Plant Pathogen Ralstonia Solanacearum Research Articles

HrpY protein of Ralstonia solanacearum exhibits spontaneous formation of pilus like assembly: analysis of its stability

Type 3 secretory system (T3SS), a complex protein machinery has a unique virulence mechanism that involves injecting effector proteins directly into host cells. The T3SS effector proteins are transported through an extracellular long hollow needle made up of multiple copies of a small protein. In T3SS of the plant pathogen Ralstonia solanacearum, the 8.6 kDa HrpY protein assembles into a large needle like apparatus (pilus) for transporting effector proteins. To study structural details of HrpY, we recombinantly expressed and purified HrpY in E. coli. The dynamic light scattering (DLS) analysis showed that rHrpY has spontaneously formed oligomers of large order (>100 nm). Transmission electron microscopy of rHrpY samples revealed that the large structures are tube like assembly having dimensions 86.3–166.6 nm and 5.8–6.8 nm in length and width respectively. Different molecular sizes of the purified rHrpY hindered the crystallization of the protein. The stability of oligomer assembly was studied with denaturants and surfactants. Denaturants like urea and guanidine HCl could not break them apart; however, detergents like SDS, sarkosyl, Octyl-β-Glucoside, CHAPS, Tween 20, Tween 80 and Triton X-100 showed disassembly of the oligomer. rHrpY assembly was found to withstand up to 50 °C and the circular dichroism analysis revealed that there is no significant change in the secondary structural composition with increase in temperature. However, change in the secondary structure was observed with the addition of SDS. Communicated by Ramaswamy H. Sarma

QMRA of Ralstonia solanacearum in potato cultivation: Risks associated with irrigation water recycled through managed aquifer recharge

Agricultural aquifer storage recovery and transfer (ASTR) stores excess fresh water for later reuse in irrigation. Moreover, water quality improves because chemical pollutants and pathogens will be removed by degradation and attachment to the aquifer material. The source water may contain the bacterial plant pathogen Ralstonia solanacearum which causes plant infections and high yield losses. We used quantitative microbial risk assessment (QMRA) to investigate the removal of R. solanacearum during ASTR to predict infection risks of potato plants after irrigation with the recovered water. Laboratory experiments analyzed the ASTR treatment by investigating the bacterial die-off in the water phase and the removal by attachment to the aquifer sediment. Die-off in the water phase depends on the residence time and ranged between 1.3 and 2.7 log10 after 10 or 60 days water storage, respectively. A subpopulation of the bacteria persisted for a prolonged time at low concentrations which may pose a risk if the water is recovered too early. However, the natural aquifer sand filtration proofed to be highly effective in removing R. solanacearum by attachment which depends on the distance between injection and abstraction well. The high removal by attachment alone (18 log10 after 1 m) would reduce bacterial concentrations to negligible numbers. Upscaling to longer soil passages is discussed in the paper. Infection risks of potato plants were calculated using a dose-response model and ASTR treatment resulted in negligible infection risks of a single plant, but also when simulating the irrigation of a 5 ha potato field. This is the first QMRA that analyzed an agricultural ASTR and the fate of a plant pathogen focusing on plant health. QMRA is a useful (water) management tool to evaluate the treatment steps of water reclamation technologies with the aim to provide safe irrigation water and reduce risks disseminating plant diseases.

Biologically Synthesized Silver Nanoparticles Efficiently Control Plant Pathogenic Bacteria-Erwinia carotovora and Ralstonia solanacearum

Biogenic nanoparticles are considered effective alternatives to chemical pesticides for the management of pathogenic plant diseases. This study was focused on the synthesis of stable silver nanoparticles (AgNPs) to control challenging plant pathogenic bacteria in vitro and in planta. We synthesized AgNPs by reacting different proportions of silver nitrate and aqueous extract of Hedera nepalensis. The physicochemical properties of the synthesized AgNPs were determined by using various physical techniques. The TEM analysis revealed the AgNPs less than 50 nm in size and spherical shaped. For antibacterial assays, different concentrations (1000–15.62 µg/mL, 2-fold dilutions) of the extract-free AgNPs (Ef-AgNPs) or extract-mixed AgNPs (Em-AgNPs), and fruit extracts (FE) were used against plant pathogenic bacteria Erwinia carotovora subsp. carotovora, Erwinia carotovora subsp. atroseptica, and Ralstonia solanacearum. In the in vitro assays, we found significant inhibition of both bacterial species in response to maximum concentrations of AgNPs. Overall, Ef-AgNPs exhibited a higher percent inhibition of bacterial pathogens. In potato tubers assay, complete inhibition of Erwinia carotovora was observed, except for the lowest AgNPs concentration of 15.62 µg/mL. Similarly, exposure of tomato plants to Ralstonia solanacearum suspensions (OD600 = 0.2) in the soil-drenching experiment and post-exposure treatment with 1000 µg/mL and 125 µg/mL of AgNPs resulted in disease inhibition. This study provides the basis that biogenic nanoparticles prepared from Hedera nepalensis are one of the best substitutes to synthetic pesticide, having displayed better results to control the growth of phytopathogenic microbes. However, field studies need to be conducted in a controlled environment to scale up the current work and find out the efficacy of nanoparticles on a larger scale.

Analysis of the speciation process suggests a dual lifestyle in the plant pathogen Ralstonia solanacearum species complex

Analysis of the speciation process suggests a dual lifestyle in the plant pathogen Ralstonia solanacearum species complex

Chryseochelins-structural characterization of novel citrate-based siderophores produced by plant protecting Chryseobacterium spp.

Bacteria secrete siderophores whose function is to acquire iron. In recent years, the siderophores of several Chryseobacterium species were shown to promote the health and growth of various plants such as tomato or rice. However, the chemical nature of Chryseobacterium siderophores remained unexplored despite great interest. In this work, we present the purification and structure elucidation by nuclear magnetic resonance (NMR) spectroscopy and tandem mass spectrometry (MS/MS) of chryseochelin A, a novel citrate-based siderophore secreted by three Chryseobacterium strains involved in plant protection. It contains the unusual building blocks 3-hydroxycadaverine and fumaric acid. Furthermore, the unstable structural isomer chryseochelin B and its stable derivative containing fatty acid chains, named chryseochelin C, were identified by mass spectrometric methods. The latter two incorporate an unusual ester connectivity to the citrate moiety showing similarities to achromobactin from the plant pathogen Dickeya dadantii. Finally, we show that chryseochelin A acts in a concentration-dependent manner against the plant-pathogenic Ralstonia solanacearum strain by reducing its access to iron. Thus, our study provides valuable knowledge about the siderophores of Chryseobacterium strains, which have great potential in various applications.

Rhizosphere phage communities drive soil suppressiveness to bacterial wilt disease

BackgroundBacterial viruses, phages, play a key role in nutrient turnover and lysis of bacteria in terrestrial ecosystems. While phages are abundant in soils, their effects on plant pathogens and rhizosphere bacterial communities are poorly understood. Here, we used metagenomics and direct experiments to causally test if differences in rhizosphere phage communities could explain variation in soil suppressiveness and bacterial wilt plant disease outcomes by plant-pathogenic Ralstonia solanacearum bacterium. Specifically, we tested two hypotheses: (1) that healthy plants are associated with stronger top-down pathogen control by R. solanacearum-specific phages (i.e. ‘primary phages’) and (2) that ‘secondary phages’ that target pathogen-inhibiting bacteria play a stronger role in diseased plant rhizosphere microbiomes by indirectly ‘helping’ the pathogen.ResultsUsing a repeated sampling of tomato rhizosphere soil in the field, we show that healthy plants are associated with distinct phage communities that contain relatively higher abundances of R. solanacearum-specific phages that exert strong top-down pathogen density control. Moreover, ‘secondary phages’ that targeted pathogen-inhibiting bacteria were more abundant in the diseased plant microbiomes. The roles of R. solanacearum-specific and ‘secondary phages’ were directly validated in separate greenhouse experiments where we causally show that phages can reduce soil suppressiveness, both directly and indirectly, via top-down control of pathogen densities and by alleviating interference competition between pathogen-inhibiting bacteria and the pathogen.ConclusionsTogether, our findings demonstrate that soil suppressiveness, which is most often attributed to bacteria, could be driven by rhizosphere phage communities that regulate R. solanacearum densities and strength of interference competition with pathogen-suppressing bacteria. Rhizosphere phage communities are hence likely to be important in determining bacterial wilt disease outcomes and soil suppressiveness in agricultural fields.9CDhWVdEuw3PsngifdxC8SVideo

Bacterial volatile organic compounds attenuate pathogen virulence via evolutionary trade-offs.

Volatile organic compounds (VOCs) produced by soil bacteria have been shown to exert plant pathogen biocontrol potential owing to their strong antimicrobial activity. While the impact of VOCs on soil microbial ecology is well established, their effect on plant pathogen evolution is yet poorly understood. Here we experimentally investigated how plant-pathogenic Ralstonia solanacearum bacterium adapts to VOC-mixture produced by a biocontrol Bacillus amyloliquefaciens T-5 bacterium and how these adaptations might affect its virulence. We found that VOC selection led to a clear increase in VOC-tolerance, which was accompanied with cross-tolerance to several antibiotics commonly produced by soil bacteria. The increasing VOC-tolerance led to trade-offs with R. solanacearum virulence, resulting in almost complete loss of pathogenicity in planta. At the genetic level, these phenotypic changes were associated with parallel mutations in genes encoding lipopolysaccharide O-antigen (wecA) and type-4 pilus biosynthesis (pilM), which both have been linked with outer membrane permeability to antimicrobials and plant pathogen virulence. Reverse genetic engineering revealed that both mutations were important, with pilM having a relatively larger negative effect on the virulence, while wecA having a relatively larger effect on increased antimicrobial tolerance. Together, our results suggest that microbial VOCs are important drivers of bacterial evolution and could potentially be used in biocontrol to select for less virulent pathogens via evolutionary trade-offs.

Resource availability drives bacteria community resistance to pathogen invasion via altering bacterial pairwise interactions.

Microbial interactions within resident communities are a major determinant of resistance to pathogen invasion. Yet, interactions vary with environmental conditions, raising the question of how community composition and environments interactively shape invasion resistance. Here, we use resource availability (RA) as a model parameter altering the resistance of model bacterial communities to invasion by the plant pathogenic bacterium Ralstonia solanacearum. We found that at high RA, interactions between resident bacterial species were mainly driven by the direct antagonism, in terms of the means of invader inhibition. Consequently, the competitive resident communities with a higher production of antibacterial were invaded to a lesser degree than facilitative communities. At low RA, bacteria produced little direct antagonist potential, but facilitative communities reached a relatively higher community productivity, which showed higher resistance to pathogen invasion than competitive communities with lower productivities. This framework may lay the basis to understand complex microbial interactions and biological invasion as modulated by the dynamic changes of environmental resource availability.

Inactivation of plant pathogenic bacterium Ralstonia solanacearum in drainage solution from hydroponic system by a rotating advanced oxidation contactor equipped with TiO2/zeolite composite sheets

A rotating advanced oxidation contactor (RAOC) equipped with TiO2/zeolite composite sheets was developed to inactivate the plant pathogenic bacterium Ralstonia solanacearum in drainage solution (DS) from a hydroponic system. The inactivation efficiency of R. solanacearum in DS and pure culture solution (PS) by the RAOC was compared with that achieved by a submerged composite sheet photocatalysis reactor (SSPR). The initial number of living bacteria (N0) was adjusted to around 106–107 CFU mL−1. The inactivation efficiency of R. solanacearum by the SSPR at 4.0 × 107 CFU mL−1 of N0 significantly decreased compared with that at 1.8 × 106 CFU mL−1 of N0 owing to the attenuation of UV intensity by light absorption and scattering by solids derived from R. solanacearum, while the RAOC achieved >2-log inactivation during 24 h of treatment regardless of N0. The inactivation of R. solanacearum by the RAOC decelerated after 6 h, possibly because of competition for reactive oxygen species between R. solanacearum and products accumulated by inactivation of R. solanacearum. The ratio of rate constants for inactivation of R. solanacearum in DS to that in PS by the RAOC was 8 times that for the SSPR. This shows that the RAOC greatly mitigates the light attenuation and inhibitory effects of coexisting substances on inactivation of R. solanacearum in the DS. The RAOC is therefore a promising and upscalable photocatalytic reactor for efficient inactivation of R. solanacearum in DS.

Mutation in phcA Enhanced the Adaptation of Ralstonia solanacearum to Long-Term Acid Stress.

Bacterial wilt, caused by the plant pathogen Ralstonia solanacearum, occurs more severely in acidified soil according to previous reports. However, R. solanacearum cannot grow well in acidic environments under barren nutrient culture conditions, especially when the pH is lower than 5. With the worsening acidification of farmland, further determination of how R. solanacearum adapts to the long-term acidic environment is worthwhile. In this study, experimental evolution was applied to evaluate the adaptability and mechanism of the R. solanacearum experimental population responding to long-term acid stress. We chose the CQPS-1 strain as the ancestor, and minimal medium (MM medium) with different pH values as the culture environment to simulate poor soil. After 1500 generations of serial passage experiments in pH 4.9 MM, acid-adapted experimental strains (denoted as C49 strains) were obtained, showing significantly higher growth rates than the growth rates of control experimental strains (serial passage experiment in pH 6.5 MM, denoted as C65 strains). Competition experiments showed that the competitive indices (CIs) of all selected clones from C49 strains were superior to the ancestor in acidic environment competitiveness. Based on the genome variation analysis and functional verification, we confirmed that loss of function in the phcA gene was associated with the acid fitness gain of R. solanacearum, which meant that the inactivation of the PhcA regulator caused by gene mutation mediated the population expansion of R. solanacearum when growing in an acidic stress environment. Moreover, the swimming motility of acid evolution strains and the phcA deletion mutant was significantly enhanced compared to CQPS-1. This work provided evidence for understanding the adaptive strategy of R. solanacearum to the long-term acidic environment.

Global diversity and potential functioning of prophages in plant pathogenic Ralstonia solanacearum bacterium

Ralstonia solanacearum is a destructive plant pathogenic bacterium which harbours a wide variety of virulence genes allowing it to infect over 200 plant species worldwide. Its virulence is also affected by the presence of integrated bacteriophages, termed prophages. While several such prophages have been identified, the global distribution and diversity of R. solanacearum prophages is unknown. To study this, we first identified prophages present in a diverse collection of 192 assembled R. solanacearum genomes. Prophage diversity was explored by calculating prophage genetic distances and clustering with characterised prophages in a neighbour-joining tree. Prophage clusters were further verified by assessing gene content, GC content, and prophage length. Prophage identities were determined using the NCBI Virus database, and prophage-encoded virulence genes identified by analysing pangenome content. 343 intact prophages were identified, forming ten prophage clusters with distinct gene content, GC content, and length profiles. Five prophage clusters, containing 159 prophages, belonged to the Inoviridae, Myoviridae, and Siphoviridae phage families. The remaining 184 prophages were uncharacterised and may therefore represent novel prophages. Transcriptional regulators with potential virulence effects were identified in three prophage clusters, including one uncharacterised cluster. These prophage clusters were unequally distributed throughout the R. solanacearum population being host genotype specific. This research demonstrates that R. solanacearum contains a high level of uncharacterised prophage diversity and highlights novel prophages that could contribute to pathogen virulence. Given their potential host-genotype-specific virulence effects, R. solanacearumprophages could be co-evolving with their hosts, and may contribute to global variation in R. solanacearum virulence.

The First Complete Genome Resource of a Ralstonia solanacearum Phage UAM5 from Colombia.

The First Complete Genome Resource of a Ralstonia solanacearum Phage UAM5 from Colombia.

NorA, HmpX, and NorB Cooperate to Reduce NO Toxicity during Denitrification and Plant Pathogenesis in Ralstonia solanacearum.

ABSTRACTRalstonia solanacearum, which causes bacterial wilt disease of many crops, requires denitrifying respiration to survive in its plant host. In the hypoxic environment of plant xylem vessels, this pathogen confronts toxic oxidative radicals like nitric oxide (NO), which is generated by both bacterial denitrification and host defenses. R. solanacearum has multiple distinct mechanisms that could mitigate this stress, including putative NO-binding protein (NorA), nitric oxide reductase (NorB), and flavohaemoglobin (HmpX). During denitrification and tomato pathogenesis and in response to exogenous NO, R. solanacearum upregulated norA, norB, and hmpX. Single mutants lacking ΔnorB, ΔnorA, or ΔhmpX increased expression of many iron and sulfur metabolism genes, suggesting that the loss of even one NO detoxification system demands metabolic compensation. Single mutants suffered only moderate fitness reductions in host plants, possibly because they upregulated their remaining protective genes. However, ΔnorA/norB, ΔnorB/hmpX, and ΔnorA/hmpX double mutants grew poorly in denitrifying culture and in planta. It is likely that the loss of norA, norB, and hmpX is lethal, since the methods used to construct the double mutants could not generate a triple mutant. Functional aconitase activity assays showed that NorA, HmpX, and especially NorB are important for maintaining iron-sulfur cluster proteins. Additionally, plant defense genes were upregulated in tomatoes infected with the NO-overproducing ΔnorB mutant, suggesting that bacterial detoxification of NO reduces the ability of the plant host to perceive the presence of the pathogen. Thus, R. solanacearum’s three NO detoxification systems each contribute to and are collectively essential for overcoming metabolic nitrosative stress during denitrification, for virulence and growth in the tomato, and for evading host plant defenses.IMPORTANCE The soilborne plant pathogen Ralstonia solanacearum (Rs) causes bacterial wilt, a serious and widespread threat to global food security. Rs is metabolically adapted to low-oxygen conditions, using denitrifying respiration to survive in the host and cause disease. However, bacterial denitrification and host defenses generate nitric oxide (NO), which is toxic and also alters signaling pathways in both the pathogen and its plant hosts. Rs mitigates NO with a trio of mechanistically distinct proteins: NO-reductase (NorB), predicted iron-binding (NorA), and oxidoreductase (HmpX). This redundancy, together with analysis of mutants and in-planta dual transcriptomes, indicates that maintaining low NO levels is integral to Rs fitness in tomatoes (because NO damages iron-cluster proteins) and to evading host recognition (because bacterially produced NO can trigger plant defenses).

Effect of Phyto‐Assisted Synthesis of Magnesium Oxide Nanoparticles (MgO‐NPs) on Bacteria and the Root‐Knot Nematode

The root-knot nematode was examined using magnesium oxide nanoparticles (MgO-NPs) made from strawberries. The biologically synthesized MgO-NPs were characterized by UV, SEM, FTIR, EDS, TEM, and dynamic light scattering (DLS). Nanoparticles (NPs) were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and shown to be spherical to hexagonal nanoparticles with an average size of 100 nm. MgO-NPs were tested on the root-knot nematode M. incognita (Meloidogynidae) and the plant pathogenic bacteria Ralstonia solanacearum. The synthesized MgO-NPs showed a significant inhibition of R. solanacearum and the root-knot nematode. MgO-NPs cause mortality and inhibit egg hatching of second-stage juveniles (J2) of M. incognita under the in vitro assay. This study aims to examine the biological activity of biogenic MgO-NPs. The findings marked that MgO-NPs may be utilized to manage R. solanacearum and M. incognita and develop effective nematicides. In addition, the antioxidant capacity of MgO-NPs was determined by using 2, 2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH).

Inactivation of Plant Pathogenic Bacterium Ralstonia Solanacearum in Drainage Solution from Hydroponic System by a Rotating Advanced Oxidation Contactor Equipped with Tio2/Zeolite Composite Sheets

Inactivation of Plant Pathogenic Bacterium Ralstonia Solanacearum in Drainage Solution from Hydroponic System by a Rotating Advanced Oxidation Contactor Equipped with Tio2/Zeolite Composite Sheets

Antimicrobial and Antioxidant properties of medicinal mushroom Ganoderma P. Karst

Ganoderma species have been known all over the world as highly medicinal mushrooms. Antimicrobial activity of it is an attractive approach which raises the global interests from the scientific community. In this study, the antimicrobial assay of ethanol and methanol extracts of Ganoderma were prepared by using the dried mycelial powder obtained from five different liquid media; was performed against seven plant pathogenic fungi viz., Alternaria macrospora, Aspergilus niger, A. flavus, Colletotrichum falcatum, Fusarium oxysporum, Pestalotiopsis mangiferae and Penicillium sp. and two plant pathogenic bacteria Xanthomonas oryzae and Ralstonia solanacearum. The extracts of mycelia obtained from Yeast Wine Media exhibited the highest inhibition percentage as compared to rest. At concentration 1000ppm, there was complete inhibition of mycelial growth for Alternaria macrospora, Aspergilus niger and A. flavus while for Fusarium oxysporum and Penicillum sp. complete inhibition was observed at 500ppm but for Colletotrichum falcatum and Pestalotiopsis mangiferae, more than 80% mycelial inhibition at concentration 1000ppm in both ethanol and methanol extracts. In the case of Xanthomonas oryzae and Ralstonia solanacearum, at concentration 1000ppm, methanol extract showed the highest inhibition zone (3.50mm, 3.75mm). Ganoderma exhibited antagonistic effect against plant pathogenic fungi could add to the interest of developing Ganoderma as a successful bioagent in the near future. Antioxidant activities were evaluated by using DPPH radical scavenging assay and Metal chelating activity on ferrous ions. The DPPH radical scavenging effect was detected in methanol extract (Inhibition% = 27.312%) was higher than that of the ethanol extract (Inhibition% = 24.79%) and also Ferrous ion chelating ability of methanol extract (Inhibition% =22.27%) was higher than the ethanol extract (Inhibition% =12.55%). It is clearly indicated that both methanol and ethanol extract of the Ganoderma show antioxidant properties and Ganoderma extracts act as an effective antioxidant agents.

Secondary-structure switch regulates the substrate binding of a YopJ family acetyltransferase

The Yersinia outer protein J (YopJ) family effectors are widely deployed through the type III secretion system by both plant and animal pathogens. As non-canonical acetyltransferases, the enzymatic activities of YopJ family effectors are allosterically activated by the eukaryote-specific ligand inositol hexaphosphate (InsP6). However, the underpinning molecular mechanism remains undefined. Here we present the crystal structure of apo-PopP2, a YopJ family member secreted by the plant pathogen Ralstonia solanacearum. Structural comparison of apo-PopP2 with the InsP6-bound PopP2 reveals a substantial conformational readjustment centered in the substrate-binding site. Combining biochemical and computational analyses, we further identify a mechanism by which the association of InsP6 with PopP2 induces an α-helix-to-β-strand transition in the catalytic core, resulting in stabilization of the substrate recognition helix in the target protein binding site. Together, our study uncovers the molecular basis governing InsP6-mediated allosteric regulation of YopJ family acetyltransferases and further expands the paradigm of fold-switching proteins.

Biological and Molecular Characterization of a Jumbo Bacteriophage Infecting Plant Pathogenic Ralstonia solanacearum Species Complex Strains.

A jumbo phage infecting Ralstonia solanacearum species complex strains, designated RsoM2USA, was isolated from soil of a tomato field in Florida, United States, and belongs to the family Myoviridae. The phage has a long latent period of 270 min and completed its infection cycle in 360 min with a burst size of approximately 32 particles per cell. With a genome size of 343,806 bp, phage RsoM2USA is the largest Ralstonia-infecting phage sequenced and reported to date. Out of the 486 ORFs annotated for RsoM2USA, only 80 could be assigned putative functions in replication, transcription, translation including 44 tRNAs, and structure with the main structural proteins experimentally confirmed. Phylogenetic analyses placed RsoM2USA in the same clade as Xanthomonas phage XacN1, prompting a proposal of a new genus for the two jumbo phages. Jumbo phage RsoM2USA is a lytic phage and has a wide host range, infecting each of the three newly established Ralstonia species: R. solanacearum, R. pseudosolanacearum, and R. syzygii, and significantly reduced the virulence of its susceptible R. solanacearum strain RUN302 in tomato plants, suggesting that this jumbo phage has the potential to be developed into an effective control against diseases caused by R. solanacearum species complex strains.

The inhibitory effects of different types of Brassica seed meals on the virulence of Ralstonia solanacearum.

Understanding the specific inhibitory effects of different Brassica seed meals (BSMs) on soilborne pathogens is important for their application as biocontrol agents for controlling plant disease. In this study, the seed meals of Brassica napus L. (BnSM), Brassica campestris L. (BcSM), and Brassica juncea L. (BjSM), and the combined seed meal of BcSM and BjSM (CSM, 1:1), were selected for investigation. The inhibitory effects of these seed meals on the plant pathogen Ralstonia solanacearum (Smith) and tomato bacterial wilt, were assessed and compared. All the BSMs significantly inhibited the growth of R. solanacearum in vitro. Furthermore, the BSMs could effectively suppress R. solanacearum virulence traits, including motility, exopolysaccharide production, dehydrogenase activity, virulence-related gene expression, and colonization in the soil. Among them, BjSM showed the best inhibiting effects, and CSM displayed synergic toxicity against R. solanacearum. In addition, the predominant antibacterial compounds in BcSM and BjSM were identified as the volatile compounds, 3-butenyl isothiocyanate and allyl isothiocyanate, respectively. Finally, pot experiment verified that the control effects of BjSM and CSM on tomato wilt reached more than 90%. This is the first study to report on the ability of different kinds of BSMs to suppress the virulence of R. solanacearum and biocontrol efficiencies against bacterial wilt in tomato plants. Furtherly, the main antibacterial compounds in the BSMs were identified. The results demonstrated that CSM may possess potential for controlling bacterial wilt caused by R. solanacearum. The results provide a fresh perspective for comprehending the mechanism underlying BSM suppression of pathogens and plant disease.

A bacterial effector protein uncovers a plant metabolic pathway involved in tolerance to bacterial wilt disease

Bacterial wilt caused by the soil-borne plant pathogen Ralstonia solanacearum is a devastating disease worldwide. Upon plant colonization, R. solanacearum replicates massively, causing plant wilting and death; collapsed infected tissues then serve as a source of inoculum. In this work, we show that the plant metabolic pathway mediated by pyruvate decarboxylases (PDCs) contributes to plant tolerance to bacterial wilt disease. Arabidopsis and tomato plants respond to R. solanacearum infection by increasing PDC activity, and plants with deficient PDC activity are more susceptible to bacterial wilt. Treatment with either pyruvic acid or acetic acid (substrate and product of the PDC pathway, respectively) enhances plant tolerance to bacterial wilt disease. An effector protein secreted by R. solanacearum, RipAK, interacts with PDCs and inhibits their oligomerization and enzymatic activity. Collectively, our work reveals a metabolic pathway involved in plant resistance to biotic and abiotic stresses, and a bacterial virulence strategy to promote disease and the completion of the pathogenic life cycle.