Erwinia Strains Research Articles

Widespread and largely unknown prophage activity, diversity, and function in two genera of wheat phyllosphere bacteria

Environmental bacteria host an enormous number of prophages, but their diversity and natural functions remain largely elusive. Here, we investigate prophage activity and diversity in 63 Erwinia and Pseudomonas strains isolated from flag leaves of wheat grown in a single field. Introducing and validating Virion Induction Profiling Sequencing (VIP-Seq), we identify and quantify the activity of 120 spontaneously induced prophages, discovering that some phyllosphere bacteria produce more than 108 virions/mL in overnight cultures, with significant induction also observed in planta. Sequence analyses and plaque assays reveal E. aphidicola prophages contribute a majority of intraspecies genetic diversity and divide their bacterial hosts into antagonistic factions engaged in widespread microbial warfare, revealing the importance of prophage-mediated microdiversity. When comparing spontaneously active prophages with predicted prophages we also find insertion sequences are strongly correlated with non-active prophages. In conclusion, we discover widespread and largely unknown prophage diversity and function in phyllosphere bacteria.

The silver lining of antibiotic resistance: Bacterial-mediated reduction of tetracycline plant stress via antibiotrophy

The reuse of water using effluents containing antibiotics from anthropogenic activities has been mainly linked to the development of antibiotic resistance. However, we report that the development of bacterial tolerance promotes plant growth. In the present study, we aimed to evaluate the efficiency of inoculation of a new antibiotic-degrading bacterium, Erwinia strain S9, in augmenting the tolerance of pea (Pisum sativum L.) plants to tetracycline (TET) (10 and 20 mg/L). Physiological parameters such as tissue elongation and biomass, as well as relative water content, were remarkably lower in plants exposed to TET than in the control. The inhibitory effects of TET were associated with reduced CO2 assimilation, stomatal conductance, transpiration, dark respiration, and light saturation point (LSP). High concentrations of TET-induced oxidative stress are attested by the overproduction of superoxide radicals (O2•−), hydrogen peroxide (H2O2), and hydroxyl radicals (HO•), resulting in increased malondialdehyde content and cell death. The high activity of antioxidant enzymes such as catalase, ascorbate peroxidase, and guaiacol peroxidase validated the proposed mechanism. Under TET stress conditions, supplementation with Erwinia strain S9 was beneficial to pea plants through osmotic adjustment, increased nutrient uptake, gas exchange optimization, and increased antioxidant activities. Its presence not only ensures plant survival and growth during antibiotic stress but also degrades TET via significant antibiotrophy. This strategy is a cost-effective environmental chemical engineering tool that can be used to depollute wastewater or to improve crop resistance in rhizofiltration treatment when treated wastewater is reused for irrigation.

Novel Detection and Quantification Approach of Erwinia amylovora In Vitro and In Planta Using SYBR Green-Based Real-Time PCR Assay.

Fire blight, caused by the bacterial pathogen Erwinia amylovora, is a highly destructive disease of apple and pear. Because the apple tree gets systemically infected with E. amylovora and eventually dies, E. amylovora is a considerably important pathogen in the orchard that requires long-term management. In addition, it is crucial to prevent the spread of the pathogen by expeditious diagnosis. In this study, via comparative approaches to the genome sequences of the strains of various Erwinia spp., we designed specific primers targeting a hypothetical gene that is single copy and located in the chromosomal DNA of E. amylovora. This primer set specifically amplified the DNA of E. amylovora but no other bacteria, including E. pyrifoliae, Pectobacterium spp., Pantoea spp., and Dickeya chrysanthemi. Furthermore, the SYBR Green-based real-time PCR using the primer set allowed accurate estimation of the population of E. amylovora. Developing a rapid and accurate diagnostic method using the novel primer set enables effective defense against pathogen spread through continuous monitoring and quick response.

Efficient CRISPR-Cas9 based cytosine base editors for phytopathogenic bacteria

Phytopathogenic bacteria play important roles in plant productivity, and developments in gene editing have potential for enhancing the genetic tools for the identification of critical genes in the pathogenesis process. CRISPR-based genome editing variants have been developed for a wide range of applications in eukaryotes and prokaryotes. However, the unique mechanisms of different hosts restrict the wide adaptation for specific applications. Here, CRISPR-dCas9 (dead Cas9) and nCas9 (Cas9 nickase) deaminase vectors were developed for a broad range of phytopathogenic bacteria. A gene for a dCas9 or nCas9, cytosine deaminase CDA1, and glycosylase inhibitor fusion protein (cytosine base editor, or CBE) was applied to base editing under the control of different promoters. Results showed that the RecA promoter led to nearly 100% modification of the target region. When residing on the broad host range plasmid pHM1, CBERecAp is efficient in creating base edits in strains of Xanthomonas, Pseudomonas, Erwinia and Agrobacterium. CBE based on nCas9 extended the editing window and produced a significantly higher editing rate in Pseudomonas. Strains with nonsynonymous mutations in test genes displayed expected phenotypes. By multiplexing guide RNA genes, the vectors can modify up to four genes in a single round of editing. Whole-genome sequencing of base-edited isolates of Xanthomonas oryzae pv. oryzae revealed guide RNA-independent off-target mutations. Further modifications of the CBE, using a CDA1 variant (CBERecAp-A) reduced off-target effects, providing an improved editing tool for a broad group of phytopathogenic bacteria.

Draft Genome Sequences of Phytase Active Endophytic and Epiphytic Erwinia gerundensis Isolated from Wheat (Triticum aestivum) Seeds

Here, we provide draft genome sequences of an epiphytic strain (HEP01) and an endophytic strain (HEN01) of Erwinia gerundensis, isolated from wheat (Triticum aestivum) seeds. Genome sizes of HEP01 and HEN01 were 3,771,322 bp and 3,750,048 bp, respectively. HEP01 and HEN01 carried one plasmid each with sizes of 565,617 bp and 576,781 bp, respectively. Both showed phenotypic phytase activity.

Tenebrionicola larvae gen. nov., sp. nov., isolated from larvae of mealworm Tenebrio molitor L., and a proposal to transfer Erwinia teleogrylli Liu et al. 2016 to a new genus Entomohabitans as Entomohabitans teleogrylli comb. nov.

Two enterobacterial strains, designated YMB-R21T and YMB-R22, were isolated from larvae of mealworm Tenebrio molitor L. and examined for their taxonomic characteristics. A 16S rRNA gene-based neighbour-joining tree showed that the two isolates formed two distinct sublineages within the family Enterobacteriaceae and were separated from other genera of the family. The isolates showed 16S rRNA gene sequence similarity of 98.9 % to each other and ≤96.5 % to members of the order Enterobacteriales. The phylogenomic analysis based on 92 singly-copy core genes showed that the two isolates belonged to the family Enterobacteriaceae and formed a distinct sublineage at a position located remotely from the genera of the family. The loosely associated members were the type strain of Erwinia teleogrylli and members of the genus Shimwellia. Average nucleotide identity and digital DNA-DNA hybridization values showed that the isolates represented members of a novel species in the family Enterobacteriaceae. The values of amino acid identity between the two isolates and the closest relatives were 74.5-75.0 % with the type strain of E. teleogrylli and 74.5-74.8 % with the type strains of two Shimwellia species, while E. teleogrylli showed the amino acid identity values of 76.3-76.5 % with two Shimwellia species. Based on the results obtained here, we propose a new genus Tenebrionicola with the description of Tenebrionicola larvae sp. nov. (type strain YMB-R21T=KCTC 82597T=CCM 9152T and strain YMB-R22=KCTC 82598=CCM 9153), with the transfer of Erwinia teleogrylli Liu et al. 2016 to a new genus Entomohabitans as Entomohabitans teleogrylli comb. nov. (type strain SCU-B244T=CGMCC 1.12772T=DSM 28222T=KCTC 42022T).

A Re-evaluation of the Taxonomy and Classification of the Type III Secretion System in a Pathogenic Bacterium Causing Soft Rot Disease of Pleurotus eryngii.

Pantoea beijingensis, a gram-negative pathogenic bacterium, causes soft rot disease in the fungus Pleurotus eryngii in China. However, the taxonomic classification of this pathogen is controversial due to close relationships between bacteria of the genera Pantoea and Erwinia. This study aimed to resolve the identity of P. beijingensis using phylogenomic and systematic analyses of Pantoea and Erwinia by whole-genome sequencing. Single-copy orthologs identified from the Erwinia/Pantoea core genomes were used to delineate Erwinia/Pantoea phylogeny. P. beijingensis LMG27579T clustered within a single Erwinia clade. A whole-genome-based phylogenetic tree and average nucleotide and amino-acid identity values indicate that P. beijingensis LMG27579T should be renamed Erwinia beijingensis. The hrp/hrc genes encoding type III secretion system (T3SS) proteins in Erwinia and Pantoea were divided into five groups according to gene contents and organization. Neighbor-joining-inferred phylogenetic trees based on concatenated HrcU, HrcN, and HrcR in the main hrp/hrc cluster showed that E. beijingensis T3SS proteins are closely related to those in Ewingella americana, implying that E. beijingensis and E. americana have a recent common hrp/hrc gene ancestor. Furthermore, T3SS proteins of Erwinia and Pantoea were clustered in different clades separated by other bacterial T3SS proteins. Thus, T3SS genes in Pantoea and Erwinia strains might have been acquired by horizontal gene transfer. Overall, our findings clarify the taxonomy of the bacterium causing soft rot in P. eryngii, as well as the genetic structure and classification of the hrp/hrc T3SS virulence factor. We propose that T3SS acquisition is important for E. beijingensis emergence and pathogenesis.

Microbial prospection of communities that produce biosurfactants from the water column and sediments of the Gulf of Mexico.

Microbial communities capable of hydrocarbon degradation linked to biosurfactant (BS) and bioemulsifier (BE) production are basically unexplored in the Gulf of México (GOM). In this work, the BS and BE production of culturable marine bacterial hydrocarbonoclasts consortia isolated from two sites (the Perdido Fold Belt and Coatzacoalcos area) was investigated. The prospection at different locations and depths led to the screening and isolation of a wide variety of bacterial consortia with BS and BE activities, after culture enrichment with crude oil and glycerol as the carbon sources. At least 55 isolated consortia presented reduction in surface tension (ST) and emulsifying activity (EI24 ). After colony purification, bacteria were submitted to polyphasic analysis assays that resulted in the identification of different strains of cultivable Gammaproteobacteria Gram (-) Citrobacter, Enterobacter, Erwinia, Pseudomonas, Vibrio, Shewanella, Thalassospira, Idiomarina, Pseudoalteromonas, Photobacterium, and Gram (+) Staphylococcus, Bacillus, and Microbacterium. Overall, the best results for ST reduction and EI24 were obtained with consortia. Individually, Pseudomonas, Bacillus, and Enterobacter strains showed the best results for the reduction of ST after 6 days, while Thalassospira and Idiomarina strains showed the best results for EI24 (above 68% after 9 days). Consortia isolates from the GOM had the ability to degrade crude oil by up to 40-80% after 24 and 36 months, respectively. In all cases, biodegradation of crude oil was related to the reduction in ST and bioemulsifying activity and was independent from the depth in the water column.

Complete Genome Sequence of the Fire Blight Pathogen Strain Erwinia amylovora Ea1189.

Erwinia amylovora causes fire blight, the most devastating bacterial disease of apples and pears in the United States and worldwide. The model strain E. amylovora Ea1189 has been extensively used to understand bacterial pathogenesis and molecular mechanisms of bacterial-plant interactions. In this work, we sequenced and assembled the de novo genome of Ea1189, using a combination of long Oxford Nanopore Technologies and short Illumina sequence reads. A complete gapless genome assembly of Ea1189 consists of a 3,797,741-bp circular chromosome and a 28,259-bp plasmid with 3,472 predicted genes, including 78 transfer RNAs, 22 ribosomal RNAs, and 20 noncoding RNAs. A comparison of the Ea1189 genome to previously sequenced E. amylovora complete genomes showed 99.94 to 99.97% sequence similarity with 314 to 946 single nucleotide polymorphisms. We believe that the availability of the complete genome sequence of strain Ea1189 will further support studies to understand evolution, diversity and structural variations of Erwinia strains, as well as the molecular basis of E. amylovora pathogenesis and its interactions with host plants, thus facilitating the development of effective management strategies for this important disease.

Imidazolium salts as alternative compounds to control diseases caused by plant pathogenic bacteria.

To evaluate the inhibitory effect of five structurally different imidazolium salts on the in vitro growth of plant pathogenic bacteria that belong to divergent taxonomic genera as well as their ability to reduce the severity of common bacterial blight of common bean caused by Xanthomonas axonopodis pv. phaseoli and bacterial speck of tomato caused by Pseudomonas syringae pv. tomato. Growth inhibition of Xanthomonas, Pseudomonas, Erwinia, Pectobacterium and Dickeya strains by imidazolium salts was assessed in vitro by radial diffusion on agar medium and by ressazurin reduction in liquid medium. The reduction of common bacterial blight and bacterial speck symptoms and the area under de disease progress curves were determined by spraying two selected imidazolium salts on healthy plants 48h prior to inoculation with virulent strains of the bacterial pathogens. All imidazolium salts inhibited the growth of all plant pathogenic bacteria when tested by radial diffusion on agar medium. The strength of inhibition differed among imidazolium salts when tested on the same bacterial strain and among bacterial strains when tested with the same imidazolium salt. In liquid medium, most imidazolium salts presented the same minimum inhibitory concentration (MIC) and minimum bactericidal concentration values (200µmoll-1 ), the most notable exception of which was the MIC (at least 1000µmoll-1 ) for the dicationic MImC10 MImBr2 . The imidazolium salts C16 MImBr and C16 MImCl caused significant reductions in the severity of common bacterial blight symptoms when compared with nontreated plants. Imidazolium salts inhibit the in vitro growth of plant pathogenic bacteria and reduce plant disease symptoms to levels comparable to an authorized commercial antibiotic product. New compounds exhibiting broad-spectrum antibacterial activity with potential use in agriculture were identified.

Community assembly of the native C. elegans microbiome is influenced by time, substrate and individual bacterial taxa.

Microbiome communities are complex assemblages of bacteria. The dissection of their assembly dynamics is challenging because it requires repeated sampling of both host and source communities. We used the nematode Caenorhabditis elegans as a model to study these dynamics. We characterized microbiome variation from natural worm populations and their substrates for two consecutive years using 16S rDNA amplicon sequencing. We found conservation in microbiome composition across time at the genus, but not amplicon sequencing variant (ASV) level. Only three ASVs were consistently present across worm samples (Comamonas ASV10859, Pseudomonas ASV7162 and Cellvibrio ASV9073). ASVs were more diverse in worms from different rather than the same substrates, indicating an influence of the source community on microbiome assembly. Surprisingly, almost 50% of worm-associated ASVs were absent in corresponding substrates, potentially due to environmental filtering. Ecological network analysis revealed strong effects of bacteria-bacteria interactions on community composition: While a dominant Erwinia strain correlated with decreased alpha-diversity, predatory bacteria of the Bdellovibrio and like organisms associated with increased alpha-diversity. High alpha-diversity was further linked to high worm population growth, especially on species-poor substrates. Our results highlight that microbiomes are individually shaped and sensitive to dramatic community shifts in response to particular competitive species.

Reactive oxygen species induce cyanide-resistant respiration in potato infected by Erwinia carotovora subsp. Carotovora

Studies have shown that pathogenic bacteria infections induce the overproduction of reactive oxygen species (ROS) in plants. Cyanide-resistant respiration, an energy-dissipating pathway in plants, has also been induced by a pathogenic bacteria infection. However, it is unknown whether the induction of cyanide-resistant respiration under the pathogenic bacteria infection was caused by ROS. In this study, two pathogenic Erwinia strains were used to infect potato tuber, and membrane lipid peroxidation levels and the cyanide-resistant respiration capacity were determined. In addition, StAOX expression and regulation by ROS in potato tuber were analyzed. Moreover, the role of the Ca2+ pathway in regulating cyanide-resistant respiration was determined. The results showed that ROS induced cyanide-resistant respiration in potato tuber infected by Erwinia. Cyanide-resistant respiration inhibited the production of H2O2. Intracellular Ca2+ regulated the expression of calcium-dependent protein kinase (StCDPK1, StCDPK4, and StCDPK5) in potato, which indirectly controlled intracellular ROS levels. These results indicate that Ca2+ metabolism is involved in ROS-induced cyanide-resistant respiration.

Bacterial Metabolites Produced Under Iron Limitation Kill Pinewood Nematode and Attract Caenorhabditis elegans.

Pine Wilt Disease (PWD) is caused by Bursaphelenchus xylophilus, the pinewood nematode, and affects several species of pine trees worldwide. The ecosystem of the Pinus pinaster trees was investigated as a source of bacteria producing metabolites affecting this ecosystem: P. pinaster trees as target-plant, nematode as disease effector and its insect-vector as shuttle. For example, metals and metal-carrying compounds contribute to the complex tree-ecosystems. This work aimed to detect novel secondary metabolites like metallophores and related molecules produced under iron limitation by PWD-associated bacteria and to test their activity on nematodes. After screening 357 bacterial strains from Portugal and United States, two promising metallophore-producing strains Erwinia sp. A41C3 and Rouxiella sp. Arv20#4.1 were chosen and investigated in more detail. The genomes of these strains were sequenced, analyzed, and used to detect genetic potential for secondary metabolite production. A combinatorial approach of liquid chromatography-coupled tandem mass spectrometry (LC-MS) linked to molecular networking was used to describe these compounds. Two major metabolites were detected by HPLC analyses and described. One HPLC fraction of strain Arv20#4.1 showed to be a hydroxamate-type siderophore with higher affinity for chelation of Cu. The HPLC fraction of strain A41C3 with highest metal affinity showed to be a catecholate-type siderophore with higher affinity for chelation of Fe. LC-MS allowed the identification of several desferrioxamines from strain Arv20#4.1, in special desferrioxamine E, but no hit was obtained in case of strain A41C3 which might indicate that it is something new. Bacteria and their culture supernatants showed ability to attract C. elegans. HPLC fractions of those supernatant-extracts of Erwinia strain A41C3, enriched with secondary metabolites such as siderophores, were able to kill pinewood nematode. These results suggest that metabolites secreted under iron limitation have potential to biocontrol B. xylophilus and for management of Pine Wilt Disease.

Preparation and In Vitro Characterization of Chitosan Nanoparticles and Their Broad-Spectrum Antifungal Action Compared to Antibacterial Activities against Phytopathogens of Tomato

The present study was to prepare chitosan nanoparticles (CNPs) from chitosan (CS) to evaluate their in vitro antimicrobial activities against phytopathogens of tomato. We prepared and characterized CNPs for their particle size, polydispersity index, and structures. The antifungal properties of CS and CNPs against phytopathogenic fungi namely Colletotrichum gelosporidies, Phytophthora capsici, Sclerotinia sclerotiorum, Fusarium oxysporum, Gibberella fujikuori were investigated. CNPs showed the maximum growth inhibitory effects on mycelial growth of F. oxysporum followed by P. capsici. We also studied antibacterial activities against phytopathogenic bacteria, such as three strains of Erwinia carotovora subsp. carotovora and one strain of Xanthomonas campestris pv. vesicatoria. Our results showed that both CS and CNPs markedly inhibited the growth of the both Xanthomonas and Erwinia strains. From our study, it is evident that both CS and CNPs have tremendous potential against phytopathogens of tomato for further field screening towards crop protection.

Variability of Aggressiveness and Virulence of Erwinia carotovora subsp. Carotovorum Causing the Soft Rot on Potato Tubers in the Western of Algeria

Soft rot symptoms were observed on potato plants in several potato cultivars in the western part of Algeria. A total of four strains of Erwinia are devided as follow: (i) three strains of bacteria isolated from diseased tissues and soil, identified as Erwinia carotovora subsp carotovorum using conventional bacteriological and biochemical methods; and (ii) one strain as Erwinia sp, not pathogens. In vitro tests, on tuber slices were set up to determine slices weight lost, which allows to find differences in cultivar susceptibility and isolate aggressiveness. Among the five cultivars, Laura was the most susceptible than the others tested cultivars. Moreover, it was found that MAI isolate was the most virulent than the other bacterial isolates. The results of this study should allow an optimization of the potato storage, after considering the susceptibility of a given cultivar to soft rot development and the aggressiveness.

Conservation of Erwinia amylovora pathogenicity-relevant genes among Erwinia genomes

The Erwinia genus comprises species that are plant pathogens, non-pathogen, epiphytes, and opportunistic human pathogens. Within the genus, Erwinia amylovora ranks among the top 10 plant pathogenic bacteria. It causes the fire blight disease and is a global threat to commercial apple and pear production. We analyzed the presence/absence of the E. amylovora genes reported to be important for pathogenicity towards Rosaceae within various Erwinia strains genomes. This simple bottom-up approach, allowed us to correlate the analyzed genes to pathogenicity, host specificity, and make useful considerations to drive targeted studies.

Morphological heterogeneity of temperate erwiniophage 59

To investigate the basic properties of erwiniophage 59 heteroge- neous population obtained from different isogenic strains of amilovora-like bacterium Erwinia "horticola" (Eho). Erwiniophage 59 was obtained by propagation on its traditional host Eho 450, as well as on its three isogenic strains and a related bacterium E. "horticola" 60. Physical and chemical properties of the phage particles were studied using centrifugation in CsCl-gradients, electrophoresis in agarose gels, electron micros- copy, restriction analysis ofDNA and SDS-PA GE of the virion polypeptides. It was shown that the pool oftemperatephage 59 is a heterogeneous population consisting of two phage types when propagated on the mentioned hosts. These types are discrete and have buoyant-density difference of 0.02 g/cm3, that allowed to separate subpopulations for a de- tailed investigation. The subpopulation with the higher density was determined as the au- thentic bacteriophage 59 (subpopulation II with capsid diameter of55.36 nm). The capsid diameter of the subpopulation Iparticles equals 51.16 nm. Both types ofparticles do not differ by DNA size and have identical restriction patterns. Based on the SmaI-restriction analysis it may be concluded that the DNA packaging remains unchangeable and is carried out according to the headfull packaging mechanism. However; the subpopulation I differs from the original one by a relative content of some polypeptides. Curiously, the subpopulations I and II have different values of lysogenization and spontaneous induction frequencies. An unusual type of morphological heterogeneity ofthe phage 59 particles was observedfor thefirst time; this heterogeneity is associated with the presence of two equimolar subpopulations with different physical and chemical parametrs of the virions. Morphological heterogeneity of temperate erwiniophage 59 significantly differs from such of the classical coliphages as T4, P1 and the phage system P2-P4.

Detection of local Erwinia Isolates Causing Diseases in Potato by Using DNA Amplification by Polymerase Chain Reaction Technique (PCR)

Seventy samples of infected potato’s tubers were collected from Baghdad city during the period from September 2011 to February 2012. These samples were collected from Alradwaniyah potato’s store/ Albyaa market and from Awrad Alnahar potato’s store in Abu ghraib and two bacterial strains of Erwinia were obtained from Plant Protection department/ College of Agriculture/ Baghdad University. The Crystal Violet Pectate (CVP) used as a selective- diagnostic medium to isolate and purify Erwinia. The strains and isolates of Erwinia were characterized according to the morphology and microscopic characteristics, along with the biochemical tests and API 20E tests. The Erwinia isolates have a positive reaction for Catalase, Raffinose and Cellobiose and a negative reaction for Oxidase and Sorbitol. By using Reagent Genomic DNA Kit method for Total DNA extraction, during electrophoresis process, the results showed that some of selected isolates and the two standard strains of Erwinia contained at least two bands of small plasmid DNA. The identification was confirmed by using DNA amplification by polymerase chain reaction technique (PCR) and Erwinia carotovora subsp. carotovora specific primer such as (Ec001), the selected local isolates of Erwinia and Erwinia carotovora subsp. carotovora ATCC 15713 potato’s pathogen had a positive reaction (one band 312 bp) for the former primer.

Polymyxin P is the active principle in suppressing phytopathogenic Erwinia spp. by the biocontrol rhizobacterium Paenibacillus polymyxa M-1

BackgroundNine gene clusters dedicated to nonribosomal synthesis of secondary metabolites with possible antimicrobial action, including polymyxin and fusaricidin, were detected within the whole genome sequence of the plant growth-promoting rhizobacterium (PGPR) Paenibacillus polymyxa M-1. To survey the antimicrobial compounds expressed by M-1 we analyzed the active principle suppressing phytopathogenic Erwinia spp.ResultsP. polymyxa M-1 suppressed the growth of phytopathogenic Erwinia amylovora Ea 273, and E. carotovora, the causative agents of fire blight and soft rot, respectively. By MALDI-TOF mass spectrometry and reversed-phase high-performance liquid chromatography (RP-HPLC), two antibacterial compounds bearing molecular masses of 1190.9 Da and 1176.9 Da were detected as being the two components of polymyxin P, polymyxin P1 and P2, respectively. The active principle acting against the two Erwinia strains was isolated from TLC plates and identified by postsource decay (PSD)-MALDI-TOF mass spectrometry as polymyxin P1 and polymyxin P2. These findings were corroborated by domain structure analysis of the polymyxin (pmx) gene cluster detected in the M-1 chromosome which revealed that corresponding to the chemical structure of polymyxin P, the gene cluster is encoding D-Phe in position 6 and L-Thr in position 7.ConclusionsIdentical morphological changes in the cell wall of the bacterial phytopathogens treated with either crude polymyxin P or culture supernatant of M-1 corroborated that polymyxin P is the main component of the biocontrol effect exerted by strain M-1 against phytopathogenic Erwinia spp.

Gene‐for‐gene relationship in the host–pathogen system Malus × robusta 5–Erwinia amylovora

Fire blight is a destructive bacterial disease caused by Erwinia amylovora affecting plants in the family Rosaceae, including apple. Host resistance to fire blight is present mainly in accessions of Malus spp. and is thought to be quantitative in this pathosystem. In this study we analyzed the importance of the E. amylovora effector avrRpt2(EA) , a homolog of Pseudomonas syringae avrRpt2, for resistance of Malus × robusta 5 (Mr5). The deletion mutant E. amylovora Ea1189ΔavrRpt2(EA) was able to overcome the fire blight resistance of Mr5. One single nucleotide polymorphism (SNP), resulting in an exchange of cysteine to serine in the encoded protein, was detected in avrRpt2(EA) of several Erwinia strains differing in virulence to Mr5. E. amylovora strains encoding serine (S-allele) were able to overcome resistance of Mr5, whereas strains encoding cysteine (C-allele) were not. Allele specificity was also observed in a coexpression assay with Arabidopsis thaliana RIN4 in Nicotiana benthamiana. A homolog of RIN4 has been detected and isolated in Mr5. These results suggest a system similar to the interaction of RPS2 from A. thaliana and AvrRpt2 from P. syringae with RIN4 as guard. Our data are suggestive of a gene-for-gene relationship for the host-pathogen system Mr5 and E. amylovora.