A Community-Curated DokuWiki Resource on Diagnostics, Diversity, Pathogenicity, and Genetic Control of Xanthomonads.

Xanthomonads, including Xanthomonas and Xylella species, constitute a large and significant group of economically and ecologically important plant pathogens. Up-to-date knowledge of these pathogens and their hosts is essential for the development of suitable control measures. Traditional review articles or book chapters have inherent limitations, including static content and rapid obsolescence. To address these challenges, we have developed a Web-based knowledge platform dedicated to xanthomonads, inspired by the concept of living systematic reviews. This platform offers a dynamic resource that encompasses bacterial virulence factors, plant resistance genes, and tools for diagnostics and genetic diversity studies. Our goal is to facilitate access for newcomers to the field, provide continuing education opportunities for students, assist plant protection services with diagnostics, provide valuable information to breeders on sources of resistance and breeding targets, and offer comprehensive expert knowledge to other stakeholders interested in plant-pathogenic xanthomonads. This resource is available for queries and updates at https://euroxanth.ipn.pt. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Comparative genomics to examine the endophytic potential of Pantoea agglomerans DAPP-PG 734.

Pantoea agglomerans DAPP-PG 734 was isolated as endophyte from knots (tumors) caused by Pseudomonas savastanoi pv. savastanoi DAPP-PG 722 in olive trees. To understand the plant pathogen-endophyte interaction on a genomic level, the whole genome of P. agglomerans DAPP-PG 734 was sequenced and annotated. The complete genome had a total size of 5'396'424 bp, containing one circular chromosome and four large circular plasmids. The aim of this study was to identify genomic features that could play a potential role in the interaction between P. agglomerans DAPP-PG 734 and P. savastanoi pv. savastanoi DAPP-PG 722. For this purpose, a comparative genomic analysis between the genome of P. agglomerans DAPP-PG 734 and those of related Pantoea spp. was carried out. In P. agglomerans DAPP-PG 734, gene clusters for the synthesis of the Hrp-1 type III secretion system (T3SS), type VI secretion systems (T6SS) and autoinducer, which could play an important role in a plant-pathogenic community enhancing knot formation in olive trees, were identified. Additional gene clusters for the biosynthesis of two different antibiotics, namely dapdiamide E and antibiotic B025670, which were found in regions between integrative conjugative elements (ICE), were observed. The in-depth analysis of the whole genome suggested a characterization of the P. agglomerans DAPP-PG 734 isolate as endophytic bacterium with biocontrol activity rather than as a plant pathogen.

Complete Genome and Plasmid Sequence Data of Three Strains of Xanthomonas arboricola pv. corylina, the Bacterium Responsible for Bacterial Blight of Hazelnut.

Xanthomonas arboricola pv. corylina is the causal agent of bacterial blight of hazelnut. The bacterium has been listed as an A2 quarantine pathogen in Europe since 1978 and on the regulated non-quarantine pest list since 2019. Three isolates from various geographic regions and isolated at different times were sequenced using a hybrid approach with short- and long-read technologies to generate closed genome and plasmid sequences in order to better understand the biology of this pathogen.

Taxonomic Refinement of Xanthomonas arboricola.

Xanthomonas arboricola comprises a number of economically important fruit tree pathogens classified within different pathovars. Dozens of nonpathogenic and taxonomically unvalidated strains are also designated as X. arboricola, leading to a complicated taxonomic status in the species. In this study, we have evaluated the whole-genome resources of all available Xanthomonas spp. strains designated as X. arboricola in the public databases to refine the members of the species based on DNA similarity indexes and core genome-based phylogeny. Our results show that, of the nine validly described pathovars within X. arboricola, pathotype strains of seven pathovars are taxonomically genuine, belonging to the core clade of the species regardless of their pathogenicity on the host of isolation (thus the validity of pathovar status). However, strains of X. arboricola pv. guizotiae and X. arboricola pv. populi do not belong to X. arboricola because of the low DNA similarities between the type strain of the species and the pathotype strains of these two pathovars. Thus, we propose to elevate the two pathovars to the rank of a species as X. guizotiae sp. nov. with the type strain CFBP 7408T and X. populina sp. nov. with the type strain CFBP 3123T. In addition, other mislabeled strains of X. arboricola were scattered within Xanthomonas spp. that belong to previously described species or represent novel species that await formal description.

Xanthomonas hydrangeae sp. nov., a novel plant pathogen isolated from Hydrangea arborescens.

This paper describes a novel species isolated in 2011 and 2012 from nursery-grown Hydrangea arborescens cultivars in Flanders, Belgium. After 4 days at 28 °C, the strains yielded yellow, round, convex and mucoid colonies. Pathogenicity of the strains was confirmed on its isolation host, as well as on Hydrangea quercifolia. Analysis using MALDI-TOF MS identified the Hydrangea strains as belonging to the genus Xanthomonas but excluded them from the species Xanthomonas hortorum. A phylogenetic tree based on gyrB confirmed the close relation to X. hortorum. Three fatty acids were dominant in the Hydrangea isolates: anteiso-C15 : 0, iso-C15 : 0 and summed feature 3 (C16 : 1 ω7c/C16 : 1 ω6c). Unlike X. hortorum pathovars, the Hydrangea strains were unable to grow in the presence of lithium chloride and could only weakly utilize d-fructose-6-PO4 and glucuronamide. Phylogenetic characterization based on multilocus sequence analysis and phylogenomic characterization revealed that the strains are close to, yet distinct from, X. hortorum. The genome sequences of the strains had average nucleotide identity values ranging from 94.35-95.19 % and in silico DNA-DNA hybridization values ranging from 55.70 to 59.40 % to genomes of the X. hortorum pathovars. A genomics-based loop-mediated isothermal amplification assay was developed which was specific to the Hydrangea strains for its early detection. A novel species, Xanthomonas hydrangeae sp. nov., is proposed with strain LMG 31884T (=CCOS 1956T) as the type strain.

Bradyrhizobium ivorense sp. nov. as a potential local bioinoculant for Cajanus cajan cultures in Côte d'Ivoire.

For many smallholder farmers of Sub-Saharan Africa, pigeonpea (Cajanus cajan) is an important crop to make ends meet. To ascertain the taxonomic status of pigeonpea isolates of Côte d'Ivoire previously identified as bradyrhizobia, a polyphasic approach was applied to strains CI-1BT, CI-14A, CI-19D and CI-41S. Phylogeny of 16S ribosomal RNA (rRNA) genes placed these nodule isolates in a separate lineage from current species of the B. elkanii super clade. In phylogenetic analyses of single and concatenated partial dnaK, glnII, gyrB, recA and rpoB sequences, the C. cajan isolates again formed a separate lineage, with strain CI-1BT sharing the highest sequence similarity (95.2 %) with B. tropiciagri SEMIA 6148T. Comparative genomic analyses corroborated the novel species status, with 86 % ANIb and 89 % ANIm as the highest average nucleotide identity (ANI) values with B. elkanii USDA 76T. Although CI-1BT, CI-14A, CI-19D and CI-41S shared similar phenotypic and metabolic properties, growth of CI-41S was slower in/on various media. Symbiotic efficacy varied significantly between isolates, with CI-1BT and CI-41S scoring on the C. cajan 'Light-Brown' landrace as the most and least proficient bacteria, respectively. Also proficient on Vigna radiata (mung bean), Vigna unguiculata (cowpea, niébé) and additional C. cajan cultivars, CI-1BT represents a potential bioinoculant adapted to local soil conditions and capable of fostering the growth of diverse legume crops in Côte d'Ivoire. Given the data presented here, we propose the 19 C. cajan isolates to belong to a novel species called Bradyrhizobium ivorense sp. nov., with CI-1BT (=CCOS 1862T=CCMM B1296T) as a type strain.

Xanthomonas euroxanthea sp. nov., a new xanthomonad species including pathogenic and non-pathogenic strains of walnut.

We describe a novel species isolated from walnut (Juglans regia) which comprises non-pathogenic and pathogenic strains on walnut. The isolates, obtained from a single ornamental walnut tree showing disease symptoms, grew on yeast extract-dextrose-carbonate agar as mucoid yellow colonies characteristic of Xanthomonas species. Pathogenicity assays showed that while strain CPBF 424T causes disease in walnut, strain CPBF 367 was non-pathogenic on walnut leaves. Biolog GEN III metabolic profiles disclosed some differences between strains CPBF 367 and CPBF 424T and other xanthomonads. Multilocus sequence analysis with seven housekeeping genes (fyuA, gyrB, rpoD, atpD, dnaK, efp, glnA) grouped these strains in a distinct cluster from Xanthomonas arboricola pv. juglandis and closer to Xanthomonas prunicola and Xanthomonas arboricola pv. populi. Average nucleotide identity (ANI) analysis results displayed similarity values below 93 % to X. arboricola strains. Meanwhile ANI and digital DNA-DNA hybridization similarity values were below 89 and 50 % to non-arboricola Xanthomonas strains, respectively, revealing that they do not belong to any previously described Xanthomonas species. Furthermore, the two strains show over 98 % similarity to each other. Genomic analysis shows that strain CPBF 424T harbours a complete type III secretion system and several type III effector proteins, in contrast with strain CPBF 367, shown to be non-pathogenic in plant bioassays. Taking these data altogether, we propose that strains CPBF 367 and CPBF 424T belong to a new species herein named Xanthomonas euroxanthea sp. nov., with CPBF 424T (=LMG 31037T=CCOS 1891T=NCPPB 4675T) as the type strain.

Isolation and Identification of Actinomycetes Strains from Switzerland and their Biotechnological Potential.

Actinomycetes strains isolated from different habitats in Switzerland were investigated for production of antibacterial and antitumoral compounds. Based on partial 16S rRNA gene sequences, the isolated strains were identified to genus level. Streptomyces as the largest genus of Actinobacteriawas isolated the most frequently. A screening assay using the OmniLog instrument was established to facilitate the detection of active compounds from actinomycetes. Extracts prepared from the cultivated strains able to inhibit Staphylococcus aureusand Escherichia coliwere further analysed by HPLC and MALDI-TOF MS to identify the produced antibiotics. In this study, the bioactive compound echinomycin was identified from two isolated Streptomycesstrains. Natural compounds similar to TPU-0037-C, azalomycin F4a 2-ethylpentyl ester, a derivative of bafilomycin A1, milbemycin-α8 and dihydropicromycin were detected from different isolated Streptomyces strains. Milbemycin-α8 showed cytotoxic activity against HT-29 colon cancer cells. The rare actinomycete,Micromonospora sp. Stup16_C148 produced a compound that matches with the antibiotic bottromycin A2. The draft genome sequence from Actinokineospora strain B136.1 was determined using Illumina and nanopore-based technologies. The isolated strain was not able to produce antibacterial compounds under standard cultivation conditions. The antiSMASH bioinformatics analyses of the genome from strain B136.1 identified biosynthetic gene clusters with identity values between 4% to 90% to known gene clusters encoding antibiotics. The combinations of cultivation conditions, screening assays, analytical methods and genome mining are important tools to characterize strains of actinomycetes for the identification of their potential to produce natural compounds with antimicrobial activity.

Comparative genomics and pathogenicity potential of members of the Pseudomonas syringae species complex on Prunus spp.

BACKGROUND: Diseases on Prunus spp. have been associated with a large number of phylogenetically different pathovars and species within the P. syringae species complex. Despite their economic significance, there is a severe lack of genomic information of these pathogens. The high phylogenetic diversity observed within strains causing disease on Prunus spp. in nature, raised the question whether other strains or species within the P. syringae species complex were potentially pathogenic on Prunus spp. RESULTS: To gain insight into the genomic potential of adaptation and virulence in Prunus spp., a total of twelve de novo whole genome sequences of P. syringae pathovars and species found in association with diseases on cherry (sweet, sour and ornamental-cherry) and peach were sequenced. Strains sequenced in this study covered three phylogroups and four clades. These strains were screened in vitro for pathogenicity on Prunus spp. together with additional genome sequenced strains thus covering nine out of thirteen of the currently defined P. syringae phylogroups. Pathogenicity tests revealed that most of the strains caused symptoms in vitro and no obvious link was found between presence of known virulence factors and the observed pathogenicity pattern based on comparative genomics. Non-pathogenic strains were displaying a two to three times higher generation time when grown in rich medium. CONCLUSION: In this study, the first set of complete genomes of cherry associated P. syringae strains as well as the draft genome of the quarantine peach pathogen P. syringae pv. persicae were generated. The obtained genomic data were matched with phenotypic data in order to determine factors related to pathogenicity to Prunus spp. Results of this study suggest that the inability to cause disease on Prunus spp. in vitro is not the result of host specialization but rather linked to metabolic impairments of individual strains.

Frankia canadensis sp. nov., isolated from root nodules of Alnus incana subspecies rugosa.

Strain ARgP5T, an actinobacterium isolated from a root nodule present on an Alnus incana subspecies rugosa shrub growing in Quebec City, Canada, was the subject of polyphasic taxonomic studies to clarify its status within the genus Frankia. 16S rRNA gene sequence similarities and ANI values between ARgP5T and type strains of species of the genus Frankiawith validly published names were 98.8 and 82 % or less, respectively. The in silico DNA G+C content was 72.4 mol%. ARgP5T is characterised by the presence of meso-A2pm, galactose, glucose, mannose, rhamnose (trace), ribose and xylose as whole-organism hydrolysates; MK-9(H8) as predominant menaquinone; diphosphatidylglycerol, phosphatidylinositol and phosphatidylglycerol as polar lipids and iso-C16 : 0 and C17 : 1ω8c as major fatty acids. The proteomic results confirmed the distinct position of ARgP5T from its closest neighbours in Frankiacluster 1. ARgP5T was found to be infective on two alder (Alnus glutinosa and Alnusalnobetula subsp. crispa) and on one bayberry (Morella pensylvanica) species and to fix nitrogen in symbiosis and in pure culture. On the basis of phylogenetic (16S rRNA gene sequence), genomic, proteomic and phenotypic results, strain ARgP5T (=DSM 45898=CECT 9033) is considered to represent a novel species within the genus Frankia for which the name Frankia canadensis sp. nov., is proposed.

Role of the type VI secretion systems during disease interactions of Erwinia amylovora with its plant host.

BACKGROUND: Type VI secretion systems (T6SS) are widespread among Gram-negative bacteria and have a potential role as essential virulence factors or to maintain symbiotic interactions. Three T6SS gene clusters were identified in the genome of E. amylovora CFBP 1430, of which T6SS-1 and T6SS-3 represent complete T6SS machineries, while T6SS-2 is reduced in its gene content. RESULTS: To assess the contribution of T6SSs to virulence and potential transcriptomic changes of E. amylovora CFBP 1430, single and double mutants in two structural genes were generated for T6SS-1 and T6SS-3. Plant assays showed that mutants in T6SS-3 were slightly more virulent in apple shoots while inducing less disease symptoms on apple flowers, indicating that T6SSs have only a minor effect on virulence of E. amylovora CFBP 1430. The mutations led under in vitro conditions to the differential expression of type III secretion systems, iron acquisition, chemotaxis, flagellar, and fimbrial genes. Comparison of the in planta and in vitro transcriptome data sets revealed a common differential expression of three processes and a set of chemotaxis and motility genes. Additional experiments proved that T6SS mutants are impaired in their motility. CONCLUSION: These results suggest that the deletion of T6SSs alters metabolic and motility processes. Nevertheless, the difference in lesion development in apple shoots and flower necrosis of T6SS mutants was indicative that T6SSs influences the disease progression and the establishment of the pathogen on host plants.

Ribosomal protein biomarkers provide root nodule bacterial identification by MALDI-TOF MS.

Accurate identification of soil bacteria that form nitrogen-fixing associations with legume crops is challenging given the phylogenetic diversity of root nodule bacteria (RNB). The labor-intensive and time-consuming 16S ribosomal RNA (rRNA) sequencing and/or multilocus sequence analysis (MLSA) of conserved genes so far remain the favored molecular tools to characterize symbiotic bacteria. With the development of mass spectrometry (MS) as an alternative method to rapidly identify bacterial isolates, we recently showed that matrix-assisted laser desorption ionization (MALDI) time-of-flight (TOF) can accurately characterize RNB found inside plant nodules or grown in cultures. Here, we report on the development of a MALDI-TOF RNB-specific spectral database built on whole cell MS fingerprints of 116 strains representing the major rhizobial genera. In addition to this RNB-specific module, which was successfully tested on unknown field isolates, a subset of 13 ribosomal proteins extracted from genome data was found to be sufficient for the reliable identification of nodule isolates to rhizobial species as shown in the putatively ascribed ribosomal protein masses (PARPM) database. These results reveal that data gathered from genome sequences can be used to expand spectral libraries to aid the accurate identification of bacterial species by MALDI-TOF MS.

Phylogeography and population structure of the biologically invasive phytopathogen Erwinia amylovora inferred using minisatellites.

Erwinia amylovora causes a major disease of pome fruit trees worldwide, and is regulated as a quarantine organism in many countries. While some diversity of isolates has been observed, molecular epidemiology of this bacterium is hindered by a lack of simple molecular typing techniques with sufficiently high resolution. We report a molecular typing system of E. amylovora based on variable number of tandem repeats (VNTR) analysis. Repeats in the E. amylovora genome were identified with comparative genomic tools, and VNTR markers were developed and validated. A Multiple-Locus VNTR Analysis (MLVA) was applied to E. amylovora isolates from bacterial collections representing global and regional distribution of the pathogen. Based on six repeats, MLVA allowed the distinction of 227 haplotypes among a collection of 833 isolates of worldwide origin. Three geographically separated groups were recognized among global isolates using Bayesian clustering methods. Analysis of regional outbreaks confirmed presence of diverse haplotypes but also high representation of certain haplotypes during outbreaks. MLVA analysis is a practical method for epidemiological studies of E. amylovora, identifying previously unresolved population structure within outbreaks. Knowledge of such structure can increase our understanding on how plant diseases emerge and spread over a given geographical region.

Dickeya solani sp. nov., a pectinolytic plant-pathogenic bacterium isolated from potato (Solanum tuberosum).

Pectinolytic bacteria have been recently isolated from diseased potato plants exhibiting blackleg and slow wilt symptoms found in a number of European countries and Israel. These Gram-reaction-negative, motile, rods were identified as belonging to the genus Dickeya, previously the Pectobacterium chrysanthemi complex (Erwinia chrysanthemi), on the basis of production of a PCR product with the pelADE primers, 16S rRNA gene sequence analysis, fatty acid methyl esterase analysis, the production of phosphatases and the ability to produce indole and acids from α-methylglucoside. Differential physiological assays used previously to differentiate between strains of E. chrysanthemi, showed that these isolates belonged to biovar 3. Eight of the isolates, seven from potato and one from hyacinth, were analysed together with 21 reference strains representing all currently recognized taxa within the genus Dickeya. The novel isolates formed a distinct genetic clade in multilocus sequence analysis (MLSA) using concatenated sequences of the intergenic spacer (IGS), as well as dnaX, recA, dnaN, fusA, gapA, purA, rplB, rpoS and gyrA. Characterization by whole-cell MALDI-TOF mass spectrometry, pulsed field gel electrophoresis after digestion of whole-genome DNA with rare-cutting restriction enzymes, average nucleotide identity analysis and DNA-DNA hybridization studies, showed that although related to Dickeya dadantii, these isolates represent a novel species within the genus Dickeya, for which the name Dickeya solani sp. nov. (type strain IPO 2222(T) = LMG25993(T) = NCPPB4479(T)) is proposed.

Draft genome sequence of Xanthomonas arboricola pv. pruni PVCT 262.1 isolated from Prunus dulcis in italy.

Here, we report the draft genome sequence of Xanthomonas arboricola pv. pruni strain PVCT 262.1, isolated from almond (Prunus dulcis) leaves affected by bacterial spots in Italy in 2020. Genome size is 5,076,418 bp and G+C content is 65.44%. A total of 4,096 protein-coding genes and 92 RNAs are predicted.

High-Quality Draft Genome Sequence of Streptomyces albidoflavus CCOS 2040, Isolated from a Swiss Soil Sample.

Here, we report the high-quality draft genome sequence of the actinomycete Streptomyces albidoflavus CCOS 2040, isolated from a Swiss soil sample. The genome contains 7,136,301 bp with 73.35% GC content. In total, 22 biosynthetic gene clusters, including polyketides and terpenes, were predicted within the sequenced genome.

Specific and sensitive detection tools for Xanthomonas arboricola pv. corylina, the causal agent of bacterial blight of hazelnut, developed with comparative genomics.

Xanthomonas arboricola pv. corylina (Xac; formerly Xanthomonas campestris pv. corylina) is the causal agent of the bacterial blight of hazelnuts, a devastating disease of trees in plant nurseries and young orchards. Currently, there are no PCR assays to distinguish Xac from all other pathovars of X. arboricola. A comparative genomics approach with publicly available genomes of Xac was used to identify unique sequences, conserved across the genomes of the pathogen. We identified a 2,440 bp genomic region that was unique to Xac and designed identification and detection systems for conventional PCR, qPCR (SYBR® Green and TaqMan™), and loop-mediated isothermal amplification (LAMP). All PCR assays performed on genomic DNA isolated from eight X. arboricola pathovars and closely related bacterial species confirmed the specificity of designed primers. These new multi-platform molecular diagnostic tools may be used by plant clinics and researchers to detect and identify Xac in pure cultures and hazelnut tissues rapidly and accurately.

Race-specific genotypes of Pseudomonas syringae pv. tomato are defined by the presence of mobile DNA elements within the genome.

Pseudomonas syringae pv. tomato is the causal agent of bacterial speck of tomato, an important disease that results in severe crop production losses worldwide. Currently, two races within phylogroup 01a (PG01a) are described for this pathogen. Race 0 strains have avirulence genes for the expression of type III system-associated effectors AvrPto1 and AvrPtoB, that are recognized and targeted by the effector-triggered immunity in tomato cultivars having the pto race-specific resistance gene. Race 1 strains instead lack the avrPto1 and avrPtoB genes and are therefore capable to aggressively attack all tomato cultivars. Here, we have performed the complete genome sequencing and the analysis of P. syringae pv. tomato strain DAPP-PG 215, which was described as a race 0 strain in 1996. Our analysis revealed that its genome comprises a 6.2 Mb circular chromosome and two plasmids (107 kb and 81 kb). The results indicate that the strain is phylogenetically closely related to strains Max13, K40, T1 and NYS-T1, all known race 1 strains. The chromosome of DAPP-PG 215 encodes race 1-associated genes like avrA and hopW1 and lacks race 0-associated genes like hopN1, giving it a race 1 genetic background. However, the genome harbors a complete ortholog of avrPto1, which allows the strain to display a race 0 phenotype. Comparative genomics with several PG01a genomes revealed that mobile DNA elements are rather involved in the evolution of the two different races.

Assessment of transcriptional reprogramming of lettuce roots in response to chitin soil amendment.

Chitin soil amendment is known to improve soil quality, plant growth and stress resilience, but the underlying mechanisms are not well understood. In this study, we monitored chitin's effect on lettuce physiology every two weeks through an eight-week growth period, analyzed the early transcriptional reprogramming and related metabolomic changes of lettuce, in response to crab chitin treatment in peat-based potting soil. In commercial growth conditions, chitin amendment still promoted lettuce growth, increased chlorophyll content, the number of leaves and crop head weight from week six. The flavonoid content in lettuce leaves was altered as well, showing an increase at week two but a decrease from week six. Transcriptomic analysis showed that over 300 genes in lettuce root were significantly differentially expressed after chitin soil treatment. Gene Ontology-term (GO) enrichment analysis revealed statistical overrepresentation of GO terms linked to photosynthesis, pigment metabolic process and phenylpropanoid metabolic process. Further analysis of the differentially expressed genes (DEGs) showed that the flavonoid pathway was mostly upregulated whereas the bifurcation of upstream phenylpropanoid pathway towards lignin biosynthesis was mostly downregulated. Metabolomic analysis revealed the upregulation of salicylic acid, chlorogenic acid, ferulic acid, and p-coumaric acid in chitin-treated lettuce seedlings. These phenolic compounds (PCs) mainly influence the phenylpropanoid biosynthesis pathway and may play important roles in plant defense reactions. Our results suggest that chitin soil amendments might activate induced resistance by priming lettuce plants and promote lettuce growth via transcriptional changes.