Comparative genomic analysis of Pectobacterium carotovorum subsp. brasiliense SX309 provides novel insights into its genetic and phenotypic features.

BACKGROUND: Pectobacterium carotovorum subsp. brasiliense is a broad host range bacterial pathogen, which causes blackleg of potatoes and bacterial soft rot of vegetables worldwide. Production of plant cell wall degrading enzymes is usually critical for Pectobacterium infection. However, other virulence factors and the mechanisms of genetic adaptation still need to be studied in detail. RESULTS: In this study, the complete genome of P. carotovorum subsp. brasiliense strain SX309 isolated from cucumber was compared with eight other pathogenic bacteria belonging to the Pectobacterium genus, which were isolated from various host plants. Genome comparison revealed that most virulence genes are highly conserved in the Pectobacterium strains, especially for the key virulence determinants involved in the biosynthesis of extracellular enzymes and others including the type II and III secretion systems, quorum sensing system, flagellar and chemotactic genes. Nevertheless, some variable regions of the T6SS and the CRISP-Cas immune system are unique for P. carotovorum subsp. brasiliense. CONCLUSIONS: The extensive comparative genomics analysis revealed highly conserved virulence genes in the Pectobacterium strains. However, several variable regions of type VI secretion system and two subtype Cas mechanism-Cas immune systems possibly contribute to the process of Pectobacterium infection and adaptive immunity.

A structural in silico analysis of the immunogenicity of l-asparaginase from Escherichia coli and Erwinia carotovora.

Acute lymphoblastic leukemia (ALL) is a type of cancer with a high incidence in children. The enzyme l-asparaginase (ASNase) constitutes a key element in the treatment of this disease. Four formulations of ASNase from a bacterial source are currently available. However, these formulations are characterized by their high immunogenicity, resulting in the inactivation of the drug, as well as in the occurrence of hypersensitivity reactions in a large number of patients. In this work, we performed an immunoinformatic analysis in order to clarify structural aspects of the immunogenicity of the asparaginase from Escherichia coli and Erwinia carotovora. For this purpose, we performed the prediction of immunogenic and allergenic epitopes in the structure of asparaginases by using the relative frequency of immunogenic peptides for the eight alleles most frequently distributed worldwide. This study showed that there are no significant differences in the level of immunogenicity between the two enzymes, while asparaginase from E. coli presented a higher relative frequency of allergenic epitopes. These results are consistent with previously published reports. However, from a structural point of view, to the best of our knowledge, this is the first report describing the structural determinants that contribute to the hypersensitivity response to this treatment.

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.

Plant Growth-Promoting Genes can Switch to be Virulence Factors via Horizontal Gene Transfer.

There are increasing evidences that horizontal gene transfer (HGT) is a critical mechanism of bacterial evolution, while its complete impact remains unclear. A main constraint of HGT effects on microbial evolution seems to be the conservation of the function of the horizontally transferred genes. From this perspective, inflexible nomenclature and functionality criteria have been established for some mobile genetic elements such as pathogenic and symbiotic islands. Adhesion is a universal prerequisite for both beneficial and pathogenic plant-microbe interactions, and thus, adhesion systems (e.g., the Lap cluster) are candidates to have a dual function depending on the genomic background. In this study, we showed that the virulent factor Lap of the phytopathogen Erwinia carotovora SCRI1043, which is located within a genomic island, was acquired by HGT and probably derived from Pseudomonas. The transformation of the phytopathogen Erwinia pyrifoliae Ep1/96 with the beneficial factor Lap from the plant growth-promoting bacterium Pseudomonas fluorescens Pf-5 significantly increased its natural virulence, experimentally recapitulating the beneficial-to-virulence functional switch of the Lap cluster via HGT. To our knowledge, this is the first report of a functional switch of an individual gene or a cluster of genes mediated by HGT.

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 IFB5232T 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 (=PCM2893T=LMG30269T=SCRI179T) with the name Pectobacterium peruviense sp. nov.

Influence of the ferric uptake regulator (Fur) protein on pathogenicity in Pectobacterium carotovorum subsp. brasiliense.

Iron is an important nutrient for the survival and growth of many organisms. In order to survive, iron uptake from the environment must be strictly regulated and maintained to avoid iron toxicity. The ferric uptake regulator protein (Fur) regulates genes involved in iron homeostasis in many bacteria, including phytopathogens. However, to date, the role played by Fur in the biology of Pectobacterium carotovorum subsp. brasiliense (Pcb1692), an important pathogen of potatoes, has not yet been studied. To this end, we used the lambda recombineering method to generate a fur mutant strain of Pcb1692 and assessed the virulence and fitness of the mutant strain. The results showed that production of siderophores in Pcb1692Δfur increased compared to the Pcb1692 wild-type and the complemented strain Pcb1692Δfur-pfur. However, production of N-acyl homoserine lactone (AHLs), biofilm formation, exopolysaccharide (EPS) production, virulence on potato tubers and swimming motility, were all significantly decreased in Pcb1692Δfur compared to the wild-type and complemented Pcb1692Δfur-pfur strains. The Pcb1692Δfur mutant also demonstrated significant sensitivity to oxidative stress when exposed to H2O2. Consistent with phenotypic results, qRT-PCR results demonstrated that Fur down-regulates genes which encode proteins associated with: iron uptake (HasA-extracellular heme-binding protein and Ferrodoxin-AED-0004132), stress response (SodC-superoxide dismutase), plant cell wall degrading enzymes (PrtA and CelV) and motility (FlhC and MotA). We conclude that the ferric uptake regulator protein (Fur) of Pcb1692 regulates traits that are important to host-pathogens interactions.

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.(AU)

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

Abstract 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.

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 4,820,279bp 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.

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.

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.

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

AIMS: Pectobacterium carotovorum is a heterogeneous species consisting of two named subspecies, P. carotovorum subsp. carotovorum and P. carotovorum subsp. odoriferum. A third subspecies, P. carotovorum subsp. brasiliense, was previously proposed. The study aimed to confirm the subspecies status and validate the proposed name of P. carotovorum subsp. brasiliense using a novel and standard microbial taxonomy. METHODS AND RESULTS: DNA-DNA hybridization confirmed that P. carotovorum subsp. brasiliense is a different species from P. wasabiae, P. betavasculorum and P. atrosepticum, with 28, 35 and 55% similarity values, respectively, but is a member of the P. carotovorum species with 73-77% similarity values. Sequencing the entire 16S rRNA gene of two polymorphic copies from strains of each of the P. carotovorum subspecies demonstrated that the average 16S rRNA gene sequence diversity between P. carotovorum subsp. brasiliense and P. carotovorum subsp. carotovorum was lower than the maximum genetic distances between two sequence types obtained from the same strain. Multilocus sequence analysis based on eight housekeeping genes (mtlD, acnA, icdA, mdh, pgi, gabA, proA and rpoS) differentiated the subspecies and delineated two P. carotovorum subsp. brasiliense clades. CONCLUSION: Pectobacterium carotovorum subsp. brasiliense clade I was comprised of strains isolated from Brazil and Peru, while clade II included strains from Asia, North America and Europe. Strains in clade I but not clade II were phenotypically consistent with the original description of P. carotovorum subsp. brasiliense in that they produced reducing substances from sucrose and acid from α-methyl glucoside. The type strain for P. carotovorum subsp. brasiliense 212(T) (= LMG2137(T) = IBSBF1692(T) = CFBP6617(T) ) was previously designated. The GC mol content of the type strain is 51·7%. SIGNIFICANT AND IMPACT OF THE STUDY: the study introduces a full description for the strains belonging to the two different clades assigned to P. carotovorum subsp. brasiliense.

Characterization of atypical Erwinia carotovora strains causing blackleg of potato in Brazil.

AIMS: To determine the characteristics of bacteria associated with the blackleg disease of potato in Brazil and compare them with species and subspecies of pectolytic Erwinia. METHODS AND RESULTS: Biochemical and physiological characteristics of 16 strains from blackleg-infected potatoes in State of Rio Grande do Sul, Brazil, were determined and differentiated them from all the E. carotovora subspecies and E. chrysanthemi. Pathogenicity and maceration ability of the Brazilian strains were greater than those of E. carotovora subsp. atroseptica, the causal agent of potato blackleg in temperate zones. Analyses of serological reaction and fatty acid composition confirmed that the Brazilian strains differed from E. carotovora subsp. atroseptica, but the sequence of 16S rDNA gene and the 16S-23S intergenic spacer (IGS) region confirmed the Brazilian strains as pectolytic Erwinia. Restriction analysis of the IGS region differentiated the Brazilian strains from the subspecies of E. carotovora and from E. chrysanthemi. A unique SexAI restriction site in the IGS region was used as the basis for a primer to specifically amplify DNA from the Brazilian potato blackleg bacterium in PCR. CONCLUSIONS: The bacterium that causes the blackleg disease of potato in Brazil differs from E. carotovora subsp. atroseptica, the blackleg pathogen in temperate zones. It also differs from other subspecies of E. carotovora and from E. chrysanthemi and warrants status as a new subspecies, which would be appropriately named E. carotovora subsp. brasiliensis. SIGNIFICANCE AND IMPACT OF THE STUDY: The blackleg disease of potato is caused by a different strain of pectolytic Erwinia in Brazil than in temperate potato-growing regions. The Brazilian strain is more virulent than E. carotovora subsp. atroseptica, the usual causal agent of potato blackleg.