Bacterial Plant Pathogens Research Articles

Sustainable Protocols for Cellulose Nanocrystals Synthesis from Tomato Waste and Their Antimicrobial Properties against Pseudomonas syringae pv. tomato

Nanotechnology is rapidly gaining ground in crop protection, with the growing quest for sustainable nanopesticides and nanocarriers for plant pathogen management. Among them, cellulose nanocrystals (CNC) are emerging as innovative agrofood-waste-derived antimicrobial materials. In this work, new chemical and enzymatic CNC extraction methods from tomato harvest residues were evaluated. The obtained nanomaterials were characterized and tested for their antimicrobial properties on Pseudomonas syringae pv. tomato (Pto), the causal agent of bacterial speck disease on tomato. Both protocols were efficient. The enzymatic extraction method was greener, producing purer CNC at slightly lower yield. The obtained CNC, although they weakly inhibited cell growth and did not promote reactive oxygen species (ROS) formation, provoked bacterial aggregation and the inhibition of biofilm production and swimming motility. Both protocols produced CNC with similar morpho-chemical features, as well as promising antimicrobial activity against plant bacterial pathogens, suggesting their potential role in sustainable crop protection strategies. The new protocols could be a valuable alternative to conventional methods.

Evaluation of the Effect of ‘Candidatus Liberibacter Solanacearum’ Haplotypes in Tobacco Infection

‘Candidatus Liberibacter solanacearum’ (Lso) is a phloem-limited bacterial plant pathogen infecting solanaceous plants in the Americas and New Zealand and is associated with diseases of apiaceous crops in Europe, Northern Africa, and the Middle East. This pathogen is also related to other Liberibacter species that infect other crops. In the USA, two haplotypes of Lso, LsoA and LsoB, are predominant and responsible for diseases in potato and tomato. Tobacco, Nicotiana tabacum, a model species to study plant defenses, is a host for Lso; therefore, the interaction between Lso and this host plant could be used to study Liberibacter−plant interactions. In this study, we characterized the infection associated with LsoA and LsoB in tobacco. Under laboratory conditions, LsoB caused more severe symptoms than LsoA, and LsoA and LsoB titers were dynamic during the 7 weeks of the experiment. We also measured SA and other metabolites, including oxylipins, at an early point of infection and found that SA was accumulated in plants infected with LsoB but not with LsoA; whereas ABA levels were reduced in LsoA- but not in LsoB-infected plants.

The natural pyrazolotriazine pseudoiodinine from Pseudomonas mosselii 923 inhibits plant bacterial and fungal pathogens

Natural products largely produced by Pseudomonads-like soil-dwelling microorganisms are a consistent source of antimicrobial metabolites and pesticides. Herein we report the isolation of Pseudomonas mosselii strain 923 from rice rhizosphere soils of paddy fields, which specifically inhibit the growth of plant bacterial pathogens Xanthomonas species and the fungal pathogen Magnaporthe oryzae. The antimicrobial compound is purified and identified as pseudoiodinine using high-resolution mass spectra, nuclear magnetic resonance and single-crystal X-ray diffraction. Genome-wide random mutagenesis, transcriptome analysis and biochemical assays define the pseudoiodinine biosynthetic cluster as psdABCDEFG. Pseudoiodinine biosynthesis is proposed to initiate from guanosine triphosphate and 1,6-didesmethyltoxoflavin is a biosynthetic intermediate. Transposon mutagenesis indicate that GacA is the global regulator. Furthermore, two noncoding small RNAs, rsmY and rsmZ, positively regulate pseudoiodinine transcription, and the carbon storage regulators CsrA2 and CsrA3, which negatively regulate the expression of psdA. A 22.4-fold increase in pseudoiodinine production is achieved by optimizing the media used for fermentation, overexpressing the biosynthetic operon, and removing the CsrA binding sites. Both of the strain 923 and purified pseudoiodinine in planta inhibit the pathogens without affecting the rice host, suggesting that pseudoiodinine can be used to control plant diseases.

Treatment of Rapamycin and Evaluation of an Autophagic Response in the Gut of Bactericera cockerelli (Sulč)

Autophagy is a catabolic process that results in the autophagosomic-lysosomal degradation of bulk cytoplasmic content, abnormal protein aggregates, and excess of/or damaged organelles to promote cell survival. Autophagy is also a component of innate immunity in insects and is involved in the clearance of pathogens, including bacteria. The potato psyllid, Bactericera cockerelli, transmits the plant bacterial pathogen 'Candidatus Liberibacter solanacearum' (Lso) in the Americas and causes serious damage to solanaceous crops. Our previous studies showed that autophagy could be involved in the psyllid response to Lso and could affect pathogen acquisition. However, the tools to evaluate this response have not been validated in psyllids. To this end, the effect of rapamycin, a commonly used autophagy inducer, on potato psyllid survival and the expression of autophagy-related genes was evaluated. Further, the autophagic activity was assessed via microscopy and by measuring the autophagic flux. Artificial diet-feeding assays using rapamycin resulted in significant psyllid mortality, an increase in the autophagic flux, as well as an increase in the amount of autolysosomes. This study represents a stepping stone in determining the role of autophagy in psyllid immunity.

Prevention of Stomatal Entry as a Strategy for Plant Disease Control against Foliar Pathogenic Pseudomonas Species.

The genus Pseudomonas includes some of the most problematic and studied foliar bacterial pathogens. Generally, in a successful disease cycle there is an initial epiphytic lifestyle on the leaf surface and a subsequent aggressive endophytic stage inside the leaf apoplast. Leaf-associated bacterial pathogens enter intercellular spaces and internal leaf tissues by natural surface opening sites, such as stomata. The stomatal crossing is complex and dynamic, and functional genomic studies have revealed several virulence factors required for plant entry. Currently, treatments with copper-containing compounds, where authorized and admitted, and antibiotics are commonly used against bacterial plant pathogens. However, strains resistant to these chemicals occur in the fields. Therefore, the demand for alternative control strategies has been increasing. This review summarizes efficient strategies to prevent bacterial entry. Virulence factors required for entering the leaf in plant-pathogenic Pseudomonas species are also discussed.

CRISPR/FnCas12a-mediated efficient multiplex and iterative genome editing in bacterial plant pathogens without donor DNA templates.

CRISPR-based genome editing technology is revolutionizing prokaryotic research, but it has been rarely studied in bacterial plant pathogens. Here, we have developed a targeted genome editing method with no requirement of donor templates for convenient and efficient gene knockout in Xanthomonas oryzae pv. oryzae (Xoo), one of the most important bacterial pathogens on rice, by employing the heterologous CRISPR/Cas12a from Francisella novicida and NHEJ proteins from Mycobacterium tuberculosis. FnCas12a nuclease generated both small and large DNA deletions at the target sites as well as it enabled multiplex genome editing, gene cluster deletion, and plasmid curing in the Xoo PXO99A strain. Accordingly, a non-TAL effector-free polymutant strain PXO99AD25E, which lacks all 25 xop genes involved in Xoo pathogenesis, has been engineered through iterative genome editing. Whole-genome sequencing analysis indicated that FnCas12a did not have a noticeable off-target effect. In addition, we revealed that these strategies are also suitable for targeted genome editing in another bacterial plant pathogen Pseudomonas syringae pv. tomato (Pst). We believe that our bacterial genome editing method will greatly expand the CRISPR study on microorganisms and advance our understanding of the physiology and pathogenesis of Xoo.

In vitro antibacterial activity of essential oils from Carum copticum and Ziziphora clinopodioides plants against the phytopathogen Pseudomonas syringae pv. syringae

The present study aimed to determine the in vitro antibacterial activity and the chemical composition of essential oils (EOs) from two medicinal plants (seeds of Carum copticum L. and leaves of Ziziphora clinopodioides Lam) against the bacterial plant pathogen Pseudomonas syringae pv. syringae. The sensitivity of P. syringae to the two types of EOs was investigated through three methods including disc diffusion, well diffusion, and vapor phase tests. Gas chromatography (GC) and gas chromatography attached to a mass spectrometer (GC-MS) were used to identify and quantify the essential oil compounds. The greatest growth inhibition zones for disc diffusion, well diffusion, and vapor tests were observed for the highest essential oil volume (50 µL) of Z. clinopodioides as 0.925 cm, 1.75 cm, and 1.45 cm, respectively. Concerning the EOs from C. copticum seeds, the diameters of growth inhibition zones were 0.775 cm, 1 cm, and 0 cm, respectively. Based on the obtained results, the highest antibacterial activity, with a growth inhibition zone of 1.75 cm, belonged to 50 µL EOs of Z. clinopodioides on Luria-Bertani (LB) agar medium. The minimum bactericidal concentration (MBC) and minimum inhibitory concentration (MIC) for the EOs of Z. clinopodioides were 8 µL mL−1 and 1 µL mL−1 in LB agar medium. The MBC and MIC values for EOs of C. copticum were 16 µL mL−1 and 1 µL mL−1, in LB agar medium, respectively. According to the chromatography results, 16 different compounds were identified in the EOs of C. copticum, of which thymol (54.6%) was the major constituent. Moreover, 27 different compounds were identified in the Z. clinopodioides EOs, of which pulegone (23%) and 1,8 cineole (20.3%) were the main essential oil constituents. The results demonstrated that the EOs of Z. clinopodioides plants had higher chemical diversity and displayed stronger antibacterial activities against P. syringe pv. syringae, compared to those of C. copticum.

Natural Recombination among Type I Restriction-Modification Systems Creates Diverse Genomic Methylation Patterns among Xylella fastidiosa Strains.

Xylella fastidiosa is an important bacterial plant pathogen causing high-consequence diseases in agricultural crops around the world. Although as a species X. fastidiosa can infect many host plants, there is significant variability between strains regarding virulence on specific host plant species and other traits. Natural competence and horizontal gene transfer are believed to occur frequently in X. fastidiosa and likely influence the evolution of this pathogen. However, some X. fastidiosa strains are difficult to manipulate genetically using standard transformation techniques. Several type I restriction-modification (R-M) systems are encoded in the X. fastidiosa genome, which may influence horizontal gene transfer and recombination. Type I R-M systems themselves may undergo recombination, exchanging target recognition domains (TRDs) between specificity subunits (hsdS) to generate novel alleles with new target specificities. In this study, several conserved type I R-M systems were compared across 129 X. fastidiosa genome assemblies representing all known subspecies and 32 sequence types. Forty-four unique TRDs were identified among 50 hsdS alleles, which are arrayed in 31 allele profiles that are generally conserved within a monophyletic cluster of strains. Inactivating mutations were identified in type I R-M systems of specific strains, showing heterogeneity in the complements of functional type I R-M systems across X. fastidiosa. Genomic DNA methylation patterns were characterized in 20 X. fastidiosa strains and associated with type I R-M system allele profiles. Overall, these data suggest hsdS genes recombine among Xylella strains and/or unknown donors, and the resulting TRD reassortment establishes differential epigenetic modifications across Xylella lineages. IMPORTANCE Economic impacts on agricultural production due to X. fastidiosa have been severe in the Americas, Europe, and parts of Asia. Despite a long history of research on this pathogen, certain fundamental questions regarding the biology, pathogenicity, and evolution of X. fastidiosa have still not been answered. Wide-scale whole-genome sequencing has begun to provide more insight into X. fastidiosa genetic diversity and horizontal gene transfer, but the mechanics of genomic recombination in natural settings and the extent to which this directly influences bacterial phenotypes such as plant host range are not well understood. Genome methylation is an important factor in horizontal gene transfer and bacterial recombination that has not been comprehensively studied in X. fastidiosa. This study characterizes methylation associated with type I restriction-modification systems across a wide range of X. fastidiosa strains and lays the groundwork for a better understanding of X. fastidiosa biology and evolution through epigenetics.

Endophytic Fungi Associated with Mango Show In Vitro Antagonism against Bacterial and Fungal Pathogens

Endophytic fungi live in inter-cellular spaces of healthy plant tissues without causing any apparent symptoms of diseases for the host plant. Some fungal endophytes help their plant hosts to survive under biotic and abiotic stresses. In this study, we collected healthy mango leaves at the Honghe mango plantations (Yunnan Province) in the winter. A total of 34 different fungal endophytic strains were isolated, and their phylogenetic placements were estimated based on the ITS gene. Members of genus Chaetomium were the dominant fungal endophytes (26%). Common bacterial plant pathogens (Erwinia amylovora and Pseudomonas syringae) and fungal plant pathogens (Botrytis cinerea and Penicillium digitatum) were selected to test the antagonism of the fungal endophytes isolated from mango leaves through co-cultivation in vitro assay. Three strains of Chaetomium sp. viz. KUNCC22-0749, UNCC22-10750, and KUNCC22-10752 showed great inhibition against two bacterial pathogens viz. Erwinia amylovora and Pseudomonas syringae, and Alternaria sp. KUNCC22-10760, Chaetomium sp. KUNCC22-10749, Daldinia sp. KUNCC22-10744, and Rosellinia sp. KUNCC22-10751 also showed great to moderate antagonistic effects against two fungal pathogens viz. Botrytis cinerea and Penicillium digitatum.

Seaweed as a Natural Source against Phytopathogenic Bacteria.

Plant bacterial pathogens can be devastating and compromise entire crops of fruit and vegetables worldwide. The consequences of bacterial plant infections represent not only relevant economical losses, but also the reduction of food availability. Synthetic bactericides have been the most used tool to control bacterial diseases, representing an expensive investment for the producers, since cyclic applications are usually necessary, and are a potential threat to the environment. The development of greener methodologies is of paramount importance, and some options are already available in the market, usually related to genetic manipulation or plant community modulation, as in the case of biocontrol. Seaweeds are one of the richest sources of bioactive compounds, already being used in different industries such as cosmetics, food, medicine, pharmaceutical investigation, and agriculture, among others. They also arise as an eco-friendly alternative to synthetic bactericides. Several studies have already demonstrated their inhibitory activity over relevant bacterial phytopathogens, some of these compounds are known for their eliciting ability to trigger priming defense mechanisms. The present work aims to gather the available information regarding seaweed extracts/compounds with antibacterial activity and eliciting potential to control bacterial phytopathogens, highlighting the extracts from brown algae with protective properties against microbial attack.

The γ-Core Motif Peptides of Plant AMPs as Novel Antimicrobials for Medicine and Agriculture.

The γ-core motif is a structural element shared by most host antimicrobial peptides (AMPs), which is supposed to contribute to their antimicrobial properties. In this review, we summarized the available data on the γ-core peptides of plant AMPs. We describe γ-core peptides that have been shown to exhibit inhibitory activity against plant and human bacterial and fungal pathogens that make them attractive scaffolds for the development of novel anti-infective agents. Their advantages include origin from natural AMP sequences, broad-spectrum and potent inhibitory activity, and cost-effective production. In addition, some γ-core peptides combine antimicrobial and immunomodulatory functions, thus broadening the spectrum of practical applications. Some act synergistically with antimycotics and fungicides, so combinations of peptides with conventionally used antifungal agents can be suggested as an effective strategy to reduce the doses of potentially harmful chemicals. The presented information will pave the way for the design of novel antimicrobials on the basis of γ-core motif peptides, which can find application in medicine and the protection of crops from diseases.

Manuka Honey Reduces the Virulence of Pectobacterium brasiliense by Suppressing Genes That Encode Plant Cell Wall-Degrading Enzymes

The primary virulence of soft rot pectobacteria, including Pectobacterium brasiliense, is mainly determined by the massive production of plant cell wall-degrading enzymes (PCWDEs), which promote plant tissue maceration in many crops. The antibiotic treatment to treat bacterial soft rot causes environmental problems and potentially affects resistance. Antibiotic resistance is driving interest in antimicrobial treatments, and no organism has been reported to have acquired resistance to honey. However, the use of honey as a therapeutic agent for plant bacterial pathogens has rarely been studied. Therefore, this study was undertaken to determine the in vitro effect of Manuka honey against P. brasiliense at the phenotypic and genotypic levels. A sublethal concentration of honey was determined by a growth inhibition assay in broth medium containing different concentrations of Manuka honey. A macerating assay was performed on orchid leaves, and the activities of the PCWDEs were examined in plate assays. The expression of PCWDE-associated genes was investigated using semi-quantitative reverse transcription-polymerase chain reaction analysis. The exposure of P. brasiliense to a sublethal concentration of Manuka honey significantly decreased the maceration ability of the orchid and the synthesis of PCWDEs, i.e., pectate lyase, polygalacturonase, and protease. Moreover, five PCWDEs-encoding genes, such as pelA, pelB, pelC, pehA, and prtW, had lower expression levels after the honey treatment compared with recA as the internal standard. The honey treatment decreased the virulence of P. brasiliense associated with the synthesis of PCWDEs. Therefore, Manuka honey reduced virulence by suppressing the expression of the PCWDE genes.

Diversity of Antimicrobial Peptide Genes in Bacillus from the Andaman and Nicobar Islands: Untapped Island Microbial Diversity for Disease Management in Crop Plants.

Taxonomic and functional characterization of a total of 90 bacterial isolates representing bulk and rhizosphere soils of diverse niches of Andaman and Nicobar Islands, India were carried out. Twelve bacterial isolates were found promising for the biological suppression of agriculturally important fungal and bacterial plant pathogens such as Ralstonia solanacearum, Xanthomonas oryzae pv. oryzae, and Colletotrichum gloeosporioides. The 16S rRNA gene sequence analysis revealed their identity as belonging to Bacillus subtilis, Bacillus amyloliquefaciens, and Lysinibacillus sphaericus. The isolates were positive for plant growth promotion (PGP) traits including siderophore production, and nutrient solubilization especially phosphorous, zinc, and potassium. Interestingly, the PCR test confirmed the presence of 62 antimicrobial peptides (AMP) biosynthesis genes specific to the genus Bacillus. Whilst all tested species of Bacillus harboured the bacD biosynthesis gene, the B. subtilis (Ba_Abi), and B. amyloliquefaciens (Ba_Abi) harboured the maximum AMP biosynthesis genes analysed in the study. Upon in planta evaluation, the biocontrol potential of the bacterial isolates against leaf spot disease of chilli was observed. The study culminated in the isolation and identification of diverse Bacillus species for exploitation as bioinoculants for plant health management programmes.

RdmA Is a Key Regulator in Autoinduction of DSF Quorum Quenching in Pseudomonas nitroreducens HS-18.

Diffusible signal factor (DSF) represents a family of widely conserved quorum-sensing (QS) signals which regulate virulence factor production and pathogenicity in numerous Gram-negative bacterial pathogens. We recently reported the identification of a highly potent DSF-quenching bacterial isolate, Pseudomonas nitroreducens HS-18, which contains an operon with four DSF-inducible genes, digABCD, or digA-D, that are responsible for degradation of DSF signals. However, the regulatory mechanisms that govern the digA-D response to DSF induction have not yet been characterized. In this study, we identified a novel transcriptional regulator we designated RdmA (regulator of DSF metabolism) which negatively regulates the expression of digA-D and represses DSF degradation. In addition, we found that a gene cluster located adjacent to rdmA was also negatively regulated by RdmA and played a key role in DSF degradation; this cluster was hence named dmg (DSF metabolism genes). An electrophoretic mobility shift assay and genetic analysis showed that RdmA represses the transcriptional expression of the dmg genes in a direct manner. Further studies demonstrated that DSF acts as an antagonist and binds to RdmA, which abrogates RdmA binding to the target promoter and its suppression on transcriptional expression of the dmg genes. Taken together, the results from this study have unveiled a central regulator and a gene cluster associated with the autoinduction of DSF degradation in P. nitroreducens HS-18, and this will aid in the understanding of the genetic basis and regulatory mechanisms that govern the quorum-quenching activity of this potent biocontrol agent. IMPORTANCE DSF family quorum-sensing (QS) signals play important roles in regulation of bacterial physiology and virulence in a wide range of plant and human bacterial pathogens. Quorum quenching (QQ), which acts by either degrading QS signals or blocking QS communication, has proven to be a potent disease control strategy, but QQ mechanisms that target DSF family signals and associated regulatory mechanisms remain largely unknown. Recently, we identified four autoinduced DSF degradation genes (digABCD) in P. nitroreducens HS-18. By using a combination of transcriptome and genetic analysis, we identified a central regulator that plays a key role in autoinduction of dig expression, as well as a new gene cluster (dmgABCDEFGH) involved in DSF degradation. The significance of our study is in unveiling the autoinduction mechanism that governs DSF signal quorum quenching for the first time, to our knowledge, and in identification of new genes and enzymes responsible for DSF degradation. The findings from this study shed new light on our understanding of the DSF metabolism pathway and the regulatory mechanisms that modulate DSF quorum quenching and will provide useful clues for design and development of a new generation of highly potent QQ biocontrol agents against DSF-mediated bacterial infections.

The Complete Genome Resource of Xanthomonas oryzae pv. oryzae CIX2779 Includes the First Sequence of a Plasmid for an African Representative of This Rice Pathogen.

The bacterial plant pathogen Xanthomonas oryzae pv. oryzae is responsible for the foliar rice bacterial blight disease. Genetically contrasted, continent-specific, sublineages of this species can cause important damages to rice production both in Asia and Africa. We report on the genome of the CIX2779 strain of this pathogen, previously named NAI1 and originating from Niger. Oxford Nanopore long reads assembly and Illumina short reads polishing produced a genome sequence composed of a 4,725,792-bp circular chromosome and a 39,798-bp-long circular plasmid designated pCIX2779_1. The chromosome structure and base-level sequence are highly related to reference strains of African X. oryzae pv. oryzae and encode identical transcription activator-like effectors for virulence. Importantly, our in silico analysis strongly indicates that pCIX2779_1 is a genuine conjugative plasmid, the first indigenous one sequenced from an African strain of the X. oryzae species. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Advancements in the Use of Bacteriophages to Combat the Kiwifruit Canker Phytopathogen Pseudomonas syringae pv. actinidiae.

Over the last several decades, kiwifruit production has been severely damaged by the bacterial plant pathogen Pseudomonas syringae pv. actinidiae (Psa), resulting in severe economic losses worldwide. Currently, copper bactericides and antibiotics are the main tools used to control this bacterial disease. However, their use is becoming increasingly ineffective due to the emergence of antibiotic resistance. In addition, environmental issues and the changes in the composition of soil bacterial communities are also concerning when using these substances. Although biocontrol methods have shown promising antibacterial effects on Psa infection under in vitro conditions, the efficiency of antagonistic bacteria and fungi when deployed under field conditions remains unclear. Therefore, it is crucial to develop a phage-based biocontrol strategy for this bacterial pathogen. Due to the specificity of the target bacteria and for the benefit of the environment, bacteriophages (phages) have been widely regarded as promising biological agents to control plant, animal, and human bacterial diseases. An increasing number of studies focus on the use of phages for the control of plant diseases, including the kiwifruit bacterial canker. In this review, we first introduce the characteristics of the Psa-induced kiwifruit canker, followed by a description of the diversity and virulence of Psa strains. The main focus of the review is the description of recent advances in the isolation of Psa phages and their characterization, including morphology, host range, lytic activity, genome characterization, and lysis mechanism, but we also describe the biocontrol strategies together with potential challenges introduced by abiotic factors, such as high temperature, extreme pH, and UV irradiation in kiwifruit orchards. The information presented in this review highlights the potential role of phages in controlling Psa infection to ensure plant protection.

Characterization of the antagonistic potential of the glyphosate-tolerant Pseudomonas resinovorans SZMC 25872 strain against the plant pathogenic bacterium Agrobacterium tumefaciens.

The utilization of microorganisms with biocontrol activity against fungal and bacterial pathogens of plants is recognized as a promising, effective, and environment-friendly strategy to protect agricultural crops. We report the glyphosate-tolerant Pseudomonas resinovorans SZMC 25872 isolate as a novel strain with antagonistic potential towards the plant pathogenic bacterium Agrobacterium tumefaciens. In our studies, the growth of the P. resinovorans SZMC 25872 and A. tumefaciens SZMC 14557 isolates in the presence of 74 different carbon sources, and the effect of 11 carbon sources utilized by both strains on the biocontrol efficacy was examined. Seven variations of media with different carbon sources were selected for the assays to observe the biocontrol potential of the P. resinovorans strain. Also, 50% concentrations of the cell-free culture filtrates (CCF) obtained from medium amended with L-alanine or succinic acid as sole carbon source were found to be effective for the growth suppression of A. tumefaciens by 83.03 and 56.80%, respectively. The effect of 7 media on siderophore amount and the activity of extracellular trypsin- and chymotrypsin-like proteases, as well as esterases were also evaluated. Significant positive correlation was found between the siderophore amount and the percentage of inhibition, and the inhibitory effect of the CCFs obtained from medium amended with succinic acid was eliminated in the presence of an additional iron source, suggesting that siderophores produced by P. resinovorans play an important role in its antagonistic potential. The metabolic profile analysis of the P. resinovorans SZMC 25872 strain, performed by high performance liquid chromatography - high resolution mass spectrometry (HPLC-HRMS), has identified several previously not reported metabolites that might play role in the antagonistic effect against A. tumefaciens. Based on our findings we suggest that the possible inhibition modes of A. tumefaciens SZMC 14557 by P. resinovorans SZMC 25872 include siderophore-mediated suppression, extracellular enzyme activities and novel bioactive metabolites.

Synthesis of copper (II) citrate and evaluation ofits in vitro antifungaland antibacterial activities, and the suitability of using this chemicalas a plant protection agent

In this paper, copper (II) citrate Cu3(C6H5O7)2 was successfully synthesised in an aqueous solution. The factors for the synthesis process such as temperature and molar ratio of the reactants were investigated. The structural, properties and composition characteristics of the elements were investigated and evaluated by X-ray diffraction pattern (XRD), Fourier-transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and UV-Vis spectroscopy. The yield of the copper (II) citrate in the reaction was 82.46% at the molar ratio of the CuSO4/C6H5Na3O7 of 1.5/1 at 70oC. The in vitro results showed that copper (II) citrate at a concentration of 1,000 ppm inhibits the mycelial growth of Sclerotium rolfsii and Fusarium oxysporumwith control values ranging from 19 to 53% after 2 days of incubation. Besides, it strongly suppressed the plant bacterial pathogens Xanthomonas axonopodis (bacterial strain causing citrus canker), Ralstonia solanacearum(bacterial wilt of tomato), and Clavibacter michiganensis subsp. michiganensis (cause of bacterial wilt and canker of tomato). These results suggested that copper (II) citrate can be used as a promising fungicide/bactericide to control fungal and bacterial diseases on citrus and tomato plants.

Linalool reduces the virulence of Pseudomonas syringae pv. tomato DC 3000 by modulating the PsyI/PsyR quorum-sensing system

Quorum sensing modulatory effect of linalool was tested for the first time against Pseudomonas syringae pv. tomato DC 3000, a bacterial plant pathogen responsible for causing huge losses worldwide. DC 3000 extensively regulates its virulence traits through quorum sensing mechanism involving expression of psyI, an acyl–homoserine lactone (AHL) synthase gene and psyR, a luxR-type regulator. In this study, exposure of DC 3000 to 80 ppm linalool concentration resulted in reduced biofilm formation, hampered motility, decreased AHL production, and reduced secretion of plant cell wall-degrading enzymes followed by negligible effect on the bacterial count and its metabolic activity. Extracellular polymeric substances (EPS), which play a crucial role in the development of biofilm and subsequent infection was significantly reduced which was further confirmed by Fourier Transform Infrared Spectroscopy. The qRT PCR analysis of the gene expression analysis of virulence genes (syringafactin production gene syfA, type III secretion system gene hrpA, flagellar genes fleQ and fliC, and coronatine production gene cfl unveiled significant downregulation of the same under Lin 80 ppm concentration. To further confirm the aforementioned possibilities, docking simulations run between PsyR and linalool suggested a strong interaction with the developed protein model. Overall, the treatment of DC 3000 with Lin 80 ppm affected the phenotypic and genotypic expressions associated with quorum sensing, thereby significantly reducing the infection rate as observed in in-vivo plant assay.

Cytoplasmic molecular chaperones in Pseudomonas species.

Pseudomonas is widespread in various environmental and host niches. To promote rejuvenation, cellular protein homeostasis must be finely tuned in response to diverse stresses, such as extremely high and low temperatures, oxidative stress, and desiccation, which can result in protein homeostasis imbalance. Molecular chaperones function as key components that aid protein folding and prevent protein denaturation. Pseudomonas, an ecologically important bacterial genus, includes human and plant pathogens as well as growth-promoting symbionts and species useful for bioremediation. In this review, we focus on protein quality control systems, particularly molecular chaperones, in ecologically diverse species of Pseudomonas, including the opportunistic human pathogen Pseudomonas aeruginosa, the plant pathogen Pseudomonas syringae, the soil species Pseudomonas putida, and the psychrophilic Pseudomonas antarctica.