Molecular Epidemiology of Xanthomonas euvesicatoria Strains from the Balkan Peninsula Revealed by a New Multiple-Locus Variable-Number Tandem-Repeat Analysis Scheme

Genetic Structure and TALome Analysis Highlight a High Level of Diversity in Burkinabe Xanthomonas Oryzae pv. oryzae Populations

Bacterial Leaf Blight of rice (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major threat for food security in many rice growing countries including Burkina Faso, where the disease was first reported in the 1980's. In line with the intensification of rice cultivation in West-Africa, BLB incidence has been rising for the last 15 years. West-African strains of Xoo differ from their Asian counterparts as they (i) are genetically distant, (ii) belong to new races and, (iii) contain reduced repertoires of Transcription Activator Like (TAL) effector genes. In order to investigate the evolutionary dynamics of Xoo populations in Burkina Faso, 177 strains were collected from 2003 to 2018 in three regions where BLB is occurring. Multilocus VNTR Analysis (MLVA-14) targeting 10 polymorphic loci discriminated 24 haplotypes and showed that Xoo populations were structured according to their geographical localization and year of collection. Considering their major role in Xoo pathogenicity, we assessed the TAL effector repertoires of the 177 strains upon RFLP-based profiling. Surprisingly, an important diversity was revealed with up to eight different RFLP patterns. Finally, comparing neutral vs. tal effector gene diversity allowed to suggest scenarios underlying the evolutionary dynamics of Xoo populations in Burkina Faso, which is key to rationally guide the deployment of durably resistant rice varieties against BLB in the country.

Genomic and phenotypic insight into Xanthomonas vesicatoria strains with different aggressiveness on tomato

Xanthomonas vesicatoria is one of the causal agents of bacterial spot, a disease that seriously affects the production of tomato (Solanum lycopersicum) and pepper (Capsicum annum) worldwide. In Argentina, bacterial spot is found in all tomato producing areas, with X. vesicatoria being one of the main species detected in the fields. Previously, we isolated three X. vesicatoria strains BNM 208, BNM 214, and BNM 216 from tomato plants with bacterial spot, and found they differed in their ability to form biofilm and in their degree of aggressiveness. Here, the likely causes of those differences were explored through genotypic and phenotypic studies. The genomes of the three strains were sequenced and assembled, and then compared with each other and also with 12 other publicly available X. vesicatoria genomes. Phenotypic characteristics (mainly linked to biofilm formation and virulence) were studied in vitro. Our results show that the differences observed earlier between BNM 208, BNM 214, and BNM 216 may be related to the structural characteristics of the xanthan gum produced by each strain, their repertoire of type III effectors (T3Es), the presence of certain genes associated with c-di-GMP metabolism and type IV pili (T4P). These findings on the pathogenicity mechanisms of X. vesicatoria could be useful for developing bacterial spot control strategies aimed at interfering with the infection processes.

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.

Integrating Science on Xanthomonas and Xylella for Integrated Plant Disease Management

Present, emerging or re-emerging plant diseases due to infection by bacteria of the Lysobacteraceae (syn: Xanthomonadaceae) family are continually challenging food security and cause significant losses to the economies of European countries each year [...].

Whole-Genome Resources and Species-Level Taxonomic Validation of 89 Plant-Pathogenic Xanthomonas Strains Isolated from Various Host Plants

Bacterial spot disease caused by Xanthomonas spp. is a global threat to tomato and pepper plants. A recent classification of these pathogens indicated the need for a diverse dataset of whole-genome resources. We report whole-genome resources of 89 Xanthomonas strains isolated from Canada (n = 44), the United States (n = 29), Argentina (n = 4), Brazil (n = 3), Costa Rica (n = 3), New Zealand (n = 1), Australia (n = 1), Mexico (n = 1), Taiwan (n = 1), Thailand (n = 1), and unknown (n = 1). Of these strains, 48 were previously identified to species-level based on nongenome-based approaches while 41 strains were classified only at the genus level. The average coverage of the sequencing reads was 103×. The draft genome sizes ranged from 4.53 to 5.46 Mbp with a G + C content of 63.53 to 67.78% and comprised 4,233-5,178 protein-coding sequences. Using average nucleotide identity (ANI) and genome-based DNA-DNA hybridization (gDDH) values, the taxonomic classifications were validated for 38 of the 48 strains previously assigned to species level using other methods. Ten strains previously identified as Xanthomonas campestris, X. axonopodis, X. vasicola, and X. arboricola were incorrectly assigned, and new species-level delineations are proposed. Data from ANI, gDDH, and pangenome phylogeny of shared protein families were used to assign the 41 strains, previously identified only to genus level, into five distinct species: X. euvesicatoria (pv. euvesicatoria or pv. perforans), X. hortorum pv. gardneri, X. vesicatoria, X. campestris, and X. arboricola. These 89 whole-genome sequences of Xanthomonas strains, the majority (49.4%) of which are from Canada, could be useful resources in our understanding of the global population structure and evolution of these pathogens.

Antibacterial Activity of Copper Nanoparticles against Xanthomonas campestris pv. vesicatoria in Tomato Plants

Copper-based bactericides have appeared as a new tool in crop protection and offer an effective solution to combat bacterial resistance. In this work, two copper nanoparticle products that were previously synthesized and evaluated against major bacterial and fungal pathogens were tested on their ability to control the bacterial spot disease of tomato. Growth of Xanthomonas campestris pv. vesicatoria, the causal agent of the disease, was significantly suppressed by both nanoparticles, which had superior function compared to conventional commercial formulations of copper. X-ray fluorescence spectrometry measurements in tomato leaves revealed that bioavailability of copper is superior in the case of nanoparticles compared to conventional formulations and is dependent on synthesis rather than size. This is the first report correlating bioavailability of copper to nanoparticle efficacy.

Trends in Molecular Diagnosis and Diversity Studies for Phytosanitary Regulated Xanthomonas

Bacteria in the genus Xanthomonas infect a wide range of crops and wild plants, with most species responsible for plant diseases that have a global economic and environmental impact on the seed, plant, and food trade. Infections by Xanthomonas spp. cause a wide variety of non-specific symptoms, making their identification difficult. The coexistence of phylogenetically close strains, but drastically different in their phenotype, poses an added challenge to diagnosis. Data on future climate change scenarios predict an increase in the severity of epidemics and a geographical expansion of pathogens, increasing pressure on plant health services. In this context, the effectiveness of integrated disease management strategies strongly depends on the availability of rapid, sensitive, and specific diagnostic methods. The accumulation of genomic information in recent years has facilitated the identification of new DNA markers, a cornerstone for the development of more sensitive and specific methods. Nevertheless, the challenges that the taxonomic complexity of this genus represents in terms of diagnosis together with the fact that within the same bacterial species, groups of strains may interact with distinct host species demonstrate that there is still a long way to go. In this review, we describe and discuss the current molecular-based methods for the diagnosis and detection of regulated Xanthomonas, taxonomic and diversity studies in Xanthomonas and genomic approaches for molecular diagnosis.