Burkholderia Tropica Research Articles

Designing and validation of specific primers for the quantitative detection of bacteria in sugarcane inoculant.

Endophytic diazotrophic plant growth-promoting bacteria Herbaspirillum rubrisubalbicans (HCC103), Herbaspirillum seropedicae (HRC54), Paraburkholderia tropica (Ppe8T), Gluconacetobacter diazotrophicus (Pal5T), and Nitrospirillum amazonense (CBAmC) have been used as inoculants for sugarcane. The genome sequences of these strains were used to design a set of specific primers for the real-time PCR (qPCR) assay. Primer specificity was confirmed by conventional PCR using the genomic DNAs of 25 related bacterial species and the five target strains. The qPCR assays were conducted using root and shoot samples from two sugarcane varieties (RB867515 and RB92579). These samples were collected both with and without inoculation, using the target strains specified in this study. The sugarcane plants were grown in a greenhouse, utilizing a substrate composed of sterile sand and vermiculite in a 2:1 ratio, for a duration of 55days. The primers designed for this study successfully amplified target DNA fragments from each of the bacterial species, enabling their differentiation at the species level. The total bacterial population present in the sugarcane quantified using qPCR was on average 105.2 cells g-1 of fresh tissue. Across both evaluated varieties, it was observed that the population of inoculated bacteria tended to decrease over time and became more concentrated in the sugarcane roots compared to the aerial parts. The qPCR results suggest that both the host and the microbes influence the endophytic population and the bacterial number decreases with plant age.

Survival of five diazotrophic bacterial strains in different substrates used in sugarcane seedling propagation.

An inoculant containing selected bacterial strains can be easily applied during the nursery please process, but in this case, substrate composition can affect its survival and, in consequence, bacterial colonization. The aim of this study was to evaluate the survival of five diazotrophic bacterial strains/species applied individually on 13 different substrates used in sugarcane seedling nurseries considering an active population higher than 105 cells g-1. In addition, one experiment was performed using two commercial substrates, coconut fiber, and Multiplant™, inoculated or not with a mixture of five bacterial strains to evaluate plant growth after 30days. These strains are combined inoculants selected for sugarcane acting as plant growth promoters. Bacterial counts were determined every seven days using the Most Probable Number technique with four different semi-solid N-free media specific for each strain tested over 35days. The survival order, independent of the substrate tested, was: Paraburkholderia tropica Pt-PPe8T > Nitrospirillum amazonense Na-CBAMc > Herbaspirillum seropedicae Hs-HRC54 = H. rubrisubalbicans Hr-HCC103 > Gluconacetobacter diazotrophicus Gd-PAL5T. All tested substrates influenced the bacterial survival, especially after 21days of incubation. The population size can be partially controlled by the substrate pH and stimulated by the addition of slow-release fertilizer. Besides the differences in the bacterial population present in the two commercial substrates, plant growth was found to be stimulated by the inoculated bacteria, depending on the substrate and its sugarcane cultivar tested. The selection of a substrate used to produce new plantlets of sugarcane can contribute to bacterial survival and improve bacterial colonization.

Paraburkholderia tropica PKI7 and Kosakonia arachidis PKI8: Two newly reported tannase producing bacteria isolated from forest soil and study of their tannase producing potentiality

Tannins are the polyphenolic secondary metabolites of plants and having antimicrobial properties due to their protein precipitation abilities and other toxic effects towards microbes. However, with the help of an inducible enzyme called tannase, a variety of microbes including bacteria can resist tannin toxicity. Tannase catalyses the dissociation of ester bonds in gallotannins like tannic acid, resulting in release of gallic acid and glucose. Because of its vast industrial applications and ease of manipulation, interest in identifying and applying bacteria as tannase producers has grown in recent years. The bacterial strains reported in the present work were isolated from soil and identified as Paraburkholderia tropica PKI7 and Kosakonia arachidis PKI8 through morphological, biochemical, and 16s rDNA molecular approach. Simultaneous tannase and gallic acid production by these two bacterial strains were observed through submerged fermentation. This is the first report of Paraburkholderia tropica PKI7 and Kosakonia arachidis PKI8 strains as tannase producing bacteria. The initial tannase production were 0.75 U/ml and 1.49 U/ml respectively for P. tropica PKI7 and K. arachidis PKI8 after 24 h of submerged fermentation while gallic acid release was 8.4 µg/ml and 10.74 µg/ml respectively. There is a potential scope in higher tannase and gallic acid biosynthesis by the two strains.

Bacteria-plant interactions synergistically enhance biodegradation of diesel fuel hydrocarbons

The biotechnological application of microorganisms for rhizoremediation of contaminated sites requires the development of plant-microbe symbionts capable of plant growth promotion and hydrocarbon degradation. Here, we present a study aimed at isolating single microbial strains that are capable of promoting plant growth as well as rhizoremediation of diesel fuel hydrocarbons. Through genomic analyses and greenhouse-based experiments, we examined the synergistic interactions of Medicago sativa L. and Paraburkholderia tropica WTPI1 for enhanced rhizoremediation of diesel fuel-contaminated soils. Plant growth-based experiments confirmed that the inoculation of M. sativa with P. tropica led to a 99% increase in plant biomass. Furthermore, organic geochemical analysis revealed that 96% of all the distinctive diesel fuel hydrocarbons, including C10–C25n-alkanes, branched alkanes, cycloalkanes and aromatic hydrocarbons were degraded in the M. sativa + P. tropica treatment. These results will prove beneficial for biotechnological application of P. tropica WTPI1 for plant growth promotion and most importantly for environmental remediation of organic pollutants.

Tracking and plant growth-promoting effect of Paraburkholderia tropica MTo-293 applied to Solanum lycopersicum.

Paraburkholderia tropica MTo-293 was applied as an experimental bio-input to Solanum lycopersicum (tomato) cv. Platense. Different plant growth systems and inoculation strategies were tested to evaluate P. tropica plant colonization at the seedling stage (growth chamber) using culture-dependent and -independent techniques. The effect of P. tropica on plant growth was evaluated in the growth chamber and greenhouse (productive stage) by biomass accumulation and fruit production, respectively. P. tropica was able to colonize the surface and inner root and stem of tomato seedlings regardless of the inoculation strategy-at sowing and/or before transplanting-showing the competitive nature of P. tropica in nonsterile substrate systems. A nested polymerase chain reaction was validated to track P. tropica in tomato plants even in the inner stem with endophytic P. tropica populations of less than 102 CFU g-1 of fresh weight. Efficient colonization of P. tropica correlated with a positive effect on tomato growth when applied at sowing and/or before transplanting: plant growth promotion was observed not only at the seedling stage but also at productive stages improving crop yield in two different seasons. To our knowledge, this report is the first to track and evaluate the plant growth-promoting effect of P. tropica MTo-293 in tomato plants grown in nonsterile substrate systems.

Characterization of PGPR isolated from rhizospheric soils of various plant and its effect on growth of radish (Raphanus sativus L.)

Plant growth promoting rhizobacteria (PGPR) are commonly used as biofertilizers for agricultural crops. In addition, screening and selection of effective PGPR for a particular plant is necessary to meet plants specific need and condition. Present study was aimed to obtain PGPR isolates which are effective and compatible for Radish. A total of 15 PGPR isolates had been isolated from various plant roots and in vitro screening was done for different plant growth promotion activities. The result showed that 7 isolates were able to produce IAA at the range of 10.2-125.3 μg ml−1, 10 isolates were positive for phosphate solubilizing, 10 isolates had nitrogen fixing activities, 11 isolates were protease positive, 12 isolates were capable to produce ACC-deaminase enzyme, 7 isolates produced siderophore, 8 isolates produced HCN, and 9 isolates produced ammonia. The effect of 15 PGPR on Radish growth in the green house showed that all isolates had effects on increasing growth and tuber formation compared to control. Nine isolates significantly increased the wet weight shoot plants, the highest effect was reached by Kbm 10.3 isolate (168.5 g), while control only reached 81.5 g. Eight isolates had a significant effect on increasing tuber formation, the highest was Kbm 2.10 isolate (176 g), while control only reached 54.7 g. Kbm 10.3 and Kbm 2.10 isolates seemed to have the highest impact in promoting growth and tuber formation. Those two isolates were analyzed using 16s rDNA sequences, they have close evolutionary relationship with Bacillus megaterium (Kbm 2.10) and Paraburkholderia tropica (Kbm 10.3).

Plant Growth Promoting Abilities of Novel Burkholderia-Related Genera and Their Interactions With Some Economically Important Tree Species

A survey of bacterial endophytes associated with the leaves of oil palm and acacias resulted in the isolation of 19 bacterial strains belonging to the genera Paraburkholderia, Caballeronia, and Chitinasiproducens, which are now regarded as distinctively different from the parent genus Burkholderia. Most strains possessed one or more plant growth promotion (PGP) traits although nitrogenase activity was present in only a subset of the isolates. The diazotrophic Paraburkholderia tropica strain S39-2 with multiple PGP traits and the non-diazotrophic Chitinasiproducens palmae strain JS23T with a significant level of 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity were selected to investigate the influence of bacterial inoculation on some economically important tree species. Microscopic examination revealed that P. tropica S39-2 was rhizospheric as well as endophytic while C. palmae JS23T was endophytic. P. tropica strain S39-2 significantly promoted the growth of oil palm, eucalyptus, and Jatropha curcas. Interestingly, the non-diazotrophic, non-auxin producing C. palmae JS23T strain also significantly promoted the growth of oil palm and eucalyptus although it showed negligible effect on J. curcas. Our results suggest that strains belonging to the novel Burkholderia-related genera widely promote plant growth via both N-independent and N-dependent mechanisms. Our results also suggest that the induction of defense response may prevent the colonization of an endophyte in plants.

Rearranging the sugarcane holobiont via plant growth-promoting bacteria and nitrogen input

The development and productivity of plants are governed by their genetic background, nutrient input, and the microbial communities they host, i.e. the holobiont. Accordingly, engineering beneficial root microbiomes has emerged as a novel and sustainable approach to crop production with reduced nutrient input. Here, we tested the effects of six bacterial strains isolated from sugarcane stalks on sugarcane growth and physiology as well as the dynamics of prokaryote community assembly in the rhizosphere and root endosphere under two N fertilization regimes. All six strains, Paraburkholderia caribensis IAC/BECa 88, Kosakonia oryzae IAC/BECa 90, Kosakonia radicincitans IAC/BECa 95, Paraburkholderia tropica IAC/BECa 135, Pseudomonas fluorescens IAC/BECa 141 and Herbaspirillum frisingense IAC/BECa 152, increased in shoot and root dry mass, and influenced the concentration and accumulation of important macro- and micronutrients. However, N input reduced the impact of inoculation by shifting the sugarcane microbiome (rhizosphere and root endosphere) and weakening the co-dependence between soil microbes and sugarcane biomass and nutrients. The results show that these beneficial microbes improved plant nutrient uptake conditioned to a reduced N nutrient input. Therefore, reduced fertilization is not only desirable consequence of bacterial inoculation but essential for higher impact of these beneficial bacteria on the sugarcane microbiome.

The modulation of sugarcane growth and nutritional profile under aluminum stress is dependent on beneficial endophytic bacteria and plantlet origin

Plant growth-promoting bacteria (PGPB) are claimed to not only improve plant fitness but also alleviate plant stress. In this study, we evaluated the effect of five PGPB strains on plantlet growth and nutrient and aluminum (Al) uptake under acid soil conditions characterized by low P and K nutrient availability and high metal and aluminum (Al) bioavailability, which may represent a stress condition for crop plants. The PGPB strains were inoculated in sugarcane plantlets produced by meristem tissue culture (MCPs) or one-bud stalks (O-BSPs) and cultivated in soil at 37% Al saturation and pH 4.0. Biomass accumulation and Al and nutrient content in roots and shoots were determined after 30 days of growth. Bacterial inoculation increased root and shoot biomass. However, the magnitudes of these increases were dependent on bacterial strain and plantlet origin. The inoculated plantlets exhibited increased Al content and shifts in Al allocation and calcium (Ca) and boron (B) content among different plant parts (root or shoot), and these changes also depended on plantlet origin and the inoculated strain. The higher Ca uptake of inoculated MCPs and higher B uptake of inoculated O-BSPs may have contributed to reducing the damage caused by excessive Al content. The beneficial microbes also caused changes in plant uptake of micronutrients and slightly reduced macronutrient content. Pseudomonas fluorescens (IAC/BECa 141), Kosakonia radicincitans (IAC/BECa 95), Paraburkholderia tropica (IAC/BECa 135) and Herbaspirillum frisingense (IAC/BECa 152) showed potential for alleviating Al stress in sugarcane plantlets.

Sorghum Growth Promotion by Paraburkholderia tropica and Herbaspirillum frisingense: Putative Mechanisms Revealed by Genomics and Metagenomics.

Bacteria from the genera Paraburkholderia and Herbaspirillum can promote the growth of Sorghum bicolor, but the underlying mechanisms are not yet known. In a pot experiment, sorghum plants grown on sterilized substrate were inoculated with Paraburkholderia tropica strain IAC/BECa 135 and Herbaspirillum frisingense strain IAC/BECa 152 under phosphate-deficient conditions. These strains significantly increased Sorghum bicolor cultivar SRN-39 root and shoot biomass. Shotgun metagenomic analysis of the rhizosphere revealed successful colonization by both strains; however, the incidence of colonization was higher in plants inoculated with P. tropica strain IAC/BECa 135 than in those inoculated with H. frisingense strain IAC/BECa 152. Conversely, plants inoculated with H. frisingense strain IAC/BECa 152 showed the highest increase in biomass. Genomic analysis of the two inoculants implied a high degree of rhizosphere fitness of P. tropica strain IAC/BECa 135 through environmental signal processing, biofilm formation, and nutrient acquisition. Both genomes contained genes related to plant growth-promoting bacterial (PGPB) traits, including genes related to indole-3-acetate (IAA) synthesis, nitrogen fixation, nodulation, siderophore production, and phosphate solubilization, although the P. tropica strain IAC/BECa 135 genome contained a slightly more extensive repertoire. This study provides evidence that complementary mechanisms of growth promotion in Sorghum might occur, i.e., that P. tropica strain IAC/BECa 135 acts in the rhizosphere and increases the availability of nutrients, while H. frisingense strain IAC/BECa 152 influences plant hormone signaling. While the functional and taxonomic profiles of the rhizobiomes were similar in all treatments, significant differences in plant biomass were observed, indicating that the rhizobiome and the endophytic microbial community may play equally important roles in the complicated plant-microbial interplay underlying increased host plant growth.

The importance of antimicrobial compounds produced by beneficial bacteria on the biocontrol of phytopathogens

Bacteria produce antimicrobial compounds to compete for nutrients and space in a particular habitat. Antagonistic interactions can be evaluated by several methodologies including the double-layer agar and simultaneous inhibition assays. Among the well-known inhibitory substances produced by bacteria are the broad-spectrum antibiotics, organic acids, siderophores, antifungal, and bacteriocins. The most studied bacterial genera able to produce these inhibitory substances are Enterococcus, Lactococcus, Streptomyces, Bacillus, Pseudomonas, Klebsiella, Escherichia, and Burkholderia. Some beneficial bacteria can promote plant growth and degrade toxic compounds in the environment representing an attractive solution to diverse issues in agriculture and soil pollution, particularly in fields with damaged soils where pesticides and fertilizers have been indiscriminately used. Beneficial bacteria may increase plant health by inhibiting pathogenic microorganisms; some examples include Gluconacetobacter diazotrophicus, Azospirullum brasilense, Pseudomonas fluorescens, Pseudomonas protegens, and Burkholderia tropica. However, most studies showing the antagonistic potential of these bacteria have been performed in vitro, and just a few of them have been evaluated in association with plants. Several inhibitory substances involved in pathogen antagonism have not been elucidated yet; in fact, we know only 1 % of the bacterial diversity in a natural environment leading us to assume that many other inhibitory substances remain unexplored. In this review, we will describe the characteristics of some antimicrobial compounds produced by beneficial bacteria, the principal methodologies performed to evaluate their production, modes of action, and their importance for biotechnological purposes.

Evaluating antibacterial and anticancer activity of crude extracts of bacterial endophytes from Crinum macowanii Baker bulbs.

The results from this study revealed that crude extracts isolated from bacterial endophytes obtained from Crinum macowanii bulbs showed activity against both Gram‐positive and Gram‐negative pathogenic bacteria, while Acinetobacter guillouiae crude extracts displayed anticancer activity. This study aimed to isolate and characterize bacterial endophytes and their crude extracts from C. macowanii bulbs. Endophytes were isolated using validated surface sterilization techniques, followed by phenotypic and genotypic profiles of the isolates. Crude extracts were extracted from the endophytes using ethyl acetate, while methanol:dichloromethane (1:1) was used to obtain crude extracts from the bulbs. Antibacterial activity of crude extract from each endophyte was investigated against selected pathogenic strains using the broth microdilution method, and anticancer activity against U87MG glioblastoma and A549 lung carcinoma cells was determined by the MTS (3‐(4,5‐dimethylthiazol‐2‐yl)‐5‐(3‐carboxymethoxy‐phenyl)‐2‐(4‐sulfophenyl)‐2H‐tetrazolium) assay. Acinetobacter guillouiae, Pseudomonas moraviensis, Pseudomonas sp., Rahnella aquatilis, Bacillus cereus, Novosphingobium sp., Raoultella ornithinolytica, and Burkholderia tropica were successfully isolated. The crude extracts from the majority of endophytes showed antibacterial activity, ranging from 0.125 to >16.00 mg/ml against Gram‐negative and Gram‐positive pathogenic bacteria. Acinetobacter guillouiae extracts showed a high bioactive potential against U87MG glioblastoma cell lines by reducing their growth by 50% at concentrations of 12.5, 6.25, and 3.13 µg/ml. Crude extracts isolated from C. macowanii bulbs showed potential for possible drug lead against common pathogenic bacteria.

Paraburkholderia tropica as a plant-growth–promoting bacterium in barley: characterization of tissues colonization by culture-dependent and -independent techniques for use as an agronomic bioinput

Characterization of barley-tissue–colonization efficiency (Hordeum vulgare L.) by Paraburkholderia tropica MTo-293 after seed inoculation was studied in two plant-growth systems: (1) in flasks with semisolid agar-containing sterile medium, as a suitable environment to study plant-bacteria interaction and also optimize molecular-biology techniques, and (2) in a pot-substrate system as an approach to understand their potential behavior as bioinput. Culture-dependent techniques were implemented to quantify surface and endophytic bacterial populations in plant tissues. Culture-independent techniques were employed to detect and localize the inoculated bacteria in tissue samples along with evaluating the biofilm-forming capability by epifluorescent, confocal-laser-scanning, and scanning-electron microscopy. Plant-growth parameters were measured to evaluate the effects of the inoculated bacteria on the development of the barley plants. Paraburkholderia tropica grew as a biofilm on both abiotic and biotic surfaces and efficiently colonized barley roots and stems in plants grown in flasks in presence of other microorganisms. The bacteria was localized on root surfaces, hairs, and central-cylinder areas. Paraburkholderia tropica also colonized the roots and stems in plants grown in the pot-substrate system. Although no endophytic root colonization occurred, the presence of the inoculated bacteria improved the aerial weight. A nested PCR detected P. tropica in the tissue samples. Paraburkholderia tropica MTo-293 was characterized as an efficient biofilm-forming and barley-tissue–colonizing bacterium despite the presence of other microorganisms, but root endophytic colonization resulted dependent on the plant-growth system. Molecular-biology techniques were optimized, and also, its presence was correlated with plant-growth–promoting activity.

Interaction between sugarcane families and plant growth-promoting bacteria in two crop cycles

The response of sugarcane (Saccharum spp.) families to the inoculation with plant growth-promoting bacteria (PGPB) may show positive or negative interaction values depending on the plant genotype, allowing the selection of responsive genotypes to the association. Based on these precepts, this study aimed to evaluate the response of 27 sugarcane families treated with two PGPB-based inoculants in two sugarcane cycles: plant-cane and first ratoon. Four months after germination, 27 families from crosses between clones of sugarcane were: (T0) not inoculated; (T1) inoculated with Triazo, which consists of a mixture of the strains Abv5, Abv6, and Abv7 of Azospirillum brasilense; and (T2) inoculated with an inoculant called Mix, which contains five strains of PGPB (Gluconacetobacter diazotrophicus Pal5, Azospirillum amazonense CBAmC, Burkholderia tropica Ppe8, Herbaspirillum rubrisubalbicans HCc103, and Herbaspirillum seropedicae HRC54). The productivity traits evaluated were the number of stalks, average height, stalk diameter, and Brix. The correlation values between the two cycles were 0.87 for the number of stalks, 0.70 for average height, 0.48 for stalk diameter, and 0.63 for Brix. Differences were observed between treatments for average height, stalk diameter, and Brix. Differences were also observed between families for all the studied traits. Brix was the only parameter that presented a significant interaction between family and inoculant. Different responses were observed between cycles for some families, showing that other factors can also influence the association.

Rooting and growth of pre-germinated sugarcane seedlings inoculated with diazotrophic bacteria

Renovation of Brazilian sugarcane plantations using the pre-sprouted seedling technique (PSS) was undertaken to increase sanitation and productivity while reducing the cost of sugarcane planting. The objective of this study was to evaluate growth, nutrient acquisition, and contribution of biological nitrogen fixation (BNF) in two sugarcane cultivars RB867515 and IACSP95-5000, inoculated with five strains/species of diazotrophic bacteria, applied together and individually, for 60 days during growth. The cultivars were grown in a greenhouse in boxes filled with a sterile substrate followed by growth in tubes filled with a commercial substrate in the second phase; finally the plants were transferred to pots containing soil enriched with 15N and grown outdoors. The treatments used were control (no inoculation); mixed inoculation with the five strains, Gluconacetobacter diazotrophicus (PAL5T), Herbaspirillum rubrisubalbicans (HCC103), Herbaspirillum seropedicae (HRC54), Nitrospirillum amazonense (CBAmC) and Paraburkholderia tropica (PPe4T); and individual inoculation with each strain. Increases of up to 50% in the root dry mass was observed following mixed inoculation of the seedlings in the germination phase, with a significant increase in root initiation, volume, and area, especially of the fine roots. Inoculation of seedlings of both cultivars led to increased biomass in tubes of non-sterile substrate. In soil, a higher nitrogen accumulation was also observed in the cvar. IACSP95-5000 in all treatments except plants inoculated with N. amazonense. For the cvar. RB867515 shoots, the opposite was observed were the highest N accumulation was observed for N. amazonense, H. seropedicae followed by the mixture. In this experiment using soil labelled with 15N there was a response on N uptake caused by all bacteria used in one cvar but only by 2 of the 5 strains in other cvar. Using the 15N enrichment of the plants the results showed that the control and inoculated plants all derived 60–70% of N from the atmosphere, and inoculation had no effect on BNF contribution. For P and K levels, RB867515 showed no effect of inoculation, but the other cvar. did respond to inoculation.

Characterization of Respiration in Paraburkholderia tropica Ppe8T under Static Culture Conditions

Objective: To investigate the respiratory chain of Paraburkholderia tropica under limited oxygen conditions would allow us to better understand their functions in plant tissue. Methods: We first optimized the medium for P. tropica biomass production in static culture. Oxidase and Oxidoreductase activities were determined in absence and presence de inhibitors. Spectroscopic analysis of cytochromes was obtained at room and liquid nitrogen temperature. Findings: Isolated membranes showed respiratory oxidase activities with succinate, glucose, NADH and ascorbate-N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD). Succinate and glucose respiration were inhibited by 2-heptyl-4-hydroxyquinoline-N-oxide, antimycin A and myxothiazol, suggesting the presence of a bc1 complex.KCN inhibition curves in the presence of ascorbate-TMPD, succinate or glucose were biphasic, with KCN-sensitive and -resistant oxidases. Spectral analysis with physiological or artificial substrates revealed the presence of only cytochromes b and c, with remarkable cytochrome reduction by ascorbate alone. The CO difference and photodissociation spectra of glucosereduced membranes revealed one component with the spectral features of a cytochrome o´-like CO complex. Air-oxidation spectra of the cytochromes with KCN showed that cytochrome c is an obligate participant in the KCN-sensitive pathway and revealed the presence of a cyanide-resistant oxidase cytochrome bo. Novelty: The characterization of the electron transport system of P. tropica allowed us to propose the following components: 1. Dehydrogenases for succinate, glucose and NADH, 2. A ubiquinone, 3. A bc complex and 4. Two oxidases, cbb-type cytochrome c oxidase and bo-type quinol oxidase. Keywords: bc1 complex, cbb oxidase, Cytochromes, Paraburkholderia tropica, Quinol Oxidase, Respiration

Assessment of bacterial inoculant formulated with Paraburkholderia tropica to enhance wheat productivity.

Paraburkholderia tropica is an endophytic nitrogen-fixing bacterium isolated from the rhizosphere, rhizoplane, and internal tissues of sugarcane and corn plants in different geographical regions. Other plant-growth-promoting abilities, such as phosphate solubilization and antifungal activity, have also been reported for this bacterium. With an aim at investigating the potential use of P. tropica as an inoculant for improving the performance of wheat crop, in this work we evaluated an experimental inoculant formulated with P. tropica MTo-293 with respect to root colonization, the practical aspects of its application, and the effects under field conditions when applied to wheat seeds. Bacterial colonization was monitored by culture dependent techniques and the wheat yield determined by quantifying the total grain production in two different seasons. Rhizoplane and endophytic colonization in wheat roots was achieved efficiently (on average, 8 and 4 log colony-forming units/g fresh weight, respectively) even at relatively low concentrations of viable bacteria in the inoculum under controlled conditions. P. tropica was compatible with a widely used fungicide, maintained viability for 48h once applied to seeds, and was also able to colonize wheat roots efficiently. Furthermore, we were able to formulate an inoculant that maintained bacterial viability for relatively long time periods. Preliminary field assays were realized, and even though the average yields values for the inoculated treatments remained above the uninoculated ones, no significant effects of inoculation were detected with or without fertilization. The correct physiologic behavior of P. tropica suggests the necessity to continue with field experiments under different conditions.

Nitrogen source contribution in sugarcane-inoculated plants with diazotrophic bacterias under urea-N fertigation management

Although Brazilian sugarcane crops use lower nitrogen rates when compared to other producing countries, the biological nitrogen fixation (BFN) could be performed aiming to reduce costs, since almost all nitrogen fertilization used in Brazil is imported. BFN can occur in sugarcane; however, its role in non-leguminous plants is controversial. Therefore, this study aimed to assess the nitrogen source contribution (using N isotope 15N technique) along a growing period in sugarcane plants under different management (diazotrophic bacteria inoculation and N fertigation rates). The natural abundance of nitrogen isotope (15N) abundance in + 1 leaves of fourth ratoon cultivar SP 80-3280 was used to indicate the comparative importance of N sources, including BFN for sugarcane nutrition. The treatments were irrigated with two levels of nitrogen fertilizer 50 and 100 kg ha−1 (urea source), including a control without fertilizer, with (I) and without (NI) inoculation of nitrogen-fixing bacterias. The bacteria cocktail used consisted of five strains: Gluconacetobacter diazotrophicus, Herbaspirillum seropedicae, H. rubrisubalbicans, Burkholderia tropica and Azospirillum amazonense. Although the nitrogen content in + 1 leaves, the above ground dry matter, cane yield and stalk sugar content expanded by increasing nitrogen fertilizer rates, no significant interactions between nitrogen-fixing bacteria inoculation and nitrogen fertilizer rates were observed. In the treatment without N fertilizer application, no differences in δ15N‰ (per thousand) values between sugarcane-inoculated and sugarcane-non-inoculated sugarcane leaves was found. The temporal variation of δ15N‰ in sugarcane + 1 leaves indicated that nitrogen content and δ15N‰ values decreased during the phenological development stages and that the main sources of nitrogen for sugarcane were from synthetic fertilizer and mineralization of nitrogen from soil organic matter.

Draft genome sequence of Paraburkholderia tropica Ppe8 strain, a sugarcane endophytic diazotrophic bacterium.

Paraburkholderia tropica (syn Burkholderia tropica) are nitrogen-fixing bacteria commonly found in sugarcane. The Paraburkholderia tropica strain Ppe8 is part of the sugarcane inoculant consortium that has a beneficial effect on yield. Here, we report a draft genome sequence of this strain elucidating the mechanisms involved in its interaction mainly with Poaceae. A genome size of approximately 8.75 Mb containing 7844 protein coding genes distributed in 526 subsystems was de novo assembled with ABySS and annotated by RAST. Genes related to the nitrogen fixation process, the secretion systems (I, II, III, IV, and VI), and related to a variety of metabolic traits, such as metabolism of carbohydrates, amino acids, vitamins, and proteins, were detected, suggesting a broad metabolic capacity and possible adaptation to plant association.

Burkholderia tropica as a Potential Microalgal Growth-Promoting Bacterium in the Biosorption of Mercury from Aqueous Solutions

The use of microalgal biomass is an interesting technology for the removal of heavy metals from aqueous solutions owing to its high metal-binding capacity, but the interactions with bacteria as a strategy for the removal of toxic metals have been poorly studied. The goal of the current research was to investigate the potential of Burkholderia tropica co-immobilized with Chlorella sp. in polyurethane discs for the biosorption of Hg(II) from aqueous solutions and to evaluate the influence of different Hg(II) concentrations (0.041, 1.0, and 10 mg/l) and their exposure to different contact times corresponding to intervals of 1, 2, 4, 8, 16, and 32 h. As expected, microalgal bacterial biomass adhered and grew to form a biofilm on the support. The biosorption data followed pseudo-second-order kinetics, and the adsorption equilibrium was well described by either Langmuir or Freundlich adsorption isotherm, reaching equilibrium from 1 h. In both bacterial and microalgal immobilization systems in the coimmobilization of Chlorella sp. and B. tropica to different concentrations of Hg(II), the kinetics of biosorption of Hg(II) was significantly higher before 60 min of contact time. The highest percentage of biosorption of Hg(II) achieved in the co-immobilization system was 95% at pH 6.4, at 3.6 g of biosorbent, 30 ± 1°C, and a mercury concentration of 1 mg/l before 60 min of contact time. This study showed that co-immobilization with B. tropica has synergistic effects on biosorption of Hg(II) ions and merits consideration in the design of future strategies for the removal of toxic metals.