Taxonomic relatedness between Pectobacterium carotovorum subsp. carotovorum, Pectobacterium carotovorum subsp. odoriferum and Pectobacterium carotovorum subsp. brasiliense subsp. nov

Multilocus sequence and phenotypic analysis of Pectobacterium and Dickeya type strains for identification of soft rot Pectobacteriaceae from symptomatic potato stems and tubers in Pennsylvania

Outbreaks of potato blackleg and soft rot caused by Pectobacterium species and more recently Dickeya species across the U.S. mid-Atlantic region have caused yield loss due to poor emergence as well as losses from stem and tuber rot. To develop management strategies for soft rot diseases, we must first identify which members of the soft rot Pectobacteriaceae are present in regional potato plantings. However, the rapidly expanding number of soft rot Pectobacteriaceae species and the lack of readily available comparative data for type strains of Pectobacterium and Dickeya hinder quick identification. This manuscript provides a comparative analysis of soft rot Pectobacteriaceae and a comprehensive comparison of type strains from this group using rep-PCR, MLSA and 16S sequence analysis, as well as phenotypic and physiological analyses using Biolog GEN III plates. These data were used to identify isolates cultured from symptomatic potato stems collected between 2016 and 2018. The isolates were characterized for phenotypic traits and by sequence analysis to identify the bacteria from potatoes with blackleg and soft rot symptoms in Pennsylvania potato fields. In this survey, P. actinidiae, P. brasiliense, P. polonicum, P. polaris, P. punjabense, P. parmentieri, and P. versatile were identified from Pennsylvania for the first time. Importantly, the presence of P. actinidiae in Pennsylvania represents the first report of this organism in the U.S. As expected, P. carotorvorum and D. dianthicola were also isolated. In addition to a resource for future work studying the Dickeya and Pectobacterium associated with potato blackleg and soft rot, we provide recommendations for future surveys to monitor for quarantine or emerging soft rot Pectobacteriace regionally.

The chemical structure of the O-antigen and enterobacterial common antigen of Pectobacterium brasiliense NCPPB 4609TS

Pectobacterium brasiliense is a widely distributed phytopathogenic bacterium that causes diseases such as soft rot and blackleg, leading to significant yield losses in potatoes as well as other vegetables and ornamental plants. Lipopolysaccharide (LPS) is an important virulence factor that plays an essential role in colonisation of plant tissues and overcoming the host defence mechanisms. The O-polysaccharide from the LPS of P. brasiliense strain NCPPB 4609TS (=CFBP 6617TS = LMG 21371TS = IFB5390) was structurally characterised using spectroscopic techniques and chemical methods. The analyses revealed that the polysaccharide repeating unit consists of Gal, GlcN and an unusual 3-amino-3,6-dideoxyglucose decorated with (R)-3-hydroxybutyric acid according to the structure shown below: In addition, another polysaccharide was isolated from bacterial cells, analysis of which led to the identification of an enterobacterial common antigen, containing N-acetyl-d-glucosamine, N-acetyl-d-mannosaminouronic acid, and 4-acetamido-4,6-dideoxy-d-galactose.

Pectobacterium carotovorum Subsp. brasiliense Causing Soft Rot in Eggplant in Xinjiang, China

An outbreak of stem rot in eggplants was observed in Heshuo County, Xinjiang, during winter 2021-2022 in about 12-35% of the eggplants in the region (about 40 hm2). The infected tissues yielded a total of four bacterial strains, which were subsequently subjected to physiological and biochemical assays as well as molecular identification. Based on these analyses, the pathogen was identified as Pectobacterium carotovorum subsp. brasiliense. The pathogenicity was confirmed through the fulfillment of Koch's postulates. The host range test confirmed the broad spectrum of species susceptible to infection by the strains. This study represents the first case of infection caused by P. carotovorum subsp. brasiliense resulting in stem rot in eggplant.

Phylogeographic Analysis of Soft-Rot-Causing Pectobacterium spp. Strains Obtained from Cabbage in Serbia

The aim of this study was to establish a link between genetic diversity and the geographic origin of Pectobacterium strains belonging to three species-P. carotovorum, P. versatile, and P. odoriferum-isolated from cabbage in Serbia by comparing their sequences with those of strains sourced from different hosts and countries in Europe, Asia, and North America. Phylogeographic relatedness was reconstructed using the Templeton, Crandall, and Sing's (TCS) haplotype network based on concatenated sequences of the housekeeping genes dnaX, icdA, mdh, and proA, while pairwise genetic distances were computed by applying the p-distance model. The obtained TCS haplotype networks indicated the existence of high intra-species genetic diversity among strains of all three species, as reflected in the 0.2-2.3%, 0.2-2.5%, and 0.1-1.7% genetic distance ranges obtained for P. carotovorum, P. versatile, and P. odoriferum, respectively. Five new haplotypes (denoted as HPc1-HPc5) were detected among cabbage strains of P. carotovorum, while one new haplotype was identified for both P. versatile (HPv1) and P. odoriferum (HPo1). None of the TCS haplotype networks provided evidence of significant correlation between geographic origin and the determined haplotypes, i.e., the infection origin. However, as haplotype network results are affected by the availability of sequencing data in public databases for the used genes and the number of analyzed strains, these findings may also be influenced by small sample size.

Pectobacterium jejuense sp. nov. Isolated from Cucumber Stem Tissue

A single Pectobacterium-like strain named 13-115T was isolated from a specimen of diseased cucumber stem tissue collected on Jeju Island, South Korea. The strain presented a rod-like shape and was negative for Gram staining. When grown on R2A medium at 25 °C, strain 13-115T formed round, convex and white colonies. This strain showed growth at temperatures ranging from 10 to 30 °C and tolerated a pH range of 6-9. The strain could also tolerate NaCl concentrations up to 5%. Analysis of the 16S rRNA gene sequence revealed that strain 13-115T exhibited similarity of over 99% with Pectobacterium brasiliense, P. carotovorum, P. polaris, and P. parvum. By conducting multilocus sequence analyses using dnaX, leuS, and recA genes, a separate phylogenetic lineage was discovered between strain 13-115T and other members of the genus Pectobacterium. Moreover, the strain showed relatively low in silico DNA-DNA hybridization (<60.6%) and average nucleotide identity (ANI) (<94.9%) values with recognized Pectobacterium species. The isolate has a genome size of 5,069,478 bp and a genomic G + C content of 52.04 mol%. Major fatty acids identified in the strain included C16:0 (28.99%), summed feature 3 (C16:1 ω7c and/or C16:1 ω6c; 28.85%), and C18:1 ω7c (19.01%). Pathogenicity assay confirmed that the novel strain induced soft rot symptoms in cucumber plants and Koch's postulates were fulfilled. Molecular analysis and phenotypic data indicated that strain 13-115T could be classified as a new species within the Pectobacterium genus, which has been named Pectobacterium jejuense. The type strain is 13-115T (= KCTC 92800T = JCM 35940T).

Diversity of Bacterial Soft Rot-Causing Pectobacterium Species Affecting Cabbage in Serbia

The aim of this work was to identify and characterize the pectolytic bacteria responsible for the emergence of bacterial soft rot on two summer cabbage hybrids (Cheers F1 and Hippo F1) grown in the Futog locality (Bačka, Vojvodina), known for the five-century-long tradition of cabbage cultivation in Serbia. Symptoms manifesting as soft lesions on outer head leaves were observed during August 2021, while the inner tissues were macerated, featuring cream to black discoloration. As the affected tissue decomposed, it exuded a specific odor. Disease incidence ranged from 15% to 25%. A total of 67 isolates producing pits on crystal violet pectate (CVP) medium were characterized for their phenotypic and genotypic features. The pathogenicity was confirmed on cabbage heads. Findings yielded by the repetitive element palindromic-polymerase chain reaction (rep-PCR) technique confirmed interspecies diversity between cabbage isolates, as well as intraspecies genetic diversity within the P. carotovorum group of isolates. Based on multilocus sequence typing (MLST) using genes dnaX, mdh, icdA, and proA, five representative isolates were identified as Pectobacterium carotovorum (Cheers F1 and Hippo F1), while two were identified as Pectobacterium versatile (Hippo F1) and Pectobacterium odoriferum (Hippo F1), respectively, indicating the presence of diverse Pectobacterium species even in combined infection in the same field. Among the obtained isolates, P. carotovorum was the most prevalent species (62.69%), while P. versatile and P. odoriferum were less represented (contributing by 19.40% and 17.91%, respectively). Multilocus sequence analysis (MLSA) performed with concatenated sequences of four housekeeping genes (proA, dnaX, icdA, and mdh) and constructed a neighbor-joining phylogenetic tree enabled insight into the phylogenetic position of the Serbian cabbage Pectobacterium isolates. Bacterium P. odoriferum was found to be the most virulent species for cabbage, followed by P. versatile, while all three species had comparable virulence with respect to potato. The results obtained in this work provide a better understanding of the spreading routes and abundance of different Pectobacterium spp. in Serbia.

Genetic Diversity of Pectobacterium spp. on Potato in Serbia

Pectobacterium is a diverse genus which comprises of multiple destructive bacterial species which cause soft rot/blackleg/wilt disease complex in a wide variety of crops by employing high levels of virulence factors. During the 2018, 2019 and 2020 potato growing seasons, numerous outbreaks of bacterial wilt, stem blackleg and tuber soft rot were recorded, and symptomatic plant samples from ten localities in the Province of Vojvodina (Serbia) were collected and analysed. Bacterial soft-rot pathogens were detected in 63 samples using genus and species-specific primers. Through 16S rRNA Sanger sequencing of 19 representative isolates, the identity of P. brasiliense (73.7%), P. punjabense (15.8%), and P. carotovorum (10.5%) species were revealed. To further validate the identification, genotypic profiling of Pectobacterium strains using rep-PCR (ERIC, BOX, REP) was conducted for 25 selected isolates and the phylogenetic assessment based on four selected housekeeping genes (gyrA, recA, rpoA, and rpoS). Physiological and biochemical properties were analysed using basic microbiological tests and VITEK^® 2 GN card, and pathogenicity was confirmed on cv. VR808 and cv. Desiree potato tubers and plants. This study confirmed the distinctiveness of the newly described P. punjabense in Serbia as well as the high diversity of Pectobacterium brasiliense and Pectobacterium carotovorum species in Serbia.

The International Trade of Ware Vegetables and Orna-Mental Plants—An Underestimated Risk of Accelerated Spreading of Phytopathogenic Bacteria in the Era of Globalisation and Ongoing Climatic Changes

Bacteria of the genus Pectobacterium are globally occurring pathogens that infect a broad spectrum of plants. The plant cell wall degrading enzymes allow them to cause diseases like soft rot and blackleg. Worldwide trade and exchange of plant material together with the accompanying microorganisms contributed to the rapid spread and consequently the acquisition of new traits by bacteria. The 161 pectinolytic strains were isolated from symptomless vegetables and ornamental plants acquired from Polish and foreign local food markets. All strains except four Dickeya isolates were identified as belonging to the Pectobacterium genus by PCR with species-specific primers and recA gene sequencing. The newly isolated bacteria were assigned to eight species, P. versatile (50 strains), P. carotovorum (33), P. brasiliense (27), P. atrosepticum (19), P. parmentieri (12), P. polaris (11), P. parvum (3) and P. odoriferum (2). ERIC PCR and phenotypic characteristics revealed high heterogeneity among P. carotovorum, P. brasiliense and P. versatile isolates. Moreover, a subset of the newly isolated strains was characterised by high tolerance to changing environmental conditions such as salinity, pH and water availability. These bacteria can effectively macerate the tissues of various plants, including potato, chicory and orchid. Our results indicate that Pectobacterium strains isolated from internationally traded, symptomless vegetables and ornamental plants have high potential for adaptation to adverse environmental conditions and to infect various host plants. These features may contribute to the success of the genus Pectobacterium in spreading between different climatic zones and facilitate the colonisation of different ecological niches.

Isolation and Genome Analysis of Pectobacterium colocasium sp. nov. and Pectobacterium aroidearum, Two New Pathogens of Taro

Bacterial soft rot is one of the most destructive diseases of taro (Colocasia esculenta) worldwide. In recent years, frequent outbreaks of soft rot disease have seriously affected taro production and became a major constraint to the development of taro planting in China. However, little is known about the causal agents of this disease, and the only reported pathogens are two Dickeya species and P. carotovorum. In this study, we report taro soft rot caused by two novel Pectobacterium strains, LJ1 and LJ2, isolated from taro corms in Ruyuan County, Shaoguan City, Guangdong Province, China. We showed that LJ1 and LJ2 fulfill Koch's postulates for taro soft rot. The two pathogens can infect taro both individually and simultaneously, and neither synergistic nor antagonistic interaction was observed between the two pathogens. Genome sequencing of the two strains indicated that LJ1 represents a novel species of the genus Pectobacterium, for which the name "Pectobacterium colocasium sp. nov." is proposed, while LJ2 belongs to Pectobacterium aroidearum. Pan-genome analysis revealed multiple pathogenicity-related differences between LJ1, LJ2, and other Pectobacterium species, including unique virulence factors, variation in the copy number and organization of Type III, IV, and VI secretion systems, and differential production of plant cell wall degrading enzymes. This study identifies two new soft rot Pectobacteriaceae (SRP) pathogens causing taro soft rot in China, reports a new case of co-infection of plant pathogens, and provides valuable resources for further investigation of the pathogenic mechanisms of SRP.

New PCR-Based Assay for the Identification of Pectobacterium carotovorum Causing Potato Soft Rot

Soft rot on potato tuber is a destructive disease caused by pathogenic bacterial species of the genera Pectobacterium and Dickeya. Accurate identification of the causal agent is necessary to ensure adequate disease management because different species may have distinct levels of aggressiveness and host range. One of the most important potato pathogens is Pectobacterium carotovorum, a highly heterogeneous species capable of infecting multiple hosts. The complexity of this species, until recently divided into several subspecies, has made it difficult to develop precise diagnostic tests. This study proposes a PCR assay based on the new pair of primers Pcar1F/R to facilitate the identification of potato isolates of P. carotovorum according to the most recent taxonomic description of this species. The new primers were designed on a variable segment of the 16S rRNA gene and the intergenic spacer region of available DNA sequences from classical and recently established species in the genus Pectobacterium. The results of the PCR analysis of genomic DNA from 32 Pectobacterium and Dickeya strains confirmed that the Pcar1F/R primers have sufficient nucleotide differences to discriminate between P. carotovorum and other Pectobacterium species associated with damage to potato crops, with the exception of Pectobacterium versatile, which improves the specificity of the currently available primers. The proposed assay was originally developed as a conventional PCR but was later adapted to the real-time PCR format for application in combination with the existing real-time PCR test for the potato-specific pathogen Pectobacterium parmentieri. This should be useful for the routine diagnosis of potato soft rot.

Genome-informed loop-mediated isothermal amplification assay for specific detection of Pectobacterium parmentieri in infected potato tissues and soil

Pectobacterium parmentieri (formerly Pectobacterium wasabiae), which causes soft rot disease in potatoes, is a newly established species of pectinolytic bacteria within the family Pectobacteriaceae. Despite serious damage caused to the potato industry worldwide, no field-deployable diagnostic tests are available to detect the pathogen in plant samples. In this study, we aimed to develop a reliable, rapid, field-deployable loop-mediated isothermal amplification (LAMP) assay for the specific detection of P. parmentieri. Specific LAMP primers targeting the petF1 gene region, found in P. parmentieri but no other Pectobacterium spp., were designed and validated in silico and in vitro using extensive inclusivity (15 strains of P. parmentieri) and exclusivity (94 strains including all other species in the genus Pectobacterium and host DNA) panels. No false positives or negatives were detected when the assay was tested directly with bacterial colonies, and with infected plant and soil samples. Sensitivity (analytical) assays using serially diluted bacterial cell lysate and purified genomic DNA established the detection limit at 10 CFU/mL and 100 fg (18-20 genome copies), respectively, even in the presence of host crude DNA. Consistent results obtained by multiple users/operators and field tests suggest the assay's applicability to routine diagnostics, seed certification programs, biosecurity, and epidemiological studies.

Occurrence, Characteristics, and PCR-Based Detection of Pectobacterium polaris Causing Soft Rot of Chinese Cabbage in China

Bacterial soft rot is an important disease of Chinese cabbage (Brassica rapa L. ssp. pekinensis) in China and many other countries. Four pectinolytic bacterial strains (WBC1, WBC6, WBC9, and WBC11) were isolated from soft-rotted Chinese cabbage in Beijing, China. Based on 16S rDNA and pmrA gene sequence analyses, multilocus sequence analysis (MLSA), and genomic average nucleotide identity (ANI) analysis, these four strains were identified as Pectobacterium polaris. This species, previously reported from potato in countries not including China, is a new soft rot pathogen of Chinese cabbage in China. Biochemical characteristics of these P. polaris strains tested by Biolog were mostly consistent with those of P. polaris NIBIO1006^T. Their pathogenicity on Chinese cabbage is temperature dependent, with all four strains as well as the type strain exhibiting high pathogenicity at 23°C and 28°C. These four strains infected Lactuca sativa, Daucus carota, Solanum tuberosum, and Capsicum annuum by artificial inoculation. Specific polymerase chain reaction (PCR) and quantitative PCR (qPCR) primers for P. polaris were developed on the basis of its specific gene sequences (determined by genome comparison methods). Both PCR and qPCR detected not only genomic DNA of P. polaris but also the pathogen from diseased plant tissues even before external symptoms appeared. Their detection sensitivities were as low as 1 pg and 100 pg genomic DNA of P. polaris, respectively. To our knowledge, this study is the first to both report the emergence of P. polaris on Chinese cabbage in China and provide rapid and accurate PCR/qPCR-based detection systems specific for P. polaris.

The First Polish Isolate of a Novel Species Pectobacterium aquaticum Originates from a Pomeranian Lake

Pectinolytic bacteria from the genus Pectobacterium cause high economic losses in various crops, vegetables, and ornamentals including potato. Thus far, these strains have been isolated from distinct environments such as rotten or asymptomatic plants, soil, and waterways. The prevalence of soft rot Pectobacteriaceae in different depths of Pomeranian lakes was performed by a qualified scuba diver over 2 years of monitoring. It allowed for the isolation and broad characterization of a strain from the newly established species Pectobacterium aquaticum. Phylogenetic analysis on the sequences of dnaX and recA genes revealed the highest similarity of this strain to P. aquaticum CFBP 8637^T. In addition to the determination of analytical profile index (API 20E), we discovered that this strain possesses a smooth form of a lipopolysaccharide with O-polysaccharide consisting of mannose, glucose, and abequose. Moreover, the characterized strain, described as P. aquaticum IFB5637, produced plant-cell–wall-degrading enzymes, such as pectinases, cellulases, proteases, and was capable of macerating potato and chicory tissues under laboratory conditions. In view of more frequent irrigation of seed potato fields resulting from the ongoing climate warming, it is important to monitor the occurrence of potential disease-causing agents in natural waterways.

The Pectobacterium pangenome, with a focus on Pectobacterium brasiliense, shows a robust core and extensive exchange of genes from a shared gene pool

BACKGROUND

Bacterial plant pathogens of the Pectobacterium genus are responsible for a wide spectrum of diseases in plants, including important crops such as potato, tomato, lettuce, and banana. Investigation of the genetic diversity underlying virulence and host specificity can be performed at genome level by using a comprehensive comparative approach called pangenomics. A pangenomic approach, using newly developed functionalities in PanTools, was applied to analyze the complex phylogeny of the Pectobacterium genus. We specifically used the pangenome to investigate genetic differences between virulent and avirulent strains of P. brasiliense, a potato blackleg causing species dominantly present in Western Europe.

RESULTS

Here we generated a multilevel pangenome for Pectobacterium, comprising 197 strains across 19 species, including type strains, with a focus on P. brasiliense. The extensive phylogenetic analysis of the Pectobacterium genus showed robust distinct clades, with most detail provided by 452,388 parsimony-informative single-nucleotide polymorphisms identified in single-copy orthologs. The average Pectobacterium genome consists of 47% core genes, 1% unique genes, and 52% accessory genes. Using the pangenome, we zoomed in on differences between virulent and avirulent P. brasiliense strains and identified 86 genes associated to virulent strains. We found that the organization of genes is highly structured and linked with gene conservation, function, and transcriptional orientation.

CONCLUSION

The pangenome analysis demonstrates that evolution in Pectobacteria is a highly dynamic process, including gene acquisitions partly in clusters, genome rearrangements, and loss of genes. Pectobacterium species are typically not characterized by a set of species-specific genes, but instead present themselves using new gene combinations from the shared gene pool. A multilevel pangenomic approach, fusing DNA, protein, biological function, taxonomic group, and phenotypes, facilitates studies in a flexible taxonomic context.

Biocontrol of Soft Rot Caused by Pectobacterium odoriferum with Bacteriophage phiPccP-1 in Kimchi Cabbage

Pectobacterium odoriferum has recently emerged as a widely infective and destructive pathogen causing soft-rot disease in various vegetables. Bacteriophage phiPccP-1 isolated from Pyeongchang, South Korea, showed lytic activity against P. odoriferum Pco14 and two other Pectobacterium species. The transmission electron microscopy and genome phylograms revealed that phiPccP-1 belongs to the Unyawovirus genus, Studiervirinae subfamily of the Autographivirinae family. Genome comparison showed that its 40,487 bp double-stranded DNA genome shares significant similarity with Pectobacterium phage DU_PP_II with the identity reaching 98% of the genome. The phiPccP-1 application significantly inhibited the development of soft-rot disease in the mature leaves of the harvested Kimchi cabbage up to 48 h after Pco14 inoculation compared to the untreated leaves, suggesting that phiPccP-1 can protect Kimchi cabbage from soft-rot disease after harvest. Remarkably, bioassays with phiPccP-1 in Kimchi cabbage seedlings grown in the growth chamber successfully demonstrated its prophylactic and therapeutic potential in the control of bacterial soft-rot disease in Kimchi cabbage. These results indicate that bacteriophage phiPccP-1 can be used as a potential biological agent for controlling soft rot disease in Kimchi cabbage.

Occurrence and Identification of Pectobacterium carotovorum subsp. brasiliensis and Dickeya dianthicola Causing Blackleg in Some Potato Fields in Serbia

Blackleg outbreaks were noticed on three fields (about 100 ha total) in 2 consecutive years (2018, 2019) in one of the main potato growing areas in Serbia (Bačka region, Vojvodina). The percentage of infected plants reached 40 to 70%, with 10.5 to 44.7% yield reductions. From the three fields, out of 90 samples Pectobacterium carotovorum subsp. brasiliensis was most frequently identified and diagnosed as causal agent of potato blackleg in Serbia for the first time (29 isolates). Dickeya dianthicola was a less frequently causative bacterium, which was also noticed for the first time (nine isolates). A total of 38 isolates were characterized based on their phenotypic and genetic features, including a pathogenicity test on potato. The repetitive element PCR (rep-PCR) using BOX, REP, and ERIC primer pairs differentiated five genetic profiles among 38 tested isolates. Multilocus sequence analysis (MLSA) of four housekeeping genes, acnA, gapA, icdA, and mdh, revealed the presence of three so far unknown P. c. subsp. brasiliensis multilocus genotypes and confirmed clustering into two main genetic clades as determined in other studies. MLSA also revealed the presence of a new genotype of D. dianthicola in Serbia.

Pectobacterium brasiliense: Genomics, Host Range and Disease Management

Pectobacterium brasiliense (Pbr) is considered as one of the most virulent species among the Pectobacteriaceae. This species has a broad host range within horticulture crops and is well distributed elsewhere. It has been found to be pathogenic not only in the field causing blackleg and soft rot of potato, but it is also transmitted via storage causing soft rot of other vegetables. Genomic analysis and other cost-effective molecular detection methods such as a quantitative polymerase chain reaction (qPCR) are essential to investigate the ecology and pathogenesis of the Pbr. The lack of fast, field deployable point-of-care testing (POCT) methods, specific control strategies and current limited genomic knowledge make management of this species difficult. Thus far, no comprehensive review exists about Pbr, however there is an intense need to research the biology, detection, pathogenicity and management of Pbr, not only because of its fast distribution across Europe and other countries but also due to its increased survival to various climatic conditions. This review outlines the information available in peer-reviewed literature regarding host range, detection methods, genomics, geographical distribution, nomenclature and taxonomical evolution along with some of the possible management and control strategies. In summary, the conclusions and a further directions highlight the management of this species.

Updated Taxonomy of Pectobacterium Genus in the CIRM-CFBP Bacterial Collection: When Newly Described Species Reveal "Old" Endemic Population

Bacterial collections are invaluable tools for microbiologists. However, their practical use is compromised by imprecise taxonomical assignation of bacterial strains. This is particularly true for soft rotting plant pathogens of the Pectobacterium genus. We analysed the taxonomic status of 265 Pectobacterium strains deposited at CIRM-CFBP collection from 1944 to 2020. This collection gathered Pectobacterium strains isolated in 27 countries from 32 plant species representing 17 botanical families or from nonhost environments. The MLSA approach completed by genomic analysis of 15 strains was performed to update the taxonomic status of these 265 strains. The results showed that the CIRM-CFBP Pectobacterium collection harboured at least one strain of each species, with the exception of P. polonicum. Yet, seven strains could not be assigned to any of the described species and may represent at least two new species. Surprisingly, P. versatile, recently described in 2019, is the most prevalent species among CIRM-CFBP strains. An analysis of P. versatile strains revealed that this species is pandemic and isolated from various host plants and environments. At the opposite, other species gathered strains isolated from only one botanical family or exclusively from a freshwater environment. Our work also revealed new host plants for several Pectobacterium spp.

Distribution of Pectobacterium Species Isolated in South Korea and Comparison of Temperature Effects on Pathogenicity

Pectobacterium, which causes soft rot disease, is divided into 18 species based on the current classification. A total of 225 Pectobacterium strains were isolated from 10 main cultivation regions of potato (Solanum tuberosum), napa cabbage (Brassica rapa subsp. pekinensis), and radish (Raphanus sativus) in South Korea; 202 isolates (90%) were from potato, 18 from napa cabbage, and five from radish. Strains were identified using the Biolog test and phylogenetic analysis. The pathogenicity and swimming motility were tested at four different temperatures. Pectolytic activity and plant cell-wall degrading enzyme (PCWDE) activity were evaluated for six species (P. carotovorum subsp. carotovorum, Pcc; P. odoriferum, Pod; P. brasiliense, Pbr; P. versatile, Pve; P. polaris, Ppo; P. parmentieri, Ppa). Pod, Pcc, Pbr, and Pve were the most prevalent species. Although P. atrosepticum is a widespread pathogen in other countries, it was not found here. This is the first report of Ppo, Ppa, and Pve in South Korea. Pectobacterium species showed stronger activity at 28°C and 32°C than at 24°C, and showed weak activity at 37°C. Pectolytic activity decreased with increasing temperature. Activity of pectate lyase was not significantly affected by temperature. Activity of protease, cellulase, and polygalacturonase decreased with increasing temperature. The inability of isolated Pectobacterium to soften host tissues at 37°C may be a consequence of decreased motility and PCWDE activity. These data suggest that future increases in temperature as a result of climate change may affect the population dynamics of Pectobacterium.

Characteristics and Rapid Diagnosis of Pectobacterium carotovorum ssp. Associated With Bacterial Soft Rot of Vegetables in China

Pectobacterium carotovorum, a causal agent of vegetable soft rot, contains three valid subspecies: P. carotovorum subsp. carotovorum (Pcc), P. carotovorum subsp. brasiliensis (Pcb), and P. carotovorum subsp. odoriferum (Pco). Using 16S rDNA sequencing and genus-specific PCR, we identified 72 P. carotovorum strains from Chinese cabbage, bok choy, and celery and assessed their pathogenicity on Chinese cabbage petioles and potato tubers. Based on phylogenetic analysis of pmrA sequences and confirmation by subspecies-specific PCR, the strains were divided into 18 Pcc, 29 Pco, and 25 Pcb. Several characteristic features were also assessed and supported the distinctiveness of the Pco strains. All P. carotovorum strains caused soft rot symptoms on Chinese cabbage and potato, but the Pco strains exhibited the greatest severity. We developed a conventional PCR and a quantitative PCR (qPCR) assay for the identification of Pco based on its specific srlE gene encoding sorbitol-specific phosphotransferase. These two methods could specifically amplify the expected products of 674 and 108 bp, respectively, from all of the Pco strains. The assays demonstrated high sensitivity and could detect as little as 1 and 100 pg/µl of bacterial genomic DNA, respectively. Both assays could also detect the pathogens directly from plant tissues infected with as little as 2.5 × 10^-2 CFU/mg of Pco, even before external symptoms appeared. These assays constitute effective tools for disease diagnosis and the rapid identification of soft rot pathogens.

Morphologically Different Pectobacterium brasiliense Bacteriophages PP99 and PP101: Deacetylation of O-Polysaccharide by the Tail Spike Protein of Phage PP99 Accompanies the Infection

Soft rot caused by numerous species of Pectobacterium and Dickeya is a serious threat to the world production of potatoes. The application of bacteriophages to combat bacterial infections in medicine, agriculture, and the food industry requires the selection of comprehensively studied lytic phages and the knowledge of their infection mechanism for more rational composition of therapeutic cocktails. We present the study of two bacteriophages, infective for the Pectobacterium brasiliense strain F152. Podoviridae PP99 is a representative of the genus Zindervirus, and Myoviridae PP101 belongs to the still unclassified genomic group. The structure of O-polysaccharide of F152 was established by sugar analysis and 1D and 2D NMR spectroscopy:

→ 4)-α-D-Manp6Ac-(1→ 2)-α-D-Manp-(1→ 3)-β-D-Galp-(1→ 3↑1α-l-6dTalpAc0−2

The recombinant tail spike protein of phage PP99, gp55, was shown to deacetylate the side chain talose residue of bacterial O-polysaccharide, thus providing the selective attachment of the phage to the cell surface. Both phages demonstrate lytic behavior, thus being prospective for therapeutic purposes.

Genome-Wide Analyses Revealed Remarkable Heterogeneity in Pathogenicity Determinants, Antimicrobial Compounds, and CRISPR-Cas Systems of Complex Phytopathogenic Genus Pectobacterium

The Pectobacterium genus comprises pectolytic enterobacteria defined as the causal agents of soft rot, blackleg, and aerial stem rot diseases of potato and economically important crops. In this study, we undertook extensive genome-wide comparative analyses of twelve species that conform the Pectobacterium genus. Bioinformatics approaches outlined a low nucleotide identity of P. parmentieri and P. wasabiae with other species, while P. carotovorum subsp. odoriferum was shown to harbor numerous pseudogenes, which suggests low coding capacity and genomic degradation. The genome atlases allowed for distinguishing distinct DNA structures and highlighted suspicious high transcription zones. The analyses unveiled a noteworthy heterogeneity in the pathogenicity determinants. Specifically, phytotoxins, polysaccharides, iron uptake systems, and the type secretion systems III-V were observed in just some species. Likewise, a comparison of gene clusters encoding antimicrobial compounds put in evidence for high conservation of carotovoricin, whereas a few species possessed the phenazine, carbapenem, and carocins. Moreover, three clustered regularly interspaced short palindromic repeats-Cas (CRISPR-Cas) systems: I-E, I-F, and III-A were identified. Surrounding some CRISPR-Cas regions, different toxin and antitoxin systems were found, which suggests bacterial suicide in the case of an immune system failure. Multiple whole-genome alignments shed light on to the presence of a novel cellobiose phosphotransferase system (PTS) exclusive to P. parmenteri, and an unreported T5SS conserved in almost all species. Several regions that were associated with virulence, microbe antagonism, and adaptive immune systems were predicted within genomic islands, which underscored the essential role that horizontal gene transfer has imparted in the dynamic evolution and speciation of Pectobacterium species. Overall, the results decipher the different strategies that each species has developed to infect their hosts, outcompete for food resources, and defend against bacteriophages. Our investigation provides novel genetic insights that will assist in understanding the pathogenic lifestyle of Pectobacterium, a genus that jeopardizes the agriculture sustainability of important crops worldwide.

Elevation of Pectobacterium carotovorum subsp. odoriferum to species level as Pectobacterium odoriferum sp. nov., proposal of Pectobacterium brasiliense sp. nov. and Pectobacterium actinidiae sp. nov., emended description of Pectobacterium carotovorum and description of Pectobacterium versatile sp. nov., isolated from streams and symptoms on diverse plants

The Pectobacteriumcarotovorum species corresponds to a complex, including two subspecies with validly published names, two proposed subspecies and two new species, Pectobacterium polaris and Pectobacterium aquaticum. Recent studies suggested that this complex needed revision. We examined the taxonomic status of 144 Pectobacterium strains isolated from a wide range of plant species, various geographical origins and waterways. Sequences of the leuS, dnaX and recA housekeeping genes clustered 114 of these Pectobacterium strains together within a not yet described clade. We sequenced eight strains of this clade and analysed them together with the 102 Pectobacterium genomes available in the NCBI database. Phylogenetic analysis, average nucleotide identity calculation and in silico DNA-DNA hybridization allowed us to differentiate seven clades. This led us to propose the elevation of Pectobacterium carotovorumsubsp. odoriferum to species level as Pectobacteriumodoriferum sp. nov. (type strain CFBP 1878^T=LMG 5863^T=NCPPB 3839^T=ICMP 11533^T), the proposal of Pectobacteriumactinidiae sp. nov. (type strain KKH3=LMG 26003 ^T=KCTC 23131^T) and Pectobacteriumbrasiliense sp. nov. (type strain CFBP 6617^T= LMG 21371^T=NCPPB 4609^T), to emend the description of Pectobacterium carotovorum (type strain CFBP 2046^T=LMG 2404^T=NCPPB 312^T=ICMP 5702^T), and to propose a novel species, Pectobacterium versatile sp. nov (type strain CFBP6051^T= NCPPB 3387^T=ICMP 9168^T) which includes the strains previously described as 'Candidatus Pectobacterium maceratum'. Phenotypic analysis performed using Biolog GENIII plates on eight strains of P. versatile sp. nov. and related strains completed our analysis.

Pectobacterium carotovorum subsp. brasiliense Causes Soft Rot and Death of Neobuxbaumia tetetzo in Zapotitlan Salinas Valley, Puebla, Mexico

Neobuxbaumia tetetzo (Coulter) Backeberg (tetecho) is a columnar cactus endemic to Mexico. Tetecho plants, flowers, fruits, and seeds play an important role in the semiarid ecosystem, as they serve as a refuge and food for insects, bats, and birds, and are widely used by ethnic groups since pre-Hispanic times. Tetecho is affected by a soft rot that damages the whole plant and causes its fall and disintegration. Eight bacterial colonies of similar morphology were isolated from plants showing soft rot and inoculated in healthy tetecho plants, reproducing typical symptoms of soft rot 9 days after inoculation. Ten representative isolates were selected for phenotypic and genetic identification using 16s rDNA, IGS 16S-23S rDNA, and rpoS genes and for pathogenicity tests on several members of the cactus family and other plants. Based on the results, these bacterial isolates were identified as Pectobacterium carotovorum subsp. brasiliense. Inoculation of this bacteria caused soft rot in different cacti, fruits, leaves, and roots of other plants. This is the first report of the subspecies brasiliense of P. carotovorum causing soft rot and death in cacti in the world and the first report of this subspecies in Mexico.

Pectobacterium aquaticum sp. nov., isolated from waterways

This work aimed to establish the taxonomic status of six strains (A212-S19-A16^T, A127-S21-F16, A105-S21-F16, A104-S21-F16, A101-S19-F16 and A35-S23-M15) isolated from three different waterways in 2015 and 2016 in south-east France. Amplification and sequencing of the gapA housekeeping gene clustered these six strains together inside the genus Pectobacterium outside of already described or proposed Pectobacterium species and supspecies. Phenotypic analysis, using GENIII Biolog plates performed with strains A212-S19-A16^T, A105-S21-F16, A101-S19-F16 and the closely related Pectobacterium polaris(CFBP 1403), Pectobacterium carotovorum subsp. odoriferum (CFBP 1878^T), 'Pectobacteriumcarotovorum subsp. actinidiae' (CFBP 7370), Pectobacterium carotovorum subsp. carotovorum (CFBP 2046^T), 'Pectobacterium carotovorum subsp. brasiliense' (CFBP 6617) or the most distantly related Pectobacteriumaroidearum (CFBP 8168^T) failed to identify specific compounds metabolized by these three strains, but weak activity was specifically observed at pH 5 with these three strains. Illumina sequencing was used to sequence these six strains. Based on phylogenetic data, average nucleotide identity values and in silico DNA-DNA hybridization results, strains A212-S19-A16^T, A127-S21-F16, A105-S21-F16, A101-S19-F16, A35-S23-M15 and A104-S21-F16 are suggested to represent a novel species of the genus Pectobacterium, for which the name Pectobacterium aquaticum sp. nov. is proposed. The type strain is A212-S19-A16 ^T (=CFBP 8637^T=NCPPB 4640^T).

Comparative genomics of 84 Pectobacterium genomes reveals the variations related to a pathogenic lifestyle

BACKGROUND

Pectobacterium spp. are necrotrophic bacterial plant pathogens of the family Pectobacteriaceae, responsible for a wide spectrum of diseases of important crops and ornamental plants including soft rot, blackleg, and stem wilt. P. carotovorum is a genetically heterogeneous species consisting of three valid subspecies, P. carotovorum subsp. brasiliense (Pcb), P. carotovorum subsp. carotovorum (Pcc), and P. carotovorum subsp. odoriferum (Pco).

RESULTS

Thirty-two P. carotovorum strains had their whole genomes sequenced, including the first complete genome of Pco and another circular genome of Pcb, as well as the high-coverage genome sequences for 30 additional strains covering Pcc, Pcb, and Pco. In combination with 52 other publicly available genome sequences, the comparative genomics study of P. carotovorum and other four closely related species P. polaris, P. parmentieri, P. atrosepticum, and Candidatus P. maceratum was conducted focusing on CRISPR-Cas defense systems and pathogenicity determinants. Our analysis identified two CRISPR-Cas types (I-F and I-E) in Pectobacterium, as well as another I-C type in Dickeya that is not found in Pectobacterium. The core pathogenicity factors (e.g., plant cell wall-degrading enzymes) were highly conserved, whereas some factors (e.g., flagellin, siderophores, polysaccharides, protein secretion systems, and regulatory factors) were varied among these species and/or subspecies. Notably, a novel type of T6SS as well as the sorbitol metabolizing srl operon was identified to be specific to Pco in Pectobacterium.

CONCLUSIONS

This study not only advances the available knowledge about the genetic differentiation of individual subspecies of P. carotovorum, but also delineates the general genetic features of P. carotovorum by comparison with its four closely related species, thereby substantially enriching the extent of information now available for functional genomic investigations about Pectobacterium.

High genomic variability in the plant pathogenic bacterium Pectobacterium parmentieri deciphered from de novo assembled complete genomes

BACKGROUND

Pectobacterium parmentieri is a newly established species within the plant pathogenic family Pectobacteriaceae. Bacteria belonging to this species are causative agents of diseases in economically important crops (e.g. potato) in a wide range of different environmental conditions, encountered in Europe, North America, Africa, and New Zealand. Severe disease symptoms result from the activity of P. parmentieri virulence factors, such as plant cell wall degrading enzymes. Interestingly, we observe significant phenotypic differences among P. parmentieri isolates regarding virulence factors production and the abilities to macerate plants. To establish the possible genomic basis of these differences, we sequenced 12 genomes of P. parmentieri strains (10 isolated in Poland, 2 in Belgium) with the combined use of Illumina and PacBio approaches. De novo genome assembly was performed with the use of SPAdes software, while annotation was conducted by NCBI Prokaryotic Genome Annotation Pipeline.

RESULTS

The pan-genome study was performed on 15 genomes (12 de novo assembled and three reference strains: P. parmentieri CFBP 8475T, P. parmentieri SCC3193, P. parmentieri WPP163). The pan-genome includes 3706 core genes, a high number of accessory (1468) genes, and numerous unique (1847) genes. We identified the presence of well-known genes encoding virulence factors in the core genome fraction, but some of them were located in the dispensable genome. A significant fraction of horizontally transferred genes, virulence-related gene duplications, as well as different CRISPR arrays were found, which can explain the observed phenotypic differences. Finally, we found also, for the first time, the presence of a plasmid in one of the tested P. parmentieri strains isolated in Poland.

CONCLUSIONS

We can hypothesize that a large number of the genes in the dispensable genome and significant genomic variation among P. parmentieri strains could be the basis of the potential wide host range and widespread diffusion of P. parmentieri. The obtained data on the structure and gene content of P. parmentieri strains enabled us to speculate on the importance of high genomic plasticity for P. parmentieri adaptation to different environments.

Draft genomes of "Pectobacterium peruviense" strains isolated from fresh water in France

Bacteria belonging to the genus Pectobacterium are responsible for soft rot disease on a wide range of cultivated crops. The "Pectobacterium peruviense" specie, recently proposed inside the Pectobacterium genus, gathers strains isolated from potato tubers cultivated in Peru at high altitude. Here we report the draft genome sequence of two strains belonging to "P. peruviense" isolated from river water in France indicating that the geographic distribution of this specie is likely to be larger than previously anticipated. We compared these genomes with the one published from the "P. peruviense" specie type strain isolated in Peru.

Pectobacterium punjabense sp. nov., isolated from blackleg symptoms of potato plants in Pakistan

Pectobacterium isolates SS95^T, SS54 and SS56 were collected from a potato field in the Chiniot district in the plains of the Punjab province, Pakistan. Sequencing of the gapA barcode revealed that these strains belong to a novel phylogenetic group separated from P.ectobacterium wasabiae and Pectobacterium parmentieri species. Furthermore, multilocus sequence analyses of 13 housekeeping genes (fusA, rpoD, acnA, purA, gyrB, recA, mdh, mtlD, groEL, secY, glyA, gapA and rplB) clearly distinguished the type strain, SS95^T, from its closest relatives, i.e. P. parmentieri RNS 08-42-1A^T and P. wasabiae CFBP3304^T, as well as from all the other known Pectobacteriumspecies. In silico DNA-DNA hybridization (<44.1 %) and average nucleotide identity (<90.75 %) values of strain SS95^T compared with other Pectobacterium type strains supported the delineation of a new species. Genomic and phenotypic comparisons permitted the identification of additional traits that distinguished the Pakistani isolates from all other known Pectobacterium type strains. The name Pectobacterium punjabense sp. nov. is proposed for this taxon with the type strain SS95^T (=CFBP 8604^T=LMG 30622^T).

Transfer of Pectobacterium carotovorum subsp. carotovorum strains isolated from potatoes grown at high altitudes to Pectobacterium peruviense sp. nov

Seven Gram-negative, rod-shaped pectinolytic bacteria strains designated as IFB5227, IFB5228, IFB5229, IFB5230, IFB5231, IFB5232, IFB5636, isolated from potato tubers cultivated in Peru at high altitude (2400-3800m) were subjected to polyphasic analyses that revealed their distinctiveness from the other Pectobacterium species. Phylogenetic analyses based on five housekeeping genes (gyrA, recA, recN, rpoA and rpoS) clearly showed strains separateness, simultaneously indicating Pectobacterium atrosepticum, Pectobacterium wasabiae, Pectobacterium parmentieri and Pectobacterium betavasculorum as the closest relatives. In silico DNA-DNA hybridization of strain IFB5232^T with other Pectobacterium type strains revealed significant drop in DDH value below 70%, which is a prerequisite to distinguish Pectobacterium peruviense. The ANI values supported the proposition of delineation of the P. peruviense. Genetic REP-PCR fingerprint and detailed MALDI-TOF MS proteomic profile sealed the individuality of the studied strains. However, phenotypic assays do not indicate immense differences. Provided results of analyses performed for seven Peruvian strains are the basis for novel species distinction and reclassification of the strains IFB5227-5232 and IFB5636, previously classified as Pectobacterium carotovorum subsp. carotovorum. Here, we propose to establish the IFB5232 isolate as a type strain (=PCM2893^T=LMG30269^T=SCRI179^T) with the name Pectobacterium peruviense sp. nov.

Pectobacterium polaris sp. nov., isolated from potato (Solanum tuberosum)

The genus Pectobacterium, which belongs to the bacterial family Enterobacteriaceae, contains numerous species that cause soft rot diseases in a wide range of plants. The species Pectobacterium carotovorum is highly heterogeneous, indicating a need for re-evaluation and a better classification of the species. PacBio was used for sequencing of two soft-rot-causing bacterial strains (NIBIO1006^T and NIBIO1392), initially identified as P. carotovorumstrains by fatty acid analysis and sequencing of three housekeeping genes (dnaX, icdA and mdh). Their taxonomic relationship to other Pectobacterium species was determined and the distance from any described species within the genus Pectobacterium was less than 94 % average nucleotide identity (ANI). Based on ANI, phylogenetic data and genome-to-genome distance, strains NIBIO1006^T, NIBIO1392 and NCPPB3395 are suggested to represent a novel species of the genus Pectobacterium, for which the name Pectobacterium polaris sp. nov. is proposed. The type strain is NIBIO1006^T (=DSM 105255^T=NCPPB 4611^T).

Molecular methods as tools to control plant diseases caused by Dickeya and Pectobacterium spp: A minireview

Dickeya spp. and Pectobacterium spp. are etiological agents of soft rot on crops, vegetables, and ornamentals. They also cause blackleg on potato. These pectinolytic phytopathogens are responsible for significant economic losses, mostly within the potato production sector. Importantly, there are no methods to eradicate these microorganisms once they have infected plant material. Solely preventive measures remain, including early detection and identification of the pathogens, monitoring of their spread in addition to planting certified seed material tested for latent infections. As proper identification of the causative agent allows for efficient limitation of disease spread, numerous detection and differentiation methods have been developed. Most commonly followed procedures involve: isolation of viable bacterial cells (alternatively post-enrichment) on semi-selective media, identification to species level by PCR (single, multiplex, Real time), serology or fatty acids profiling. Differentiation of the isolates is often accomplished by sequencing the housekeeping genes or molecular fingerprinting. In view of lowering total costs of next-generation sequencing (NGS), a huge amount of generated data reveals subtle differences between strains that have proven to be potentially useful for the establishment of specific novel detection pipelines. Successful implementation of molecular diagnostic methods is exemplified by 20-year studies on the populations of pectinolytic bacteria on potatoes in Poland. The presented work aims to gather the characteristics of Dickeya spp. and Pectobacterium spp. important for the identification process in addition to providing an overview of modern and newly developed specific, rapid, high-throughput and cost-effective screening methods for the detection and identification of these phytopathogens.

Genomic characterization of bacteriophage vB_PcaP_PP2 infecting Pectobacterium carotovorum subsp. carotovorum, a new member of a proposed genus in the subfamily Autographivirinae

Bacteriophage vB_PcaP_PP2 (PP2) is a novel virulent phage that infects the plant-pathogenic bacterium Pectobacterium carotovorum subsp. carotovorum. PP2 phage has a 41,841-bp double-stranded DNA encoding 47 proteins, and it was identified as a member of the family Podoviridae by transmission electron microscopy. Nineteen of its open reading frames (ORFs) show homology to functional proteins, and 28 ORFs have been characterized as hypothetical proteins. PP2 phage is homologous to Cronobacter phage vB_CskP_GAP227 and Dev-CD-23823. Based on phylogenetic analysis, PP2 and its homologous bacteriophages form a new group within the subfamily Autographivirinae in the family Podoviridae, suggesting the need to establish a new genus. No lysogenic-cycle-related genes or bacterial toxins were identified.

Emergence of Bacterial Soft Rot in Cucumber Caused by Pectobacterium carotovorum subsp. brasiliense in China

During 2014 to 2015, a devastating bacterial soft rot on cucumber stems and leaves occurred in Shandong, Shanxi, Hebei, Henan, and Liaoning provinces of China, resulting in serious economic losses for cucumber production. The gummosis emerged on the surface of leaves, stems, petioles, and fruit of cucumber. The basal stem color was dark brown and the stem base turned to wet rot. Yellow spots and wet rot emerged at the edge of the infected cucumber leaves and gradually infected the leaf centers. In total, 45 bacterial strains were isolated from the infected tissues. On the basis of phenotypic properties of morphology, physiology, biochemistry, and 16S ribosomal RNA gene sequence analysis, the pathogen was identified as Pectobacterium carotovorum. Multilocus sequence analysis confirmed that the isolates were P. carotovorum subsp. brasiliense, and the pathogens fell in clade II. The pathogenicity of isolated bacteria strains was confirmed. The strains reisolated were the same as the original. The host range test confirmed that strains had a wide range of hosts. As far as we know, this is the first report of cucumber stem soft rot caused by P. carotovorum subsp. brasiliense in China as well as in the world, which has a significant economic impact on cucumber production.

A quorum sensing-defective mutant of Pectobacterium carotovorum ssp. brasiliense 1692 is attenuated in virulence and unable to occlude xylem tissue of susceptible potato plant stems

Pectobacterium carotovorum ssp. brasiliense 1692 (Pcb1692) is an important emerging pathogen of potatoes causing blackleg in the field and soft rot during post-harvest storage. Blackleg diseases involve the bacterial colonization of vascular tissue and the formation of aggregates, also known as biofilms. To understand the role of quorum sensing in vascular colonization by Pcb1692, we generated a Pcb1692ΔexpI mutant strain. Inactivation of expI led to the reduced production of plant cell wall-degrading enzymes (PCWDEs), the inability to produce acyl homoserine lactone (AHL) and reduced virulence in potato tubers and stems. Complementation of the mutant strain with the wild-type expI gene in trans successfully restored AHL and PCWDE production as well as virulence. Transmission electron microscopy and in vitro motility assays demonstrated hyperpiliation and loss of flagella and swimming motility in the mutant strain compared with the wild-type Pcb1692. Furthermore, we noted that, in the early stages of infection, Pcb1692 wild-type cells had intact flagella which were shed at the later stages of infection. Confocal laser microscopy of PcbΔexpI-inoculated plants showed that the mutant strain tended to aggregate in intercellular spaces, but was unable to transit to xylem tissue. On the contrary, the wild-type strain was often observed forming aggregates within xylem tissue of potato stems. Gene expression analyses confirmed that flagella are part of the quorum sensing regulon, whereas fimbriae and pili appear to be negatively regulated by quorum sensing. The relative expression levels of other important putative virulence genes, such as those encoding different groups of PCWDEs, were down-regulated in the mutant compared with the wild-type strain.

Draft genome of a South African strain of Pectobacterium carotovorum subsp. brasiliense

The draft genome of Pectobacterium carotovorum subsp. brasiliense (Pcb) which causes blackleg of potato was submitted to the NCBI and released with reference number NZ_LGRF00000000.1. The estimated genome size based on the draft genome assembly is 4,820,279 bp from 33 contigs ranging in length from 444 to 1,660,019 nucleotides. The genome annotation showed 4250 putative genes, 4114 CDS and 43 pseudo-genes. Three complete rRNA gene species were detected: nine 5S, one 16S and one 23S. Other partial rRNA gene fragments were also identified, nine 16S rRNA and three 23S rRNA. A total of 69 tRNA genes and one ncRNA gene were also annotated in this genome.

Expression levels of antimicrobial peptide tachyplesin I in transgenic Ornithogalum lines affect the resistance to Pectobacterium infection

The genus Ornithogalum includes several ornamental species that suffer substantial losses from bacterial soft rot caused by Pectobacteria. The absence of effective control measures for use against soft rot bacteria led to the initiation of a project in which a small antimicrobial peptide from an Asian horseshoe crab, tachyplesin (tpnI), was introduced into two commercial cultivars: O. dubium and O. thyrsoides. Disease severity and bacterial colonization were examined in transgenic lines expressing this peptide. Disease resistance was evaluated in six lines of each species by measuring bacterial proliferation in the plant tissue. Three transgenic lines of each species were subjected to further analysis in which the expression level of the transgene was evaluated using RT-PCR and qRT-PCR. The development of disease symptoms and bacterial colonization of the plant tissue were also examined using GFP-expressing strain of P. carotovorum subsp. brasiliense Pcb3. Confocal-microscopy imaging revealed significantly reduced quantities of bacterial cells in the transgenic plant lines that had been challenged with the bacterium. The results clearly demonstrate that tpnI expression reduces bacterial proliferation, colonization and disease symptom (reduced by 95-100%) in the transgenic plant tissues. The quantity of tpnI transcripts, as measured by qRT-PCR, was negatively correlated with the protection afforded to the plants, as measured by the reduced severity of disease symptoms in the tissue.

When Genome-Based Approach Meets the "Old but Good": Revealing Genes Involved in the Antibacterial Activity of Pseudomonas sp. P482 against Soft Rot Pathogens

Dickeya solani and Pectobacterium carotovorum subsp. brasiliense are recently established species of bacterial plant pathogens causing black leg and soft rot of many vegetables and ornamental plants. Pseudomonas sp. strain P482 inhibits the growth of these pathogens, a desired trait considering the limited measures to combat these diseases. In this study, we determined the genetic background of the antibacterial activity of P482, and established the phylogenetic position of this strain. Pseudomonas sp. P482 was classified as Pseudomonas donghuensis. Genome mining revealed that the P482 genome does not contain genes determining the synthesis of known antimicrobials. However, the ClusterFinder algorithm, designed to detect atypical or novel classes of secondary metabolite gene clusters, predicted 18 such clusters in the genome. Screening of a Tn5 mutant library yielded an antimicrobial negative transposon mutant. The transposon insertion was located in a gene encoding an HpcH/HpaI aldolase/citrate lyase family protein. This gene is located in a hypothetical cluster predicted by the ClusterFinder, together with the downstream homologs of four nfs genes, that confer production of a non-fluorescent siderophore by P. donghuensis HYS^T. Site-directed inactivation of the HpcH/HpaI aldolase gene, the adjacent short chain dehydrogenase gene, as well as a homolog of an essential nfs cluster gene, all abolished the antimicrobial activity of the P482, suggesting their involvement in a common biosynthesis pathway. However, none of the mutants showed a decreased siderophore yield, neither was the antimicrobial activity of the wild type P482 compromised by high iron bioavailability. A genomic region comprising the nfs cluster and three upstream genes is involved in the antibacterial activity of P. donghuensis P482 against D. solani and P. carotovorum subsp. brasiliense. The genes studied are unique to the two known P. donghuensis strains. This study illustrates that mining of microbial genomes is a powerful approach for predictingthe presence of novel secondary-metabolite encoding genes especially when coupled with transposon mutagenesis.

Plant phenolic acids affect the virulence of Pectobacterium aroidearum and P. carotovorum ssp. brasiliense via quorum sensing regulation

Several studies have reported effects of the plant phenolic acids cinnamic acid (CA) and salicylic acid (SA) on the virulence of soft rot enterobacteria. However, the mechanisms involved in these processes are not yet fully understood. Here, we investigated whether CA and SA interfere with the quorum sensing (QS) system of two Pectobacterium species, P. aroidearum and P. carotovorum ssp. brasiliense, which are known to produce N-acyl-homoserine lactone (AHL) QS signals. Our results clearly indicate that both phenolic compounds affect the QS machinery of the two species, consequently altering the expression of bacterial virulence factors. Although, in control treatments, the expression of QS-related genes increased over time, the exposure of bacteria to non-lethal concentrations of CA or SA inhibited the expression of QS genes, including expI, expR, PC1_1442 (luxR transcriptional regulator) and luxS (a component of the AI-2 system). Other virulence genes known to be regulated by the QS system, such as pecS, pel, peh and yheO, were also down-regulated relative to the control. In agreement with the low levels of expression of expI and expR, CA and SA also reduced the level of the AHL signal. The effects of CA and SA on AHL signalling were confirmed in compensation assays, in which exogenous application of N-(β-ketocaproyl)-l-homoserine lactone (eAHL) led to the recovery of the reduction in virulence caused by the two phenolic acids. Collectively, the results of gene expression studies, bioluminescence assays, virulence assays and compensation assays with eAHL clearly support a mechanism by which CA and SA interfere with Pectobacterium virulence via the QS machinery.

Draft Genome Sequence for ICMP 5702, the Type Strain of Pectobacterium carotovorum subsp. carotovorum That Causes Soft Rot Disease on Potato

Pectobacterium species are economically important bacteria that cause soft rotting of potato tubers in the field and in storage. Here, we report the draft genome sequence of the type strain for P. carotovorum subsp. carotovorum, ICMP 5702 (ATCC 15713). The genome sequence of ICMP 5702 will provide an important reference for future phylogenomic and taxonomic studies of the phytopathogenic Enterobacteriaceae.

Genomic, proteomic and morphological characterization of two novel broad host lytic bacteriophages ΦPD10.3 and ΦPD23.1 infecting pectinolytic Pectobacterium spp. and Dickeya spp

Pectinolytic Pectobacterium spp. and Dickeya spp. are necrotrophic bacterial pathogens of many important crops, including potato, worldwide. This study reports on the isolation and characterization of broad host lytic bacteriophages able to infect the dominant Pectobacterium spp. and Dickeya spp. affecting potato in Europe viz. Pectobacterium carotovorum subsp. carotovorum (Pcc), P. wasabiae (Pwa) and Dickeya solani (Dso) with the objective to assess their potential as biological disease control agents. Two lytic bacteriophages infecting stains of Pcc, Pwa and Dso were isolated from potato samples collected from two potato fields in central Poland. The ΦPD10.3 and ΦPD23.1 phages have morphology similar to other members of the Myoviridae family and the Caudovirales order, with a head diameter of 85 and 86 nm and length of tails of 117 and 121 nm, respectively. They were characterized for optimal multiplicity of infection, the rate of adsorption to the Pcc, Pwa and Dso cells, the latent period and the burst size. The phages were genotypically characterized with RAPD-PCR and RFLP techniques. The structural proteomes of both phages were obtained by fractionation of phage proteins by SDS-PAGE. Phage protein identification was performed by liquid chromatography-mass spectrometry (LC-MS) analysis. Pulsed-field gel electrophoresis (PFGE), genome sequencing and comparative genome analysis were used to gain knowledge of the length, organization and function of the ΦPD10.3 and ΦPD23.1 genomes. The potential use of ΦPD10.3 and ΦPD23.1 phages for the biocontrol of Pectobacterium spp. and Dickeya spp. infections in potato is discussed.

Genetic Diversity of Pectobacterium carotovorum subsp. brasiliensis Isolated in Korea

The plant pathogenic bacterial genus Pectobacteirum consists of heterogeneous strains. The P. carotovorum species is a complex strain showing divergent characteristics, and a new subspecies named P. carotovorum subsp. brasiliensis has been identified recently. In this paper, we re-identified the P. carotovorum subsp. brasiliensis isolates from those classified under the subspecies carotovorum and newly isolated P. carotovorum subsp. brasiliensis strains. All isolates were able to produce plant cell-wall degrading enzymes such as pectate lyase, polygalacturonase, cellulase and protease. We used genetic and biochemical methods to examine the diversity of P. carotovorum subsp. brasiliensis isolates, and found genetic diversity within the brasiliensis subsp. isolates in Korea. The restriction fragment length polymorphism analysis based on the recA gene revealed a unique pattern for the brasiliensis subspecies. The Korean brasiliensis subsp. isolates were divided into four clades based on pulsed-field gel electrophoresis. However, correlations between clades and isolated hosts or year could not be found, suggesting that diverse brasiliensis subsp. isolates existed.

Colonization patterns of an mCherry-tagged Pectobacterium carotovorum subsp. brasiliense strain in potato plants

Pectobacterium carotovorum subsp. brasiliense is a newly identified member of the potato soft rot enterobacteriaceae. The pathogenesis of this pathogen is still poorly understood. In this study, an mCherry-P. carotovorum subsp. brasiliense-tagged strain was generated to study P. carotovorum subsp. brasiliense-potato plant interactions. Prior to use, the tagged strain was evaluated for in vitro growth, plasmid stability, and virulence on potato tubers and shown to be similar to the wild type. Four potato cultivars were evaluated for stem-based resistance against P. carotovorum subsp. brasiliense. Confocal laser-scanning microscopy and in vitro viable cell counts showed that P. carotovorum subsp. brasiliense is able to penetrate roots of a susceptible potato cultivar as early as 12 h postinoculation and migrate upward into aerial stem parts. Due to the phenotypic differences observed between tolerant and susceptible cultivars, a comparison of P. carotovorum subsp. brasiliense colonization patterns in these cultivars was undertaken. In the susceptible cultivar, P. carotovorum subsp. brasiliense cells colonized the xylem tissue, forming "biofilm-like" aggregates that led to occlusion of some of the vessels. In contrast, in the tolerant cultivar, P. carotovorum subsp. brasiliense appeared as free-swimming planktonic cells with no specific tissue localization. This suggests that there are resistance mechanisms in the tolerant cultivar that limit aggregation of P. carotovorum subsp. brasiliense in planta and, hence, the lack of symptom development in this cultivar.

Pectobacterium aroidearum sp. nov., a soft rot pathogen with preference for monocotyledonous plants

Several pectolytic bacterial strains, mainly isolated from monocotyledonous plants and previously identified as Pectobacterium carotovorum, were thought to belong to a novel species after several taxonomic analyses including DNA-DNA hybridization. In 16S rRNA gene sequence analyses, these strains had a similarity of >97.9 % to the 16S rRNA gene sequence of strains representing six other pectobacterial species and subspecies. These strains, represented by strain SCRI 109(T), also showed some unique chemotaxonomic features and quantitative differences in polar lipids, lipoquinones and fatty acids. A specific feature of strain SCRI 109(T) was the presence of DMK-8 lipoquinone, while the dominant fatty acids were the summed feature 3 (iso-C15 : 0 2-OH/C16 : 1ω7c), the unsaturated fatty acid C18 : 1ω7c and straight chain fatty acids, mainly C16 : 0. The DNA G+C content of strain SCRI 109(T) was 50.2 mol%. The taxonomic status of strain SCRI 109(T) and related strains in 16S rRNA gene sequence, chemotaxonomic, and physiological analyses was corroborated by the distinct clustering of these strains in multi-locus sequence analyses. It is proposed that these strains represent a novel species for which the name Pectobacterium aroidearum sp. nov. is proposed; the type strain is SCRI 109(T) ( = NCPPB 929(T) = LMG 2417(T) = ICMP 1522(T)).