PDA) particles with whey protein isolate (WPI)-glycerol formulation was effective for enhancing the stability of T7 phages in spraying solution and on a model leaf surface during 4 h exposure to UV-A and 1 h exposure to the simulated sunlight, respectively. The T7 phages incorporated with the biopolymer formulation effectively improved the antimicrobial activity of phages, as exhibited by greater than 2.8 log reduction in model bacteria Escherichia coli BL21 and also illustrated by significant potential of this formulation to prevent bacterial contamination and colonization of the plant surface. In summary, this study illustrates that phages combined with a biopolymer formulation can be an effective approach for a field deployable biocontrol solution of bacterial contamination in the agricultural environment.

Phage biocontrol to combat Pseudomonas syringae pathogens causing disease in cherry

Bacterial canker is a major disease of Prunus species, such as cherry (Prunus avium). It is caused by Pseudomonas syringae pathovars, including P. syringae pv. syringae (Pss) and P. syringae pv. morsprunorum race 1 (Psm1) and race 2 (Psm2). Concerns over the environmental impact of, and the development of bacterial resistance to, traditional copper controls calls for new approaches to disease management. Bacteriophage-based biocontrol could provide a sustainable and natural alternative approach to combat bacterial pathogens. Therefore, seventy phages were isolated from soil, leaf and bark of cherry trees in six locations in the south east of England. Subsequently, their host range was assessed against strains of Pss, Psm1 and Psm2. While these phages lysed different Pss, Psm and some other P. syringae pathovar isolates, they did not infect beneficial bacteria such as Pseudomonas fluorescens. A subset of thirteen phages were further characterized by genome sequencing, revealing five distinct clades in which the phages could be clustered. No known toxins or lysogeny-associated genes could be identified. Using bioassays, selected phages could effectively reduce disease progression in vivo, both individually and in cocktails, reinforcing their potential as biocontrol agents in agriculture.

A Hundred Years of Bacteriophages: Can Phages Replace Antibiotics in Agriculture and Aquaculture?

Agriculture, together with aquaculture, supplies most of the foodstuffs required by the world human population to survive. Hence, bacterial diseases affecting either agricultural crops, fish, or shellfish not only cause large economic losses to producers but can even create food shortages, resulting in malnutrition, or even famine, in vulnerable populations. Years of antibiotic use in the prevention and the treatment of these infections have greatly contributed to the emergence and the proliferation of multidrug-resistant bacteria. This review addresses the urgent need for alternative strategies for the use of antibiotics, focusing on the use of bacteriophages (phages) as biocontrol agents. Phages are viruses that specifically infect bacteria; they are highly host-specific and represent an environmentally-friendly alternative to antibiotics to control and kill pathogenic bacteria. The information evaluated here highlights the effectiveness of phages in the control of numerous major pathogens that affect both agriculture and aquaculture, with special emphasis on scientific and technological aspects still requiring further development to establish phagotherapy as a real universal alternative to antibiotic treatment.

Effectiveness of Bacteriophage Therapy in Field Conditions and Possible Future Applications

BACKGROUND

Bacteriophages are viruses, which are obligate parasites of specific bacteria for the completion of their lifecycle. Bacteriophages could be the possible alternative to antibioticresistant bacterial diseases. With this objective, extensive research in different fields is published which are discussed in this article.

METHODS

After a review of bacteriophage therapy, bacteriophages were found to be effective against the multidrug-resistant bacteria individually or synergistically with antibiotics. They were found to be more effective, even better than the bacteria in the development of a vaccine.

RESULTS

Apart from the bacteriophages, their cell contents like Lysin enzymes were found equally very much effective. Only the major challenge faced in phage therapy was the identification and characterization of bacteria-specific phages due to the wide genetic diversity of bacterial populations. Similarly, the threshold level of bacteriophages to act effectively was altered by ultraviolet radiation and heat exposure.

CONCLUSION

Thus, bacteriophage therapy offers promising alternatives in the treatment of antibioticresistant bacteria in different fields. However, their effectiveness is determined by a triad of bacteriophages (type & quantity), host (bacteria) and environmental factors.

Bacteriophage Usage for Bacterial Disease Management and Diagnosis in Plants

In nature, plants are always under the threat of pests and diseases. Pathogenic bacteria are one of the major pathogen types to cause diseases in diverse plants, resulting in negative effects on plant growth and crop yield. Chemical bactericides and antibiotics have been used as major approaches for controlling bacterial plant diseases in the field or greenhouse. However, the appearance of resistant bacteria to common antibiotics and bactericides as well as their potential negative effects on environment and human health demands bacteriologists to develop alternative control agents. Bacteriophages, the viruses that can infect and kill only target bacteria very specifically, have been demonstrated as potential agents, which may have no negative effects on environment and human health. Many bacteriophages have been isolated against diverse plant-pathogenic bacteria, and many studies have shown to efficiently manage the disease development in both controlled and open conditions such as greenhouse and field. Moreover, the specificity of bacteriophages to certain bacterial species has been applied to develop detection tools for the diagnosis of plant-pathogenic bacteria. In this paper, we summarize the promising results from greenhouse or field experiments with bacteriophages to manage diseases caused by plant-pathogenic bacteria. In addition, we summarize the usage of bacteriophages for the specific detection of plant-pathogenic bacteria.