Pathogenicity islands and virulence plasmids of bacterial plant pathogens.
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Animals↗
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Results for “bacterial plant pathogen”
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Diversification of an emerging bacterial plant pathogen; insights into the global spread of Xanthomonas euvesicatoria pv. perforans.
Emerging and re-emerging plant diseases continue to present multifarious threats to global food security. Considerable recent efforts are therefore being channeled towards understanding the nature of pathogen emergence, their spread and evolution. Xanthomonas euvesicatoria pv. perforans (Xep), one of the causal agents of bacterial spot of tomato, rapidly emerged and displaced other bacterial spot xanthomonads in many tomato production regions around the world. In less than three decades, it has become a dominant xanthomonad pathogen in tomato production systems across the world and presents a compelling example for understanding diversification of recently emerged bacterial plant pathogens. Although Xep has been continuously monitored in Florida since its discovery, the global population structure and evolution at the genome-scale is yet to be fully explored. The objectives of this work were to determine genetic diversity globally to ascertain if different tomato production regions contain genetically distinct Xep populations, to examine genetic relatedness of strains collected in tomato seed production areas in East Asia and other production regions, and to evaluate variation in type III secretion effectors, which are critical pathogenicity and virulence factors, in relationship to population structure. We used genome data from 270 strains from 13 countries for phylogenetic analysis and characterization of type III effector gene diversity among strains. Our results showed notable genetic diversity in the pathogen. We found genetically similar strains in distant tomato production regions, including seed production regions, and diversification over the past 100 years, which is consistent with intercontinental dissemination of the pathogen in hybrid tomato production chains. Evolution of the Xep pangenome, including the acquisition and loss of type III secreted effectors, is apparent within and among phylogenetic lineages. The apparent long-distance movement of the pathogen, together with variants that may not yet be widely distributed, poses risks of emergence of new variants in tomato production.
Xanthomonas↗
Streptocycline, an effective antibiotic against bacterial plant pathogens.
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Anti-Bacterial Agents↗
The effectiveness of antibiotics against some bacterial plants pathogens.
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Anti-Bacterial Agents↗
Inhibition of fungal and bacterial plant pathogens by synthetic peptides: in vitro growth inhibition, interaction between peptides and inhibition of disease progression.
Four synthetic cationic peptides, pep6, pep7, pep11 and pep20, were tested alone and in combinations for their antimicrobial activities against economically important plant pathogenic fungi (Phytophthora infestans and Alternaria solani) and bacteria (Erwinia carotovora subsp. carotovora and E. carotovora subsp. atroseptica). In in vitro studies, P. infestans and A. solani were inhibited by all four peptides, while E. carotovora subsp. carotovora and E. carotovora subsp. atroseptica were inhibited only by pep11 and pep20. All peptides completely inhibited P. infestans and A. solani on potato leaves and P. infestans on tubers at concentrations comparable to the in vitro IC50 (effective concentration for 50% growth inhibition) values, suggesting that these peptides are more potent in preventing infection than in inhibiting hyphal growth in vitro. Microscopic observations of P. infestans and A. solani when treated with these peptides revealed hyphal anomalies. In tuber-infectivity assays, pep11 and pep20 reduced bacterial softrot symptoms by 50% at 2.0 to 2.30 microM and by 100% at 20 microM. In assays involving two-way combinations of these peptides, growth inhibitions of fungi and bacteria by the combinations were no more than the sum of growth inhibitions by each peptide when used alone, indicating that they act additively. pep11 and pep20 are not phytotoxic to potato plants at 200 microM. With strong and broad-spectrum antimicrobial activities of pep11 and pep20 against fungi and bacteria, and with no antagonistic activities, the expression of these peptides in transgenic potato plants could lead to enhanced disease resistance against these pathogens.
Amino Acid Sequence↗
Molecular biology of bacterial plant pathogens.
It is now possible to apply a range of genetic and recombinant DNA techniques to several plant-pathogenic bacteria, and the rapid growth of this area of research is expected to revolutionize our understanding of plant diseases. Some promising research strategies are discussed in this paper.
Bacteria↗
Atypical adaptive and cross-protective responses against peroxide killing in a bacterial plant pathogen, Agrobacterium tumefaciens.
Physiological adaptive and cross-protection responses to oxidants were investigated in Agrobacterium tumefaciens. Exposure of A. tumefaciens to sublethal concentrations of H2O2 induced adaptive protection to lethal concentrations of H2O2. Similar treatments with organic peroxide and menadione did not produce adaptive protection to subsequent exposure to lethal concentrations of these oxidants. Pretreatment of A. tumefaciens with an inducing concentration of menadione conferred cross-protection against H2O2, but not to tert-butyl hydroperoxide (tBOOH), killing. The menadione induced cross-protection to H2O2 was due to the compound's ability to highly induce the peroxide scavenging enzyme, catalase. The levels of catalase directly correlated with the bacterium's ability to survive H2O2 treatment. Some aspects of the oxidative stress response of A. tumefaciens differ from other bacteria, and these differences may be important in plant/microbe interactions.
Adaptation, Physiological↗
Production of pyruvate from 6-phosphogluconate by bacterial plant pathogens and legume bacteria.
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Bacteria↗
A Noninvasive Technique for Monitoring Peroxidative and H2O2-Scavenging Activities during Interactions between Bacterial Plant Pathogens and Suspension Cells.
Stimulation of active oxygen metabolism occurs during the early stages of interactions involving bacteria and plant cell suspensions. Although many cellular processes are known to affect active oxygen metabolism in plants, it is not known which of these factors affect active oxygen levels during plant-bacteria interactions. Extracellular peroxidases have been shown to participate in both the production and utilization of active oxygen species such as H2O2 and superoxide. Catalase and other scavenging mechanisms also affect the overall level of active oxygen. In this study the luminol-dependent chemiluminescent reaction previously used to measure H2O2 levels in suspension cells was modified to allow the assay of both peroxidase and H2O2-scavenging activity. The early stages of the interactions between tobacco (Nicotiana tabacum) and Pseudomonas syringae pv syringae, as well as between soybean (Glycine max) and P. syringae pv glycinea, were investigated. This method of monitoring peroxidase and H2O2-scavenging activity proved to be rapid, sensitive, and nonintrusive, allowing the processing of multiple samples using intact cells or cell-free preparations. The results from the study demonstrate that the scavenging activities can be significant and must be considered when studying active oxygen production in biological interactions.
Journal Article↗
Fastidious xylem-limited bacterial plant pathogens.
Numerous bacteria have been isolated from within plants, and many reported from xylem, but only three species of xylem-limited bacteria (XLB) that are fastidious in cultural requirements, are plant pathogens, and exclusively occupy xylem, have been well characterized. Two XLB, Xylella fastidiosa and Pseudomonas syzygii, are transmitted by sucking insects that feed on xylem sap but are not transmitted mechanically from plant to plant. In contrast, Clavibacter xyli is mechanically transmitted to plants by cutting tools. All of these XLB occupy a highly specialized yet diverse ecological niche: the water-conducting systems of an extremely wide range of plant hosts. A variety of detection methods are available as diagnostic aids; each method has advantages and disadvantages; no single method is best for all uses. Molecular and genetic comparisons of strains of XLB lag behind progress being made for many other plant-pathogenic bacteria, but such studies are needed to answer important questions: (a) How do XLB move from cell to cell within plants? (b) What are the physiological and genetic bases of plant host specificity for XLB? (c) Why are only xylem-feeding specialists vectors of X. fastidiosa (and probably P. syzygii), when many leafhoppers feed regularly (but not continuously) on xylem?
Journal Article↗
Surface components involved in bacterial pathogen-plant host recognition.
During their initial association with plant hosts, pathogenic bacteria interact with plant cell walls. The results of this interaction appear to determine whether bacterial multiplication will take place. With one group of bacterial plant pathogens (e.g. Agrobacterium tumefaciens), attachment to the host surface appears essential for pathogenesis. With another group (e.g. Pseudomonas solanacearum), only those strains that do not attach to the host cell wall are able to multiply in the intercellular spaces. Attachment of many incompatible strains to tobacco mesophyll cell walls leads to a rapid hypersensitive response (HR) and a drastic reduction in bacterial multiplication. Our working hypothesis is that these differences in host response to strains of P. solanacearum are the result of a recognition response in which surface components of both host and pathogen play important roles. Our approach is based on the use of spontaneous or transposon (Tn5)-generated mutants of strains K60 (virulent) and B1 (avirulent) that differ in surface components and in their ability to attach to host cells and to induce the HR. A study of the surface components of bacterial and tobacco cell walls has led to the tentative conclusion that bacterial lipopolysaccharide (LPS) and plant hydroxyproline-rich glycoproteins mediate initial attachment, apparently as a result of charge-charge interaction. This initial attachment is reversed by high salt concentrations during the first 15 min, but not thereafter. Firm attachment appears to depend on hydrophobic interactions mediated by bacterial pili. At the normal ionic strength of intercellular fluids, extracellular polysaccharide (EPS) appears to inhibit only the pili-mediated attachment. Several HR- mutants of strain B1 have been obtained by Tn5 insertion, but they remain avirulent on tobacco. We are examining the EPS, LPS and pili production, and the attachment characteristics of these strains.
Cell Adhesion↗
Amplification of DNA of Xanthomonas axonopodis pv. citri from historic citrus canker herbarium specimens.
Herbaria are important resources for the study of the origins and dispersal of plant pathogens, particularly bacterial plant pathogens that incite local lesions in which large numbers of pathogen genomes are concentrated. Xanthomonas axonopodis pv. citri (Xac), the causal agent of citrus bacterial canker disease, is a notable example of such a pathogen. The appearance of novel strains of the pathogen in Florida and elsewhere make it increasingly important to understand the relationships among strains of this pathogen. USDA-ARS at Beltsville, Maryland maintains approximately 700 herbarium specimens with citrus canker disease lesions up to 90 years old, originally collected from all over the world, and so is an important resource for phytogeographic studies of this bacterium. Unfortunately, DNA in herbarium specimens is degraded and may contain high levels of inhibitors of PCR. In this study, we compared a total of 23 DNA isolation techniques in combination with 31 novel primer pairs in order to develop an efficient protocol for the analysis of Xac DNA in herbarium specimens. We identified the most reliable extraction method, identified in terms of successful amplification by our panel of 31 primer pairs. We also identified the most robust primer pairs, identified as successful in the largest number of extracts prepared by different methods. We amplified Xac genomic sequences up to 542 bp long from herbarium samples up to 89 years old. Primers varied in effectiveness, with some primer pairs amplifying Xac DNA from a 1/10,000 dilution of extract from a single lesion from a citrus canker herbarium specimen. Our methodology will be useful to identify pathogens and perform molecular analyses of bacterial and possibly fungal genomes from herbarium specimens.
Biological Specimen Banks↗
Exposure to host resistance mechanisms drives evolution of bacterial virulence in plants.
Bacterial pathogenicity to plants and animals has evolved through an arms race of attack and defense. Key players are bacterial effector proteins, which are delivered through the type III secretion system and suppress basal defenses . In plants, varietal resistance to disease is based on recognition of effectors by the products of resistance (R) genes . When recognized, the effector or in this scenario, avirulence (Avr) protein triggers the hypersensitive resistance reaction (HR), which generates antimicrobial conditions . Unfortunately, such gene-for-gene-based resistance commonly fails because of the emergence of virulent strains of the pathogen that no longer trigger the HR . We have followed the emergence of a new virulent pathotype of the halo-blight pathogen Pseudomonas syringae pv. phaseolicola within leaves of a resistant variety of bean. Exposure to the HR led to the selection of strains lacking the avirulence (effector) gene avrPphB (or hopAR1), which triggers defense in varieties with the matching R3 resistance gene. Loss of avrPphB was through deletion of a 106 kb genomic island (PPHGI-1) that shares features with integrative and conjugative elements (ICElands) and also pathogenicity islands (PAIs) in diverse bacteria . We provide a molecular explanation of how exposure to resistance mechanisms in plants drives the evolution of new virulent forms of pathogens.
Bacterial Proteins↗
Characterization of maize cytochrome P450 monooxygenases induced in response to safeners and bacterial pathogens.
Plants use a diverse array of cytochrome P450 monooxygenases in their biosynthetic and detoxification pathways. To determine the extent to which various maize P450s are induced in response to chemical inducers, such as naphthalic anhydride (NA), triasulfuron (T), phenobarbital, and bacterial pathogens (Erwinia stuartii, Acidovorax avenae), we have analyzed the response patterns of seven P450 transcripts after treatment of seedlings with these inducers. Each of these P450 transcripts has distinct developmental, tissue-specific, and chemical cues regulating their expression even when they encode P450s within the same biosynthetic pathway. Most notably, the CYP71C1 and CYP71C3 transcripts, encoding P450s in the DIMBOA biosynthetic pathway, are induced to the same level in response to wounding and NA treatment of younger seedlings and differentially in response to NA/T treatment of younger seedlings and NA and NA/T treatment of older seedlings. NA and T induce expression of both CYP92A1 and CYP72A5 transcripts in older seedling shoots, whereas phenobarbital induces CYP92A1 expression in older seedling shoots and highly induces CYP72A5 expression in young and older seedling roots. Expressed sequence tag (EST) 6c06b11 transcripts, encoding an undefined P450 activity, are highly induced in seedling shoots infected with bacterial pathogens.
Amino Acid Sequence↗
Effect of acidic electrolyzed water on the viability of bacterial and fungal plant pathogens and on bacterial spot disease of tomato.
Acidic electrolyzed water (AEW), known to have germicidal activity, was obtained after electrolysis of 0.045% aqueous solution of sodium chloride. Freshly prepared AEW (pH 2.3-2.6, oxidation-reduction potential 1007-1025 mV, and free active chlorine concentration 27-35 ppm) was tested in vitro and (or) on tomato foliage and seed surfaces for its effects on the viability of plant pathogen propagules that could be potential seed contaminants. Foliar sprays of AEW were tested against bacterial spot disease of tomato under greenhouse and field conditions. The viability of propagules of Xanthomonas campestris pv. vesicatoria (bacterial spot pathogen), Streptomyces scabies (potato scab pathogen), and Fusarium oxysporum f.sp. lycopersici (root rot pathogen) was significantly reduced 4-8 log units within 2 min of exposure to AEW. Immersion of tomato seed from infected fruit in AEW for 1 and 3 min significantly reduced the populations of X. campestris pv. vesicatoria from the surface of the seed without affecting seed germination. Foliar sprays of AEW reduced X. campestris pv. vesicatoria populations and leaf spot severity on tomato foliage in the greenhouse. In the field, multiple sprays of AEW consistently reduced bacterial spot severity on tomato foliage. Disease incidence and severity was also reduced on fruit, but only in 2003. Fruit yield was either enhanced or not affected by the AEW sprays. These results indicate a potential use of AEW as a seed surface disinfectant or contact bactericide.
Disinfectants↗
Genetic diversity, recombination and cryptic clades in Pseudomonas viridiflava infecting natural populations of Arabidopsis thaliana.
Species-level genetic diversity and recombination in bacterial pathogens of wild plant populations have been nearly unexplored. Pseudomonas viridiflava is a common natural bacterial pathogen of Arabidopsis thaliana, for which pathogen defense genes and mechanisms are becoming increasing well known. The genetic variation contained within a worldwide sample of P. viridiflava collected from wild populations of A. thaliana was investigated using five genomic sequence fragments totaling 2.3 kb. Two distinct and deeply diverged clades were found within the P. viridiflava sample and in close proximity in multiple populations, each genetically diverse with synonymous variation as high as 9.3% in one of these clades. Within clades, there is evidence of frequent recombination within and between each sequenced locus and little geographic differentiation. Isolates from both clades were also found in a small sample of other herbaceous species in Midwest populations, indicating a possibly broad host range for P. viridiflava. The high levels of genetic variation and recombination together with a lack of geographic differentiation in this pathogen distinguish it from other bacterial plant pathogens for which intraspecific variation has been examined.
Arabidopsis↗
Integrated regulation of the type III secretion system and other virulence determinants in Ralstonia solanacearum.
In many plant and animal bacterial pathogens, the Type III secretion system (TTSS) that directly translocates effector proteins into the eukaryotic host cells is essential for the development of disease. In all species studied, the transcription of the TTSS and most of its effector substrates is tightly regulated by a succession of consecutively activated regulators. However, the whole genetic programme driven by these regulatory cascades is still unknown, especially in bacterial plant pathogens. Here, we have characterised the programme triggered by HrpG, a host-responsive regulator of the TTSS activation cascade in the plant pathogen Ralstonia solanacearum. We show through genome-wide expression analysis that, in addition to the TTSS, HrpG controls the expression of a previously undescribed TTSS-independent pathway that includes a number of other virulence determinants and genes likely involved in adaptation to life in the host. Functional studies revealed that this second pathway co-ordinates the bacterial production of plant cell wall-degrading enzymes, exopolysaccharide, and the phytohormones ethylene and auxin. We provide experimental evidence that these activities contribute to pathogenicity. We also show that the ethylene produced by R. solanacearum is able to modulate the expression of host genes and can therefore interfere with the signalling of plant defence responses. These results provide a new, integrated view of plant bacterial pathogenicity, where a common regulator activates synchronously upon infection the TTSS, other virulence determinants and a number of adaptive functions, which act co-operatively to cause disease.
Adaptation, Physiological↗
Pathogen local adaptation shapes Pierce's disease of grapevines outcomes under field conditions.
Climate change is broadly expected to increase the range of many plant diseases, yet the current status of local thermal adaptation in many pathogens is poorly understood. Xylella fastidiosa (Xf) is a global bacterial plant pathogen that causes Pierce's disease (PD) of grapevines and infects over 700 other host plant species, impacting both agricultural and natural ecosystems. In a common garden experiment with 477 vines in the field, we compared PD outcomes from a local (colder climate in CA) vs non-local (warmer climate in CA) bacterial strain in 13 Mediterranean grapevine varieties over 3 years. Relative to the local strain, there was 77% lower overwinter survival in the non-local strain from a warmer climate, strongly indicating local adaptation in these CA Xf populations. Host genotype also had a significant effect on pathogen winter survival, and grapevine varieties differed in PD susceptibility. Additionally, we assessed in planta evolution of the two pathogen strains over 3 years by whole-genome sequencing 58 field-derived isolates. There were convergent loss-of-function mutations in genes encoding minor Type IV pilin (T4P) proteins, which control twitching motility and other virulence phenotypes, suggesting rapid adaptive evolution. Our results suggest local adaptation to cold temperatures in a bacterial plant pathogen and a possible role for minor Type IV pilins in thermal adaptation. These findings demonstrate the urgent need to incorporate X. fastidiosa evolution and local thermal adaptation into global models of PD spread. Differentiating pathotypes with distinct thermal adaptations will improve disease forecasting and inform quarantine decisions.IMPORTANCEForecasting the movement of plant pathogens is a critical issue under global warming to effectively manage future plant disease outbreaks. Yet, current plant pathogen local thermal adaptation is often unaccounted for, especially in bacterial pathogens. Our study examines local adaptation to temperature in a bacterial plant pathogen, Xylella fastidiosa, that causes disease in grapevines in addition to infecting 700 other plant species. In a large-scale field experiment across 13 grapevine varieties, we demonstrate local adaptation in pathogen winter survival in distinct Xylella fastidiosa strains. Additionally, we found evidence of adaptive evolution in just 3 years, as we observed convergent mutations after resequencing strains that evolved in the field. Our results suggest that X. fastidiosa populations-even within a small geographic area-have distinct adaptations to winter temperatures and may exhibit differential responses to warming winters.
Type IV pili↗