Pseudomonas syringae is a plant pathogen well known for its capacity to grow epiphytically on diverse plants and for its ice-nucleation activity. The ensemble of its known biology and ecology led us ...to postulate that this bacterium is also present in non-agricultural habitats, particularly those associated with water. Here, we report the abundance of P. syringae in rain, snow, alpine streams and lakes and in wild plants, in addition to the previously reported abundance in epilithic biofilms. Each of these substrates harbored strains that corresponded to P. syringae in terms of biochemical traits, pathogenicity and pathogenicity-related factors and that were ice-nucleation active. Phylogenetic comparisons of sequences of four housekeeping genes of the non-agricultural strains with strains of P. syringae from disease epidemics confirmed their identity as P. syringae. Moreover, strains belonging to the same clonal lineage were isolated from snow, irrigation water and a diseased crop plant. Our data suggest that the different substrates harboring P. syringae modify the structure of the associated populations. Here, we propose a comprehensive life cycle for P. syringae--in agricultural and non-agricultural habitats--driven by the environmental cycle of water. This cycle opens the opportunity to evaluate the importance of non-agricultural habitats in the evolution of a plant pathogen and the emergence of virulence. The ice-nucleation activity of all strains from snow, unlike from other substrates, strongly suggests that P. syringae plays an active role in the water cycle as an ice nucleus in clouds.
Although there are adequate DNA sequence differences among plant-associated and plant-pathogenic bacteria to facilitate molecular approaches for their identification, identification at a taxonomic ...level that is predictive of their phenotype is a challenge. The problem is the absence of a taxonomy that describes genetic variation at a biologically relevant resolution and of a database containing reference strains for comparison. Moreover, molecular evolution, population genetics, ecology, and epidemiology of many plant-pathogenic and plant-associated bacteria are still poorly understood. To address these challenges, a database with web interface was specifically designed for plant-associated and plant-pathogenic microorganisms. The Plant-Associated Microbes Database (PAMDB) comprises, thus far, data from multilocus sequence typing and analysis (MLST/MLSA) studies of Acidovorax citrulli, Pseudomonas syringae, Ralstonia solanacearum, and Xanthomonas spp. Using data deposited in PAMDB, a robust phylogeny of Xanthomonas axonopodis and related bacteria has been inferred, and the diversity existing in the Xanthomonas genus and in described Xanthomonas spp. has been compared with the diversity in P. syringae and R. solanacearum. Moreover, we show how PAMDB makes it easy to distinguish between different pathogens that cause almost identical diseases. The scalable design of PAMDB will make it easy to add more plant pathogens in the future.
Recently, genome sequencing of many isolates of genetically monomorphic bacterial human pathogens has given new insights into pathogen microevolution and phylogeography. Here, we report a ...genome-based micro-evolutionary study of a bacterial plant pathogen, Pseudomonas syringae pv. tomato. Only 267 mutations were identified between five sequenced isolates in 3,543,009 nt of analyzed genome sequence, which suggests a recent evolutionary origin of this pathogen. Further analysis with genome-derived markers of 89 world-wide isolates showed that several genotypes exist in North America and in Europe indicating frequent pathogen movement between these world regions. Genome-derived markers and molecular analyses of key pathogen loci important for virulence and motility both suggest ongoing adaptation to the tomato host. A mutational hotspot was found in the type III-secreted effector gene hopM1. These mutations abolish the cell death triggering activity of the full-length protein indicating strong selection for loss of function of this effector, which was previously considered a virulence factor. Two non-synonymous mutations in the flagellin-encoding gene fliC allowed identifying a new microbe associated molecular pattern (MAMP) in a region distinct from the known MAMP flg22. Interestingly, the ancestral allele of this MAMP induces a stronger tomato immune response than the derived alleles. The ancestral allele has largely disappeared from today's Pto populations suggesting that flagellin-triggered immunity limits pathogen fitness even in highly virulent pathogens. An additional non-synonymous mutation was identified in flg22 in South American isolates. Therefore, MAMPs are more variable than expected differing even between otherwise almost identical isolates of the same pathogen strain.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Diverse gene products including phytotoxins, pathogen-associated molecular patterns, and type III secreted effectors influence interactions between Pseudomonas syringae strains and plants, with ...additional yet uncharacterized factors likely contributing as well. Of particular interest are those interactions governing pathogen-host specificity. Comparative genomics of closely related pathogens with different host specificity represents an excellent approach for identification of genes contributing to host-range determination. A draft genome sequence of Pseudomonas syringae pv. tomato T1, which is pathogenic on tomato but nonpathogenic on Arabidopsis thaliana, was obtained for this purpose and compared with the genome of the closely related A. thaliana and tomato model pathogen P. syringae pv. tomato DC3000. Although the overall genetic content of each of the two genomes appears to be highly similar, the repertoire of effectors was found to diverge significantly. Several P. syringae pv. tomato T1 effectors absent from strain DC3000 were confirmed to be translocated into plants, with the well-studied effector AvrRpt2 representing a likely candidate for host-range determination. However, the presence of avrRpt2 was not found sufficient to explain A. thaliana resistance to P. syringae pv. tomato T1, suggesting that other effectors and possibly type III secretion system-independent factors also play a role in this interaction.
Pseudomonas syringae pv. tomato strain DC3000 (PtoDC3000) is one of the most intensively studied bacterial plant pathogens today. Here we report a thorough investigation into PtoDC3000 and close ...relatives isolated from Antirrhinum majus (snapdragon), Apium graveolens (celery), and Solanaceae and Brassicaceae species. Multilocus sequence typing (MLST) was used to resolve the precise phylogenetic relationship between isolates and to determine the importance of recombination in their evolution. MLST data were correlated with an analysis of the locus coding for the type III secreted (T3S) effector AvrPto1 to investigate the role of recombination in the evolution of effector repertoires. Host range tests were performed to determine if closely related isolates from different plants have different host ranges. It was found that PtoDC3000 is located in the same phylogenetic cluster as isolates from several Brassicaceae and Solanaceae species and that these isolates have a relatively wide host range that includes tomato, Arabidopsis thaliana, and cauliflower. All other analyzed tomato isolates from three different continents form a distinct cluster and are pathogenic only on tomato. Therefore, PtoDC3000 is a very unusual tomato isolate. Several recombination breakpoints were detected within sequenced gene fragments, and population genetic tests indicate that recombination contributed more than mutation to the variation between isolates. Moreover, recombination may play an important role in the reassortment of T3S effectors between strains. The data are finally discussed from a taxonomic standpoint, and P. syringae pv. tomato is proposed to be divided into two pathovars.
► The phylogeny of 25 closely related plant pathogenic Pseudomonas syringae strains was determined using MLST. ► Strains were tested for host range on five different plant species. ► Combining ...phylogenetic data with host range data, reconstruction of host range of putative ancestors was attempted. ► Results provide a framework for a comparative genomics investigation into host range evolution.
Several lines of evidence suggest that highly virulent bacterial human pathogens evolved from less virulent wider host range animal pathogens since human migration out of Africa. To investigate evolution of host specificity of bacterial plant pathogens, here we report a molecular evolutionary analysis of the model plant pathogen Pseudomonas syringae pv. tomato DC3000 and of close relatives that are pathogens of a diverse set of crop plants. Extensive host range tests on five different plant species were performed. Combining phylogenetic data with host range data, a reconstruction of host range of all putative ancestors was performed. In particular, the hypothesis was tested that highly virulent narrow host range pathogens of today’s crops grown in monoculture evolved from ancestors with wider host range that were adapted to natural mixed plant communities of pre-agricultural times. We found support for this hypothesis in individual clades. However, reconstruction of host range of the most recent common ancestor of all analyzed strains was not conclusive. Based on the obtained results we stress the importance of including pathogens from wild plants when reconstructing the evolution of plant pathogenic bacteria.
Comparative genomics of closely related pathogens that differ in host range can provide insights into mechanisms of host-pathogen interactions and host adaptation. Furthermore, sequencing of multiple ...strains with the same host range reveals information concerning pathogen diversity and the molecular basis of virulence. Here we present a comparative analysis of draft genome sequences for four strains of Pseudomonas cannabina pathovar alisalensis (Pcal), which is pathogenic on a range of monocotyledonous and dicotyledonous plants. These draft genome sequences provide a foundation for understanding host range evolution across the monocot-dicot divide. Like other phytopathogenic pseudomonads, Pcal strains harboured a hrp/hrc gene cluster that codes for a type III secretion system. Phylogenetic analysis based on the hrp/hrc cluster genes/proteins, suggests localized recombination and functional divergence within the hrp/hrc cluster. Despite significant conservation of overall genetic content across Pcal genomes, comparison of type III effector repertoires reinforced previous molecular data suggesting the existence of two distinct lineages within this pathovar. Furthermore, all Pcal strains analyzed harbored two distinct genomic islands predicted to code for type VI secretion systems (T6SSs). While one of these systems was orthologous to known P. syringae T6SSs, the other more closely resembled a T6SS found within P. aeruginosa . In summary, our study provides a foundation to unravel Pcal adaptation to both monocot and dicot hosts and provides genetic insights into the mechanisms underlying pathogenicity.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Hundreds of bacterial genomes including the genomes of dozens of plant pathogenic bacteria have been sequenced. These genomes represent an invaluable resource for molecular plant pathologists. In ...this review, we describe different approaches that can be used for mining bacterial genome sequences and examples of how some of these approaches have been used to analyse plant pathogen genomes so far. We review how genomes can be mined one by one and how comparative genomics of closely related genomes releases the true power of genomics. Databases and tools useful for genome mining that are publicly accessible on the Internet are also described. Finally, the need for new databases and tools to efficiently mine today's plant pathogen genomes and hundreds more in the near future is discussed.
The present paper investigates the influence of O2 on X80 steel under the CO2 environment through polarization curves, EIS, and employing characterization by corrosion images and mechanisms, using ...the test data of the environmental content of CO2 and O2 in an oil field, while the pressure of O2 is 0.082bar~0.15bar. The results show that O2 mainly have influence on the polarization process of X80 steel cathode, and in the low O2 pressure of 0~0.12bar, corrosion potential and corrosion current density of X80 steel essentially remains the same, and with the increase of O2 pressure to 0.17bar~0.22bar, comprehensive corrosion rate and the electric double layer capacitance all increase, and also the polarization resistance, diffusion resistance, and charge transfer resistance is reduced. This behavior can be attributed due to the fact that O2 destroyed the surface of X80 steel by the corrosion film resulting in local corrosion caused by the presence of CO2.
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