Important Plant Pathogenic Bacteria Research Articles

Complete Circularized Genome Resources for Xylella fastidiosa subsp. sandyi Strains CO33 and CFBP8478

Xylella fastidiosa ( Xf) is a vascular phytopathogenic bacterium native to the Americas, known for causing severe diseases and significant economic losses in important crops. In Europe, Xf is considered a quarantine pathogen. Since its first detection in 2013 in Italy, mandatory surveys to search for Xf across Europe have revealed the presence of three Xf subspecies ( fastidiosa, multiplex, and pauca) in different outbreaks occurring in France, Spain, and Portugal. Xf subspecies sandyi and morus have not been associated with epidemic outbreaks in Europe; however, subspecies sandyi has been detected in intercepted plants imported from Costa Rica and Honduras. By combining data from the Oxford Nanopore Technologies and Illumina sequencing platforms, we obtained complete genomes for Xf strains CO33 and CFBP8478. Both strains belong to the subspecies sandyi and were isolated from coffee plants intercepted in Europe that were imported from Costa Rica. These two genome resources increase the scarce number of Xf genomes available belonging to the subspecies sandyi, which is crucial for comparative genomic analysis and population studies of this important plant-pathogenic bacterium. [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 .

Whole-genome sequence of a novel lytic bacteriophage infecting Clavibacter michiganensis subsp. michiganensis from Turkey.

Clavibacter michiganensis subsp. michiganensis (Cmm) is an important plant-pathogenic bacterium that causes canker and wilt diseases. Biological control of the disease with bacteriophages is an alternative to conventional methods. In this study, Phage33 infecting Cmm was characterized based on morphological and genomic properties. Morphological characteristics such as shape and size were investigated using electron microscopy. The whole genome was sequenced using the Illumina Novaseq 6000 platform and the sequence was assembled and annotated. VICTOR and VIRIDIC were used for determining the phylogeny and comparing viral genomes, respectively. Electron microscopy showed that Phage33 has an icosahedral head with a diameter of ~55 nm and a long, thin, non-contractile tail ~169 nm in length. The genome of Phage33 is 56 324 bp in size, has a GC content of 62.49 % and encodes 67 open reading frames. Thirty-seven ORFs showed high homology to functionally annotated bacteriophage proteins in the NCBI database. The remaining 30 ORFs were identified as hypothetical with unknown functions. The genome contains no antimicrobial resistance, no lysogenicity and no virulence signatures, suggesting that it is a suitable candidate for biocontrol agents. The results of a blastn search showed similarity to the previously reported Xylella phage Sano, with an average nucleotide sequence identity of 92.37 % and query coverage of 91 %. This result was verified using VICTOR and VIRIDIC analysis, and suggests that Phage33 is a new member of the genus Sanovirus under the class Caudoviricetes.

Transcriptional profiling of Xanthomonas campestris pv. campestris in viable but nonculturable state

BackgroundXanthomonas campestris pv. campestris (Xcc) is an important seed-borne plant pathogenic bacteria that can cause a serious threat to cruciferous crops. Bacteria can enter into the viable but non-culturable (VBNC) state under stress conditions, and cause potential risks to agricultural production because the VBNC bacterial cells will evade culture-based detection. However, little is known about the mechanism of VBNC. Our previous study showed that Xcc could be induced into VBNC state by copper ion (Cu2+).ResultsHere, RNA-seq was performed to explore the mechanism of VBNC state. The results indicated that expression profiling was changed dramatically in the different VBNC stages (0 d, 1 d, 2 d and 10 d). Moreover, metabolism related pathways were enriched according to COG, GO and KEGG analysis of differentially expressed genes (DEGs). The DEGs associated with cell motility were down-regulated, whereas pathogenicity related genes were up-regulated. This study revealed that the high expression of genes related to stress response could trigger the active cells to VBNC state, while the genes involved in transcription and translation category, as well as transport and metabolism category, were ascribed to maintaining the VBNC state.ConclusionThis study summarized not only the related pathways that might trigger and maintain VBNC state, but also the expression profiling of genes in different survival state of bacteria under stress. It provided a new kind of gene expression profile and new ideas for studying VBNC state mechanism in X. campestris pv. campestris.

Antibacterial Activity of Different Strains of the Genus Trichoderma

The main pathogens causing plant diseases are bacteria, viruses, and fungi. A number of strategies are usually used for plant protection and control of pathogenic microorganisms. The main interest of researchers is focused on the development of alternative synthetic chemicals to control bacterial diseases of plants. Among such approaches, biological control of bacterial diseases using agents such as antagonistic fungi and some other microorganisms is considered to be one of the most effective strategies. Species of the genus Trichoderma are known for their antagonistic activity against plant pathogenic fungi and bacteria and can be an effective safety strategy to control them. An important peculiarity of fungi of this genus is their ability to inhibit target pathogenic organisms without harming non-target (beneficial) microorganisms. The study of the antagonistic activity of fungi of the genus Trichoderma was conducted mainly against pathogenic fungi of agricultural plants. At the same time, the study of the antibacterial activity of fungi of this genus has attracted much less attention. Therefore, the aim of our work was to determine the antibacterial activity of microscopic fungi of the genus Trichoderma against test cultures of bacteria causing pathogenesis of agricultural plants. Methods. The objects of research were 100 fungal strains of the genus Trichoderma and six economically important plant pathogenic bacteria such as Pseudomonas syringae UCM В-1027Т, Pseudomonas fluorescens 8573, Pectobacterium carotovorum UCM В-1095T, Xanthomonas campestris pv. campestris UCM В-1049, Clavibacter michiganensis subsp. michiganensis 102, and Agrobacterium tumefaciens UCM В-1000. Cultures of the studied fungi were grown on potato-dextrose agar. The antagonistic activity of fungi of the genus Trichoderma against plant pathogenic bacteria was studied using the conventional method of diffusion in agar and method of dual culture. The antibacterial activity of culture filtrates of Trichoderma strains was evaluated via the zone of growth inhibition of plant pathogenic bacteria. The percentages of growth inhibition of plant pathogenic bacteria were calculated, and the antagonistic activity of strains was concluded on the basis of the obtained values. Results. In general, the studied Trichoderma strains had the antagonistic activity against plant pathogenic bacteria. Using method of diffusion in agar, it was shown that among the 100 studied Trichoderma strains, 12 had the effect of growth inhibition (bacteriostatic effect) of all six studied species of pathogenic bacteria; 20 strains inhibited the growth of five ones, 36 — four, 12 — three, and 7 — of two strains. The strains with a wide spectrum of antibacterial activity were studied by the double culture method. This made it possible to demonstrate the high selectivity of the antagonistic effect of Trichoderma strains on individual test cultures of phytopathogenic bacteria. For example, strain No7A inhibited the growth of C. michiganensis subsp. michiganensis 102 by 47% and the growth of P. syringae UCM B-1027T by 30%, while the zones of growth inhibition of these test cultures, determined by the method of diffusion in agar, were 5 and 6 mm, respectively. Conclusions. The obtained results indicated the potential and overall ability of Trichoderma strains to biologically control bacterial pathogens. The most promising for the use of plant pathogenic bacteria as agents for biocontrol were strains F-60, 1515, and 320, which were active against all studied bacteria. Such strains may have the potential as a preventive biocontrol agent of plant pathogens with a wide range of action. On the other hand, Trichoderma strains with high activity against certain pathogens may have the potential to be used as a control agent against a specific target pathogen.

Synthetic Peptides against Plant Pathogenic Bacteria.

The control of plant diseases caused by bacteria that seriously compromise crop productivity around the world is still one of the most important challenges in food security. Integrated approaches for disease control generally lack plant protection products with high efficacy and low environmental and health adverse effects. Functional peptides, either from natural sources or synthetic, are considered as novel candidates to develop biopesticides. Synthetic peptides can be obtained based on the structure of natural compounds or de novo designed, considering the features of antimicrobial peptides. The advantage of this approach is that analogues can be conveniently prepared, enabling the identification of sequences with improved biological properties. Several peptide libraries have been designed and synthetized, and the best sequences showed strong bactericidal activity against important plant pathogenic bacteria, with a good profile of biodegradability and low toxicity. Among these sequences, there are bacteriolytic or antibiofilm peptides that work against the target bacteria, plant defense elicitor peptides, and multifunctional peptides that display several of these properties. Here, we report the research performed by our groups during the last twenty years, as well as our ongoing work. We also highlight those peptides that can be used as candidates to develop novel biopesticides, and the main challenges and prospects.

Whole genome resequencing and complementation tests reveal candidate loci contributing to bacterial wilt (Ralstonia sp.) resistance in tomato

Tomato (Solanum lycopersicum) is one of the most economically important vegetable crops worldwide. Bacterial wilt (BW), caused by the Ralstonia solanacearum species complex, has been reported as the second most important plant pathogenic bacteria worldwide, and likely the most destructive. Extensive research has identified two major loci, Bwr-6 and Bwr-12, that contribute to resistance to BW in tomato; however, these loci do not completely explain resistance. Segregation of resistance in two populations that were homozygous dominant or heterozygous for all Bwr-6 and Bwr-12 associated molecular markers suggested the action of one or two resistance loci in addition to these two major QTLs. We utilized whole genome sequence data analysis and pairwise comparison of six BW resistant and nine BW susceptible tomato lines to identify candidate genes that, in addition to Bwr-6 and Bwr-12, contributed to resistance. Through this approach we found 27,046 SNPs and 5975 indels specific to the six resistant lines, affecting 385 genes. One sequence variant on chromosome 3 captured by marker Bwr3.2dCAPS located in the Asc (Solyc03g114600.4.1) gene had significant association with resistance, but it did not completely explain the resistance phenotype. The SNP associated with Bwr3.2dCAPS was located within the resistance gene Asc which was inside the previously identified Bwr-3 locus. This study provides a foundation for further investigations into new loci distributed throughout the tomato genome that could contribute to BW resistance and into the role of resistance genes that may act against multiple pathogens.

Genetic differentiation of Xylella fastidiosa following the introduction into Taiwan.

The economically important plant pathogen Xylella fastidiosa has been reported in multiple regions of the globe during the last two decades, threatening a growing list of plants. Particularly, X. fastidiosa subspecies fastidiosa causes Pierce’s disease (PD) of grapevines, which is a problem in the USA, Spain, and Taiwan. In this work, we studied PD-causing subsp. fastidiosa populations and compared the genome sequences of 33 isolates found in Central Taiwan with 171 isolates from the USA and two from Spain. Phylogenetic relationships, haplotype networks, and genetic diversity analyses confirmed that subsp. fastidiosa was recently introduced into Taiwan from the Southeast USA (i.e. the PD-I lineage). Recent core-genome recombination events were detected among introduced subsp. fastidiosa isolates in Taiwan and contributed to the development of genetic diversity. The genetic diversity observed includes contributions through recombination from unknown donors, suggesting that higher genetic diversity exists in the region. Nevertheless, no recombination event was detected between X. fastidiosa subsp. fastidiosa and the endemic sister species Xylella taiwanensis , which is the causative agent of pear leaf scorch disease. In summary, this study improved our understanding of the genetic diversity of an important plant pathogenic bacterium after its invasion to a new region.

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.

Comparative genomics and pangenome-oriented studies reveal high homogeneity of the agronomically relevant enterobacterial plant pathogen Dickeya solani

BackgroundDickeya solani is an important plant pathogenic bacterium causing severe losses in European potato production. This species draws a lot of attention due to its remarkable virulence, great devastating potential and easier spread in contrast to other Dickeya spp. In view of a high need for extensive studies on economically important soft rot Pectobacteriaceae, we performed a comparative genomics analysis on D. solani strains to search for genetic foundations that would explain the differences in the observed virulence levels within the D. solani population.ResultsHigh quality assemblies of 8 de novo sequenced D. solani genomes have been obtained. Whole-sequence comparison, ANIb, ANIm, Tetra and pangenome-oriented analyses performed on these genomes and the sequences of 14 additional strains revealed an exceptionally high level of homogeneity among the studied genetic material of D. solani strains. With the use of 22 genomes, the pangenome of D. solani, comprising 84.7% core, 7.2% accessory and 8.1% unique genes, has been almost completely determined, suggesting the presence of a nearly closed pangenome structure. Attribution of the genes included in the D. solani pangenome fractions to functional COG categories showed that higher percentages of accessory and unique pangenome parts in contrast to the core section are encountered in phage/mobile elements- and transcription- associated groups with the genome of RNS 05.1.2A strain having the most significant impact. Also, the first D. solani large-scale genome-wide phylogeny computed on concatenated core gene alignments is herein reported.ConclusionsThe almost closed status of D. solani pangenome achieved in this work points to the fact that the unique gene pool of this species should no longer expand. Such a feature is characteristic of taxa whose representatives either occupy isolated ecological niches or lack efficient mechanisms for gene exchange and recombination, which seems rational concerning a strictly pathogenic species with clonal population structure. Finally, no obvious correlations between the geographical origin of D. solani strains and their phylogeny were found, which might reflect the specificity of the international seed potato market.

The essential genome of Ralstonia solanacearum

Ralstonia solanacearum is a scientifically/economically important plant pathogenic bacterium. The plant disease caused by R. solanacearum causes huge economic losses, and efficient control measures for the disease remain limited. To gain a better system-level understanding of R. solanacearum, we generated a near-saturated transposon insertion library of R. solanacearum GMI1000 with approximately 240,000 individual insertion mutants. Transposon sequencing (Tn-seq) allowed the mapping of 70.44%–80.96% of all potential insertion sites of the mariner C9 transposase in the genome of R. solanacearum and the identification of 465 genes essential for the growth of R. solanacearum in rich medium. Functional and comparative analyses of essential genes revealed that many basic physiological and biochemical processes such as transcription differ between R. solanacearum and other bacteria. A comparative analysis of essential genes also suggested that 34 genes might be essential only for Ralstonia group bacteria, whereas another 16 essential genes are unique to Ralstonia, providing high-priority candidate targets for developing R. solanacearum-specific drugs.

Weeds as alternate hosts of Xanthomonas euvesicatoria pv. euvesicatoria and X. campestris pv. campestris in vegetable-growing fields in the state of Pernambuco, Brazil

Plant pathogenic Xanthomonas species attack a wide range of agriculture crops and is capable of surviving on weeds. In this study, Xanthomonas strains obtained from weeds grown withing vegetable crop fields in the state of Pernambuco, Northeast Brazil, were identified. Bacterial colonies resembling Xanthomonas were obtained from Aeollanthus suaveolens (strain CCRMXe03), Amaranthus lividus (CCRMXe01 and CCRMXe02), Sida glomerata (CCRMXe04), and Emilia fosbergii (CCRMXe04). All weeds but E. fosbergii exhibited lesions on the leaves. Phylogenetic analysis of the gyrB and rpoD genes and PCR-specific assays allowed to identify X. euvesicatoria pv. euvesicatoria (CCRMXe01, CCRMXe02, CCRMXe03, and CCRMXe04) and X. campestris pv. campestris (CCRMXcc371). All strains but CCRMXe03 were pathogenic to its host of origin. All X. euvesicatoria pv. euvesicatoria strains were pathogenic to leaves and fruits of tomato and bell pepper. Two strains, CCRMXe03 and CCRMXe04, were capable of inducing soft rot in fruits. Amylolytic activity was found in all strains and two strains (CCRMXe03 and CCRMXe04) degraded pectate. Strain CCRMXcc371 was pathogenic to cabbage, kale, cauliflower, and broccoli. This work provides new knowledge of hosts for two important plant pathogenic bacteria for vegetable crops.

Complete Circularized Genome Data of Two Spanish strains of Xylella fastidiosa (IVIA5235 and IVIA5901) Using Hybrid Assembly Approaches.

Xylella fastidiosa is an economically important plant pathogenic bacterium of global importance associated, since 2013, with a devastating epidemic in olive trees in Italy. Since then, several outbreaks of this pathogen have been reported in other European member countries including Spain, France, and Portugal. In Spain, the three major subspecies (subsp. fastidiosa, multiplex, and pauca) of the bacterium have been detected in the Balearic Islands, but only subspecies multiplex in the mainland (Alicante). We present the first complete genome sequences of two Spanish strains: X. fastidiosa subsp. fastidiosa IVIA5235 from Mallorca and X. fastidiosa subsp. multiplex IVIA5901 from Alicante, using Oxford Nanopore and Illumina sequence reads, and two hybrid approaches for genome assembly. These completed genomes will provide a resource to better understand the biology of these X. fastidiosa strains.

Emergence of a Plant Pathogen in Europe Associated with Multiple Intercontinental Introductions.

Pathogen introductions have led to numerous disease outbreaks in naive regions of the globe. The plant pathogen Xylella fastidiosa has been associated with various recent epidemics in Europe affecting agricultural crops, such as almond, grapevine, and olive, but also endemic species occurring in natural forest landscapes and ornamental plants. We compared whole-genome sequences of X. fastidiosa subspecies multiplex from America and strains associated with recent outbreaks in southern Europe to infer their likely origins and paths of introduction within and between the two continents. Phylogenetic analyses indicated multiple introductions of X. fastidiosa subspecies multiplex into Italy, Spain, and France, most of which emerged from a clade with limited genetic diversity with a likely origin in California, USA. The limited genetic diversity observed in X. fastidiosa subspecies multiplex strains originating from California is likely due to the clade itself being an introduction from X. fastidiosa subspecies multiplex populations in the southeastern United States, where this subspecies is most likely endemic. Despite the genetic diversity found in some areas in Europe, there was no clear evidence of recombination occurring among introduced X. fastidiosa strains in Europe. Sequence type taxonomy, based on multilocus sequence typing (MLST), was shown, at least in one case, to not lead to monophyletic clades of this pathogen; whole-genome sequence data were more informative in resolving the history of introductions than MLST data. Although additional data are necessary to carefully tease out the paths of these recent dispersal events, our results indicate that whole-genome sequence data should be considered when developing management strategies for X. fastidiosa outbreaks.IMPORTANCEXylella fastidiosa is an economically important plant-pathogenic bacterium that has emerged as a pathogen of global importance associated with a devastating epidemic in olive trees in Italy associated with X. fastidiosa subspecies pauca and other outbreaks in Europe, such as X. fastidiosa subspecies fastidiosa and X. fastidiosa subspecies multiplex in Spain and X. fastidiosa subspecies multiplex in France. We present evidence of multiple introductions of X. fastidiosa subspecies multiplex, likely from the United States, into Spain, Italy, and France. These introductions illustrate the risks associated with the commercial trade of plant material at global scales and the need to develop effective policy to limit the likelihood of pathogen pollution into naive regions. Our study demonstrates the need to utilize whole-genome sequence data to study X. fastidiosa introductions at outbreak stages, since a limited number of genetic markers does not provide sufficient phylogenetic resolution to determine dispersal paths or relationships among strains that are of biological and quarantine relevance.

ITRAQ-based proteomic analyses of the plant-pathogenic bacterium Acidovorax citrulli during entrance into and resuscitation from the viable but nonculturable state

Acidovorax citrulli, the causal agent of bacterial fruit blotch (BFB) disease, infects cucurbit crops including watermelon and melon. This bacterium can enter the viable but nonculturable (VBNC) state following exposure to copper sulfate. Moreover, copper-induced VBNC A. citrulli cells can be resuscitated by EDTA. In this study, isobaric tag for relative and absolute quantification (iTRAQ) was used to compare protein profiles of VBNC cells, resuscitated cells at different stages and log-phase cells of the A. citrulli model strain AAC00-1. A total of 2672 proteins were identified, with 60 being differentially abundant in VBNC cells compared with log-phase cells, and 469 being differentially abundant in resuscitated cells compared with VBNC cells. Proteins involved in the arginine and proline metabolism pathway and degradation of aromatic compounds could be important for the VBNC cells. In the early resuscitation process, proteins associated with carbon metabolism, and degradation of naphthalene and aromatic compounds were significantly enriched, while proteins involved in oxidative phosphorylation, bacterial chemotaxis, ABC transporters and quorum sensing were significantly enriched at the late resuscitation stages. This is the first study reporting thorough protein profile analyses of VBNC and resuscitating cells of a plant-pathogenic bacterium. Biological significanceThe VBNC state is a dormant-like condition that was reported to occur in many bacterial species, upon facing a variety of environmental stresses. Acidovorax citrulli is a seed borne pathogenic bacterium that threatens cucurbit production worldwide. Moreover, A. citrulli can enter into the VBNC state after treatment of copper sulfate, thus increasing its survival and dissemination probabilities. This study enriches our understanding of the mechanisms of entrance into and resuscitation from the VBNC state of this important plant-pathogenic bacterium. This knowledge could be exploited in the future to develop novel approaches to interfere with these processes, thus contributing to a more efficient management of this pathogen. In a broader perspective, the knowledge emerging from this study has implications to the general understanding of the VBNC state in bacteria.

Ralstonia solanacearum Species Complex: A Quick Diagnostic Guide

Ralstonia solanacearum (Smith 1896) Yabuuchi et al. 1996 is ranked second among the top 10 most economically important plant pathogenic bacteria. The soil-borne bacterium affects over 200 plant species worldwide, including economically and nutritionally important crops, such as potato (Solanum tuberosum), tomato (Solanum lycopersicum), and bananas (Musa spp.). R. solanacearum is a species complex, meaning that the species is composed of strains with differential characteristics, including different metabolic requirements, centers of origin, host range, and ideal environmental conditions for infection. Its nature and the fact that it is a species complex can make R. solanacearum a difficult bacterium to work with, especially when lacking experience. Inappropriate isolation or storage of the pathogen can lead to inaccurate diagnostics or misleading conclusions. Thus, the objectives of this diagnostic guide are to provide adequate methods for isolation, storage, and identification and to discuss other relevant aspects related to this important plant pathogenic bacterium.

Comparative genomic analysis of Pseudomonas amygdali pv. lachrymans NM002: Insights into its potential virulence genes and putative invasion determinants

Pseudomonas amygdali pv. lachrymans is currently of important plant pathogenic bacteria that causes cucumber angular leaf spot worldwide. The pathogen has been studied for its roles in pathogenicity and plant inheritance resistance. To further delineate traits critical to virulence, invasion and survival in the phyllosphere, we reported the first complete genome of P. amygdali pv. lachrymans NM002. Analysis of the whole genome in comparison with three closely-related representative pathovars of P. syringae identified the conservation of virulence genes, including flagella and chemotaxis, quorum-sensing systems, two-component systems, and lipopolysaccharide and antiphagocytosis. It also revealed differences of invasion determinants, such as type III effectors, phytotoxin (coronatine, syringomycin and phaseolotoxin) and cell wall-degrading enzyme, which may contribute to infectivity. The aim of this study was to derive genomic information that would reveal the probable molecular mechanisms underlying the virulence, infectivity and provide a better understanding of the pathogenesis of the P. syringae pathovars.

Interactions of free-living amoebae with rice bacterial pathogens Xanthomonas oryzae pathovars oryzae and oryzicola.

BackgroundFree-living amoebae (FLA) are voracious feeders, consuming bacteria and other microbes during colonization of the phytobiome. FLA are also known to secrete bacteriocidal or bacteriostatic compounds into their growth environment.Methodology and principal findingsHere, we explore the impacts of co-cultivation of five FLA species, including Acanthamoeba castellanii, A. lenticulata, A. polyphaga, Dictyostelium discoideum and Vermamoeba vermiformis, on survival of two devastating bacterial pathogens of rice, Xanthomonas oryzae pathovars (pv.) oryzae and oryzicola. In co-cultivation assays, the five FLA species were either bacteriostatic or bactericidal to X. oryzae pv. oryzae and X. oryzae pv. oryzicola. Despite these effects, bacteria were rarely detected inside amoebal cells. Furthermore, amoebae did not disrupt X. oryzae biofilms. The bactericidal effects persisted when bacteria were added to a cell-free supernatant from amoebal cultures, suggesting some amoebae produce an extracellular bactericidal compound.Conclusions/SignificanceThis work establishes novel, basal dynamics between important plant pathogenic bacteria and diverse amoebae, and lays the framework for future mechanistic studies.

Functional characterization of the citrus canker susceptibility gene CsLOB1.

Xanthomonas citri ssp. citri (Xcc) is an important plant-pathogenic bacterium that causes citrus canker disease worldwide. PthA, a transcriptional activator-like (TAL) effector, directs the expression of the canker susceptibility gene CsLOB1. Here, we report our recent progress in the functional characterization of CsLOB1. Subcellular localization analysis of CsLOB1 protein in citrus protoplast revealed that CsLOB1 is primarily localized in the nucleus. We showed that CsLOB1 expression driven by dexamethasone (DEX) in CsLOB1-GR transgenic plants is associated with pustule formation following treatment with DEX. Pustule formation was not observed in DEX-treated wild-type plants and in non-treated CsLOB1-GR transgenic plants. Water soaking is typically associated with symptoms of citrus canker. Weaker water soaking was observed with pustule formation in CsLOB1-GR transgenic plants following DEX treatment. When CsLOB1-GR-transgenic Duncan grapefruit leaves were inoculated with Xcc306ΔpthA4 and treated with DEX, typical canker symptoms, including hypertrophy, hyperplasia and water soaking symptoms, were observed on DEX-treated transgenic plant leaves, but not on mock-treated plants. Twelve citrus genes that are induced by PthA4 are also stimulated by the DEX-induced expression of CsLOB1. As CsLOB1 acts as a transcriptional factor, we identified putative targets of CsLOB1 via bioinformatic and electrophoretic mobility shift assays. Cs2g20600, which encodes a zinc finger C3HC4-type RING finger protein, has been identified to be a direct target of CsLOB1. This study advances our understanding of the function of CsLOB1 and the molecular mechanism of how Xcc causes canker symptoms via CsLOB1.

Ankyrin-Like Protein AnkB Interacts with CatB, Affects Catalase Activity, and Enhances Resistance of Xanthomonas oryzae pv. oryzae and Xanthomonas oryzae pv. oryzicola to Phenazine-1-Carboxylic Acid.

Xanthomonas oryzae pv. oryzae, which causes rice bacterial leaf blight, and Xanthomonas oryzae pv. oryzicola, which causes rice bacterial leaf streak, are important plant-pathogenic bacteria. A member of the adaptor protein family, ankyrin protein, has been investigated largely in humans but rarely in plant-pathogenic bacteria. In this study, a novel ankyrin-like protein, AnkB, was identified in X. oryzae pv. oryzae and X. oryzae pv. oryzicola. The expression of ankB was significantly upregulated when these bacteria were treated with phenazine-1-carboxylic acid (PCA). ankB is located 58 bp downstream of the gene catB (which encodes a catalase) in both bacteria, and the gene expression of catB and catalase activity were reduced following ankB deletion in X. oryzae pv. oryzae and X. oryzae pv. oryzicola. Furthermore, we demonstrated that AnkB directly interacts with CatB by glutathione S-transferase (GST) pulldown assays. Deletion of ankB increased the sensitivity of X. oryzae pv. oryzae and X. oryzae pv. oryzicola to H2O2 and PCA, decreased bacterial biofilm formation, swimming ability, and exopolysaccharide (EPS) production, and also reduced virulence on rice. Together our results indicate that the ankyrin-like protein AnkB has important and conserved roles in antioxidant systems and pathogenicity in X. oryzae pv. oryzae and X. oryzae pv. oryzicola.IMPORTANCE This study demonstrates that the ankyrin protein AnkB directly interacts with catalase CatB in Xanthomonas oryzae pv. oryzae and Xanthomonas oryzae pv. oryzicola. Ankyrin protein AnkB can affect the gene expression of catB, catalase activity, and sensitivity to H2O2 In Xanthomonas spp., the locations of genes ankB and catB and the amino acid sequence of AnkB are highly conserved. It is suggested that in prokaryotes, AnkB plays a conserved role in the defense against oxidative stress.

A preliminary study of antibacterial activity of thirty essential oils against several important plant pathogenic bacteria

Numerous scientific research studies all over the world have addressed the problem of agriculture in the 21st century as being particularly sensitive to climate change, which has caused phytopathogenic bacteria to spread. Therefore, there is a clear and urgent need to contain this kind of risk in agricultural production (both conventional and organic farming). The objective of this study was to determine the antibacterial activity of 30 essential oils (EOs) against three harmful plant pathogenic bacteria of agricultural importance, Erwinia amylovora, Xanthomonas campestris pv. campestris and Pseudomonas syringae pv. syringae. The study included in vitro testing, using an agar-diffusion assay. The EOs of Ceylon cinnamon (leaf and bark), oregano, clove bud and palmarosa revealed antibacterial activity against the test bacteria, and the maximum mean inhibition zone diameters of 35 mm was found against E. amylovora and X. campestris pv. campestris (highly sensitive reaction), while it was smaller in the case of P. syringae pv. syringae, from 18.25-26.25 mm (sensitive to very sensitive reaction). Maximum diameter of the zone of inhibition (35 mm) was obtained using basil and peppermint against E. amylovora, and rosemary, blue gum and camphor tree against X. campestris pv. campestris. Not a single EO inhibited P. syringae pv. syringae with the resulting total diameter zone of 35 mm, and this test bacteria was resultingly classified as the least susceptible bacterium of the three tested. EOs of lemongrass, aniseed, ylang ylang, silver fir, lemon, dwarf mountain pine, bay laurel and scots pine caused sensitive reaction of the tested bacteria. Peppermint, black cumin, Indian frankincense, bergamot orange, common juniper, bitter orange and neem produced variable reactions from total to weakly or no inhibition at all. Weakly activity was found in niaouli and Atlas cedar. Eastern red cedar, patchouli, Indian sandalwood and ginger caused no reaction of any of the test bacteria. The results offer a basis for further work based on in vivo testing for the purpose of developing ?natural pesticides? for control of phytopathogenic bacteria, thus giving a significant contribution to reducing yield losses in agriculture and sustainable development.