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In order to evaluate the feasibility of using Burkholderia sp. Y4 as a cadmium （Cd）-reducing bacterial agent in contaminated wheat fields， the changes in the rhizosphere soil microbial community and Cd available state， as well as the content and transport characteristics of Cd in the wheat root， basal node， internode， and grain under the treatment of strain Y4 were tested using microbial high-throughput sequencing， step-by-step extraction， subcellular distribution， and occurrence analyses. The results showed that root application of strain Y4 significantly reduced the root and grain Cd content of wheat by 7.7% and 30.3%， respectively， compared with that in the control treatment. The Cd content and Cd transfer factor results in wheat vegetative organs showed that strain Y4 reduced the Cd transfer factor from basal node to internode by 79.3%， and Cd content in the wheat internode stem also decreased by 50.9%. The study of Cd occurrence morphology showed that strain Y4 treatment increased the proportion of residual Cd in roots and basal ganglia， decreased the contents of inorganic and water-soluble Cd in roots， and increased the content of residual Cd in basal ganglia. Further examination of the subcellular distribution of Cd showed that the Cd content in root cell walls and basal ganglia cell fluid increased by 21.3% and 98.2%， respectively， indicating that the Cd fixation ability of root cell walls and basal ganglia cell fluid was improved by the strain Y4 treatment. In the rhizosphere soil， it was found that the microbial community structure was changed by strain Y4 application. Under the Y4 treatment， the relative abundance of Burkholderia increased from 9.6% to 11.5%， whereas that of Acidobacteriota decreased. Additionally， the relative abundance of Gemmatimonadales， Pseudomonadales， and Chitinophagales were also increased by strain Y4 treatment. At the same time， the application of strain Y4 increased the pH value of rhizosphere soil by 8.3%. The contents of exchangeable Cd， carbonate-bound Cd， and iron-manganese oxide-bound Cd in the soil decreased by 44.4%， 21.7%， and 15.9%， respectively， whereas the proportion of residual Cd reached 53.6%. Root application of strain Y4 increased the contents of nitrate nitrogen and ammonium nitrogen in the soil by 22.0% and 21.4%， respectively， and the contents of alkaline nitrogen also increased to a certain extent. In conclusion， the root application of strain Y4 not only improved soil nitrogen availability but also inhibited Cd transport and accumulation from contaminated soil to wheat grains in a "two-stage" manner by reducing Cd availability in rhizosphere soil and improving Cd interception and fixation capacity of wheat roots and basal nodes. Therefore， Burkholderia Y4 has application potential as a Cd-reducing and growth-promoting agent in wheat.

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Salt stress is one of the most serious abiotic stresses leading to reduced agricultural productivity. Polysaccharides from seaweed have been used as biostimulants to promote crop growth and improve plant resistance to abiotic stress. In this study, PGPR strain Burkholderia sp. BK01 was isolated from the rhizosphere of wheat, and it was characterized for phosphorus (Pi) dissolution, indole-3-acetic acid (IAA) production, ammonia (NH3) and exopolysaccharides (EPS). In particular, strain BK01 can efficiently produce extracellular polysaccharide with a yield of 12.86 g/L, using sorbitol as carbon source. BK01 EPS was identified as an heteropolysaccharide with Mw 3.559 × 106 Da, composed of (D)-galactose (75.3%), (D)-glucose (5.5%), (L)-rhamnose (5.5%), (D)-galactouronic acid (4.9%) and (D)-glucuronic acid (8.8%). The present work aims to highlight the effect of the BK01 EPS on growth and biochemical changes in Arabidopsis thaliana under salt stress (100 mM). The purified BK01 EPS at a concentration of 100 mg/L efficiently promoted the growth of plants in pot assays, improved the chlorophyll content, enhanced the activities of SOD, POD and CAT, and decreased the content of MDA. This results suggested that the polysaccharides produced by PGPR strain Burkholderia sp. BK01 can be used as biostimulants to promote plant growth and improve plant resistance to salt stress.

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Aniline aerofloat (AAF) is a refractory organic pollutant in floatation wastewater. Little information is currently available on its biodegradation. In this study, a novel AAF-degrading strain named Burkholderia sp. WX-6 was isolated from mining sludge. The strain could degrade more than 80% of AAF at different initial concentrations (100-1000 mg/L) within 72 h. AAF degrading curves were fitted well with the four-parameter logistic model (R2 >0.97), with the degrading half-life ranging from 16.39 to 35.55 h. This strain harbors metabolic pathway for complete degradation of AAF and is resistant to salt, alkali, and heavy metals. Immobilization of the strain on biochar enhanced both tolerance to extreme conditions and AAF removal, with up to 88% of AAF removal rate in simulated wastewater under alkaline (pH 9.5) or heavy metal pollution condition. In addition, the biochar-immobilized bacteria removed 59.4% of COD in the wastewater containing AAF and mixed metal ions within 144 h, significantly (P < 0.05) higher than those by free bacteria (42.6%) and biochar (48.2%) only. This work is helpful to understand AAF biodegradation mechanism and provides viable references for developing practical biotreatment technique of mining wastewater.

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The acephate-degrading microbes that are currently available are not optimal. In this study, Burkholderia sp. A11, an efficient degrader of acephate, presented an acephate-removal efficiency of 83.36% within 56 h (100 mg·L-1). The A11 strain has a broad substrate tolerance and presents a good removal effect in the concentration range 10-1600 mg·L-1. Six metabolites from the degradation of acephate were identified, among which the main products were methamidophos, acetamide, acetic acid, methanethiol, and dimethyl disulfide. The main degradation pathways involved include amide bond breaking and phosphate bond hydrolysis. Moreover, strain A11 successfully colonized and substantially accelerated acephate degradation in different soils, degrading over 90% of acephate (50-200 mg·kg-1) within 120 h. 16S rDNA sequencing results further confirmed that the strain A11 gradually occupied a dominant position in the soil microbial communities, causing slight changes in the diversity and composition of the indigenous soil microbial community structure.

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N-Acetyl-(R)-ß-phenylalanine acylase is an enzyme that hydrolyzes the amide bond of N-acetyl-(R)-ß-phenylalanine to produce enantiopure (R)-ß-phenylalanine. In previous studies, Burkholderia sp. AJ110349 and Variovorax sp. AJ110348 were isolated as (R)-enantiomer-specific N-acetyl-(R)-ß-phenylalanine acylase-producing organisms and the properties of the native enzyme from Burkholderia sp. AJ110349 were characterized. In this study, structural analyses were carried out in order to investigate the structure-function relationships of the enzymes derived from both organisms. The recombinant N-acetyl-(R)-ß-phenylalanine acylases were crystallized by the hanging-drop vapor-diffusion method under multiple crystallization solution conditions. The crystals of the Burkholderia enzyme belonged to space group P41212, with unit-cell parameters a = b = 112.70-112.97, c = 341.50-343.32 Å, and were likely to contain two subunits in the asymmetric unit. The crystal structure was solved by the Se-SAD method, suggesting that two subunits in the asymmetric unit form a dimer. Each subunit was composed of three domains, and they showed structural similarity to the corresponding domains of the large subunit of N,N-dimethylformamidase from Paracoccus sp. strain DMF. The crystals of the Variovorax enzyme grew as twinned crystals and were not suitable for structure determination. Using size-exclusion chromatography with online static light-scattering analysis, the N-acetyl-(R)-ß-phenylalanine acylases were clarified to be dimeric in solution.

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Peanut stem rot caused by Sclerotium rolfsii Sacc. is the most common disease of peanut worldwide and has become increasingly serious in recent years. This study is aimed at obtaining peanut endophytic bacteria with high antagonistic/protective effects against peanut stem rot. In total, 45 bacterial strains were isolated from healthy peanut plants from a severely impacted area. Of these, 6 exhibited antagonistic activity against S. rolfsii, including F-1 and R-11 with the most robust activity with an inhibition zone width of 20.25 and 15.49 mm, respectively. These two were identified as Bacillus sp. and Burkholderia sp., respectively, based on morphological, physiological, and biochemical characteristics and 16S rDNA sequencing. To the best of our knowledge, this is the first study to report the Burkholderia sp. antagonistic effect on S. rolfsii as a biological control agent for peanut stem rot. Their culture filtrates potently inhibited the hyphal growth, sclerotial formation, and germination of S. rolfsii. Also, the strain-produced volatile compounds inhibited the fungal growth. Pot experiments showed that F-1 and R-11 significantly reduced the peanut stem rot disease with the efficacy of 77.13 and 64.78%, respectively, which was significantly higher compared with carbendazim medicament (35.22%; P < 0.05). Meanwhile, F-1 and R-11 improved the activity of plant defense enzymes such as phenylalaninase (PAL), polyphenol oxidase (PPO), and peroxidase (POD) enhancing the systemic resistance of the peanut plants. This study demonstrated that Bacillus sp. F-1 and Burkholderia sp. R-11, with a strong antagonistic effect on S. rolfsii, can be potential biocontrol agents for peanut stem rot.

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Burkholderia sp. SP4, isolated from agricultural soils, has a high capability of degrading di-2-ethylhexyl-phthalate (DEHP). It degrades up to 99% of DEHP (300 mg l-1) in minimal salt (MS) media within 48 h without adding additionally auxiliary carbon source. The optimal conditions for SP4 to degrade DEHP are determined to be at 35 °C and pH 6.0. Supplementation of glucose (3.0 g l-1), sodium dodecyl sulfate (SDS) (0.2%), peptone (0.5 g l-1), or non-ionic surfactant Brij 35 (0.2%, 0.5% or 1%) in MS-DEHP media increases the DEHP degradation activity. Furthermore, kinetic analyses for DEHP degradation by SP4 reveals that it is a first-order reaction, and the half-life analyses also demonstrates that SP4 has a better degradative activity compared to other previously identified microbes. By means of HPLC-ESI-QTOF-MS, the metabolic intermediates of DEHP are identified for SP4, which include mono-2-ethylhexylphthalate (MEHP), mono-butyl phthalate (MBP), phthalic acid (PA), salicylic acid (SA), and 4-oxo-hexanoic acid. The presence of SA indicates that SP4 can consume DEHP using a dual biodegradation pathway diverged from the isomeric products of benzoate. Taken together, our study identifies a resilient DEHP-degradable bacterium and characterizes a novel degradation pathway for DEHP biodegradation. We plan to build on this finding in the context of removing DEHP from various environments.

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In order to investigate the effects of Burkholderia sp. Y4 on rice seedlings under cadmium (Cd) stress, seed germination and vermiculite culture experiments were conducted using low Cd-accumulation xiangzaoxian 24 (X24) and high Cd-accumulation Tyou 705 (T705) varieties. The effects of Burkholderia sp. Y4 on rice growth, oxidative damage caused by Cd, and Cd accumulation were studied. Additionally, the Cd2+ flux rates in the elongation zone of rice roots under Burkholderia sp. Y4 application were detected using non-invasive micro-test technology. Burkholderia sp. Y4 alleviated the inhibition effect of Cd on rice seed germination by 13.8%. After inoculation with Burkholderia sp. Y4 for 7 d, the length of rice roots and buds increased by 83.3% and 12.2%, and their dry weight increased by 56.8% and 12.5%, respectively; those in the 10 d Y4 inoculation group increased by 28.6% and 20.0% in length and by 113.2% and 46.0% in dry weight, respectively. Burkholderia sp. Y4 inoculation also alleviated rice oxidative stress damage caused by Cd. The application of strain Y4 significantly reduced the content of the oxidative damage product malondialdehyde (MDA) in the shoots and roots of rice seedlings by 21.5% and 16.9%, respectively. Under Burkholderia sp. Y4 inoculation, the significant changes in antioxidant enzyme SOD and CAT activities caused by Cd stress disappeared in rice roots; those in shoots also decreased from 176.9% and 74.8% to 53.3% and 21.5%, respectively. Conversely, Burkholderia sp. Y4 inhibited Cd uptake by rice seedlings with different genotypes, including the low Cd-accumulation variety X24 and high Cd-accumulation variety T705. The root application of strain Y4 significantly reduced Cd accumulation in the shoots and roots of rice seedlings by 79.2% and 62.7% in T705 and by 57.3% and 24.1% in X24, respectively. The Cd2+ flux rate of high Cd-accumulation variety T705 was significantly higher than that of low Cd-accumulation variety X24. Under Burkholderia sp. Y4 inoculation, the yellow membrane was formed on the root surface of rice seedlings, and the Cd2+ flux rate in the elongation zone of T705 and X24 roots decreased by 36.0% and 35.0% in 3-day-old seedlings, as well as by 44.6% and 24.9% in 10-day-old seedlings, respectively. In conclusion, Burkholderia sp. Y4 inoculation inhibited the toxic effects of Cd on rice seedling growth through alleviating oxidative stress and damage caused by Cd. Furthermore, the root application of Burkholderia sp. Y4 effectively decreased the Cd2+ flux rate in the elongation zone of roots to inhibit the Cd uptake and accumulation in roots and shoots of rice seedlings. This study provides theoretical basis and data support for the application of Burkholderia sp. Y4 as a Cd-reducing and growth-promoting agent for rice in contaminated farmland.

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Burkholderia sp. SSG is a potent biological control agent. Even though its survival on the leaf surface declined rapidly, SSG provided extended, moderate plant protection from a broad spectrum of pathogens. This study used Arabidopsis Col-0 and its mutants, eds16-1, npr1-1, and pad4-1 as model plants and compared treated plants with non-treated controls to elucidate whether SSG triggers plant defense priming. Only eds16-1 leaves with SSG became purplish, suggesting the involvement of salicylic acid (SA) in SSG-induced priming. cDNA sequencing of Col-0 plants and differential gene expression analysis identified 120 and 119 differentially expressed genes (DEGs) at 6- and 24-h post-treatment (hpt) with SSG, respectively. Most of these DEGs encoded responses to biotic and abiotic stimuli or stresses; four DEGs had more than two isoforms. A total of 23 DEGs were shared at 6 and 24 hpt, showing four regulation patterns. Functional categorization of these shared DEGs, and 44 very significantly upregulated DEGs revealed that SSG triggered various defense priming mechanisms, including responses to phosphate or iron deficiency, modulation of defense-linked SA, jasmonic acid, ethylene, and abscisic acid pathways, defense-related gene regulation, and chromatin modification. These data support that SSG is an induced systemic resistance (ISR) trigger conferring plant protection upon pathogen encounter.

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Aflatoxin is a secondary metabolite produced by Aspergillus fungi and presents a major food safety concern globally. Among the available methods for prevention and control of aflatoxin, the application of antifungal bacteria has gained favor in recent years. An endophytic bacterium MS455, isolated from soybean, exhibited broad-spectrum antifungal activity against economically important pathogens, including Aspergillus flavus. MS455 was identified as a strain of Burkholderia based on genomic analysis. Random and site-specific mutations were used in discovery of the genes that share high homology to the ocf gene cluster of Burkholderia contaminans strain MS14, which is responsible for production of the antifungal compound occidiofungin. RNA sequencing analysis demonstrated that ORF1, a homolog to the ambR1 LuxR-type regulatory gene, regulates occidiofungin biosynthesis in MS455. Additionally, 284 differentially expressed genes, including 138 upregulated and 146 downregulated genes, suggesting that, in addition to its role in occidiofungin production, ORF1 is involved in expression of multiple genes, especially those involved in ornibactin biosynthesis. Plate bioassays showed the growth of A. flavus was significantly inhibited by the wild-type strain MS455 as compared with the ORF1 mutant. Similarly, corn kernel assays showed that growth of A. flavus and aflatoxin production were reduced significantly by MS455 as compared with buffer control and the ORF1 mutant. Collectively, the results demonstrated that production of occidiofungin is essential for antifungal activity of the endophytic bacterium MS455. This research has provided insights about antifungal mechanisms of MS455 and development of biological approaches to prevent aflatoxin contamination in plant production.

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Heavy metal-resistant siderophore-producing bacteria (SPB) with plant growth-promoting traits can assist in phytoremediation of heavy metal-contaminated soil. We isolated siderophore-producing bacteria from Pb and Zn mine soil in Shangyu, Zhejiang, China. The isolate with the highest siderophore production, strain SX9, was identified as Burkholderia sp. Burkholderia sp. SX9 produced catecholate-type siderophore, with the highest production at a pH range of 6.0 to 8.0, a temperature range of 20 to 30 °C and NaCl concentration below 2%. Siderophore production was highest without Fe3+ and became gradually lower with increasing Fe3+ concentration. Minimal inhibitory concentrations (MIC) of Pb2+, Zn2+, Cu2+, and Cd2+ were 4000, 22000, 5000, and 2000 µmol L-1, respectively. The strain had a strong metal solubilization ability: the contents of Cu2+, Zn2+, and Cd2+ in the supernatant were 47.4%, 133.0%, and 35.4% higher, respectively, in strain SX9-inoculated cultures than in the not inoculated controls. The siderophore produced by strain SX9 could combine with Fe3+, Zn2+, and Cd2+ with good effectiveness. The plant growth-promoting traits of the strain included indole acetic acid (IAA) production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, and phosphate solubilization capability. Compared to the uninoculated growth medium and SX9 culture supernatant, the germination rate of Lolium perenne seeds was higher when inoculated with strain SX9 culture. In the experiment of seed germination, adding bacterial culture or supernatant could alleviate the toxicity of heavy metals to L. perenne seed germination. Under Cu2+ and Zn2+ stress, strain SX9 promoted the germination rate. Taken together, Burkholderia sp. SX9 had properties beneficial in the microbial enhancement of phytoremediation of soil contaminated with heavy metals.

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Burkholderia sp. Nafp2/4-1b (=SARCC-3049) is a plant growth-promoting rhizobacteria (PGPR) initially isolated from the rhizosphere of pristine grassland in South Africa, and its ability to enhance growth was previously evaluated on maize (Zea mays L.). Here, the bacterium was tested with the aim of investigating its role in improving the nodulation and growth of the forage legume lucerne (Medicago sativa L.) when it is co-inoculated with the rhizobial symbionts of this legume in the glasshouse. When the co-inoculation resulted in a statistically significant (P = 0·05) increase in the number of nodules and improved plant biomass compared with single inoculation, we sequenced and analysed its genome to gain a better understanding of the genetic determinants responsible for the observed PGPR traits. The Illumina HiSeq 2500-sequenced genome resulted in 92 scaffolds, with an N50 of 322 407 bp, a total draft genome size of 7 788 045 bp and GC content of 66·2%. Analysis of the genome sequence confirmed the presence of a number of essential genes that code for various PGPR traits. The main plant beneficial genes associated with PGPR traits in Burkholderia sp. Nafp2/4-1b include pyoverdine siderophores biosynthesis gene (PvdF); acdS that codes for 1-aminocyclopropane-1-carboxylate (ACC) deaminase; the tryptophan synthase genes involved in auxin biosynthesis (TSA1, TSB1) and the pqqABCDE operon related to phosphate solubilization. This study generated valuable information on the potential of the PGPR Burkholderia sp. strain Nafp2/4-1b as an effective commercial inoculant, which warrants further formulation and field application studies before developing it into a low cost, environmentally safe and effective biofertilizer.

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4-Nitrophenol, a priority pollutant, is degraded by Gram-positive and Gram-negative bacteria via 1,2,4-benzenetriol (BT) and hydroquinone (HQ), respectively. All enzymes involved in the two pathways have been functionally identified. So far, all Gram-negative 4-nitrophenol utilizers are from the genera Pseudomonas and Burkholderia. But it remains a mystery why pnpG, an apparently superfluous BT 1,2-dioxygenase-encoding gene, always coexists in the catabolic cluster (pnpABCDEF) encoding 4-nitrophenol degradation via HQ. Here, the physiological role of pnpG in Burkholderia sp. strain SJ98 was investigated. Deletion and complementation experiments established that pnpG is essential for strain SJ98 growing on 4-nitrocatechol rather than 4-nitrophenol. During 4-nitrophenol degradation by strain SJ98 and its two variants (pnpG deletion and complementation strains), 1,4-benzoquinone and HQ were detected, but neither 4-nitrocatechol nor BT was observed. When the above-mentioned three strains (the wild type and complementation strains with 2,2'-dipyridyl) were incubated with 4-nitrocatechol, BT was the only intermediate detected. The results established the physiological role of pnpG that encodes BT degradation in vivo. Biotransformation analyses showed that the pnpA-deleted strain was unable to degrade both 4-nitrophenol and 4-nitrocatechol. Thus, the previously characterized 4-nitrophenol monooxygenase PnpASJ98 is also essential for the conversion of 4-nitrocatechol to BT. Among 775 available complete genomes for Pseudomonas and Burkholderia, as many as 89 genomes were found to contain the putative pnpBCDEFG genes. The paucity of pnpA (3 in 775 genomes) implies that the extension of BT and HQ pathways enabling the degradation of 4-nitrophenol and 4-nitrocatechol is rarer, more recent, and likely due to the release of xenobiotic nitroaromatic compounds. IMPORTANCE An apparently superfluous gene (pnpG) encoding BT 1,2-dioxygenase is always found in the catabolic clusters involved in 4-nitrophenol degradation via HQ by Gram-negative bacteria. Our experiments reveal that pnpG is not essential for 4-nitrophenol degradation in Burkholderia sp. strain SJ98 but instead enables its degradation of 4-nitrocatechol via BT. The presence of pnpG genes broadens the range of growth substrates to include 4-nitrocatechol or BT, intermediates from the microbial degradation of many aromatic compounds in natural ecosystems. In addition, the existence of pnpCDEFG in 11.6% of the above-mentioned two genera suggests that the ability to degrade BT and HQ simultaneously is ancient. The extension of BT and HQ pathways including 4-nitrophenol degradation seems to be an adaptive evolution for responding to synthetic nitroaromatic compounds entering the environment since the industrial revolution.

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BACKGROUND: Burkholderia sp. SSG is a bacterial endophyte isolated from boxwood leaves showing a resistant response to infection by the boxwood blight pathogen Calonectria pseudonaviculata. SSG acted as a protective and curative biocontrol agent for boxwood blight and as a bio-sanitizer of disease inoculum in the field. Many gene clusters involved in antibiotic production and plant growth promotion (PGP) were found in the genome, giving this endophyte great application potential as a treatment for plant protection. However, the PGP features have not been documented. This study investigated the plant growth promotion activity of SSG in boxwood. METHODS: To determine whether SSG is a plant growth promoting bacterium, four PGP traits, auxin and siderophore production, nitrogen fixation and phosphate solubilization, were examined in the laboratory with colorimetric or agar plate assays. The plant growth promoting activity of SSG was tested on three boxwood varieties characterized by slow, intermediate and fast growth rates, namely Justin Brouwers, Buddy and Winter Gem, respectively. These plants were drenched with an SSG cell suspension or water and washed plant weight was compared before and after treatment to determine growth changes after 10 months. RESULTS: The SSG culture was sustainable on nitrogen free media, suggesting that SSG may fix atmospheric nitrogen. It was also a strong phosphate solubilizer and a potent siderophore and indole-3-acetic acid (IAA) producer. Significant growth promotion was observed on boxwood cultivars Justin Brouwers, Buddy and Winter Gem 10 months after plant roots were drenched with SSG cells. The growth rate of treated plants was 76.1, 58.3, and 37.3% higher than that of the control, respectively. The degree of growth promotion was significantly different among plant varieties, notably more pronounced with the slow and intermediate growers. This study demonstrates that the SSG bacterium has multiple PGP traits and is a prospective plant biofertilizer.

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The present study aims to investigate the endophytic bacteria, isolated from the roots of Taxus wallichiana Zucc. and designated as GBPI_TWL and GBPI_TWr, for their plant growth promoting traits. On the basis of phenotypic and molecular characters, the bacteria are identified as species of Burkholderia and Enterobacter, respectively. Both the bacteria could grow at wide range of temperature (5-40 °C, opt=25 °C) and pH (1.5-11.0, opt = 6-7), and tolerate salt concentration up to 12 %. While both the bacterial endophytes possessed siderophore, HCN, ammonia, and salicyclic acid producing abilities, GBPI_TWL showed IAA and ACC deaminase producing abilities, in addition. The bacteria were found to be potential phosphate solubilizers at wide temperature range (5-35 °C) by utilizing tricalcium, iron, and aluminium phosphate as substrate. Further, the bacterial isolates produced phytase and phosphatase enzymes in both acidic and alkaline conditions. Positive influence of the inoculation with the bioformulations of GBPI_TWL and GBPI_TWr was demonstrated on the test crops namely rice (Oryza sativa) and soybean (Glycine max) with respect to physico-chemical and plant growth parameters in net house experiments. The study will have implications in developing bioformulations, specifically for low temperature environments, in view of environmental sustainability.

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4-Hydroxy-3-methyl-2(1H)-quinolone (1), a molecule known for a long time and recently discovered from a Brassicaceae plant Isatis tinctoria without providing sufficient evidence to support the structure, was isolated from a fermentation extract of Burkholderia sp. 3Y-MMP isolated from a soil by a Zn2+ enrichment culture. Detailed spectroscopic analyses by MS and NMR, combined with 13C chemical shift comparison with literature values of the related compounds and a synthetic preparation of 1, allowed its first full NMR characterization and identification of 2-quinolone but not 2-quinolinol (2) as the preferred tautomer for this heterocyclic system. While the metal-chelating activity was negligible, compound 1 at 10 µM, a concentration lower than that in liquid production cultures, quenched hydroxy radical-induced chemiluminescence emitted by luminol by 86%. Because some Burkholderia species are pathogenic to plants and animals, the above result suggests that 1 is a potential antioxidant to counteract reactive oxygen species-based immune response in the host organisms.

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Burkholderia sp. strain SSG is a boxwood endophyte with potent antagonistic activities against a variety of plant pathogens. Here we present its complete genome sequence that is 8.6 Mb long with a GC content of 66.9%, 10,209 predicted protein-coding sequences, and 866 secondary metabolism gene clusters. Many of these genes and clusters involve antibiosis and other antagonistic activities against plant pathogens and insect pests as well as plant growth promoting traits but none for the Burkholderia cepacia epidemic strain marker. This genome sequence supports SSG as a potent biocontrol agent and source of other biotechnological applications.

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Microbial tolerance to phenolic pollutants is the key to their efficient biodegradation. However, the metabolic mechanisms that allow some microorganisms to adapt to high phenol concentrations remain unclear. In this study, to reveal the underlying mechanisms of how Burkholderia sp. adapt to high phenol concentrations, the strain's tolerance ability and time-course transcriptome in combination with cell phenotype were evaluated. Surprisingly, Burkholderia sp. still grew normally after a long adaptation to a relatively high phenol concentration (1500 mg/L) and exhibited some time-dependent changes compared to unstressed cells prior to the phenol addition. Time-course transcriptome analysis results revealed that the mechanism of adaptations to phenol was an evolutionary process that transitioned from tolerance to positive degradation through precise gene regulation at appropriate times. Specifically, basal stress gene expression was upregulated and contributed to phenol tolerance, which involved stress, DNA repair, membrane, efflux pump and antioxidant protein-coding genes, while a phenol degradation gene cluster was specifically induced. Interestingly, both the catechol and protocatechuate branches of the ß-ketoadipate pathway contributed to the early stage of phenol degradation, but only the catechol branch was used in the late stage. In addition, pathways involving flagella, chemotaxis, ATP-binding cassette transporters and two-component systems were positively associated with strain survival under phenolic stress. This study provides the first insights into the specific response of Burkholderia sp. to high phenol stress and shows potential for application in remediation of polluted environments. KEY POINTS: • Shock, DNA repair and antioxidant-related genes contributed to phenol tolerance. • ß-Ketoadipate pathway branches differed at different stages of phenol degradation. • Adaptation mechanisms transitioned from negative tolerance to positive degradation.

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Microbial remediation of heavy metal-polluted soil is a commonly used method. Burkholderia sp. Y4, isolated from cadmium (Cd)-contaminated rice rhizosphere soil, was investigated for its direct and indirect effects on Cd accumulation in rice by SEM-EDS, FITR and sequencing analysis of the soil bacterial community. Burkholderia sp. Y4 inoculation reduced Cd accumulation in rice roots, rachises, and grains of the two rice varieties T705 and X24 and increased levels of essential elements, especially Fe and Mn, which competitively inhibited Cd transport through cationic channels. Living Burkholderia sp. Y4 cells, rather than non-living ones, could colonize the surface of rice roots and accumulated more Cd through direct biosorption associated with -CO and -NH/-CO bonds of amino acids and proteins. The results of soil microbial community showed that the colonization of externally added Burkholderia sp. Y4 could be maintained over some time to impact the total rhizospheric environment. Burkholderia sp. Y4 inoculation decreased the abundance of microbes involved in the iron cycle (Acidobacteria) as well as of those mediating the transformation of ammonium nitrogen to nitrate nitrogen (Nitrosomonadaceae and Nitrospira). So Burkholderia sp. Y4 inoculation may indirectly change the availability of micronutrients and Cd in rice rhizosphere soil through iron-nitrogen coupled cycles to increase essential nutrient uptake and inhibit Cd accumulation in rice by preferential Cd-biosorption. Therefore, Burkholderia sp. Y4 is potentially suitable for the bioremediation of Cd-contaminated paddy soil.

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The endophyte Burkholderia sp. WYAT7 isolated from the medicinal plant Artemisia nilagirica (Clarke) Pamp. was analyzed for its ability to produce biosurfactant. The evaluation of biosurfactant production was conducted using different screening methods which confirmed the presence of biosurfactant in the culture supernatant. CTAB- methylene blue agar plate method was used for the screening of glycolipid biosurfactant production. The biosurfactant produced by the bacteria effectively metabolized hydrocarbons present in the bacterial culture media. Fourier transform infrared spectroscopic (FTIR) analysis of biosurfactant provided the details regarding OH stretching, stretching vibrations of acyl chain, CO stretching, stretching vibrations of ether and vibrations of glycosidic linkages in the biosurfactant. The stretching vibrations of glycosidic linkage in the fingerprint regions of FTIR spectrum (1200 cm-1 to 800 cm-1 regions) confirms that the biosurfactant produced was a glycolipid. The GC-MS analysis confirmed the methyl and ethyl esters of fatty acids. The biosurfactant from the bacteria exhibited antibacterial activity against bacterial pathogens such as Pseudomonas aeruginosa (MTCC 2453), Escherichia coli (MTCC 1610), Salmonella paratyphi and Bacillus subtilis. The glycolipid biosurfactant had antibiofilm activity as evidenced in Staphylococcus aureus (MTCC 1430). All these results indicated the beneficial effect of the biosurfactant in plant-endophyte interactions. The properties exhibited by the biosurfactant suggest that it can be exploited commercially for the production of novel antibiotics.

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