Platinum-based fluorescent nanozyme-driven "loong frolic pearls" multifunctional nanoplatform for tri-mode ultrasensitive detection and synergistic sterilization of Burkholderia gladioli.

Rapid and accurate detection of Burkholderia gladioli (B. gladioli) and effective sterilization are crucial for ensuring food safety. Hence, a novel "loong frolic pearls" platform based on platinum-based fluorescent nanozymes (Pt-OCDs) and strand exchange amplification (SEA) was reported. Magnetic nanoparticles were modified on primer SEAF, while Pt-OCDs were covalently coupled with primer SEA-R. The highly efficient amplification capability of SEA permitted the accumulation of a large number of double-labeled amplicons. After magnetic adsorption, the supernatant was detected in reverse direction to collect colorimetric-fluorescence-photothermal signal values, enabling ultra-precise detection within 1 h. Furthermore, the Pt-based multifunctional nanoplatform generated abundant •OH and 1O2, which synergistically attacked B. gladioli and its biofilm, resulting in significant bactericidal efficacy within 30 min. This "triple-detection and double-sterilization" platform has been successfully applied in the field of food analysis with good recovery rates and immediate control over B. gladioli, thus demonstrating promising prospects for broad applications.

Prophylactic phage biocontrol prevents Burkholderia gladioli infection in a quantitative ex planta model of bacterial virulence.

Agricultural crop yield losses and food destruction due to infections by phytopathogenic bacteria such as Burkholderia gladioli, which causes devastating diseases in onion, mushroom, corn, and rice crops, pose major threats to worldwide food security and cause enormous damage to the global economy. Biocontrol using bacteriophages has emerged as a promising strategy against a number of phytopathogenic species but has never been attempted against B. gladioli due to a lack of quantitative infection models and a scarcity of phages targeting this specific pathogen. In this study, we present a novel, procedurally straightforward, and highly generalizable fully quantitative ex planta maceration model and an accompanying quantitative metric, the ex planta maceration index (xPMI). In utilizing this model to test the ex planta virulence of a panel of 12 strains of B. gladioli in Allium cepa and Agaricus bisporus, we uncover substantial temperature-, host-, and strain-dependent diversity in the virulence of this fascinating pathogenic species. Crucially, we demonstrate that Burkholderia phages KS12 and AH2, respectively, prevent and reduce infection-associated onion tissue destruction, measured through significant (P < 0.0001) reductions in xPMI, by phytopathogenic strains of B. gladioli, thereby demonstrating the potential of agricultural phage biocontrol targeting this problematic microorganism.IMPORTANCEAgricultural crop destruction is increasing due to infections caused by bacteria such as Burkholderia gladioli, which causes plant tissue diseases in onion, mushroom, corn, and rice crops. These bacteria pose a major threat to worldwide food production, which, in turn, damages the global economy. One potential solution being investigated to prevent bacterial infections of plants is "biocontrol" using bacteriophages (or phages), which are bacterial viruses that readily infect and destroy bacterial cells. In this article, we demonstrate that Burkholderia phages KS12 and AH2 prevent or reduce infection-associated plant tissue destruction caused by strains of B. gladioli, thereby demonstrating the inherent potential of agricultural phage biocontrol.

The potential of Burkholderia gladioli KRS027 in plant growth promotion and biocontrol against Verticillium dahliae revealed by dual transcriptome of pathogen and host.

Verticillium dahliae is a destructive, soil-borne pathogen that causes significant losses on numerous important dicots. Recently, beneficial microbes inhabiting the rhizosphere have been exploited and used to control plant diseases. In the present study, Burkholderia gladioli KRS027 demonstrated excellent inhibitory effects against Verticillium wilt in cotton seedlings. Plant growth and development was promoted by affecting the biosynthesis and signaling pathways of brassinosteroids (BRs), gibberellins (GAs), and auxins, consequently promoting stem elongation, shoot apical meristem, and root apical tissue division in cotton. Furthermore, based on the host transcriptional response to V. dahliae infection, it was found that KRS027 modulates the plants to maintain cell homeostasis and respond to other pathogen stress. Moreover, KRS027 induced disruption of V. dahliae cellular structures, as evidenced by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. Based on the comparative transcriptomic analysis between KRS027 treated and control group of V. dahliae, KRS027 induced substantial alterations in the transcriptome, particularly affecting genes encoding secreted proteins, small cysteine-rich proteins (SCRPs), and protein kinases. In addition, KRS027 suppressed the growth of different clonal lineages of V. dahliae strains through metabolites, and volatile organic compounds (VOCs) released by KRS027 inhibited melanin biosynthesis and microsclerotia development. These findings provide valuable insights into an alternative biocontrol strategy for Verticillium wilt, demonstrating that the antagonistic bacterium KRS027 holds promise as a biocontrol agent for promoting plant growth and managing disease occurrence.

Burkholderia gladioli deep pyoderma in a dog secondary to immunosuppressive ciclosporin and prednisone therapy.

A dog presented with deep pyoderma on the paw, following treatment with ciclosporin and prednisone for immune-mediated haemolytic anaemia. Cytological evaluation, skin biopsy, aerobic culture, next-generation DNA sequencing and PCR were used to detect the first reported case of Burkholderia gladioli in a dog.

Thiosulfinate Tolerance Gene Clusters Are Common Features of Burkholderia Onion Pathogens.

Burkholderia gladioli pv. alliicola, B. cepacia, and B. orbicola are common bacterial pathogens of onion. Onions produce organosulfur thiosulfinate defensive compounds after cellular decompartmentalization. Using whole-genome sequencing and in silico analysis, we identified putative thiosulfinate tolerance gene (TTG) clusters in multiple onion-associated Burkholderia species similar to those characterized in other Allium-associated bacterial endophytes and pathogens. Sequence analysis revealed the presence of three Burkholderia TTG cluster types, with both Type A and Type B being broadly distributed in B. gladioli, B. cepacia, and B. orbicola in both the chromosome and plasmids. Based on isolate natural variation and generation of isogenic strains, we determined the in vitro and in vivo contribution of TTG clusters in B. gladioli, B. cepacia, and B. orbicola. The Burkholderia TTG clusters contributed to enhanced allicin tolerance and improved growth in filtered onion extracts by all three species. TTG clusters also made clear contributions to B. gladioli foliar necrosis symptoms and bacterial populations. Surprisingly, the TTG cluster did not contribute to bacterial populations in onion bulb scales by these three species. Based on our findings, we hypothesize onion-associated Burkholderia may evade or inhibit the production of thiosulfinates in onion bulb tissues. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Bongkrekic Acid and Burkholderia gladioli pathovar cocovenenans: Formidable Foe and Ascending Threat to Food Safety.

Bongkrekic acid (BKA) poisoning, induced by the contamination of Burkholderia gladioli pathovar cocovenenans, has a long-standing history of causing severe outbreaks of foodborne illness. In recent years, it has emerged as a lethal food safety concern, presenting significant challenges to public health. This review article highlights the recent incidents of BKA poisoning and current research discoveries on the pathogenicity of B. gladioli pv. cocovenenans and underlying biochemical mechanisms for BKA synthesis. Moreover, the characterization of B. gladioli pv. cocovenenans and the identification of the bon gene cluster provide a crucial foundation for developing targeted interventions to prevent BKA accumulation in food matrices. The prevalence of the bon gene cluster, which is the determining factor distinguishing B. gladioli pv. cocovenenans from non-pathogenic B. gladioli strains, has been identified in 15% of documented B. gladioli genomes worldwide. This finding suggests that BKA poisoning has the potential to evolve into a more prevalent threat. Although limited, previous research has proved that B. gladioli pv. cocovenenans is capable of producing BKA in diverse environments, emphasizing the possible food safety hazards associated with BKA poisoning. Also, advancements in detection methods of both BKA and B. gladioli pv. cocovenenans hold great promise for mitigating the impact of this foodborne disease. Future studies focusing on reducing the threat raised by this vicious foe is of paramount importance to public health.

The Genomic-Driven Discovery of Glutarimide-Containing Derivatives from Burkholderia gladioli.

Glutarimide-containing polyketides exhibiting potent antitumor and antimicrobial activities were encoded via conserved module blocks in various strains that favor the genomic mining of these family compounds. The bioinformatic analysis of the genome of Burkholderia gladioli ATCC 10248 showed a silent trans-AT PKS biosynthetic gene cluster (BGC) on chromosome 2 (Chr2C8), which was predicted to produce new glutarimide-containing derivatives. Then, the silent polyketide synthase gene cluster was successfully activated via in situ promoter insertion and heterologous expression. As a result, seven glutarimide-containing analogs, including five new ones, gladiofungins D-H (3-7), and two known gladiofungin A/gladiostatin (1) and 2 (named gladiofungin C), were isolated from the fermentation of the activated mutant. Their structures were elucidated through the analysis of HR-ESI-MS and NMR spectroscopy. The structural diversities of gladiofungins may be due to the degradation of the butenolide group in gladiofungin A (1) during the fermentation and extraction process. Bioactivity screening showed that 2 and 4 had moderate anti-inflammatory activities. Thus, genome mining combined with promoter engineering and heterologous expression were proved to be effective strategies for the pathway-specific activation of the silent BGCs for the directional discovery of new natural products.

Heterologous Biosynthesis of Complex Bacterial Natural Products in Burkholderia gladioli.

Bacterial natural products (NPs) are an indispensable source of drugs and biopesticides. Heterologous expression is an essential method for discovering bacterial NPs and the efficient biosynthesis of valuable NPs, but the chassis for Gram-negative bacterial NPs remains inadequate. In this study, we built a Burkholderiales mutant Burkholderia gladioli Δgbn::attB by introducing an integrated site (attB) to inactivate the native gladiolin (gbn) biosynthetic gene cluster, which stabilizes large foreign gene clusters and reduces the native metabolite profile. The growth and successful heterologous production of high-value NPs such as phylogenetically close Burkholderiales-derived antitumor polyketides (PKs) rhizoxins, phylogenetically distant Gammaproteobacteria-derived anti-MRSA (methicillin-resistant Staphylococcus aureus) antibiotics WAP-8294As, and Deltaproteobacteria-derived antitumor PKs disorazols demonstrate that this strain is a potential chassis for Gram-negative bacterial NPs. We further improved the yields of WAP-8294As through promoter insertions and precursor pathway overexpression based on heterologous expression in this strain. This study provides a robust bacterial chassis for genome mining, efficient production, and molecular engineering of bacterial NPs.

Lower female survival from an opportunistic infection reveals progesterone-driven sex bias in trained immunity.

Immune responses differ between females and males, although such sex-based variance is incompletely understood. Observing that bacteremia of the opportunistic pathogen Burkholderia gladioli caused many more deaths of female than male mice bearing genetic deficiencies in adaptive immunity, we determined that this was associated with sex bias in the innate immune memory response called trained immunity. Female attenuation of trained immunity varies with estrous cycle stage and correlates with serum progesterone, a hormone that decreases glycolytic capacity and recall cytokine secretion induced by antigen non-specific stimuli. Progesterone receptor antagonism rescues female trained immune responses and survival from controlled B. gladioli infection to magnitudes similar to those of males. These data demonstrate progesterone-dependent sex bias in trained immunity where attenuation of female responses is associated with survival outcomes from opportunistic infection.

First report of bacterial panicle blight (BPB) in Rice caused by Burkholderia gladioli in Bangladesh.

Bacterial panicle blight (BPB) has become one of the most destructive diseases of rice worldwide and Burkholderia gladioli and B. glumae are two major pathogens causing BPB (1). This disease causes several types of damage, most importantly grain spotting, rot, and panicle blight, which can result in yield losses of 75% or more (1,3). In recent years, symptoms including sheath rot, grain spotting, grain rot, and panicle blight have been observed in both inbred and hybrid rice varieties. These symptoms resemble those of BPB and cause cultivar-dependent yield losses. (3) also reported the same symptoms for BPB. To confirm the cause of the disease, 21 rice panicles (Haridhan, a local variety) with typical BPB symptoms were collected from a farmer's field in the region of Mymensingh, Bangladesh during the rainy season in mid-October, 2021. Due to the severity of the outbreak, the panicles became dark brown and produced chaffy grains; nearly 100% of the rice panicles in that field were severely infected. To identify the causal pathogen(s), 1g of rice grains from 20 plants with typical BPB symptoms were surface-sterilized by immersing them in 70% ethanol for a few seconds followed by sodium hypochlorite solution (3%) for 1min. The grains were then rinsed with sterilized distilled water three times. Surface-sterilized grains were then ground with a mortar and pestle; 5mL of sterile distilled water was added during grinding. The extracted suspension (20µL) was then either streaked or spread onto the selective medium (S-PG) (2). Bacterial colonies showing purple color on the S-PG medium were selected and purified as candidate pathogens. For molecular characterization, species specific primers targeting gyrB gene were used to perform PCR and resulted in 479bp as reported by (4). To verify further, the PCR products of 16SF & 16SR were amplified and sequenced partially producing around 1400bp (1) and five 16SF partial sequences were deposited into NCBI GenBank (OP108276 to OP108280). 16S rDNA and gyrB revealed almost 99% homology with Burkholderia gladioli (KU851248.1, MZ425424.1) and B. gladioli (AB220893, CP033430) respectively using BLAST analysis. These purified bacterial isolates produced a diffusible light-yellow pigment on King's B medium indicating toxoflavin production (3). The candidate five bacterial isolates were then confirmed by inoculating 10ml suspension 108CFU/mL into the panicles and sheaths of BRRIdhan28 in net house condition as described previously (1). All of the bacterial isolates obtained from the spotted rice grains produced light brown lesions on the inoculated leaf sheath as well as spotting on the grain. To fulfill Koch's postulates, the bacteria were re-isolated from the symptomatic panicles and were confirmed as B. gladioli by analyzing the sequences of gyrB and 16s rDNA genes. Taken together, these results confirmed that B. gladioli is responsible for causing BPB in the rice grain samples that we collected. To our knowledge, this is the first report of BPB caused by B. gladioli in Bangladesh and further research is necessary to develop an effective disease management technique, or else the production of rice will be severely hampered.

Rapid and Simple Detection of Burkholderia gladioli in Food Matrices Using RPA-CRISPR/Cas12a Method.

Pathogenic variants of Burkholderia gladioli pose a serious threat to human health and food safety, but there is a lack of rapid and sensitive field detection methods for Burkholderia gladioli. In this study, the CRISPR/Cas12a system combined with recombinant enzyme polymerase amplification (RPA) was used to detect Burkholderia gladioli in food. The optimized RPA-CRISPR/Cas12a assay was able to specifically and stably detect Burkholderia gladioli at a constant 37 °C without the assistance of large equipment. The detection limit of the method was evaluated at two aspects, the genomic DNA (gDNA) level and bacterial quantity, of which there were 10-3 ng/µL and 101 CFU/mL, respectively. Three kinds of real food samples were tested. The detection limit for rice noodles, fresh white noodles, and glutinous rice flour samples was 101 CFU/mL, 102 CFU/mL, and 102 CFU/mL, respectively, without any enrichment steps. The whole detection process, including sample pretreatment and DNA extraction, did not exceed one hour. Compared with the qPCR method, the established RPA-CRISPR /Cas12a method was simpler and even more sensitive. Using this method, a visual detection of Burkholderia gladioli that is suitable for field detection can be achieved quickly and easily.

Pan-genome analysis of the Burkholderia gladioli PV. Cocovenenans reveal the extent of variation in the toxigenic gene cluster.

Burkholderia gladioli has been reported as the pathogen responsible for cases of foodborne illness in many countries. The poisonous bongkrekic acid (BA) produced by B. gladioli was linked to a gene cluster absent in non-pathogenic strains. The whole genome sequence of eight bacteria strains, which were screened from the collected 175 raw food and environmental samples, were assembled and analyzed to detect a significant association of 19 protein-coding genes with the pathogenic status. Except for the common BA synthesis-related gene, several other genes, including the toxin-antitoxin genes, were also absent in the non-pathogenic strains. The bacteria strains with the BA gene cluster were found to form a single cluster in the analysis of all B. gladioli genome assemblies for the variants in the gene cluster. Divergence of this cluster was detected in the analysis for both the flanking sequences and those of the whole genome level, which indicates its complex origin. Genome recombination was found to cause a precise sequence deletion in the gene cluster region, which was found to be predominant in the non-pathogenic strains indicating the possible effect of horizontal gene transfer. Our study provided new information and resources for understanding the evolution and divergence of the B. gladioli species.

Nicotinic Acid Catabolism Modulates Bacterial Mycophagy in Burkholderia gladioli Strain NGJ1.

Burkholderia gladioli strain NGJ1 exhibits mycophagous activity on a broad range of fungi, including Rhizoctonia solani, a devastating plant pathogen. Here, we demonstrate that the nicotinic acid (NA) catabolic pathway in NGJ1 is required for mycophagy. NGJ1 is auxotrophic to NA and it potentially senses R. solani as a NA source. Mutation in the nicC and nicX genes involved in NA catabolism renders defects in mycophagy and the mutant bacteria are unable to utilize R. solani extract as the sole nutrient source. As supplementation of NA, but not FA (fumaric acid, the end product of NA catabolism) restores the mycophagous ability of ΔnicC/ΔnicX mutants, we anticipate that NA is not required as a carbon source for the bacterium during mycophagy. Notably, nicR, a MarR-type of transcriptional regulator that functions as a negative regulator of the NA catabolic pathway is upregulated in ΔnicC/ΔnicX mutant and upon NA supplementation the nicR expression is reduced to the basal level in both the mutants. The ΔnicR mutant produces excessive biofilm and is completely defective in swimming motility. On the other hand, ΔnicC/ΔnicX mutants are compromised in swimming motility as well as biofilm formation, potentially due to the upregulation of nicR. Our data suggest that a defect in NA catabolism alters the NA pool in the bacterium and upregulates nicR which in turn suppresses bacterial motility as well as biofilm formation, leading to mycophagy defects. IMPORTANCE Mycophagy is an important trait through which certain bacteria forage over fungal mycelia and utilize fungal biomass as a nutrient source to thrive in hostile environments. The present study emphasizes that nicotinic acid (NA) is important for bacterial motility and biofilm formation during mycophagy by Burkholderia gladioli strain NGJ1. Defects in NA catabolism potentially alter the cellular NA pool, upregulate the expression of nicR, a negative regulator of biofilm, and therefore suppress bacterial motility as well as biofilm formation, leading to mycophagy defects.

Insights into the Biocontrol Function of a Burkholderia gladioli Strain against Botrytis cinerea.

Pathogenic fungi are the main cause of yield loss and postharvest loss of crops. In recent years, some antifungal microorganisms have been exploited and applied to prevent and control pathogenic fungi. In this study, an antagonistic bacteria KRS027 isolated from the soil rhizosphere of a healthy cotton plant from an infected field was identified as Burkholderia gladioli by morphological identification, multilocus sequence analysis, and typing (MLSA-MLST) and physiobiochemical examinations. KRS027 showed broad spectrum antifungal activity against various phytopathogenic fungi by secreting soluble and volatile compounds. KRS027 also has the characteristics of plant growth promotion (PGP) including nitrogen fixation, phosphate, and potassium solubilization, production of siderophores, and various enzymes. KRS027 is not only proven safe by inoculation of tobacco leaves and hemolysis test but also could effectively protect tobacco and table grapes against gray mold disease caused by Botrytis cinerea. Furthermore, KRS027 can trigger plant immunity by inducing systemic resistance (ISR) activated by salicylic acid- (SA), jasmonic acid- (JA), and ethylene (ET)-dependent signaling pathways. The extracellular metabolites and volatile organic compounds (VOCs) of KRS027 affected the colony extension and hyphal development by downregulation of melanin biosynthesis and upregulation of vesicle transport, G protein subunit 1, mitochondrial oxidative phosphorylation, disturbance of autophagy process, and degrading the cell wall of B. cinerea. These results demonstrated that B. gladioli KRS027 would likely become a promising biocontrol and biofertilizer agent against fungal diseases, including B. cinerea, and would promote plant growth. IMPORTANCE Searching the economical, eco-friendly and efficient biological control measures is the key to protecting crops from pathogenic fungi. The species of Burkholderia genus are widespread in the natural environment, of which nonpathogenic members have been reported to have great potential for biological control agents and biofertilizers for agricultural application. Burkholderia gladioli strains, however, need more study and application in the control of pathogenic fungi, plant growth promotion, and induced systemic resistance (ISR). In this study, we found that a B. gladioli strain KRS027 has broad spectrum antifungal activity, especially in suppressing the incidence of gray mold disease caused by Botrytis cinerea, and can stimulate plant immunity response via ISR activated by salicylic acid- (SA), jasmonic acid- (JA), and ethylene (ET)-dependent signaling pathways. These results indicate that B. gladioli KRS027 may be a promising biocontrol and biofertilizer microorganism resource in agricultural applications.

Burkholderia gladioli strain KJ-34 exhibits broad-spectrum antifungal activity.

Introduction: Plant pathogens are one of the major constraints on worldwide food production. The antibiotic properties of microbes identified as effective in managing plant pathogens are well documented. Methods: Here, we used antagonism experiments and untargeted metabolomics to isolate the potentially antifungal molecules produced by KJ-34. Results: KJ-34 is a potential biocontrol bacterium isolated from the rhizosphere soil of rice and can fight multiple fungal pathogens (i.e. Ustilaginoidea virens, Alternaria solani, Fusarium oxysporum, Phytophthora capsica, Corynespora cassiicola). The favoured fermentation conditions are determined and the fermentation broth treatment can significantly inhibit the infection of Magnaporthe oryzae and Botryis cinerea. The fermentation broth suppression ratio is 75% and 82%, respectively. Fermentation broth treatment disrupted the spore germination and led to malformation of hyphae. Additionally, we found that the molecular weight of antifungal products were less than 1000 Da through semipermeable membranes on solid medium assay. To search the potentially antifungal molecules that produce by KJ-34, we used comparative and bioinformatics analyses of fermentation broth before and after optimization by mass spectrometry. Untargeted metabolomics analyses are presumed to have a library of antifungal agents including benzoylstaurosporine, morellin and scopolamine. Discussion: These results suggest that KJ-34 produced various biological control agents to suppress multiple phytopathogenic fungi and showed a strong potential in the ecological technologies of prevention and protection.

Fatal Case of Burkholderia gladioli Pneumonia in a Patient With COVID-19.

Background: Burkholderia gladioli (B gladioli) is a rare, gram-negative rod that was initially regarded as a plant pathogen. However, B gladioli has been reported as the primary pathogen causing pneumonia in organ transplant recipients and in patients with cystic fibrosis. We report a case of bacterial pneumonia caused by B gladioli in a patient hospitalized for coronavirus disease 2019 (COVID-19). Case Report: A 68-year-old male was admitted for acute hypoxic respiratory failure secondary to COVID-19 pneumonia. He was treated with dexamethasone and convalescent plasma, resulting in improvement in the hypoxemia. However, during the latter part of his inpatient stay, the patient developed pneumonia caused by B gladioli. The isolate of B gladioli was sensitive to meropenem, levofloxacin, and trimethoprim/sulfamethoxazole and intermediate to ceftazidime. He was treated with meropenem and levofloxacin. Despite treatment, the patient developed acute respiratory distress syndrome with multiorgan failure, suffered cardiac arrest, and died. Conclusion: To the best of our knowledge, this case is the first report of B gladioli coinfection in a patient hospitalized for COVID-19 and provides insight into the possible detrimental outcome of B gladioli and COVID-19 coinfection.

Crystal structure of a Burkholderia peptidase and modification of the substrate-binding site for enhanced hydrolytic activity toward gluten-derived pro-immunogenic peptides.

Celiac disease (CD) is a human autoimmune disease triggered by toxic gluten peptides. Recently, oral enzyme therapy has been proposed to ameliorate the health condition of CD patients based on the concept of removing pepsin-insensitive gluten-derived pro-immunogenic peptides. A Burkholderia peptidase, Bga1903, with promising gluten-degrading activity was characterized previously. Here, we report the crystal structure of Bga1903, in which the core has a α/ß/α fold featured with a twisted six-stranded parallel ß-sheet sandwiched between two layers of α-helices. The mutations at the substrate-binding pocket that might enhance the peptidase's affinity toward tetrapeptide PQPQ were predicted by FoldX. Accordingly, four single-substitution mutants, G351A, E380L, S386F, and S387L, were created. The specificity constant (kcat/KM) of wild type toward chromogenic peptidyl substrates Z-HPK-pNA, Z-HPQ-pNA, Z-HPL-pNA, and Z-QPQ-pNA are 30.2, 7.9, 3.3, and 0.79 s-1·mM-1, respectively, indicating that the QPQ motif, which frequently occurs in pro-immunogenic peptides, is not favorable. Among the mutants, E380L loses the hydrolytic activity toward Z-HPK-pNA, suggesting a critical role of E380 in preferring a lysine residue at the P1 position. S387L shows a 17-fold increase in the specificity constant toward Z-QPQ-pNA and hydrolyzes the pro-immunogenic peptides more efficiently than the wild-type peptidase.

Cold-adapted strains as plant growth-promoting bacteria on soybean seeds and biocontrol agents against Macrophomina phaseolina.

AIM: The aim was to characterize cold-adapted bacteria by testing their PGP features and antagonistic activity against Macrophomina phaseolina, both in vitro and coating soybean seeds (Glycine max [L.] Merr.). METHODS AND RESULTS: Burkholderia gladioli MB39, Serratia proteamaculans 136 and Serratia proteamaculans 137 were evaluated. In vitro tests showed that S. proteamaculans 136 and 137 produce siderophore and indole-acetic acid (IAA), solubilize phosphate and fix nitrogen. Additionally, B. gladioli MB39 and S. proteamaculans 137 showed hydrolase activity and potent antifungal effects. The biocontrol efficacy over soybean seeds was evaluated using in vitro and greenhouse methods by immersing seeds into each bacterial suspension. As a result, S. proteamaculans 136 has improved the performance in all the seed germination evaluated parameters. In addition, S. proteamaculans 137 and B. gladioli MB39 strongly inhibited M. phaseolina, reducing the infection index values to 10% and 0%, respectively. CONCLUSION: Serratia proteamaculans 136, 137 and Burkholderia gladioli MB39 showed plant growth promotion features and inhibition of Macrophomina phaseolina infection by producing different antifungal compounds. SIGNIFICANCE AND IMPACT OF THE STUDY: Our results reinforce the application of cold-adapted Serratia proteamaculans and Burkholderia gladioli bacterial strains as candidates for developing microbial formulation to promote plant growth and guarantee antifungal protection in soybean crops.