Genomic and pathogenic properties of Pseudomonas syringae pv. syringae strains isolated from apricot in East Azerbaijan province, Iran

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.

Diversity of pathogenic Pseudomonas isolated from citrus in Tunisia

The damages observed in Tunisian citrus orchards have prompted studies on the Pseudomonas spp. responsible for blast and black pit. Prospective orchards between 2015 and 2017 showed that the diseases rapidly spread geographically and to new cultivars. A screening of Pseudomonas spp. isolated from symptomatic trees revealed their wide diversity according to phylogenetic analysis of their housekeeping rpoD and cts genes. The majority of strains were affiliated to Pseudomonas syringae pv. syringae (Phylogroup PG02b), previously described in Tunisia. However, they exhibited various BOX-PCR fingerprints and were not clonal. This work demonstrated, for the first time in Tunisia, the involvement of Pseudomonas cerasi (PG02a) and Pseudomonas congelans (PG02c). The latter did not show significant pathogenicity on citrus, but was pathogenic on cantaloupe and active for ice nucleation that could play a role in the disease. A comparative phylogenetic study of citrus pathogens from Iran, Montenegro and Tunisia revealed that P. syringae (PG02b) strains are closely related but again not clonal. Interestingly P. cerasi (PG02a) was isolated in two countries and seems to outspread. However, its role in the diseases is not fully understood and it should be monitored in future studies. The diversity of pathogenic Pseudomonas spp. and the extension of the diseases highlight that they have become complex and synergistic. It opens questions about which factors favor diseases and how to fight against them efficiently and with sustainable means.

Detection of the Plant Pathogen Pseudomonas Syringae pv. Lachrymans on Antibody-Modified Gold Electrodes by Electrochemical Impedance Spectroscopy

The present work describes an impedimetric immunosensor for Pseudomonas syringae pv. lachrymans (Psl) detection. This pathogen infects many crop species causing considerable yield losses, thus fast and cheap detection method is in high demand. In the assay, the gold disc electrode was modified with 4-aminothiophenol (4-ATP), glutaraldehyde (GA), and anti-Psl antibodies, and free-sites were blocked with bovine serum albumin (BSA). Sensor development was characterized by cyclic voltammetry (CV) and antigen detection by electrochemical impedance spectroscopy (EIS) measurements. Seven analyzed strains of Psl were verified as positive by the reference method (PCR) and this immunoassay, proving sensor specificity. Label-free electrochemical detection was in the linear range 1 × 10³–1.2 × 10⁵ CFU/mL (colony-forming unit) with an R² coefficient of 0.992 and a detection limit (LOD) of 337 CFU/mL. The sensor did not interfere with negative probes like buffers and other bacteria. The assay was proven to be fast (10 min detection) and easy in preparation. The advantage was the simplicity and availability of the verified analyte (whole bacteria) as the method does not require sample pretreatment (e.g., DNA isolation). EIS biosensing technique was chosen as one of the simplest and most sensitive with the least destructive influence on the probes compared to other electrochemical methods.

Efficiency of Phage φ6 for Biocontrol of Pseudomonas syringae pv. syringae: An in Vitro Preliminary Study

Pseudomonas syringae is a plant-associated bacterial species that has been divided into more than 60 pathovars, with the Pseudomonas syringae pv. syringae being the main causative agent of diseases in a wide variety of fruit trees. The most common treatments for biocontrol of P. syringae pv. syringae infections has involved copper derivatives and/or antibiotics. However, these treatments should be avoided due to their high toxicity to the environment and promotion of bacterial resistance. Therefore, it is essential to search for new approaches for controlling P. syringae pv. syringae. Phage therapy can be a useful alternative tool to the conventional treatments to control P. syringae pv. syringae infections in plants. In the present study, the efficacy of bacteriophage (or phage) φ6 (a commercially available phage) was evaluated in the control of P. syringae pv. syringae. As the plants are exposed to the natural variability of physical and chemical parameters, the influence of pH, temperature, solar radiation and UV-B irradiation on phage φ6 viability was also evaluated in order to develop an effective phage therapy protocol. The host range analysis revealed that the phage, besides its host (P. syringae pv. syringae), also infects the Pseudomonas syringae pv. actinidiae CRA-FRU 12.54 and P. syringae pv. actinidiae CRA-FRU 14.10 strains, not infecting strains from the other tested species. Both multiplicities of infection (MOIs) tested, 1 and 100, were effective to inactivate the bacterium, but the MOI 1 (maximum reduction of 3.9 log CFU/mL) was more effective than MOI 100 (maximum reduction of 2.6 log CFU/mL). The viability of phage φ6 was mostly affected by exposure to UV-B irradiation (decrease of 7.3 log PFU/mL after 8 h), exposure to solar radiation (maximum reduction of 2.1 PFU/mL after 6 h), and high temperatures (decrease of 8.5 PFU/mL after 6 days at 37 °C, but a decrease of only 2.0 log PFU/mL after 67 days at 15 °C and 25 °C). The host range, high bacterial control and low rates of development of phage-resistant bacterial clones (1.20 × 10-3) suggest that this phage can be used to control P. syringae pv. syringae infections in plants, but also to control infections by P. syringae pv. actinidiae, the causal agent of bacterial canker of kiwifruit. Although the stability of phage φ6 was affected by UV-B and solar radiation, this can be overcome by the application of phage suspensions at the end of the day or at night.

Prospecting Plant Growth-Promoting Bacteria Isolated from the Rhizosphere of Sugarcane Under Drought Stress

In the rhizosphere, the soil bacteria and the plants are closely related, with the plant-associated microbiota playing an important role in promoting plant growth under both normal and stress conditions. In this study, the cultivable bacteria in the sugarcane rhizosphere under different levels of drought stress were characterized and screened for plant growth activities. The results suggested that the microbial community associated with the sugarcane rhizosphere was strongly affected by drought, but some important genera of bacteria such as Arthrobacter, Pseudomonas, Microbacterium, and Bacillus remained present during the entire experiment, indicating the adaptability of these organisms and their importance in the rhizosphere community. Many isolates exhibited positive results for one or more plant growth activity, and they were also capable of growing under simulated drought stress, suggesting that the microorganisms isolated from the sugarcane rhizosphere could be explored for uses such as biofertilizers or biocontrol agents in agriculture.