Soft Rot Enterobacteriaceae Research Articles

Development of PCR-Based Detection System for Soft Rot Pectobacteriaceae Pathogens Using Molecular Signatures.

Pectobacterium and Dickeya species, usually referred to as soft rot Enterobacteriaceae, are phytopathogenic genera of bacteria that cause soft rot and blackleg diseases and are responsible for significant yield losses in many crops across the globe. Diagnosis of soft rot disease is difficult through visual disease symptoms. Pathogen detection and identification methods based on cultural and morphological identification are time-consuming and not always reliable. A polymerase chain reaction (PCR)-based detection method with the species-specific primers is fast and reliable for detecting soft rot pathogens. We have developed a specific and sensitive detection system for some species of soft rot Pectobacteriaceae pathogens in the Pectobacterium and Dickeya genera based on the use of species-specific primers to amplify unique genomic segments. The specificities of primers were verified by PCR analysis of genomic DNA from 14 strains of Pectobacterium, 8 strains of Dickeya, and 6 strains of non-soft rot bacteria. This PCR assay provides a quick, simple, powerful, and reliable method for detection of soft rot bacteria.

The Impact of Type VI Secretion System, Bacteriocins and Antibiotics on Bacterial Competition of Pectobacterium carotovorum subsp. brasiliense and the Regulation of Carbapenem Biosynthesis by Iron and the Ferric-Uptake Regulator.

The complexity of plant microbial communities provides a rich model for investigating biochemical and regulatory strategies involved in interbacterial competition. Within these niches, the soft rot Enterobacteriaceae (SRE) represents an emerging group of plant–pathogens causing soft rot/blackleg diseases resulting in economic losses worldwide in a variety of crops. A preliminary screening using next-generation sequencing of 16S rRNA comparatively analyzing healthy and diseased potato tubers, identified several taxa from Proteobacteria to Firmicutes as potential potato endophytes/plant pathogens. Subsequent to this, a range of molecular and computational techniques were used to determine the contribution of antimicrobial factors such as bacteriocins, carbapenem and type VI secretion system (T6SS), found in an aggressive SRE (Pectobacterium carotovorum subsp. brasiliense strain PBR1692 – Pcb1692) against these endophytes/plant pathogens. The results showed growth inhibition of several Proteobacteria by Pcb1692 depends either on carbapenem or pyocin production. Whereas for targeted Firmicutes, only the Pcb1692 pyocin seems to play a role in growth inhibition. Furthermore, production of carbapenem by Pcb1692 was observably dependent on the presence of environmental iron and oxygen. Additionally, upon deletion of fur, slyA and expI regulators, carbapenem production ceased, implying a complex regulatory mechanism involving these three genes. Finally, the results demonstrated that although T6SS confers no relevant advantage during in vitro competition, a significant attenuation in competition by the mutant strain lacking a functional T6SS was observed in planta.IMPORTANCESoft rot Enterobacteriaceae (SRE) represents important phytopathogens causing soft rot/blackleg diseases in a variety of crops leading to huge economic losses worldwide. These pathogens have been isolated alongside other bacteria from different environments such as potato tubers, stems, roots and from the soil. In these environments, SREs coexist with other bacteria where they have to compete for scarce nutrients and other resources. In this report, we show that Pectobacterium carotovorum subsp. brasiliense strain PBR1692 – Pcb1692, which represents one of the SREs, inhibits growth of several different bacteria by producing different antimicrobial compounds. These antimicrobial compounds can be secreted inside or outside the plant host, allowing Pcb1692 to effectively colonize different types of ecological niches. By analyzing the genome sequences of several SREs, we show that other SREs likely deploy similar antimicrobials to target other bacteria.

The Gene Encoding NAD-Dependent Epimerase/Dehydratase, wcaG, Affects Cell Surface Properties, Virulence, and Extracellular Enzyme Production in the Soft Rot Phytopathogen, Pectobacterium carotovorum.

Pectobacterium carotovorum is a gram-negative bacterium that, together with other soft rot Enterobacteriaceae causes soft rot disease in vegetables, fruits, and ornamental plants through the action of exoproteins including plant cell wall-degrading enzymes (PCWDEs). Although pathogenicity in these bacteria is complex, virulence levels are proportional to the levels of plant cell wall-degrading exoenzymes (PCWDEs) secreted. Two low enzyme-producing transposon Tn5 mutants were isolated, and compared to their parent KD100, the mutants were less virulent on celery petioles and carrot disks. The inactivated gene responsible for the reduced virulence phenotype in both mutants was identified as wcaG. The gene, wcaG (previously denoted fcl) encodes NAD-dependent epimerase/dehydratase, a homologue of GDP-fucose synthetase of Escherichia coli. In Escherichia coli, GDP-fucose synthetase is involved in the biosynthesis of the exopolysaccharide, colanic acid (CA). The wcaG mutants of P. carotovorum formed an enhanced level of biofilm in comparison to their parent. In the hydrophobicity test the mutants showed more hydrophobicity than the parent in hexane and hexadecane as solvents. Complementation of the mutants with extrachromosomal copies of the wild type gene restored these functions to parental levels. These data indicate that NAD-dependent epimerase/dehydratase plays a vital rule in cell surface properties, exoenzyme production, and virulence in P. carotovorum.

Unlocking the Potential of 46 New Bacteriophages for Biocontrol of Dickeya Solani.

Modern agriculture is expected to face an increasing global demand for food while also needing to comply with higher sustainability standards. Therefore, control of crop pathogens requires new, green alternatives to current methods. Potatoes are susceptible to several bacterial diseases, with infections by soft rot Enterobacteriaceae (SRE) being a significant contributor to the major annual losses. As there are currently no efficient ways of combating SRE, we sought to develop an approach that could easily be incorporated into the potato production pipeline. To this end, 46 phages infecting the emerging potato pathogen Dickeya solani were isolated and thoroughly characterized. The 46 isolated phages were grouped into three different groups based on DNA similarity, representing two distinct clusters and a singleton. One cluster showed similarity to phages previously used to successfully treat soft rot in potatoes, whereas the remaining phages were novel and showed only very limited similarity to previously isolated phages. We selected six diverse phages in order to create the hereto most complex phage cocktail against SRE. The cocktail was applied in a proof-of-principle experiment to treat soft rot in potatoes under simulated storage conditions. We show that the phage cocktail was able to significantly reduce the incidence of soft rot as well as disease severity after 5 days of storage post-infection with Dickeya solani. This confirms results from previous studies that phages represent promising biocontrol agents against SRE infection in potato.

Bioinformatic analysis of the complete genome sequence of Pectobacterium carotovorum subsp. brasiliense BZA12 and candidate effector screening

Pectobacterium carotovorum subsp. brasiliense (Pcb) is a gram-negative, plant pathogenic bacterium of the soft rot Enterobacteriaceae (SRE) family. We present the complete genome sequence of Pcb strain BZA12, which reveals that Pcb strain BZA12 carries a single 4,924,809 bp chromosome with 51.97% GC content and comprises 4508 predicted protein-coding genes. Gene annotation of these genes utilized GO, KEGG, and COG databases. In comparison with three closely related soft-rot pathogens, strain BZA12 has 3797 gene families, among which 3107 gene families are identified as orthologous with those of both P. carotovorum subsp. carotovorum PCC21 and P. carotovorum subsp. odoriferum BCS7, as well as 36 putative Unique Gene Families. We selected five putative effectors from the BZA12 genome and transiently expressed them in Nicotiana benthamiana. Candidate effector A12GL002483 was localized in the cell nucleus and induced cell death. This study provides a foundation for a better understanding of the genomic structure and function of Pcb, particularly in the discovery of potential pathogenic factors and for the development of more effective strategies against this pathogen.

Soft Rot Enterobacteriaceae Are Carried by a Large Range of Insect Species in Potato Fields.

Pathogenic soft rot Enterobacteriaceae (SRE) belonging to the genera Pectobacterium and Dickeya cause diseases in potato and numerous other crops. Seed potatoes are the most important source of infection, but how pathogen-free tubers initially become infected remains an enigma. Since the 1920s, insects have been hypothesized to contribute to SRE transmission. To validate this hypothesis and to map the insect species potentially involved in SRE dispersal, we have analyzed the occurrence of SRE in insects recovered from potato fields over a period of 2 years. Twenty-eight yellow sticky traps were set up in 10 potato fields throughout Norway to attract and trap insects. Total DNA recovered from over 2,000 randomly chosen trapped insects was tested for SRE, using a specific quantitative PCR (qPCR) TaqMan assay, and insects that tested positive were identified by DNA barcoding. Although the occurrence of SRE-carrying insects varied, they were found in all the tested fields. While Delia species were dominant among the insects that carried the largest amount of SRE, more than 80 other SRE-carrying insect species were identified, and they had different levels of abundance. Additionally, the occurrence of SRE in three laboratory-reared insect species was analyzed, and this suggested that SRE are natural members of some insect microbiomes, with herbivorous Delia floralis carrying more SRE than the cabbage moth (Plutella xylostella) and carnivorous green lacewing larvae (Chrysoperla carnea). In summary, the high proportion, variety, and ubiquity of insects that carried SRE show the need to address this source of the pathogens to reduce the initial infection of seed material.IMPORTANCE Soft rot Enterobacteriaceae are among the most important pathogens of a wide range of vegetables and fruits. The bacteria cause severe rots in the field and in storage, leading to considerable harvest losses. In potato, efforts to understand how soft rot bacteria infect and spread between healthy plants have been made for over a century. Early on, fly larvae were implicated in the transmission of these bacteria. This work aimed at investigating the occurrence of soft rot bacteria in insects present in potato fields and at identifying the species of these insects to better understand the potential of this suspected source of transmission. In all tested potato fields, a large proportion of insects were found to carry soft rot bacteria. This suggests a need to give more weight to the role of insects in soft rot ecology and epidemiology to design more effective pest management strategies that integrate this factor.

First Report of Stem Rot on Potato Caused by Dickeya chrysanthemi in Minnesota

Bacterial soft rot and black leg diseases of potato occur sporadically in the Upper Midwestern United States. Multiple members of the soft rot Enterobacteriaceae (SRE) cause diseases in potato. The taxonomy of SREs has undergone extensive revision, resulting in the establishment of new genera and species to better reflect the phylogeny and diversity of strains formerly classified as Erwinia carotovora or E. chrysanthemi (Marrero et al. 2013). One such species, Dickeya dianthicola, has been associated with recent severe black leg outbreaks in the eastern United States. To identify the SREs in the Upper Midwest, a 2016 survey of commercial and seed potato fields in Minnesota and North Dakota was conducted. SREs (123) were isolated from 78 tissue samples exhibiting symptoms of black leg, stem rot, and soft rot. Small tissue samples from the margin of symptomatic and healthy tissues were suspended in 0.02 M potassium phosphate buffer, pH 7.2, for 30 min. Cell suspensions were serially diluted and spread onto crystal violet pectate (CVP) agar. Bacterial colonies producing pitting on CVP were subsequently reisolated on CVP and purified on nutrient broth yeast extract medium. Three isolates from one sample were obtained from a stem sample collected in Sherburne County, Minnesota. One isolate, SR64, was retained for phenotypic characterization and genetic identification. Symptoms associated with SR64 included dry, black-brown necrotic stem lesions with cracking and exposed vasculature. SR64 was determined to be gram negative based on reaction in 3% KOH. Growth on King’s B agar medium failed to produce fluorescence characteristic of Pseudomonas. SR64 also exhibited facultative anaerobic respiration in Hugh-Leifson medium and the ability to grow at 37°C on nutrient agar. Reinoculation of potato tuber slices with SR64 and incubation at 25°C for 2 days produced tissue maceration and dark ooze typical of SRE. DNA extracted from a pure culture of SR64 using DNeasy blood and tissue kits (Qiagen, Valencia, CA, U.S.A.) was used as template for genetic analysis. PCR was conducted using two primer sets: ADE1/ADE2 (Nassar et al. 1996) and Df/Dr (Laurila et al. 2010). SR64 template DNA produced 420 and 119 bp amplicons via ADE1/ADE2 and Df/Dr primers, respectively, as expected for Dickeya. The 16S rDNA was amplified using primer set F27/R1492 (Monciardini et al. 2002), and the ∼1.2 kb amplicon was sequenced and submitted for GenBank nucleotide BLAST analysis. SR64 shared 98% identity with that of the 16S rDNA sequence of type strain Dickeya chrysanthemi LMG 2804 (NZ_CM001974) (Samson et al. 2005). To confirm the species identification, additional housekeeping genes, dnaJ (DCH402_RS02710), dnaX (DCH402_RS15110), and gyrB (DCH402_RS00180) were amplified using primer sets reported by Marrero et al. (2013). Housekeeping gene sequences were concatenated creating a 1,955 bp fragment for analysis with CLC Main Workbench software (Qiagen). The pairwise percent identity between the concatenated sequences of SR64 and D. chrysanthemi LMG 2804ᵀ, D. zeae LMG 2505ᵀ, D. dianthicola LMG 2485ᵀ, D. dadantii subsp. dadantii LMG 25991ᵀ, and D. solani LMG 25993ᵀ was 99.13, 89.42, 90.85, 89.88, and 85.89%, respectively. The low incidence of Dickeya observed in this survey could be owing to limitations of the protocols used to isolate SREs. Alternatively, it could indicate that Dickeya is not currently prevalent in the region. This is the first report of D. chrysanthemi on potato in Minnesota.

RNA-seq Profiling Reveals Defense Responses in a Tolerant Potato Cultivar to Stem Infection by Pectobacterium carotovorum ssp. brasiliense.

Pectobacterium carotovorum subsp. brasiliense is a member of the soft rot Enterobacteriaceae (SRE) family that causes tuber soft rot and blackleg diseases of stems in potato plants. Currently, there are no effective chemical strategies for the control of members of the SRE. Thus, an understanding of the inducible defense responses in stems of potato plants is important, particularly during colonization of the vascular system. Here, time-course RNA-sequencing analysis was used to compare expressed genes between a susceptible potato cultivar (Solanum tuberosum cv Valor) and a tolerant cultivar (S. tuberosum cv BP1) at 0, 6, 12, 24, and 72 h post-inoculation with P. c. brasiliense. In total, we identified 6139 and 8214 differentially expressed genes (DEGs) in the tolerant and susceptible cultivars, compared to mock-inoculated controls, respectively. Key DEGs distinguishing between tolerance and susceptibility were associated with negative regulation of cell death and plant-type cell wall organization/biogenesis biological processes in the tolerant and susceptible cultivars, respectively. Among these were DEGs involved in signaling (mainly MAPK cascade and ethylene pathway), defense-related transcription regulation including WRKY transcription factors, and downstream secondary cell biosynthesis. Together, our results suggest that S. tuberosum cv BP1 likely employs quantitative defense response against P. c. brasiliense. Overall, our study provides the first transcriptome-wide insight into the molecular basis of tolerance and/or resistance of potato stems to SRE infection.

Genome-wide identification of potato long intergenic noncoding RNAs responsive to Pectobacterium carotovorum subspecies brasiliense infection.

BackgroundLong noncoding RNAs (lncRNAs) represent a class of RNA molecules that are implicated in regulation of gene expression in both mammals and plants. While much progress has been made in determining the biological functions of lncRNAs in mammals, the functional roles of lncRNAs in plants are still poorly understood. Specifically, the roles of long intergenic nocoding RNAs (lincRNAs) in plant defence responses are yet to be fully explored.ResultsIn this study, we used strand-specific RNA sequencing to identify 1113 lincRNAs in potato (Solanum tuberosum) from stem tissues. The lincRNAs are expressed from all 12 potato chromosomes and generally smaller in size compared to protein-coding genes. Like in other plants, most potato lincRNAs possess single exons. A time-course RNA-seq analysis between a tolerant and a susceptible potato cultivar showed that 559 lincRNAs are responsive to Pectobacterium carotovorum subsp. brasiliense challenge compared to mock-inoculated controls. Moreover, coexpression analysis revealed that 17 of these lincRNAs are highly associated with 12 potato defence-related genes.ConclusionsTogether, these results suggest that lincRNAs have potential functional roles in potato defence responses. Furthermore, this work provides the first library of potato lincRNAs and a set of novel lincRNAs implicated in potato defences against P. carotovorum subsp. brasiliense, a member of the soft rot Enterobacteriaceae phytopathogens.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2967-9) contains supplementary material, which is available to authorized users.

SigmoID: a user-friendly tool for improving bacterial genome annotation through analysis of transcription control signals.

The majority of bacterial genome annotations are currently automated and based on a ‘gene by gene’ approach. Regulatory signals and operon structures are rarely taken into account which often results in incomplete and even incorrect gene function assignments. Here we present SigmoID, a cross-platform (OS X, Linux and Windows) open-source application aiming at simplifying the identification of transcription regulatory sites (promoters, transcription factor binding sites and terminators) in bacterial genomes and providing assistance in correcting annotations in accordance with regulatory information. SigmoID combines a user-friendly graphical interface to well known command line tools with a genome browser for visualising regulatory elements in genomic context. Integrated access to online databases with regulatory information (RegPrecise and RegulonDB) and web-based search engines speeds up genome analysis and simplifies correction of genome annotation. We demonstrate some features of SigmoID by constructing a series of regulatory protein binding site profiles for two groups of bacteria: Soft Rot Enterobacteriaceae (Pectobacterium and Dickeya spp.) and Pseudomonas spp. Furthermore, we inferred over 900 transcription factor binding sites and alternative sigma factor promoters in the annotated genome of Pectobacterium atrosepticum. These regulatory signals control putative transcription units covering about 40% of the P. atrosepticum chromosome. Reviewing the annotation in cases where it didn’t fit with regulatory information allowed us to correct product and gene names for over 300 loci.

Discovery and profiling of small RNAs responsive to stress conditions in the plant pathogen Pectobacterium atrosepticum.

BackgroundSmall RNAs (sRNAs) have emerged as important regulatory molecules and have been studied in several bacteria. However, to date, there have been no whole-transcriptome studies on sRNAs in any of the Soft Rot Enterobacteriaceae (SRE) group of pathogens. Although the main ecological niches for these pathogens are plants, a significant part of their life cycle is undertaken outside their host within adverse soil environment. However, the mechanisms of SRE adaptation to this harsh nutrient-deficient environment are poorly understood.ResultsIn the study reported herein, by using strand-specific RNA-seq analysis and in silico sRNA predictions, we describe the sRNA pool of Pectobacterium atrosepticum and reveal numerous sRNA candidates, including those that are induced during starvation-activated stress responses. Consequently, strand-specific RNA-seq enabled detection of 137 sRNAs and sRNA candidates under starvation conditions; 25 of these sRNAs were predicted for this bacterium in silico. Functional annotations were computationally assigned to 68 sRNAs. The expression of sRNAs in P. atrosepticum was compared under growth-promoting and starvation conditions: 68 sRNAs were differentially expressed with 47 sRNAs up-regulated under nutrient-deficient conditions. Conservation analysis using BLAST showed that most of the identified sRNAs are conserved within the SRE. Subsequently, we identified 9 novel sRNAs within the P. atrosepticum genome.ConclusionsSince many of the identified sRNAs are starvation-induced, the results of our study suggests that sRNAs play key roles in bacterial adaptive response. Finally, this work provides a basis for future experimental characterization and validation of sRNAs in plant pathogens.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2376-0) contains supplementary material, which is available to authorized users.

Bacteriophages of Soft Rot Enterobacteriaceae-a minireview.

Soft rot Enterobacteriaceae (Pectobacterium spp. and Dickeya spp., formerly pectinolytic Erwinia spp.) are ubiquitous necrotrophic bacterial pathogens that infect a large number of different plant species worldwide, including economically important crops. Despite the fact that these bacteria have been studied for more than 50 years, little is known of their corresponding predators: bacteriophages, both lytic and lysogenic. The aim of this minireview is to critically summarize recent ecological, biological and molecular research on bacteriophages infecting Pectobacterium spp. and Dickeya spp. with the main focus on current and future perspectives in that field.

Detection, identification and differentiation of Pectobacterium and Dickeya species causing potato blackleg and tuber soft rot: a review.

The soft rot Enterobacteriaceae (SRE) Pectobacterium and Dickeya species (formerly classified as pectinolytic Erwinia spp.) cause important diseases on potato and other arable and horticultural crops. They may affect the growing potato plant causing blackleg and are responsible for tuber soft rot in storage thereby reducing yield and quality. Efficient and cost-effective detection and identification methods are essential to investigate the ecology and pathogenesis of the SRE as well as in seed certification programmes. The aim of this review was to collect all existing information on methods available for SRE detection. The review reports on the sampling and preparation of plant material for testing and on over thirty methods to detect, identify and differentiate the soft rot and blackleg causing bacteria to species and subspecies level. These include methods based on biochemical characters, serology, molecular techniques which rely on DNA sequence amplification as well as several less-investigated ones.

Identification of host-microbe interaction factors in the genomes of soft rot-associated pathogens Dickeya dadantii 3937 and Pectobacterium carotovorum WPP14 with supervised machine learning.

BackgroundA wealth of genome sequences has provided thousands of genes of unknown function, but identification of functions for the large numbers of hypothetical genes in phytopathogens remains a challenge that impacts all research on plant-microbe interactions. Decades of research on the molecular basis of pathogenesis focused on a limited number of factors associated with long-known host-microbe interaction systems, providing limited direction into this challenge. Computational approaches to identify virulence genes often rely on two strategies: searching for sequence similarity to known host-microbe interaction factors from other organisms, and identifying islands of genes that discriminate between pathogens of one type and closely related non-pathogens or pathogens of a different type. The former is limited to known genes, excluding vast collections of genes of unknown function found in every genome. The latter lacks specificity, since many genes in genomic islands have little to do with host-interaction.ResultIn this study, we developed a supervised machine learning approach that was designed to recognize patterns from large and disparate data types, in order to identify candidate host-microbe interaction factors. The soft rot Enterobacteriaceae strains Dickeya dadantii 3937 and Pectobacterium carotovorum WPP14 were used for development of this tool, because these pathogens are important on multiple high value crops in agriculture worldwide and more genomic and functional data is available for the Enterobacteriaceae than any other microbial family. Our approach achieved greater than 90% precision and a recall rate over 80% in 10-fold cross validation tests.ConclusionApplication of the learning scheme to the complete genome of these two organisms generated a list of roughly 200 candidates, many of which were previously not implicated in plant-microbe interaction and many of which are of completely unknown function. These lists provide new targets for experimental validation and further characterization, and our approach presents a promising pattern-learning scheme that can be generalized to create a resource to study host-microbe interactions in other bacterial phytopathogens.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-508) contains supplementary material, which is available to authorized users.

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.

The use of fluorescent reporter protein tagging to study the interaction between Root-Knot Nematodes and Soft Rot Enterobacteriaceae

The study of plant parasitic nematodes such as Meloidogyne spp. and their interactions with phytopathogenic bacteria remains underexplored. One of the challenges towards establishing such interactions is the dependence on symptom development as a measure of interaction. In this study, mCherry was employed as a reporter protein to investigate the interaction between the soft rot Enterobacteriaceae (SRE) Pectobacterium carotovorum subsp. brasiliensis (Pcb) and root-knot nematode (M.incognita). Pectobacterium carotovorum subsp. brasiliensis was transformed with pMP7604 generating Pcb_mCherry strain. This strain was shown to attach to the surface coat of M.incognita J2 at the optimum temperature of 28°C. This suggests that RKN juveniles may play a role in disseminating Pcb in soils that are heavily infested with Pcb. The presence of RKN juveniles was shown to play a role in introducing Pcb_mCherry into potato tubers potentially acting as a source of latent tuber infections.

The Role of Secretion Systems and Small Molecules in Soft-Rot Enterobacteriaceae Pathogenicity

Soft-rot Enterobacteriaceae (SRE), which belong to the genera Pectobacterium and Dickeya, consist mainly of broad host-range pathogens that cause wilt, rot, and blackleg diseases on a wide range of plants. They are found in plants, insects, soil, and water in agricultural regions worldwide. SRE encode all six known protein secretion systems present in gram-negative bacteria, and these systems are involved in attacking host plants and competing bacteria. They also produce and detect multiple types of small molecules to coordinate pathogenesis, modify the plant environment, attack competing microbes, and perhaps to attract insect vectors. This review integrates new information about the role protein secretion and detection and production of ions and small molecules play in soft-rot pathogenicity.

Balancing sexual selection through opposing mate choice and male competition

Male–male competition and female mate choice act contemporaneously in the cockroach Nauphoeta cinerea and the social pheromone of males influences the outcome of both forms of sexual selection. We therefore examined the joint and separate effects of male–male competition and female mate choice to determine if the selective optima for the pheromone were the same or different. Dominant males in a newly established hierarchy mated more frequently, but not exclusively. Manipulations of the multi-component social pheromone produced by males of N. cinerea showed that both long- and close-range attraction of females by males were influenced by the quantity and composition of the pheromone. The most attractive composition, however, differed from that which was most likely to confer high status to males. Since the outcome of male–male competition can conflict with mating preferences exhibited by females, there is balancing sexual selection on the social pheromone of N. cinerea. Such balancing selection might act to maintain genetic variation in sexually selected traits. We suggest that the different forms of sexual selection conflict in N. cinerea because females prefer a blend different to that which is most effective in male–male competition in order to avoid mating with overly aggressive males.