Wild mushrooms as potential reservoirs of plant pathogenic bacteria: a case study on Burkholderia gladioli.

Fruit bodies (sporocarps) of wild mushrooms growing in natural environments play a substantial role in the preservation of microbial communities, for example, clinical and food-poisoning bacteria. However, the role of wild mushrooms as natural reservoirs of plant pathogenic bacteria remains almost entirely unknown. Furthermore, bacterial transmission from a mushroom species to agricultural plants has rarely been recorded in the literature. In September 2021, a creamy-white Gram-negative bacterial strain was isolated from the sporocarp of Suillus luteus (slippery jack) growing in Bermuda grass (Cynodon dactylon) lawn in Southern Iran. A similar strain was isolated from the same fungus in the same area in September 2022. Both strains were identified as Burkholderia gladioli based on phenotypic features as well as phylogeny of 16S rRNA and three housekeeping genes. The strains were not only pathogenic on white button mushrooms (Agaricus bisporus) but also induced hypersensitive reaction (HR) on tobacco and common bean leaves and caused soft rot on a set of diverse plant species, that is, chili pepper, common bean pod, cucumber, eggplant, garlic, gladiolus, narcissus, onion, potato, spring onion, okra, kohlrabi, mango, and watermelon. Isolation of plant pathogenic B. gladioli strains from sporocarp of S. luteus in two consecutive years in the same area could be indicative of the role of this fungus in the preservation of the bacterium in the natural environment. B. gladioli associated with naturally growing S. luteus could potentially invade neighboring agricultural crops, for example, vegetables and ornamentals. The potential role of wild mushrooms as natural reservoirs of phytopathogenic bacteria is further discussed.IMPORTANCEThe bacterial genus Burkholderia contains biologically heterogeneous strains that can be isolated from diverse habitats, that is, soil, water, diseased plant material, and clinical specimens. In this study, two Gram-negative pectinolytic bacterial strains were isolated from the sporocarps of Suillus luteus in September 2021 and 2022. Molecular phylogenetic analyses revealed that both strains belonged to the complex species Burkholderia gladioli, while the pathovar status of the strains remained undetermined. Biological investigations accomplished with pathogenicity and host range assays showed that B. gladioli strains isolated from S. luteus in two consecutive years were pathogenic on a set of diverse plant species ranging from ornamentals to both monocotyledonous and dicotyledonous vegetables. Thus, B. gladioli could be considered an infectious pathogen capable of being transmitted from wild mushrooms to annual crops. Our results raise a hypothesis that wild mushrooms could be considered as potential reservoirs for phytopathogenic B. gladioli.

Garlic Bulb Decay and Soft Rot Caused by the Cross-Kingdom Pathogen Burkholderia gladioli.

In 2021, two gram-negative bacterial strains were isolated from garlic (Allium sativum) bulbs showing decay and soft rot symptoms in Central Iran. The bacterial strains were aggressively pathogenic on cactus, garlic, gladiolus, onion, potato, and saffron plants and induced soft rot symptoms on carrot, cucumber, potato, and radish discs. Furthermore, they were pathogenic on sporophores of cultivated and wild mushrooms. Phylogenetic analyses revealed that the bacterial strains belong to Burkholderia gladioli. Garlic bulb rot caused by B. gladioli has rarely been reported in the literature. Historically, B. gladioli strains had been assigned to four pathovars, namely, B. gladioli pv. alliicola, B. gladioli pv. gladioli, B. gladioli pv. agaricicola, and B. gladioli pv. cocovenenans, infecting onion, Gladiolus sp., and mushrooms and poisoning foods, respectively. Multilocus (i.e., 16S rRNA, atpD, gyrB, and lepA genes) sequence-based phylogenetic investigations including reference strains of B. gladioli pathovars showed that the two garlic strains belong to phylogenomic clade 2 of the species, which includes the pathotype strain of B. gladioli pv. alliicola. Although the garlic strains were phylogenetically closely related to the B. gladioli pv. alliicola reference strains, they possessed pathogenicity characteristics that overlapped with three of the four historical pathovars, including the ability to rot onion (pv. alliicola), gladiolus (pv. gladioli), and mushrooms (pv. agaricicola). Furthermore, the pathotype of each pathovar could infect the hosts of other pathovars, undermining the utility of the pathovar concept in this species. Overall, using phenotypic pathovar-oriented assays to classify B. gladioli strains should be replaced by phylogenetic or phylogenomic analysis.

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.

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.

Identification of the Biosynthetic Gene Cluster for the Organoarsenical Antibiotic Arsinothricin.

The soil bacterium Burkholderia gladioli GSRB05 produces the natural compound arsinothricin [2-amino-4-(hydroxymethylarsinoyl) butanoate] (AST), which has been demonstrated to be a broad-spectrum antibiotic. To identify the genes responsible for AST biosynthesis, a draft genome sequence of B. gladioli GSRB05 was constructed. Three genes, arsQML, in an arsenic resistance operon were found to be a biosynthetic gene cluster responsible for synthesis of AST and its precursor, hydroxyarsinothricin [2-amino-4-(dihydroxyarsinoyl) butanoate] (AST-OH). The arsL gene product is a noncanonical radical S-adenosylmethionine (SAM) enzyme that is predicted to transfer the 3-amino-3-carboxypropyl (ACP) group from SAM to the arsenic atom in inorganic arsenite, forming AST-OH, which is methylated by the arsM gene product, a SAM methyltransferase, to produce AST. Finally, the arsQ gene product is an efflux permease that extrudes AST from the cells, a common final step in antibiotic-producing bacteria. Elucidation of the biosynthetic gene cluster for this novel arsenic-containing antibiotic adds an important new tool for continuation of the antibiotic era. IMPORTANCE Antimicrobial resistance is an emerging global public health crisis, calling for urgent development of novel potent antibiotics. We propose that arsinothricin and related arsenic-containing compounds may be the progenitors of a new class of antibiotics to extend our antibiotic era. Here, we report identification of the biosynthetic gene cluster for arsinothricin and demonstrate that only three genes, two of which are novel, are required for the biosynthesis and transport of arsinothricin, in contrast to the phosphonate counterpart, phosphinothricin, which requires over 20 genes. Our discoveries will provide insight for the development of more effective organoarsenical antibiotics and illustrate the previously unknown complexity of the arsenic biogeochemical cycle, as well as bring new perspective to environmental arsenic biochemistry.

Efficient Hydrolysis of Gluten-Derived Celiac Disease-Triggering Immunogenic Peptides by a Bacterial Serine Protease from Burkholderia gladioli.

Celiac disease is an autoimmune disorder triggered by toxic peptides derived from incompletely digested glutens in the stomach. Peptidases that can digest the toxic peptides may formulate an oral enzyme therapy to improve the patients' health condition. Bga1903 is a serine endopeptidase secreted by Burkholderia gladioli. The preproprotein of Bga1903 consists of an N-terminal signal peptide, a propeptide region, and an enzymatic domain that belongs to the S8 subfamily. Bga1903 could be secreted into the culture medium when it was expressed in E. coli. The purified Bga1903 is capable of hydrolyzing the gluten-derived toxic peptides, such as the 33- and 26-mer peptides, with the preference for the peptide bonds at the carbonyl site of glutamine (P1 position). The kinetic assay of Bga1903 toward the chromogenic substrate Z-HPQ-pNA at 37 °C, pH 7.0, suggests that the values of Km and kcat are 0.44 ± 0.1 mM and 17.8 ± 0.4 s-1, respectively. The addition of Bga1903 in the wort during the fermentation step of beer could help in making gluten-free beer. In summary, Bga1903 is usable to reduce the gluten content in processed foods and represents a good candidate for protein engineering/modification aimed to efficiently digest the gluten at the gastric condition.

Genomics-Driven Activation of Silent Biosynthetic Gene Clusters in Burkholderia gladioli by Screening Recombineering System.

The Burkholderia genus possesses ecological and metabolic diversities. A large number of silent biosynthetic gene clusters (BGCs) in the Burkholderia genome remain uncharacterized and represent a promising resource for new natural product discovery. However, exploitation of the metabolomic potential of Burkholderia is limited by the absence of efficient genetic manipulation tools. Here, we screened a bacteriophage recombinase system Redγ-BAS, which was functional for genome modification in the plant pathogen Burkholderia gladioli ATCC 10248. By using this recombineering tool, the constitutive promoters were precisely inserted in the genome, leading to activation of two silent nonribosomal peptide synthetase gene clusters (bgdd and hgdd) and production of corresponding new classes of lipopeptides, burriogladiodins A-H (1-8) and haereogladiodins A-B (9-10). Structure elucidation revealed an unnatural amino acid Z- dehydrobutyrine (Dhb) in 1-8 and an E-Dhb in 9-10. Notably, compounds 2-4 and 9 feature an unusual threonine tag that is longer than the predicted collinearity assembly lines. The structural diversity of burriogladiodins was derived from the relaxed substrate specificity of the fifth adenylation domain as well as chain termination conducted by water or threonine. The recombinase-mediating genome editing system is not only applicable in B. gladioli, but also possesses great potential for mining meaningful silent gene clusters from other Burkholderia species.

Kill and cure: genomic phylogeny and bioactivity of Burkholderia gladioli bacteria capable of pathogenic and beneficial lifestyles.

Burkholderia gladioli is a bacterium with a broad ecology spanning disease in humans, animals and plants, but also encompassing multiple beneficial interactions. It is a plant pathogen, a toxin-producing food-poisoning agent, and causes lung infections in people with cystic fibrosis (CF). Contrasting beneficial traits include antifungal production exploited by insects to protect their eggs, plant protective abilities and antibiotic biosynthesis. We explored the genomic diversity and specialized metabolic potential of 206 B. gladioli strains, phylogenomically defining 5 clades. Historical disease pathovars (pv.) B. gladioli pv. allicola and B. gladioli pv. cocovenenans were distinct, while B. gladioli pv. gladioli and B. gladioli pv. agaricicola were indistinguishable; soft-rot disease and CF infection were conserved across all pathovars. Biosynthetic gene clusters (BGCs) for toxoflavin, caryoynencin and enacyloxin were dispersed across B. gladioli, but bongkrekic acid and gladiolin production were clade-specific. Strikingly, 13 % of CF infection strains characterized were bongkrekic acid-positive, uniquely linking this food-poisoning toxin to this aspect of B. gladioli disease. Mapping the population biology and metabolite production of B. gladioli has shed light on its diverse ecology, and by demonstrating that the antibiotic trimethoprim suppresses bongkrekic acid production, a potential therapeutic strategy to minimize poisoning risk in CF has been identified.

Genomics-Driven Discovery of a Novel Glutarimide Antibiotic from Burkholderia gladioli Reveals an Unusual Polyketide Synthase Chain Release Mechanism.

A gene cluster encoding a cryptic trans-acyl transferase polyketide synthase (PKS) was identified in the genomes of Burkholderia gladioli BCC0238 and BCC1622, both isolated from the lungs of cystic fibrosis patients. Bioinfomatics analyses indicated the PKS assembles a novel member of the glutarimide class of antibiotics, hitherto only isolated from Streptomyces species. Screening of a range of growth parameters led to the identification of gladiostatin, the metabolic product of the PKS. NMR spectroscopic analysis revealed that gladiostatin, which has promising activity against several human cancer cell lines and inhibits tumor cell migration, contains an unusual 2-acyl-4-hydroxy-3-methylbutenolide in addition to the glutarimide pharmacophore. An AfsA-like domain at the C-terminus of the PKS was shown to catalyze condensation of 3-ketothioesters with dihydroxyacetone phosphate, thus indicating it plays a key role in polyketide chain release and butenolide formation.

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A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as kadsuraol A from Kadsura longipedunculata.

Antibiotic-producing symbionts dynamically transition between plant pathogenicity and insect-defensive mutualism.

Pathogenic and mutualistic bacteria associated with eukaryotic hosts often lack distinctive genomic features, suggesting regular transitions between these lifestyles. Here we present evidence supporting a dynamic transition from plant pathogenicity to insect-defensive mutualism in symbiotic Burkholderia gladioli bacteria. In a group of herbivorous beetles, these symbionts protect the vulnerable egg stage against detrimental microbes. The production of a blend of antibiotics by B. gladioli, including toxoflavin, caryoynencin and two new antimicrobial compounds, the macrolide lagriene and the isothiocyanate sinapigladioside, likely mediate this defensive role. In addition to vertical transmission, these insect symbionts can be exchanged via the host plant and retain the ability to initiate systemic plant infection at the expense of the plant's fitness. Our findings provide a paradigm for the transition between pathogenic and mutualistic lifestyles and shed light on the evolution and chemical ecology of this defensive mutualism.

Efficient biosynthesis of ethyl (R)-4-chloro-3-hydroxybutyrate using a stereoselective carbonyl reductase from Burkholderia gladioli.

BACKGROUND: Ethyl (R)-4-chloro-3-hydroxybutyrate ((R)-CHBE) is a versatile chiral precursor for many pharmaceuticals. Although several biosynthesis strategies have been documented to convert ethyl 4-chloro-3-oxobutanoate (COBE) to (R)-CHBE, the catalytic efficiency and stereoselectivity are still too low to be scaled up for industrial applications. Due to the increasing demand of (R)-CHBE, it is essential to explore more robust biocatalyst capable of preparing (R)-CHBE efficiently. RESULTS: A stereoselective carbonyl reductase toolbox was constructed and employed into the asymmetric reduction of COBE to (R)-CHBE. A robust enzyme designed as BgADH3 from Burkholderia gladioli CCTCC M 2012379 exhibited excellent activity and enantioselectivity, and was further characterized and investigated in the asymmetric synthesis of (R)-CHBE. An economical and satisfactory enzyme-coupled cofactor recycling system was created using recombinant Escherichia coli cells co-expressing BgADH3 and glucose dehydrogenase genes to regenerate NADPH in situ. In an aqueous/octanol biphasic system, as much as 1200 mmol COBE was completely converted by using substrate fed-batch strategy to afford (R)-CHBE with 99.9 % ee at a space-time yield per gram of biomass of 4.47 mmol∙L-1∙h-1∙g DCW-1. CONCLUSIONS: These data demonstrate the promising of BgADH3 in practical synthesis of (R)-CHBE as a valuable chiral synthon. This study allows for the further application of BgADH3 in the biosynthesis of chiral alcohols, and establishes a preparative scale process for producing (R)-CHBE with excellent enantiopurity.

Differential regulation of toxoflavin production and its role in the enhanced virulence of Burkholderia gladioli.

Burkholderia gladioli is a causal agent of bacterial panicle blight and sheath/grain browning in rice in many countries. Many strains produce the yellow pigment toxoflavin, which is highly toxic to plants, fungi, animals and microorganisms. Although there have been several studies on the toxoflavin biosynthesis system of B. glumae, it is still unclear how B. gladioli activates toxoflavin biosynthesis. In this study, we explored the genomic organization of the toxoflavin system of B. gladioli and its biological functions using comparative genomic analysis between toxoflavin-producing strains (B. glumae BGR1 and B. gladioli BSR3) and a strain not producing toxoflavin (B. gladioli KACC11889). The latter exhibits normal physiological characteristics similar to other B. gladioli strains. Burkholderia gladioli KACC11889 possesses all the genes involved in toxoflavin biosynthesis, but lacks the quorum-sensing (QS) system that functions as an on/off switch for toxoflavin biosynthesis. These data suggest that B. gladioli has evolved to use the QS signalling cascade of toxoflavin production (TofI/TofR of QS → ToxJ or ToxR → tox operons) similar to that in B. glumae. However, some strains may have evolved to eliminate toxoflavin production through deletion of the QS genes. In addition, we demonstrate that the toxoflavin biosynthetic system enhances the virulence of B. gladioli. These findings provide another line of evidence supporting the differential regulation of the toxoflavin system in Burkholderia strains.

Investigation of quorum sensing-dependent gene expression in Burkholderia gladioli BSR3 through RNA-seq analyses.

The plant pathogen Burkholderia gladioli, which has a broad host range that includes rice and onion, causes bacterial panicle blight and sheath rot. Based on the complete genome sequence of B. gladioli BSR3 isolated from infected rice sheaths, the genome of B. gladioli BSR3 contains the luxI/luxR family of genes. Members of this family encode N-acyl-homoserine lactone (AHL) quorum sensing (QS) signal synthase and the LuxR-family AHL signal receptor, which are similar to B. glumae BGR1. In B. glumae, QS has been shown to play pivotal roles in many bacterial behaviors. In this study, we compared the QS-dependent gene expression between B. gladioli BSR3 and a QS-defective B. gladioli BSR3 mutant in two different culture states (10 and 24 h after incubation, corresponding to an exponential phase and a stationary phase) using RNA sequencing (RNA-seq). RNA-seq analyses including gene ontology and pathway enrichment revealed that the B. gladioli BSR3 QS system regulates genes related to motility, toxin production, and oxalogenesis, which were previously reported in B. glumae. Moreover, the uncharacterized polyketide biosynthesis is activated by QS, which was not detected in B. glumae. Thus, we observed not only common QS-dependent genes between B. glumae BGR1 and B. gladioli BSR3, but also unique QS-dependent genes in B. gladioli BSR3.

Biosynthesis of antifungal and antibacterial polyketides by Burkholderia gladioli in coculture with Rhizopus microsporus.

Fungi-bacteria interactions can impact the course of fungal infection and biotechnological use. The mucoralean fungus Rhizopus microsporus, traditionally used in food fermentations (tempe and sufu), is frequently accompanied by Burkholderia gladioli pv. cocovenenans. When producing tempe bongkrek, the bacterial contamination can lead to lethal food-related intoxications caused by the respiratory toxin bongkrekic acid. To unveil the metabolic potential of the fungus-associated bacterium, we sequenced its genome, assigned secondary metabolite biosynthesis gene clusters and monitored the metabolic profile under various growth conditions. In addition to the bongkrekic acid biosynthesis gene cluster we found gene clusters coding for the biosynthesis of toxoflavin and a complex polyketide. The orphan polyketide synthase gene cluster was activated under conditions that emulate tempe production, which enabled isolation and structure elucidation of four members of the enacyloxin family of antibiotics, out of which one is new. Moreover, we found that the fungus positively influences the growth of the bacteria and dramatically increases bongkrekic acid production in stationary culture, which inhibits the growth of the fungus. These results showcase the context-dependent formation of antifungal and antibacterial agents at the fungal-bacterial interface, which may also serve as a model for scenarios observed in mixed infections.

Identification and enzymatic characterization of acid phosphatase from Burkholderia gladioli.

BACKGROUND: The genus Burkholderia is widespread in diverse ecological niches, the majority of known species are soil bacteria that exhibit different types of non-pathogenic interactions with plants. Burkholderia species are versatile organisms that solubilize insoluble minerals through the production of organic acids, which increase the availability of nutrients for the plant. Therefore these bacteria are promising candidates for biotechnological applications. RESULTS: Burkholderia sp. (R 3.25 isolate) was isolated from agricultural soil in Ponta Grossa-PR-Brazil and identified through analysis of the 16S rDNA as a strain classified as Burkholderia gladioli. The expression of membrane-bound acid phosphatase (MBAcP) was strictly regulated with optimal expression at a concentration of phosphorus 5 mM. The apparent optimum pH for the hydrolysis of p-nitrophenylphosphate (PNPP) was 6.0. The hydrolysis of PNPP by the enzyme exhibited a hyperbolic relationship with increasing concentration of substrate and no inhibition by excess of substrate was observed. Kinetic data revealed that the hydrolysis of PNPP exhibited cooperative kinetics with n = 1.3, Vm = 113.5 U/mg and K0.5 = 65 µM. The PNPPase activity was inhibited by vanadate, p-hydroxymercuribenzoate, arsenate and phosphate, however the activity was not inhibited by calcium, levamisole, sodium tartrate, EDTA, zinc, magnesium, cobalt, ouabain, oligomycin or pantoprazol. CONCLUSION: The synthesis of membrane-bound non-specific acid phosphatase, strictly regulated by phosphate, and its properties suggest that this bacterium has a potential biotechnological application to solubilize phosphate in soils with low levels of this element, for specific crops.

Comparative analysis of two emerging rice seed bacterial pathogens.

Seed sterility and grain discoloration limit rice production in Colombia and several Central American countries. In samples of discolored rice seed grown in Colombian fields, the species Burkholderia glumae and B. gladioli were isolated, and field isolates were compared phenotypically. An artificial inoculation assay was used to determine that, although both bacterial species cause symptoms on rice grains, B. glumae is a more aggressive pathogen, causing yield reduction and higher levels of grain sterility. To identify putative virulence genes differing between B. glumae and B. gladioli, four previously sequenced genomes of Asian and U.S. strains of the two pathogens were compared with each other and with two draft genomes of Colombian B. glumae and B. gladioli isolates generated for this study. Whereas previously characterized Burkholderia virulence factors are highly conserved between the two species, B. glumae and B. gladioli strains are predicted to encode distinct groups of genes encoding type VI secretion systems, transcriptional regulators, and membrane-sensing proteins. This study shows that both B. glumae and B. gladioli can threaten grain quality, although only one species affects yield. Furthermore, genotypic differences between the two strains are identified that could contribute to disease phenotypic differences.

Heat stable antimicrobial activity of Burkholderia gladioli OR1 against clinical drug resistant isolates.

BACKGROUND & OBJECTIVES: Drug resistant microbes are a serious challenge to human health. During the search for novel antibiotics/inhibitors from the agricultural soil, a bacterial colony was found to inhibit the growth of clinical isolates including Staphylococcus (resistant to amikacin, ciprofloxacin, clindamycin, clinafloxacin, erythromycin, gentamicin and methicillin) and Candida (resistant to fluconazole and itraconazole). The culture was identified as Burkholderia gladioli and produced at least five different antimicrobial compounds which were highly stable at high temperature (121 o C) and in the broad pH range (3.0-11.0). We report here the antimicrobial activity of B. gladioli against drug resistant bacterial pathogens. METHODS: The bacterial culture was identified using morphological, biochemical and 16S rRNA gene sequencing techniques. The antimicrobial activity of the identified organism against a range of microbial pathogens was checked by Kirby-Bauer's disc diffusion method. The antimicrobial compounds in the cell free supernatant were chloroform-extracted and separated by thin layer chromatography (TLC). RESULTS: B. gladioli OR1 exhibited broad spectrum antimicrobial activity against drug resistant clinical isolates belonging to various genera of bacteria (Staphylococcus, Enterobacter, Enterococcus, Acinetobacter and Citrobacter) and a fungus (Candida). Based on TLC profile and bioautography studies, the chloroform extract of B. gladioli OR1 consisted of at least three anti-staphylococcal and two anti-Candida metabolites. The antimicrobial activity was heat stable (121 o C/20 min) as well as pH stable (3.0-11.0). INTERPRETATION & CONCLUSIONS: The bacterial soil isolate, B. gladioli OR1 possessed the ability to kill various drug resistant bacteria and a fungus. This organism produced many antimicrobial metabolites which might have the potential to be used as antibiotics in future.

Complete genome sequence of Burkholderia gladioli BSR3.

We report the complete genome sequence of Burkholderia gladioli BSR3, isolated from a diseased rice sheath in South Korea.