Search

Lytic bacteriophages able to infect and killDickeyaspp. can be readily isolated from virtually allDickeyaspp.-containing environments, yet little is known about the selective pressure those viruses exert on their hosts. Here, we identified two spontaneousD. solaniIPO 2222 mutants (0.8% of all obtained mutants), DsR34 and DsR207, resistant to infection caused by lytic phage vB_Dsol_D5 (ΦD5) that expressed a reduced ability to macerate potato tuber tissues compared to the wild-type, phage-susceptibleD. solaniIPO 2222 strain. Genome sequencing revealed that genes encoding: secretion protein HlyD (mutant DsR34) and elongation factor Tu (EF-Tu) (mutant DsR207) were altered in these strains. Both mutations impacted the proteomes of cells grown in both rich and minimal media, including the abundance of the cell envelope and transmembrane transport-associated proteins. Furthermore, features essential for the ecological success of these mutants in a plant environment, including their ability to use various carbon and nitrogen sources, produce plant cell wall degrading enzymes, ability to form biofilms, siderophore production, swimming and swarming motility and virulencein plantawere assessed. Compared to the wild-type strain,D. solanistrain IPO 2222, mutants DsR34 and DsR207 had a reduced ability to macerate chicory leaves and to colonize and cause symptoms in growing potato plants. The implications of the ΦD5 resistance on driving traits affecting the ecological performance ofD. solaniare discussed.

Microscopic datasets (TEM and AFM) supporting the manuscript entitled: Being spontaneous has its costs! Characterization of spontaneous phage ϕD5- resistant mutants of Dickeya solani strain IPO 2222, This research was financially supported by the National Science Center, Poland (Narodowe Centrum Nauki, Polska) via a research grant OPUS 13 (2017/25/B/NZ9/00036) to Robert Czajkowski

Pectobacterium atrosepticum is a narrow-host-range, pectinolytic, plant-pathogenic bacterium causing blackleg of potato (Solanum tuberosum L.) worldwide. Till present, several P. atrosepticum genomes have been sequenced and characterized in detail; however, all of these genomes have come from P. atrosepticum isolates from plants grown in temperate zones, not from hosts cultivated under different climatic conditions. Herewith, we present the first complete, high-quality genome of the P. atrosepticum strain Green1 isolated from potato plants grown under a subarctic climate in Greenland. The genome of P. atrosepticum strain Green1 consists of one chromosome of 4,959,719 bp, with a GC content of 51% and no plasmids. The genome contains 4,531 annotated features, including 4,179 protein-coding genes, 22 ribosomal RNA genes, 70 transfer RNA genes, 8 noncoding RNA genes, 2 CRISPRs, and 126 pseudogenes. We believe that the information in this first high-quality, complete, closed genome of P. atrosepticum strains isolated from host plants grown in a subarctic agricultural region will provide resources for comparative genomic studies and for analyses targeting climatic adaptation and ecological fitness mechanisms present in P. atrosepticum. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Pectobacterium parmentieri (former Pectobacterium wasabiae) is an emerging pectinolytic bacterial pathogen causing losses in potato (Solanum tuberosum L.) worldwide. Until now, there are no effective measures to protect crops from infections caused by P. parmentieri. Likewise, little is known about lytic bacteriophages that can infect and kill P. parmentieri, and that could be used in the (bio)control of this pathogen in agricultural applications. A novel lytic bacteriophage vB_Ppp_A38 (ϕA38), belonging to the order Caudovirales, was isolated and characterised in our previous studies. This report provides information about its complete genome sequence and accompanying phylogenomics. The genome of vB_Ppp_A38 consists of 75,764-bp-length, linear, double-stranded DNA with an average GC content of 48.7% and is predicted to have 97 open reading frames (ORFs), with an average length of 732 nucleotides. The open reading frames were classified into functional groups, including structural units, packing, DNA metabolism, regulation and additional (miscellaneous) functions. Comparative genomic analyses based on the whole-genome sequence indicated that the phage vB_Ppp_A38 is most similar to N4-like viruses of the family Schitoviridae, genus Cbunavirus, sharing more than 90% identity with the phages vB_PatP_CB1, vB_PatP_CB3 and vB_PatP_CB4 infecting P. atrosepticum. The bacteriophage vB_Ppp_A38 is the first Cbunavirus bacteriophage infecting other Pectobacterium spp. hosts than P. atrosepticum. As vB_Ppp_A38 is a lytic virus able to kill plant-pathogenic P. parmentieri, it can be used in the biological control of this pathogen in agricultural applications.

A simple and fast procedure has been developed to generate soft rot Pectobacteriaceae (SRP: Pectobacterium spp. and Dickeya spp.) Tn5 mutants in genes encoding receptors used by bacteriophages to interact with their hosts, for the follow-up studies. The procedure is inexpensive and does not require any specialized tools and/or dedicated technical support. The neomycin-resistant SRP Tn5 mutants are generated via conjugation with a transposon donor Escherichia coli ST18 strain (requiring 5-aminolevulinic acid (5-ALA) to survive) carrying pFAJ1819-mini-Tn5-neoR. The conjugation is done on solid medium supplemented with 5-ALA. After conjugation bacterial cells are collected, suspended in liquid bacterial medium, added to the suspension containing lytic bacteriophages and incubated for the additional 30 min with shaking (120 rpm). During this stage, the transposon recipients (Pectobacterium spp. and/or Dickeya spp. Tn5 mutants), susceptible to bacteriophage infection are lysed. Likewise, due to the lack of 5-ALA in the growth medium, E. coli ST18 (transposon donor) cells die at this stage. Finally, after incubation, the bacterial mutants with the Tn5 insertions, resistant to phage infection are selected on solid growth medium supplemented with neomycin. The Tn5 insertion sites are sequenced to acquire knowledge about the Tn5-distrupted genes and their putative function in phage-host interactions. The proposed assay allows generation of a number of immediately-available Tn5 mutants expressing phage-resistant phenotypes in a short time (ca. 48 h) that can be later characterized for various other phenotypic features. In this study, as a proof-of-concept, this method has been used to generate Dickeya solani IPO2222 Tn5 mutants resistant to infection caused by the lytic bacteriophage ɸD5.

As a part of a blackleg and soft rot survey on potato plants cultivated in the agricultural region of Southern Greenland during the growing season of 2019 diseased potato plants and tubers were collected at six localities. Samples of plants and tubers with typical blackleg and soft rot symptoms were cut into parts weighing ca. 10–15 g each and incubated in potato enrichment broth (PEB) under anaerobic conditions for 4–7 days at ca. 20–22 °C (conditions during shipment of the samples from Greenland to Poland). After enrichment plant extracts were plated on crystal violet pectate (CVP) medium to isolate individual cavity-forming bacterial colonies. The inoculated plates were incubated at 22, 25 and 28 °C to maximize the chance of finding pectinolytic bacteria with different growth temperature optima. Cavity-forming isolates were collected and purified to pure cultures on tryptone soya agar (TSA). Ten cavity-forming isolates, named Green1 – Green10, representing isolates from symptomatic plants from different locations, were selected for analyses. The isolates gave a 434 bp. product in Pectobacterium spp.-specific PCR and a 439 bp. product in P. atrosepticum (Pba) -specific PCR. These isolates were Gram (−) rods, facultative anaerobic, catalase positive, oxidase and indole negative, grew in TSB + 5% NaCl, produced acid from lactose, maltose and raffinose. BlastN analyses of the ca. 1300 bp. 16S rDNA sequences of all 10 strains indicated a 99–100% similarity to the 16S rDNA of Pectobacterium atrosepticum. All 10 isolates caused soft rot of potato tuber slices after 72 h at 28 °C. Phylogenetic analysis based on the recA gene sequence grouped the isolates together with P. atrosepticum strains CFBP1526T and SCRI1043. This is the first report on isolation of P. atrosepticum from blackleg-diseased potato plants in Greenland. The presence of P. atrosepticum and its possible impact on potato cultivation in Greenland is discussed.

Resistance to bacteriophage infections protects bacteria in phage-full environments, allowing them to survive and multiply in the presence of their viral predators. However, such resistance may cause direct costs for strains linked with the ecological fitness expressed as reduced competitiveness for resources or reduced virulence or both. Unfortunately, limited knowledge exists about such costs paid by phage-resistant plant pathogenic bacteria in their natural environments. This study analyzed the costs of phage resistance paid by broad host phytopathogenic pectinolytic bacterium Dickeya solani both in vitro and in potato (Solanum tuberosum L.) plants. Thirteen D. solani IPO 2222 Tn5 mutants were identified that exhibited resistance to infection caused by lytic bacteriophage vB_Dsol_D5 (ΦD5). The genes disrupted in these 13 mutants encoded proteins involved in the synthesis of the bacterial envelope components (viz. LPS, EPS and capsule). The ability of ΦD5-resistant D. solani mutants to colonize and cause symptoms on potato plants as well as other phenotypes that are known to contribute to the ecological fitness of D. solani in-plant environment, including growth rate, production of effectors, swimming and swarming motility, use of various carbon and nitrogen sources and biofilm formation were assessed. Although phage resistance did not affect most of the phenotypes of ΦD5-resistant D. solani evaluated in vitro, all phage resistant mutants were significantly compromised in their ability to survive on and colonize and cause disease symptoms in potato plants. This study is, to our knowledge, one of few to show the direct link between phage resistance and the fitness of plant pathogenic bacteria and the first one to assess phage-host associations for D. solani.

In bacteria, the DsbA oxidoreductase is a crucial factor responsible for the introduction of disulfide bonds to extracytoplasmic proteins, which include important virulence factors. A lack of proper disulfide bonds frequently leads to instability and/or loss of protein function; therefore, improper disulfide bonding may lead to avirulent phenotypes. The importance of the DsbA function in phytopathogens has not been extensively studied yet. Dickeya solani is a bacterium from the Soft Rot Pectobacteriaceae family which is responsible for very high economic losses mainly in potato. In this work, we constructed a D. solani dsbA mutant and demonstrated that a lack of DsbA caused a loss of virulence. The mutant bacteria showed lower activities of secreted virulence determinants and were unable to develop disease symptoms in a potato plant. The SWATH-MS-based proteomic analysis revealed that the dsbA mutation led to multifaceted effects in the D. solani cells, including not only lower levels of secreted virulence factors, but also the induction of stress responses. Finally, the outer membrane barrier seemed to be disturbed by the mutation. Our results clearly demonstrate that the function played by the DsbA oxidoreductase is crucial for D. solani virulence, and a lack of DsbA significantly disturbs cellular physiology.

Pectobacterium parmentieri is a Gram-negative plant-pathogenic bacterium able to infect potato (Solanum tuberosum L.). Little is known about lytic bacteriophages infecting P. parmentieri and how phage-resistance influences the environmental fitness and virulence of this species. A lytic phage vB_Ppp_A38 (ϕA38) has been previously isolated and characterized as a potential biological control agent for the management of P. parmentieri. In this study, seven P. parmentieri SCC 3193 Tn5 mutants were identified that exhibited resistance to infection caused by vB_Ppp_A38 (ϕA38). The genes disrupted in these seven mutants encoded proteins involved in the assembly of O-antigen, sugar metabolism, and the production of bacterial capsule exopolysaccharides. The potential of A38-resistant P. parmentieri mutants for plant colonization and pathogenicity as well as other phenotypes expected to contribute to the ecological fitness of P. parmentieri, including growth rate, use of carbon and nitrogen sources, production of pectinolytic enzymes, proteases, cellulases, and siderophores, swimming and swarming motility, presence of capsule and flagella as well as the ability to form biofilm were assessed. Compared to the wild-type P. parmentieri strain, all phage-resistant mutants exhibited a reduced ability to colonize and to cause symptoms in growing potato (S. tuberosum L.) plants. The implications of bacteriophage resistance on the ecological fitness of P. parmentieri are discussed.

We present a simple, fast and inexpensive screening assay to preselect candidate Pectobacterium spp. and Dickeya spp. Tn5 mutants, which carry transposon insertions in genes putatively encoding proteins used by lytic bacteriophages to interact with host cells, for the follow-up studies. The proposed method is fast and cost-effective and it does not need any specialized laboratory equipment and/or technical support. The Tn5 mutants are generated using random transposon mutagenesis with the mini-Tn5 transposon. The obtained bacterial mutants are incubated in the presence of viable lytic bacteriophage particles in liquid bacterial growth medium supplemented with resazurin for 12 h at 28 °C in a 96-well microtiter plate assay. During the cultivation, the Tn5 mutants that are susceptible to phage infection are lysed. The mutants that are resistant to a viral infection (not lysed after contact with bacteriophages) irreversibly reduce the resazurin violet dye to pink/yellowish-colored resorufin indicating active bacterial metabolism (a positive reaction). The change of the culture color can be observed by eye. The Tn5 mutants that are positive in the screen are selected for sequencing of the Tn5 insertion site directly from bacterial genome. The proposed assay allows generation of a number of immediately-available Tn5 mutants expressing phage-resistant phenotypes that can be later selected for further examinations. As a proof-of-concept, we used this method to evaluate resistance to viral infection of Tn5 mutants of Dickeya solani strain IPO2222 and Pectobacterium parmentieri strain SCC3193 using lytic bacteriophages ɸD5 and ɸA38, respectively.

Possibilities to protect potato tubers from rotting caused by Soft Rot Pectobacteriaceae (SRP) under disease favoring conditions were investigated using compatible mixtures of bacterial antagonists and tested with a newly developed stepwise efficacy-based screening protocol. Twenty-two bacterial antagonists were evaluated against a combination of five Pectobacterium and Dickeya strains representing species and subspecies most often associated with potato soft rot in Europe. To enable potential synergistic activity, the antagonists were initially tested against the combination of pathogens in 15 random mixtures containing up to 5 antagonists each. Three mixtures (M2, M4, and M14) out of 15 tested reduced tuber tissue maceration due to soft rot. The individual antagonists derived from M2, M4, and M14 mixtures were tested on potato slices and whole tuber injection assays. These five strains (S. plymuthica strain A294, E. amnigenus strain A167, R. aquatilis strain H145, S. rubidaea strain H440, and S. rubidaea strain H469) were combined to develop a tailored biological control mixture against potato soft rot. The new mixture, designated the Great Five (GF), was tested on seed potato tubers vacuum infiltrated with antagonists and subsequently with the combination of five SRP pathogens. In these experiments, the GF mixture provided stable protection of inoculated potato tubers, reducing soft rot by 46% (P = 0.0016) under high disease pressure conditions. The A294, A167, H145, H440, and H469 antagonists were characterized for features important for viable commercial applications including growth at different temperatures, resistance to antibiotics, and potential toxicity toward Caenorhabditis elegans. The implications for control of soft rot caused by SRP with the use of the GF mixture of antagonists are discussed.

Strain P482 was isolated from a tomato rhizosphere and classified as Pseudomonas donghuensis. The P. donghuensis species was first established in 2015 and currently consists of only four strains: P482, HYST, SVBP6, and 22G5. P. donghuensis strains antagonize plant pathogens, including bacteria, fungi, and oomycetes, and, therefore, are of high interest regarding their biological control potential to combat plant diseases. The antimicrobial activity of P. donghuensis P482 is based on the production of iron-scavenging compound 7-hydroxytropolone, antifungal volatile organic compounds, and as-yet-unidentified secondary metabolites. Here, we report a complete genome resource for P. donghuensis strain P482. The genome consists of a single chromosome (5,656,185 bp) with 5,258 open reading frames (5,158 protein-coding genes, 74 transfer RNAs, 22 ribosomal RNAs, 3 noncoding RNAs, and 1 transfer-messenger RNA) and no plasmid. We believe that information on the first high-quality, complete genome of P. donghuensis will provide resources for analyses targeting the biological control potential of this species and understanding the traits essential for plant–microbe interaction. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Pectobacterium atrosepticumis a narrow host range pectinolytic plant pathogenic bacterium causing blackleg of potato (Solanum tuberosumL.) worldwide. Till present, severalP. atrosepticumgenomes have been sequenced and characterized in detail; all of these genomes have come, however, fromP. atrosepticumstrains isolates from plants grown in temperate zones, not from hosts cultivated under different climatic conditions. Herewith, we present the first complete, high-quality genome of theP. atrosepticumstrain Green1 isolated from potato plants grown under subarctic climate in Greenland. The genome ofP. atrosepticumstrain Green1 consists of one chromosome of 4,959,719 bp., with a GC content of 51% and no plasmids. The genome contains 4531 annotated features, including 4179 protein-coding genes (CDSs), 22 rRNA genes, 70 tRNA genes, 8 ncRNA genes, 2 CRISPRs and 126 pseudogenes. We believe that the information of this first, high-quality, complete, closed genome ofP. atrosepticumstrain isolated from host plant grown in subarctic agricultural region will provide resources for comparative genomic studies and for analyses targeting climatic adaptation and ecological fitness mechanisms present inP. atrosepticum.

Temperature is one of the critical factors affecting gene expression in bacteria. Despite the general interest in the link between bacterial phenotypes and environmental temperature, little is known about temperature-dependent gene expression in plant pathogenic Pectobacterium atrosepticum, a causative agent of potato blackleg and tuber soft rot worldwide. In this study, twenty-nine P. atrosepticum SCRI1043 thermoregulated genes were identified using Tn5-based transposon mutagenesis coupled with an inducible promotorless gusA gene as a reporter. From the pool of 29 genes, 14 were up-regulated at 18 °C, whereas 15 other genes were up-regulated at 28 °C. Among the thermoregulated loci, genes involved in primary bacterial metabolism, membrane-related proteins, fitness-corresponding factors, and several hypothetical proteins were found. The Tn5 mutants were tested for their pathogenicity in planta and for features that are likely to remain important for the pathogen to succeed in the (plant) environment. Five Tn5 mutants expressed visible phenotypes differentiating these mutants from the phenotype of the SCRI1043 wild-type strain. The gene disruptions in the Tn5 transposon mutants caused alterations in bacterial generation time, ability to form a biofilm, production of lipopolysaccharides, and virulence on potato tuber slices. The consequences of environmental temperature on the ability of P. atrosepticum to cause disease symptoms in potato are discussed.

Dickeya solani is an emerging plant pathogenic bacterium, causing disease symptoms in a variety of agriculturally relevant crop species worldwide. To date a number of D. solani genomes have been sequenced and characterized, the great majority of these genomes have however come from D. solani strains isolated from potato (Solanum tuberosum L.) and not from other plant hosts. Herewith, we present the first complete, high-quality genome of D. solani strain IPO 2019 (LMG 25990) isolated from ornamental plant Hyacinthus orientalis. The genome of D. solani strain IPO 2019 consists of one chromosome of 4,919,542 bp., with a GC content of 56.2% and no plasmids. The genome contains 4502 annotated features, 22 rRNA genes, 73 tRNA genes and 1 CRISPRS. We believe that the information of this high-quality, complete, closed genome of D. solani strain isolated from host plant different than potato (i.e. hyacinth) will provide resources for comparative genomic studies as well as for analyses targeting adaptation and ecological fitness mechanisms present in Dickeya solani species.

The taxonomy of soft rot Pectobacteriaceae (SRP) has been in a state of flux for the last century. With the advent of genomic technologies, there has been a flurry of new species just in the last 2 years and no doubt new ones will emerge in the future. Nevertheless, the use of these methods has greatly advanced our understanding of the relationships between these organisms and allowed ambiguities to be resolved. It is therefore hoped that the rate of change we have seen over the last century will begin to slow. This chapter provides an overview of the latest taxonomy of SRP, gives an overview of the recent genomic techniques being used and discusses how evolution, including through bacteriophage infection, has shaped the genome and ultimately the taxonomy of this group of organisms.

Management of soft rot Pectobacteriaceae (SRP) is a challenge as there are no control agents available and no effective resistance present in commercial cultivars. In addition, many species of SRP have a broad host range and spread via rotten plant material takes place readily. In this chapter, the possibilities for disease management are outlined. Management is mainly based on seed certification to limit the risks of using infected planting material, and on hygiene and cultivation practices that reduce cross-contamination within and between seed lots. Balanced nutrition also supports the suppressiveness of crops against SRP. Experimental data show that inoculum in seed tubers can be reduced by thermotherapy and the use of biocides. Under controlled conditions, application of seed potatoes with biocontrol agents has showed promising results but few data are present on the efficacy of biocontrol in the field. Resistance in wild Solanum species against SRP has been found but to date no genes have been transferred to cultivars. However, new breeding technologies, such as CRISPR/CAS 9 and the use of true potato seed (TPS), will give us new perspectives on the generation of resistant cultivars.

The soft rot Pectobacteriaceae (SRP) infect a wide range of plants worldwide and cause economic damage to crops and ornamentals but can also colonize other plants as part of their natural life cycle. They are found in a variety of environmental niches, including water, soil and insects, where they may spread to susceptible plants and cause disease. In this chapter, we look in detail at the plants colonized and infected by these pathogens and at the diseases and symptoms they cause. We also focus on where in the environment these organisms are found and their ability to survive and thrive there. Finally, we present evidence that SRP may assist the colonization of human enteric pathogens on plants, potentially implicating them in aspects of human/animal as well as plant health.

Dickeya solani is a Gram-negative bacterium able to cause disease symptoms on a variety of crop and ornamental plants worldwide. Weeds including Solanum dulcamara (bittersweet nightshade) growing near agricultural fields have been reported to support populations of soft rot bacteria in natural settings. However, little is known about the specific interaction of D. solani with such weed plants that may contribute to its success as an agricultural pathogen. The aim of this work was to assess the interaction of D. solani with its crop plant (Solanum tuberosum) and an alternative (S. dulcamara) host plant. From a collection of 10,000 Tn5 transposon mutants of D. solani IPO2222 carrying an inducible, promotorless gusA reporter gene, 210 were identified that exhibited plant tissue-dependent expression of the gene/operon into which the Tn5 insertion had occurred. Thirteen Tn5 mutants exhibiting the greatest plant tissue induction of such transcriptional units in S. tuberosum or S. dulcamara as measured by qRT-PCR were assessed for plant host colonization, virulence, and ability to macerate plant tissue, as well as phenotypes likely to contribute to the ecological fitness of D. solani, including growth rate, carbon and nitrogen source utilization, motility, chemotaxis toward plant extracts, biofilm formation, growth under anaerobic conditions and quorum sensing. These 13 transcriptional units encode proteins involved in bacterial interactions with plants, with functions linked to cell envelope structure, chemotaxis and carbon metabolism. The selected 13 genes/operons were differentially expressed in, and thus contributed preferentially to D. solani fitness in potato and/or S. dulcamara stem, leaf, and root tissues.

Abstract “The Great Five” (GF) is an artificial bacterial consortium developed to protect potato tubers from soft rot caused by Pectobacterium spp. and Dickeya spp. To investigate the commercialization potential of the GF, we developed liquid and powder formulations of the consortium and of each of the comprising strains (Serratia plymuthica strain A294, Enterobacter amnigenus strain A167, Rahnella aquatilis strain H145, Serratia rubidaea strain H440, and S. rubidaea strain H469). To form powders, the cells were lyophilized using a newly developed lyoprotectant: Reagent PS. The shelf life of the formulations stored at 8 and 22 °C was monitored for a period of 12 months. The longest shelf life was obtained for formulations stored at 8 °C; however, the viability of all formulations was negatively affected at 22 °C. For the consortium, a 2.5 log10 cfu (colony forming units) drop in cell number was recorded for the liquid formulation after 6 months, while in case of powders, the drop remained below 1 log10 cfu following 12 months. The ability of the powder formulations to preserve biocontrol activity of the consortium was tested on potato tubers treated with the formulations and a mixture of the soft rot pathogens. The inoculated tubers were stored for 6 months at 8 °C to mimic commercial storage conditions. Soft rot severity and incidence on potato tubers treated with formulations were significantly reduced (62–75% and 48–61%, respectively) in comparison to positive control with pathogens alone. The potential use of the newly developed formulations of “The Great Five” for the biocontrol of soft rot is discussed. Key Points • An innovative reagent to protect bacterial cells during lyophilization was developed. • Powder formulations of “The Great Five” prolonged its shelf life. • The powder-formulated “The Great Five” was active against soft rot bacteria on potato tubers.

Biological control based on the use of (artificial) consortia of plant beneficial microorganisms, (the combinations of several biological control bacterial or fungal strains or a mixture of both) is receiving an increasing recognition globally. Thus far, however the number of marketed bioproducts containing microbial consortia is scarce. This situation results primarily from difficulties encountered during registration and marketing but also because of the problems in understanding the specific roles of each component of a consortium as well as their biological activity. Certain limitation for developing artificial consortia for agriculture is furthermore the compatibility of the biocontrol agents in the consortium and their collective performance on the plants under natural and/or agricultural conditions. This chapter provides insight into current state of the art in the development of the artificial microbial consortia for the agricultural applications and their commercialization mainly for plant protection and for biofertilization to increase plant fitness and crop yield.

In bacteria, the DsbA oxidoreductase is a crucial factor responsible for the introduction of disulfide bonds to extracytoplasmic proteins, which include important virulence factors. A lack of proper disulfide bonds frequently leads to instability and/or loss of protein function; therefore, improper disulfide bonding may lead to avirulent phenotypes. The importance of the DsbA function in phytopathogens has not been extensively studied yet. Dickeya solani is a bacterium from the Soft Rot Pectobacteriaceae family which is responsible for very high economic losses mainly in potato. In this work, we constructed a D. solani dsbA mutant and demonstrated that a lack of DsbA caused a loss of virulence. The mutant bacteria showed lower activities of secreted virulence determinants and were unable to develop disease symptoms in a potato plant. The SWATH-MS-based proteomic analysis revealed that the dsbA mutation led to multifaceted effects in the D. solani cells, including not only lower levels of secreted virulence factors, but also the induction of stress responses. Finally, the outer membrane barrier seemed to be disturbed by the mutation. Our results clearly demonstrate that the function played by the DsbA oxidoreductase is crucial for D. solani virulence, and a lack of DsbA significantly disturbs cellular physiology.

Two bacteriophages, ϕA38 and ϕA41, infecting Pectobacterium parmentieri strain SCC 3193 (former Pectobacterium wasabiae strain SCC 3193) were isolated from arable soil samples collected in different regions of Poland. ϕA38 and ϕA41 have a typical morphology of the members of the family Podoviride and order Caudovirales, with a head diameter of ca. 60 nm and tail length of ca. 20 nm. Phages ϕA38 and ϕA41 exhibited a similar RFLP pattern with Csp6I restriction endonuclease. They were stable in a range of pHs, temperatures and osmolarities but were rapidly inactivated by UV light. During the first 20 min., 74 and 69% of ϕA38 and ϕA41 phages, respectively, were adsorbed to SCC 3193 cells. In one-step growth experiments, ϕA38 and ϕA41 showed latent period of ca. 20–30 min and burst size of 102 and 141 phages, respectively. The optimal multiplicity of infection (MOI) was calculated to be 0.01 for both bacteriophages. In the host range experiments, both phages were able to infect six from 21 of the tested P. parmentieri isolates but the phages were unable to infect other members of the Pectobacterium spp. or Dickeya spp. In the proof-of-concept experiments, ϕA38 and ϕA41 were able to inhibit the growth of P. parmentieri strain SCC 3193 and to protect potato tuber tissue maceration caused by the bacterium. The potential use of ϕA38 and ϕA41 bacteriophages for the biocontrol of P. parmentieri in potato is discussed.

Here, we present a simple and fast screening method to preselect candidate Dickeya solani Tn5 mutants which carry transposon insertions in plant tissue-induced genes for the follow-up studies. The described method is faster and cost-effective in comparison to standard IVET, expression microarrays and RNAseq, and it does not require any specialized laboratory equipment and/or technical assistance. The Tn5 mutants are generated using mini-Tn5 transposon carrying inducible reporter gene (promoterless gusA coding for β-glucuronidase) and are screened for the β-glucuronidase positive phenotypes under non-inductive conditions with X-gluc as a glucuronidase substrate. The bacterial mutants negative in the first screen are then screened for β-glucuronidase phenotypes in the presence of plant tissues, viz. roots, stems and leaves, suspended in liquid bacterial growth medium supplemented with X-gluc in a 48-well microtiter plate assay. The mutants that are positive in the screen with plant tissues are selected for sequencing of the Tn5 insertion sites directly from bacterial genome. This method allows generation of a number of ready-to-use Tn5 mutants showing up-regulation by plant tissue which can be later selected for further studies. We used this method to evaluate interaction of D. solani IPO2222 (type strain) with bittersweet nightshade (Solanum dulcamara L.) and potato (Solanum tuberosum L.) tissues.

Soft rot and blackleg of potato caused by pectinolytic bacteria lead to severe economic losses in potato production worldwide. To investigate the species composition of bacteria causing soft rot and black leg of potato in Norway and Poland, bacteria were isolated from potato tubers and stems. Forty-one Norwegian strains and 42 Polish strains that formed cavities on pectate medium were selected for potato tuber maceration assays and sequencing of three housekeeping genes (dnaX, icdA and mdh) for species identification and phylogenetic analysis. The distribution of the species causing soft rot and blackleg in Norway and Poland differed: we have demonstrated that mainly P. atrosepticum and P. c. subsp. carotovorum are the causal agents of soft rot and blackleg of potatoes in Norway, while P. wasabiae was identified as one of the most important soft rot pathogens in Poland. In contrast to the other European countries, D. solani seem not to be a major pathogen of potato in Norway and Poland. The Norwegian and Polish P. c. subsp. carotovorum and P. wasabiae strains did not cluster with type strains of the respective species in the phylogenetic analysis, which underlines the taxonomic complexity of the genus Pectobacterium. No correlation between the country of origin and clustering of the strains was observed. All strains tested in this study were able to macerate potato tissue. The ability to macerate potato tissue was significantly greater for the P. c. subsp. carotovorum and Dickeya spp., compared to P. atrosepticum and P. wasabiae.

Colonization of Solanum dulcamara (bittersweet nightshade) plants by a GFP-tagged Dickeya solani type strain IPO2222 (IPO2254) was investigated by selective plating and epifluorescence stereomicroscopy (ESM), using in vitro plants and plants grown in compost soil. Replicated experiments were carried out in a growth chamber and the progress of infection and disease symptoms on tissue of the cultured plants, following leaf- and stem-base inoculations with bacteria, was evaluated. Microscopy observations were confirmed by spread-plating dilutions of plant extracts onto agar medium directly after the harvest. In experiments where the stem base of in vitro plants inoculated with a range of inocula of D. solani (104 to 108 colony forming units [cfu] ml−1) was examined at 14 days post infection (dpi), blackleg-like symptoms developed in more than 80% plants together with a reduction of the plant fitness (disease symptoms, weight, height, and appearance). In leaf-inoculated plants at 14 dpi, 15% of the plants exhibited severe blackleg-like symptoms. In detached S. dulcamara leaf assays, IPO2254 survived on the adaxial surface for 14 days at populations of 106 cfu per leaf. Thirty days after stem inoculation of plants grown in compost soil in pots, up to 104 cfu g−1 of GFP-tagged D. solani were found inside the stems. D. solani were detected inside the vascular tissue (xylem vessels) of stems, in the pith tissue in roots, and on the internal surface of the stem hollow. The implications of S. dulcamara infection by D. solani for the long-distance dispersal of the bacterial inoculum are discussed.