Soft rot Enterobacteriaceae(SRE) are bacterial plant pathogens that cause blackleg, wilt and soft rot diseases on a broad range of important crop and ornamental plants worldwide. These organisms ...(spanning the genera Erwinia, Pectobacterium, Dickeya, and Pantoea) cause significant economic and yield losses in the field, and in storage. They are transmissible through surface water, by trade and other movement of plant material and soil, and in some cases are subject to international legislative and quarantine restrictions. Effective detection and diagnosis in support of food security legislation and epidemiology is dependent on the ability to classify pathogenic isolates precisely. Diagnostics and classification are made more difficult by the influence of horizontal gene transfer on phenotype, and historically complex and sometimes inaccurate nomenclatural and taxonomic assignments that persist in strain collections and online sequence databases. Here, we briefly discuss the relationship between taxonomy, genotype and phenotype in the SRE, and their implications for diagnostic testing and legislation. We present novel whole-genome classifications of the SRE, illustrating inconsistencies between the established taxonomies and evidence from completely sequenced isolates. We conclude with a perspective on the future impact of widespread whole-genome sequencing and classification methods on detection and identification of bacterial plant pathogens in support of legislative and policy efforts in food security.
Potato blackleg and soft rot caused by Pectobacterium and Dickeya species are among the most significant bacterial diseases affecting potato production globally. In this study we estimate the impact ...of future temperatures on establishment of non-indigenous but confirmed Pectobacterium and Dickeya species in Great Britain (GB). The calculations are based on probabilistic climate change data and a model fitted to disease severity data from a controlled environment tuber assay with the dominant potato blackleg and soft rot-causing species in GB (P. atrosepticum), and three of the main causative agents in Europe (P. carotovorum subsp. brasiliense, P. parmentieri, Dickeya solani). Our aim was to investigate if the European strains could become stronger competitors in the GB potato ecosystem as the climate warms, on the basis of their aggressiveness in tubers at different temperatures. Principally, we found that the tissue macerating capacity of all four pathogens will increase in GB under all emissions scenarios. The predominant Pectobacterium and Dickeya species in Europe are able to cause disease in tubers under field conditions currently seen in GB but are not expected to become widely established in the future, at least on the basis of their aggressiveness in tubers relative to P. atrosepticum under GB conditions. Our key take-home messages are that the GB potato industry is well positioned to continue to thrive via current best management practices and continued reinforcement of existing legislation.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Bacterial attachment on root surfaces is an important step preceding the colonization or internalization and subsequent infection of plants by pathogens. Unfortunately, bacterial attachment is not ...well understood because the phenomenon is difficult to observe. Here we assessed whether this limitation could be overcome using optical trapping approaches. We have developed a system based on counter-propagating beams and studied its ability to guide Pectobacterium atrosepticum (Pba) cells to different root cell types within the interstices of transparent soils. Bacterial cells were successfully trapped and guided to root hair cells, epidermal cells, border cells, and tissues damaged by laser ablation. Finally, we used the system to quantify the bacterial cell detachment rate of Pba cells on root surfaces following reversible attachment. Optical trapping techniques could greatly enhance our ability to deterministically characterize mechanisms linked to attachment and formation of biofilms in the rhizosphere.
Pectobacterium atrosepticum (Pba) is a gram-negative bacterium that causes blackleg and tuber soft rot of potato but can also asymptomatically colonise other (non-host) plant species. The aim of this ...study was to investigate the molecular processes and responses involved in Pba-host (potato) and Pba-non-host (radish) interactions, under laboratory conditions. To achieve this, we used total mRNA-sequencing to measure the gene expression patterns from all three species: Pba, potato and radish. We employed an end-point dual transcriptome approach. We used hydroponically grown potato (Solanum tuberosum var. Estima) and oil radish (Raphanus sativa var. Bento) roots inoculated with Pba SCRI1039 for 14 days compared to un-inoculated control plants or cultured bacteria. Total RNA was extracted from replicates of the two plant species and the bacterium using a Macherey-Nagel Nucleospin Plant RNA kit. The RNA from the 17 samples was then subjected to total mRNA-sequencing (paired-end) on an Illumina NovaSeq 6000™ sequencing platform. This gave between 39.2-58.1M reads per sample. The high-quality reads obtained were mapped to the corresponding reference genomes using Bowtie2 and the percentages of bacterium and plant transcripts calculated. This dataset constitutes the raw read fastq files and can be used to inform on genes active in plant rhizosphere-microbe interactions.
Expansins are encoded by some phytopathogenic bacteria and evidence indicates that they act as virulence factors for host infection. Here we analysed the expression of exl1 by Pectobacterium ...brasiliense and Pectobacterium atrosepticum. In both, exl1 gene appears to be under quorum sensing control, and protein Exl1 can be observed in culture medium and during plant infection. Expression of exl1 correlates with pathogen virulence, where symptoms are reduced in a Δexl1 mutant strain of P. atrosepticum. As well as Δexl1 exhibiting less maceration of potato plants, fewer bacteria are observed at distance from the inoculation site. However, bacteria infiltrated into the plant tissue are as virulent as the wild type, suggesting that this is due to alterations in the initial invasion of the tissue. Additionally, swarming from colonies grown on MacConkey soft agar was delayed in the mutant in comparison to the wild type. We found that Exl1 acts on the plant tissue, probably by remodelling of a cell wall component or altering the barrier properties of the cell wall inducing a plant defence response, which results in the production of ROS and the induction of marker genes of the JA, ET and SA signalling pathways in Arabidopsis thaliana. Exl1 inactive mutants fail to trigger such responses. This defence response is protective against Pectobacterium brasiliense and Botrytis cinerea in more than one plant species.
The foodborne pathogen Escherichia coli O157:H7 is increasingly associated with fresh produce (fruit and vegetables). Bacterial colonization of fresh produce plants can occur to high levels on the ...external tissue but bacteria have also been detected within plant tissue. However, questions remain about the extent of internalization, its molecular basis, and internal location of the bacteria. We have determined the extent of internalization of E. coli O157:H7 in live spinach and lettuce plants and used high-resolution microscopy to examine colony formation in roots and pathways to internalization. E. coli O157:H7 was found within internal tissue of both produce species. Colonization occurred within the apoplast between plant cells. Furthermore, colonies were detected inside the cell wall of epidermal and cortical cells of spinach and Nicotiana benthamiana roots. Internal colonization of epidermal cells resembled that of the phytopathogen Pectobacterium atrosepticum on potato. In contrast, only sporadic cells of the laboratory strain of E. coli K-12 were found on spinach, with no internal bacteria evident. The data extend previous findings that internal colonization of plants appears to be limited to a specific group of plant-interacting bacteria, including E. coli O157:H7, and demonstrates its ability to invade the cells of living plants.
Quorum sensing (QS) in vitro controls production of plant cell wall degrading enzymes (PCWDEs) and other virulence factors in the soft rotting enterobacterial plant pathogen Pectobacterium ...atrosepticum (Pba). Here, we demonstrate the genome-wide regulatory role of QS in vivo during the Pba-potato interaction, using a Pba-specific microarray. We show that 26% of the Pba genome exhibited differential transcription in a QS (expI-) mutant, compared to the wild-type, suggesting that QS may make a greater contribution to pathogenesis than previously thought. We identify novel components of the QS regulon, including the Type I and II secretion systems, which are involved in the secretion of PCWDEs; a novel Type VI secretion system (T6SS) and its predicted substrates Hcp and VgrG; more than 70 known or putative regulators, some of which have been demonstrated to control pathogenesis and, remarkably, the Type III secretion system and associated effector proteins, and coronafacoyl-amide conjugates, both of which play roles in the manipulation of plant defences. We show that the T6SS and a novel potential regulator, VirS, are required for full virulence in Pba, and propose a model placing QS at the apex of a regulatory hierarchy controlling the later stages of disease progression in Pba. Our findings indicate that QS is a master regulator of phytopathogenesis, controlling multiple other regulators that, in turn, co-ordinately regulate genes associated with manipulation of host defences in concert with the destructive arsenal of PCWDEs that manifest the soft rot disease phenotype.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Blackleg and soft rot of potato, caused by Pectobacterium and Dickeya spp., are major production constraints in many potato-growing regions of the world. Despite advances in our understanding of the ...causative organisms, disease epidemiology, and control, blackleg remains the principal cause of down-grading and rejection of potato seed in classification schemes across Northern Europe and many other parts of the world. Although symptom recognition is relatively straightforward and is applied universally in seed classification schemes, attributing disease to a specific organism is problematic and can only be achieved through the use of diagnostics. Similarly as disease spread is largely through the movement of asymptomatically infected seed tubers and, possibly in the case of Dickeya spp., irrigation waters, accurate and sensitive diagnostics are a prerequisite for detection. This chapter describes the diagnostic pathway that can be applied to identify the principal potato pathogens within the genera Pectobacterium and Dickeya.
Potato blackleg is a common bacterial disease that causes serious losses in potato (
L.) production worldwide. Despite this, relatively little is known of the landscape epidemiology of this disease. ...This study provides the first national-scale analysis of spatial and spatiotemporal patterns of blackleg incidence rates and associated risk factors for disease at the landscape-scale. This was achieved through a combination of ArcGIS and interpretable machine learning applied to a longitudinal dataset of naturally infected seed potato crops from across Scotland. We found striking differences in long-term disease outcomes across the country and identified that features (variables) related to the health status and management of mother crops (seed stocks), matching features in daughter crops, and the characteristics of surrounding potato crop distributions were the most important predictors of disease, followed by field, bioclimatic, and soil features. Our approach provides a comprehensive overview of potato blackleg at a national-scale, new epidemiological insights, and an accurate model that could serve as the basis of a decision support tool for improved blackleg management.
We investigated the influence of root border cells on the colonisation of seedling
Zea mays roots by
Pseudomonas fluorescens SBW25 in sandy loam soil packed at two dry bulk densities. Numbers of ...colony forming units (CFU) were counted on sequential sections of root for intact and decapped inoculated roots grown in loose (1.0
mg
m
−3) and compacted (1.3
mg
m
−3) soil. After two days of root growth, the numbers of
P. fluorescens (CFU
cm
−1) were highest on the section of root just below the seed with progressively fewer bacteria near the tip, irrespective of density. The decapped roots had significantly more colonies of
P. fluorescens at the tip compared with the intact roots: approximately 100-fold more in the loose and 30-fold more in the compact soil. In addition, confocal images of the root tips grown in agar showed that
P. fluorescens could only be detected on the tips of the decapped roots. These results indicated that border cells, and their associated mucilage, prevented complete colonization of the root tip by the biocontrol agent
P. fluorescens, possibly by acting as a disposable surface or sheath around the cap.
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