Soft Rot Pathogen Research Articles

Regulation of corA, the Magnesium, Nickel, Cobalt Transporter, and Its Role in the Virulence of the Soft Rot Pathogen, Pectobacterium versatile Strain Ecc71.

Pectobacterium versatile (formally P. carotovorum) causes disease on diverse plant species by synthesizing and secreting copious amount of plant-cell-wall-degrading exoenzymes including pectate lyases, polygalacturonases, cellulases, and proteases. Exoenzyme production and virulence are controlled by many factors of bacterial, host, and environmental origin. The ion channel forming the magnesium, nickel, and cobalt transporter CorA is required for exoenzyme production and full virulence in strain Ecc71. We investigated CorA's role as a virulence factor and its expression in P. versatile. Inhibiting the transport function of CorA by growing a CorA+ strain in the presence of specific CorA inhibitor, cobalt (III) hexaammine (Co (III)Hex), has no effect on exoenzyme production. Transcription of pel-1, encoding a pectate lyase isozyme, is decreased in the absence of CorA, suggesting that CorA influences exoenzyme production at the transcriptional level, although apparently not through its transport function. CorA- and CorA+ strains grown in the presence of Co (III)Hex transcriptionally express corA at higher levels than CorA+ strains in the absence of an inhibitor, suggesting the transport role of corA contributes to autorepression. The expression of corA is about four-fold lower in HrpL- strains lacking the hrp-specific extracytoplasmic sigma factor. The corA promoter region contains a sequence with a high similarity to the consensus Hrp box, suggesting that corA is part of Hrp regulon. Our data suggest a complex role, possibly requiring the physical presence of the CorA protein in the virulence of the Pectobacterium versatile strain Ecc71.

Erratum: First Report of Pectobacterium versatile as the Causal Pathogen of Soft Rot in Kimchi Cabbage in Korea

Erratum: First Report of Pectobacterium versatile as the Causal Pathogen of Soft Rot in Kimchi Cabbage in Korea

Field surveys indicate taxonomically diverse Pectobacterium species inducing soft rot of vegetables and annual crops in Iran

AbstractSoft rot‐inducing bacterial pathogens are considered among the main biotic constraints on vegetables and annual crops. Most of the bacterial soft rot pathogens are members of Pectobacterium spp. and Dickeya, with the former genus encompassing a continuously increasing number of species varying in geographic distribution and host of isolation. In Iran, Pectobacterium species have rarely been investigated using high‐throughput nucleotide sequence‐based techniques, leaving the genetic diversity of these pathogens mostly undetermined. During 2021, vegetables and annual crops with symptoms of soft rot and maceration were collected from Fars, Hamedan, Isfahan, Khuzestan and Kohgiluyeh‐Boyer‐Ahmad provinces of Iran. Forty‐four pectinolytic bacterial strains were isolated from symptomatic tissues of bell pepper, cabbage, carrot, lettuce, potato and zucchini. The bacterial strains were subjected to pathogenicity and host range assays, specific PCR tests and phylogenetic analysis of three housekeeping genes (dnaX, gapA and leuS). All strains were pathogenic on their host of isolation. Among the 44 pectinolytic strains, 26 strains were identified as members of Pectobacterium based on PCR using the primer pair Y1/Y2. Multilocus sequence analysis confirmed the latter bacterial strains belonging to the genus Pectobacterium and revealed that the strains scattered into four species: P. brasiliense (five strains), P. carotovorum (eight strains), P. polaris (five strains) and P. versatile (eight strains). P. polaris and P. versatile have not previously been reported in the country. Host range assays showed that P. brasiliense and P. carotovorum have a broader host range than the other two species.

PREVALENCE OF CAUSATIVE AGENTS OF RING ROT CLAVIBACTER SEPEDONICUS, BLACKLEG AND WET ROT PECTOBACTERIUM ATROCEPTICUM IN THE 2021 YEAR POTATO HARVEST IN THE TERRITORY OF UKRAINE

Aim. To investigate the prevalence of causative agents of ring rot and soft rot in the potato harvest by the DAS ELISA method. Materials and methods. Samples of the potato harvest from Ternopil, Zhytomyr, Kyiv, Cherkasy, Dnipropetrovsk, Donetsk, Mykolaiv, Odesa, and Kherson regions were used in the study. The detection of bacterial agents was conducted by enzyme-linked immunosorbent assay using commercial test systems LOEWE® Standard Complete Kit (Germany). Results. The highest percentage of affected potatoes was registered in the Donetsk region: 11.1% – by the Clavibacter seedonicus, 31.0% – by the Pectobacterium atrosepticum, and 8.9% – by both bacteria. The causative agent of soft rot was detected twice as often as a causative agent of ring rot in tuber samples from all regions, except the Ternopil region, where the predominance of Clavibacter sepedonicus was revealed. In addition to the Donetsk region, a high prevalence of the causative agent of soft rot was found in the potato harvest from Kyiv (10.2%) and Odesa (10.0%) regions, the highest abundance of the causative agent of ring rot was detected in the Ternopil region. The mixed bacterial infection of potato tubers was diagnosed in 6 areas, and the highest rate was detected in the Donetsk region. Conclusion. The analysis of the distribution of ring rot pathogen Clavibacter sepedonicus and soft rot pathogen Pectobacterium atrocepticum in the potato crop shows the presence of research pathogens in all studied regions. It was discovered the dominance of the representative of pectolytic bacteria in all regions except Ternopil, where the distribution of Clavibacter sepedonicus, the causative agent of ring rot, was dominated. High rates of spread of the studied pathogens were associated with increased local average annual precipitation, as well as with increased annual amplitude of this indicator.

Synergistic Action of Biosynthesized Silver Nanoparticles and Culture Supernatant of Bacillus amyloliquefacience against the Soft Rot Pathogen Dickeya dadantii.

Nanomaterials are increasingly being used for crop growth, especially as a new paradigm for plant disease management. Among the other nanomaterials, silver nanoparticles (AgNPs) draw a great deal of attention because of their unique features and multiple usages. Rapid expansion in nanotechnology and utilization of AgNPs in a large range of areas resulted in the substantial release of these nanoparticles into the soil and water environment, causing concern for the safety of ecosystems and phytosanitary. In an attempt to find an effective control measure for sweet potato soft rot disease, the pathogen Dickeya dadantii was exposed to AgNPs, the cell-free culture supernatant (CFCS) of Bacillus amyloliquefaciens alone, and both in combination. AgNPs were synthesized using CFCS of Bacillus amyloliquefaciens strain A3. The green synthesized AgNPs exhibited a characteristic surface plasmon resonance peak at 410-420 nm. Electron microscopy and X-ray diffraction spectroscopy determined the nanocrystalline nature and 20-100 nm diameters of AgNPs. Release of metal Ag+ ion from biosynthesized AgNPs increases with time. AgNPs and CFCS of B. amyloliquefaciens alone exhibited antibacterial activity against the growth, biofilm formation, swimming motility, and virulence of strain A3. The antibacterial activities elevated with the elevation in AgNPs and CFCS concentration. Similar antibacterial activities against D. dadantii were obtained with AgNPs at 50 µg·mL-1, 50% CFCS alone, and the combination of AgNPs at 12 µg·mL-1 and 12% CFCS of B. amyloliquefaciens. In planta experiments indicated that all the treatments reduced D. dadantii infection and increased plant growth. These findings suggest that AgNPs along with CFCS of B. amyloliquefaciens can be applied to minimize this bacterial disease by controlling pathogen-contaminated sweet potato tuber with minimum Ag nano-pollutant in the environment.

Pectobacterium brasiliense as a Causative Agent for Soft Rot of Radish in Korea

In October 2021, soft rot disease seriously affected radish crop in Dangjin, Chungcheongnam-do, Korea. The infected radishes were stunted and turned dark green, with yellowish leaf foliage. A slimy, wet, and decayed pith region was observed in the infected roots. The bacterial strain KNUB-03-21 was isolated from infected roots. The biochemical and morphological characteristics of the isolate were similar to those of Pectobacterium brasiliense. Phylogenetic analysis based on the sequences of the 16S rRNA region and the concatenated DNA polymerase III subunit tau (dnaX), leucine-tRNA ligase (leuS), and recombinase subunit A (recA) genes confirmed that the isolate is a novel strain of P. brasiliense. Artificial inoculation of radish with P. brasiliense KNUB-03-21 resulted in soft rot symptoms similar to those observed in infected radish in the field; subsequently, P. brasiliense KNUB-03-21 was reisolated and reidentified. To our knowledge, this is the first report of P. brasiliense as a causal pathogen of radish soft rot in Korea.

First Report of Pectobacterium versatile as the Causal Pathogen of Soft Rot in Kimchi Cabbage in Korea

In September 2021, gray-to-brown discoloration and expanding water-soaked lesions were observed on the outer and inner layers and the core of kimchi cabbage (Brassica rapa subsp. pekinensis) in fields located in Samcheok, Gangwondo, Korea. A bacterial strain designated as KNUB-02-21 was isolated from infected cabbage samples. Phylogenetic analysis based on the sequences of the 16S rRNA region and the dnaX, leuS, and recA genes confirmed that the strain was affiliated with Pectobacterium versatile. Additionally, the biochemical and morphological profiles of the isolate were similar to those of P. versatile. Based on these results, the isolate was identified as a novel strain of P. versatile. Healthy kimchi cabbage slices developed soft rot upon inoculation with P. versatile KNUB-02-21 and exhibited symptoms similar to those observed in the diseased plants in fields. The re-isolated strains were similar to those of P. versatile. Prior to our study, P. versatile as the causative pathogen of kimchi cabbage soft rot had not been reported in Korea.

High-Quality Genome Resource of Gilbertella persicaria Causing Peach Soft Rot.

Peach soft rot caused by Gilbertella persicaria is an economically important disease. Here, we report a high-quality complete and annotated genome sequence of G. persicaria strain TFLB-J, isolated from peach fruit in Yuanyang county of Henan Province, China. The assembly consists of 91 scaffolds with an estimated genome size of 33.59 Mb and N50 length of 0.92 Mb, encoding 13,296 predicted protein-coding genes. The whole-genome sequence could provide gene resources for further study of pathogenic effectors and comparative genomics of peach soft rot pathogens.

ОЦІНЮВАННЯ СТІЙКОСТІ СОРТІВ КАРТОПЛІ, ПОШИРЕНИХ НА ТЕРИТОРІЇ УКРАЇНИ,ДО ЗБУДНИКА М'ЯКОЇ ГНИЛІ ТА ЧОРНОЇ НІЖКИ

B a c k g r o u n d . The potato crop is affected by various diseases, including blackleg and soft rot caused by Pectobacterium atrosepticum. One of the reasons for the rapid spread of these bacterial pathogens is the absence of commercial potato varieties with natural immunity to blackleg and soft rot. While some potato varieties may exhibit partial resistance, the lack of complete resistance contributes to the widespread occurrence of these diseases. The study aimed to evaluate the resistance of potato varieties most common in Ukraine to blackleg and soft rot pathogens. M e t h o d s . Potato varieties from different region of Ukraine were used in the study. 24 h culture of Pectobacterium atrosepticum B-1084T was used for assessing potato sensitivity to soft rot and blackleg. Potato susceptibility to soft rot pathogen was evaluated by two criteria: disease incidence (%) and disease severity (weight and area of macerated tissue). R e s u l t s . Potato tubers of different varieties, as well as of the same varieties, but grown in different regions of Ukraine, showed different levels of resistance to the museum strain of soft rot and blackleg pathogen. The disease incidence – the proportion of tubers with symptoms of rotting for all analyzed potato varieties reached 100 %.Tubers of the Riviera variety obtained from the Odesa region were significantly more affected by the pectolytic enzymes of P. atrosepticum B-1084T as compared to tubers of other cultivars: macerated area in tubers of this variety was 1.5 times higher than those in Queen Anne, Riviera (Chernihiv) and Bellarosa (Odesa) varieties. The median of maceration area of Picasso and Bellarosa (Chernihiv) tubers were 2.5 times smaller than that in the Riviera variety. These patterns of sensitivity to soft rot and blackleg pathogen were also confirmed by the results of comparative assessment of the weight of. C o n c l u s I o n s . Thus, Riviera potato variety was most susceptible to the infection with soft rot and blackleg pathogen. Potato cultivar Picasso was the least sensitive to P. atrosepticum B-1084T. Potato tubers of the same variety grown in different regions of the country had different susceptibility rates to the soft rot and blackleg pathogen, indicating that the field effect outweighs the influence of genotype.

POTENTIALLY DANGEROUS CAUSES OF BACTERIAL DISEASES OF POTATOES IN UKRAINE

An overview of bacterial causative agents of soft (wet) rot of potatoes is given, the epidemiological and etiological aspects of the diseases caused by them are analyzed. When preparing the article, general scientific methods were used: generalization, comparison, system analysis. Data from the European and Mediterranean Plant Protection Organization (EOPO), as well as data from phytosanitary services of EU countries and Ukraine, scientific literature served as material for the analytical study. Trade in plant materials, including potato seed tubers and ornamental plants, is largely responsible for the widespread distribution of pathogens. Locally, pathogens are also spread through plant debris, soil, waterways, aerosols, alternative hosts, and/or farm machinery. The main causative agents of bacterial wet rot of potatoes are gram-negative bacteria of the genera Pectobacterium and Dickeya and quarantine phytopathogens of the genera Clavibacter and Ralstonia. The main methods of detection and identification in asymptomatic potato tubers on an industrial scale are: phytopathological (visual examination of plantations and registration of symptoms of soft rot), microbiological (cultural-morphological and biochemical method, use of test systems for accelerated identification of microorganisms), immunoenzymatic ( enzyme immunosorbent assay), molecular genetic (PCR with specific primers, BIOLOG, DNA fingerprinting and nucleotide sequencing). To date, there are no completely effective pesticides to control all pathogens, so disease control measures will continue to rely primarily on avoiding infection during plant cultivation, and especially during the production of healthy certified seed. For a crop like potatoes, this is primarily based on obtaining bacteria-free minibulbs, applying strict seed certification schemes and strict phytosanitary restrictions. Knowledge of the sources of pathogens and routes of infection should be the basis for the application of phytosanitary measures, especially during and after harvest. Control of quarantine phytopathogens requires special attention. Soft rot pathogens are the main cause of limiting potato production in many regions of the world, particularly Clavibacter michiganensis subsp. sepedonicum and R. solanacearum are quarantine objects of the A-2 list of the European and Mediterranean Organization for Quarantine and Plant Protection. Upon entering our country, R. solanacearum has a high probability of acclimatization and spread in the country.

Disalicylic Acid Provides Effective Control of Pectobacterium brasiliense.

Bis(2-carboxyphenyl) succinate (disalicylic acid; DSA) is composed of two salicylic acids connected by a succinyl linker. Here, we propose its use as a new, synthetic plant-protection agent. DSA was shown to control Pectobacterium brasiliense, an emerging soft-rot pathogen of potato and ornamental crops, at minimal inhibitory concentrations (MIC) lower than those of salicylic acid. Our computational-docking analysis predicted that DSA would inhibit the quorum-sensing (QS) synthase of P. brasiliense ExpI more strongly than SA would. In fact, applying DSA to P. brasiliense inhibited its biofilm formation, secretion of plant cell wall-degrading enzymes, motility and production of acyl-homoserine lactones (AHL) and, subsequently, impaired its virulence. DSA also inhibited the production of AHL by a QS-negative Escherichia coli strain (DH5α) that had been transformed with P. brasiliense AHL synthase, as demonstrated by the biosensors Chromobacterium violaceaum CV026 and E. coli pSB401. Inhibition of the QS machinery appears to be one of the mechanisms by which DSA inhibits specific virulence determinants. A new route is proposed for the synthesis of DSA, which holds greater potential for use as an anti-virulence agent than its precursor SA. Based on these findings, DSA is an excellent candidate for repurposing for new applications.

Biocontrol potential of Bacillus subtilis CTXW 7-6-2 against kiwifruit soft rot pathogens revealed by whole-genome sequencing and biochemical characterisation.

Soft rot causes significant economic losses in the kiwifruit industry. This study isolated strain CTXW 7-6-2 from healthy kiwifruit tissue; this was a gram-positive bacterium that produced the red pigment pulcherrimin. The phylogenetic tree based on 16S ribosomal RNA, gyrA, rpoB, and purH gene sequences identified CTXW 7-6-2 as a strain of Bacillus subtilis. CTXW 7-6-2 inhibited hyphal growth of pathogenic fungi that cause kiwifruit soft rot, namely, Botryosphaeria dothidea, Phomopsis sp., and Alternaria alternata, by 81.76, 69.80, and 32.03%, respectively. CTXW 7-6-2 caused the hyphal surface to become swollen and deformed. Volatile compounds (VOC) produced by the strain inhibited the growth of A. alternata and Phomopsis sp. by 65.74 and 54.78%, respectively. Whole-genome sequencing revealed that CTXW 7-6-2 possessed a single circular chromosome of 4,221,676 bp that contained 4,428 protein-coding genes, with a guanine and cytosine (GC) content of 43.41%. Gene functions were annotated using the National Center for Biotechnology Information (NCBI) non-redundant protein, Swiss-Prot, Kyoto Encyclopedia of Genes and Genomes, Clusters of Orthologous Groups of proteins, Gene Ontology, Pathogen-Host Interactions, Carbohydrate-Active enZYmes, and Rapid Annotations using Subsystem Technology databases, revealing non-ribosomal pathways associated with antifungal mechanisms, biofilm formation, chemotactic motility, VOC 3-hydroxy-2-butanone, cell wall-associated enzymes, and synthesis of various secondary metabolites. antiSMASH analysis predicted that CTXW 7-6-2 can produce the active substances bacillaene, bacillibactin, subtilosin A, bacilysin, and luminmide and has four gene clusters of unknown function. Quantitative real-time PCR (qRT-PCR) analysis verified that yvmC and cypX, key genes involved in the production of pulcherrimin, were highly expressed in CTXW 7-6-2. This study elucidates the mechanism by which B. subtilis strain CTXW 7-6-2 inhibits pathogenic fungi that cause kiwifruit soft rot, suggesting the benefit of further studying its antifungal active substances.

Early warning of Diaporthe infection in kiwifruit soft rot by plasmonic dimer-enhanced Raman spectroscopy.

Diaporthe genus is the dominant pathogens of kiwifruit soft rot with long incubation period and rapid onset and very hard to detect in advance. It is of great significance to develop point-of-care tests for disease prevention and field management. Here we screen a pair of genus-level primers for constructing plasmonic dimer Rayleigh/Raman spectroscopy, which enables rapid, specific, and sensitive detection of Diaporthe genus in real kiwifruits. Dark-filed Rayleigh scattering clearly visualizes the target-induced dimer assembly of nanoprobes. Plasmonic dimer-enhanced Raman spectroscopy has high specificity for 12 common isolates of Diaporthe genus in one batch samples with highly accurate results and much higher sensitivity than polymerase chain reaction (PCR). It realizes the recognition of Diaporthe infection at an early stage of 24h when the kiwifruits do not have any noticeable symptoms. It demonstrates a bright prospect of point-of-care tests for early warning of kiwifruit soft rot infection and quality control.

Genome analysis of Erwinia persicina reveals implications for soft rot pathogenicity in plants.

Soft rot disease causes devastating losses to crop plants all over the world, with up to 90% loss in tropical climates. To better understand this economically important disease, we isolated four soft rot-causing Erwinia persicina strains from rotted vegetables. Notably, E. persicina has only recently been identified as a soft rot pathogen and a comprehensive genomic analysis and comparison has yet to be conducted. Here, we provide the first genomic analysis of E. persicina, compared to Pectobacterium carotovorum, P. carotovorum, and associated Erwinia plant pathogens. We found that E. persicina shares common genomic features with other Erwinia species and P. carotovorum, while having its own unique characteristics as well. The E. persicina strains examined here lack Type II and Type III secretion systems, commonly used to secrete pectolytic enzymes and evade the host immune response, respectively. E. persicina contains fewer putative pectolytic enzymes than P. carotovorum and lacks the Out cluster of the Type II secretion system while harboring a siderophore that causes a unique pink pigmentation during soft rot infections. Interestingly, a putative phenolic acid decarboxylase is present in the E. persicina strains and some soft rot pathogens, but absent in other Erwinia species, thus potentially providing an important factor for soft rot. All four E. persicina isolates obtained here and many other E. persicina genomes contain plasmids larger than 100 kbp that encode proteins likely important for adaptation to plant hosts. This research provides new insights into the possible mechanisms of soft rot disease by E. persicina and potential targets for diagnostic tools and control measures.

Comparative Pathogenomic Analysis of Two Banana Pathogenic Dickeya Strains Isolated from China and the Philippines.

Dickeya is a major and typical member of soft rot Pectobacteriaceae (SRP) with a wide range of plant hosts worldwide. Previous studies have identified D. zeae as the causal agent of banana soft rot disease in China. In 2017, we obtained banana soft rot pathogen strain FZ06 from the Philippines. Genome sequencing and analysis indicated that FZ06 can be classified as D. dadantii and represents a novel subspecies of D. dadantii, which we propose to name as subsp. paradisiaca. Compared with Chinese banana soft rot pathogenic strain D. zeae MS2, strain FZ06 has a similar host range but different virulence; FZ06 is significantly less virulent to banana and potato but more virulent to Chinese cabbage and onion. Characterization of virulence factors revealed obviously less production of pectate lyases (Pels), polygalacturonases (Pehs), proteases (Prts), and extrapolysaccharides (EPSs), as well as lower swimming and swarming motility and biofilm formation in strain FZ06. Genomic comparison of the two strains revealed five extra gene clusters in FZ06, including one Stt-type T2SS, three T4SSs, and one T4P. Expression of cell wall degrading enzyme (CWDE)-encoding genes is significantly lower in FZ06 than in MS2.

Green synthesis of silver nanoparticles from Mahonia fortunei extracts and characterization of its inhibitory effect on Chinese cabbage soft rot pathogen.

The pathogenic bacterium Pectobacterium carotovorum causes soft rot in cabbage and significantly reduces plant yield. In this study, we employed Mhonia fortunei extracts to synthesis silver nanoparticles (Mf-AgNPs) and investigated their functions against P. carotovorum. The results showed that the surface plasmon resonance (SPR) peak of AgNP was 412 nm under optimal synthesis conditions. Furthermore, the results of Scanning electron microscope-Energy dispersive spectrometer (SEM-EDS) and High-resolution transmission electron microscopy (HR-TEM) revealed that the Mf-AgNPs had a spherical structure with an average diameter of 13.19 nm and the content of Ag0 ions accounted for 82.68% of the total elemental content. The X-Ray diffraction (XRD) results confirmed that AgNPs had a face-centered cubic (FCC) crystal structure, while Fourier transform infrared spectroscopy (FTIR) results indicated the presence of various biomolecules as reducing and stabilizing agents on the AgNP surface. Antibacterial activity was first evaluated by an inhibitory zone test, which revealed that 500 μg ml-1 of AgNPs had antibacterial activity against P. carotovorum and four model bacteria including Staphylococcus aureus, Escherichia coli, Bacillus subtilis, and Pseudomonas aeruginosa, respectively with an antibacterial function comparable to 1 mM AgNO3 solution. The Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values for P. carotovorum were 8 μg ml-1, respectively. Furthermore, AgNPs at 8 μg ml-1 completely inhibited the growth of P. carotovorum, decreased their tolerance to 0.25 mM H2O2 as well as considerably reduced colony formation after 1 h of treatment and thereafter. Treatment with Mf-AgNPs resulted in bacterial cell membrane destruction and biofilm formation inhibition, respectively. With an FIC (fractional inhibitory concentration) index of 0.174, AgNP and zhongshengmycin showed a significant synergistic effect. The infection of P. carotovorum to cabbage explants was significantly inhibited in vitro by a combination of 2 μg ml-1 Mf-AgNP and 5 μg ml-1 zhongshengmycin. In conclusion, the synthesized Mf-AgNP exhibited significant antibacterial activity against P. carotovorum.

Control of the bacterial soft rot pathogen, Pectobacterium carotovorum by Bacillus velezensis CE 100 in cucumber

Pectobacterium carotovorum is a problematic bacterial pathogen causing soft rot in different vegetable crops, resulting in yield losses during pre- and post-harvest periods. In this study, Bacillus velezensis CE 100 showed antibacterial activity against P. carotovorum. Co-inoculation experiment indicated that B. velezensis CE 100 reduced the proliferation rate of P. carotovorum at the early incubation period and that a long incubation time induced a loss of viability of the bacterial pathogen. Agar well diffusion assay revealed that the culture filtrate of strain CE 100 affected the growth of P. carotovorum in a dose-dependent pattern. In time-kill assay, inoculation of P. carotovorum with 50% culture filtrate of strain CE 100 resulted in a complete loss of survival at 4 h incubation period. An antibacterial compound isolated from chloroform extract of B. velezensis CE 100 was identified as macrolactin A based on results of 1H and 13C NMR and mass spectrometry. However, time-kill assay showed that purified macrolactin A at a concentration of 200 μgmL−1 was not highly effective to control the growth of P. carotovorum although reduction in cell number of P. carotovorum was observed. Moreover, in vivo assay revealed that B. velezensis CE 100 effectively controlled bacterial soft rot. As a consequence, it significantly improved cucumber growth. Therefore, B. velezensis CE 100 could be used as an eco-friendly bioagent for effective control of bacterial soft rot to minimize global economic losses in crop production.

Genetic Diversity of Pectobacterium spp. on Potato in Serbia.

Pectobacterium is a diverse genus which comprises of multiple destructive bacterial species which cause soft rot/blackleg/wilt disease complex in a wide variety of crops by employing high levels of virulence factors. During the 2018, 2019 and 2020 potato growing seasons, numerous outbreaks of bacterial wilt, stem blackleg and tuber soft rot were recorded, and symptomatic plant samples from ten localities in the Province of Vojvodina (Serbia) were collected and analysed. Bacterial soft-rot pathogens were detected in 63 samples using genus and species-specific primers. Through 16S rRNA Sanger sequencing of 19 representative isolates, the identity of P. brasiliense (73.7%), P. punjabense (15.8%), and P. carotovorum (10.5%) species were revealed. To further validate the identification, genotypic profiling of Pectobacterium strains using rep-PCR (ERIC, BOX, REP) was conducted for 25 selected isolates and the phylogenetic assessment based on four selected housekeeping genes (gyrA, recA, rpoA, and rpoS). Physiological and biochemical properties were analysed using basic microbiological tests and VITEK® 2 GN card, and pathogenicity was confirmed on cv. VR808 and cv. Desiree potato tubers and plants. This study confirmed the distinctiveness of the newly described P. punjabense in Serbia as well as the high diversity of Pectobacterium brasiliense and Pectobacterium carotovorum species in Serbia.

Pseudomonas aeruginosa inhibits quorum-sensing mechanisms of soft rot pathogen Lelliottia amnigena RCE to regulate its virulence factors and biofilm formation.

The quorum-sensing (QS) cascade is responsible for the colonization and phenotypic behavior of the pathogenic organism and the regulation of diverse signal molecules. The disruption of the quorum-sensing system is an effective strategy to overcome the possibility of antibiotic resistance development in the pathogen. The quorum quenching does not kill the microbes. Instead, it hinders the expression of pathogenic traits. In the present experiment, Pseudomonas aeruginosa RKC1 was used to extract the metabolites responsible for quorum-sensing inhibition in soft rot pathogen Lelliottia amnigena RCE. During the initial screening, P. aeruginosa RKC1 was found to be most promising and inhibits violacein of Chromobacterium violaceum MTCC2656 pyocyanin, swarming-swimming motility of P. aeruginosa MTCC2297. The characterization of metabolites produced by the microbes which are responsible for quorum-sensing inhibition through GC-MS is very scarce in scientific literature. The ethyl acetate extract of P. aeruginosa RKC1 inhibits biofilm formation of L. amnigena RCE while inhibiting growth at higher concentrations. The GC-MS analysis suggested that Cyclic dipeptides (CDPs) such as Cyclo (L-prolyl-L-valine), Cyclo (Pro-Leu), and Cyclo(D-phenylalanyl-L-prolyl) were predominantly found in the ethyl acetate extract of the P. aeruginosa RKC1 (93.72%). This diketopiperazine (DKPs) exhibited quorum-sensing inhibition against the pathogen in liquid media during the active growth phase and regulated diverse metabolites of the pathogen. Moreover, the metabolites data from the clear zone around wells showed a higher concentration of DKSs (9.66%) compared to other metabolites. So far, very few reports indicate the role of DKPs or CDPs in inhibiting the quorum-sensing system in plant pathogenic bacteria. This is one such report that exploits metabolites of P. aeruginosa RKC1. The present investigation provided evidence to use quorum-sensing inhibitor metabolites, to suppress microbes' pathogenesis and thus develop an innovative strategy to overcome antibiotic resistance.

Analysis of the Taxonomy, Synteny, and Virulence Factors for Soft Rot Pathogen Pectobacterium aroidearum in Amorphophallus konjac Using Comparative Genomics.

Bacterial soft rot is a devastating disease for a wide range of crops, vegetables, and ornamental plants including konjac (Amorphophallus konjac). However, the pangenome and genomic plasticity of the konjac soft rot pathogens is little explored. In this study, we reported the complete genome sequences of 11 bacterial isolates that can cause typical soft rot symptoms in konjac by in vitro and in vivo pathogenicity tests. Based on in silico DNA–DNA hybridization, average nucleotide identity and phylogenomic analysis, all 11 isolates were determined to be Pectobacterium aroidearum. In addition, synteny analysis of these genomes revealed considerable chromosomal inversions, one of which is triggered by homologous recombination of ribose operon. Pangenome analysis and COG enrichment analysis showed that the pangenome of P. aroidearum is open and that accessory genes are enriched in replication, recombination, and repair. Variations in type IV secretion system and type VI secretion system were found, while plant cell wall degrading enzymes were conserved. Furthermore, sequence analyses also provided evidence for the presence of a type V secretion system in Pectobacterium. These findings advance our understanding of the pathogenicity determinants, genomic plasticity, and evolution of P. aroidearum.