RESUMO

The study of plant-microbe interactions is a rapidly growing research field, with increasing attention to the role of seed-borne microbial endophytes in protecting the plant during its development from abiotic and biotic stresses. Recent evidence suggests that seed microbiota is crucial in establishing the plant microbial community, affecting its composition and structure, and influencing plant physiology and ecology. For Theobroma cacao L., the diversity and composition of vertically transmitted microbes have yet to be addressed in detail. We explored the composition and diversity of seed-borne endophytes in cacao pods of commercial genotypes (ICS95, IMC67), recently liberated genotypes from AGROSAVIA (TCS01, TCS19), and landraces from Tumaco (Colombia) (AC9, ROS1, ROS2), to evaluate microbial vertical transmission and establishment in various tissues during plant development. We observed a higher abundance of Pseudomonas and Pantoea genera in the landraces and AGROSAVIA genotypes, while the commercial genotypes presented a higher number of bacteria species but in low abundance. In addition, all the genotypes and plant tissues showed a high percentage of fungi of the genus Penicillium. These results indicate that domestication in cacao has increased bacterial endophyte diversity but has reduced their abundance. We isolated some of these seed-borne endophytes to evaluate their potential as growth promoters and found that Bacillus, Pantoea, and Pseudomonas strains presented high production of indole acetic acid and ACC deaminase activity. Our results suggest that cacao domestication could lead to the loss of essential bacteria for seedling establishment and development. This study improves our understanding of the relationship and interaction between perennial plants and seed-borne microbiota.

Assuntos

Bactérias , Cacau , Domesticação , Endófitos , Sementes , Cacau/microbiologia , Endófitos/genética , Endófitos/classificação , Endófitos/isolamento & purificação , Endófitos/fisiologia , Sementes/microbiologia , Sementes/crescimento & desenvolvimento , Bactérias/classificação , Bactérias/genética , Bactérias/isolamento & purificação , Microbiota , Fungos/genética , Fungos/classificação , Fungos/isolamento & purificação , Genótipo , Biodiversidade

RESUMO

Climate change intensifies soil salinization and jeopardizes the development of crops worldwide. The accumulation of salts in plant tissue activates the defense system and triggers ethylene production thus restricting cell division. We hypothesize that the inoculation of plant growth-promoting bacteria (PGPB) producing ACC (1-aminocyclopropane-1-carboxylate) deaminase favors the development of arbuscular mycorrhizal fungi (AMF), promoting the growth of maize plants under saline stress. We investigated the efficacy of individual inoculation of PGPB, which produce ACC deaminase, as well as the co-inoculation of PGPB with Rhizophagus clarus on maize plant growth subjected to saline stress. The isolates were acquired from the bulk and rhizospheric soil of Mimosa bimucronata (DC.) Kuntze in a temporary pond located in Pernambuco State, Brazil. In the first greenhouse experiment, 10 halophilic PGPB were inoculated into maize at 0, 40 and 80 mM of NaCl, and in the second experiment, the PGPB that showed the best performance were co-inoculated with R. clarus in maize under the same conditions as in the first experiment. Individual PGPB inoculation benefited the number of leaves, stem diameter, root and shoot dry mass, and the photosynthetic pigments. Inoculation with PGPB 28-10 Pseudarthrobacter enclensis, 24-1 P. enclensis and 52 P. chlorophenolicus increased the chlorophyll a content by 138%, 171%, and 324% at 0, 40 and 80 mM NaCl, respectively, comparing to the non-inoculated control. We also highlight that the inoculation of PGPB 28-10, 28-7 Arthrobacter sp. and 52 increased the content of chlorophyll b by 72%, 98%, and 280% and carotenoids by 82%, 98%, and 290% at 0, 40 and 80 mM of NaCl, respectively. Co-inoculation with PGPB 28-7, 46-1 Leclercia tamurae, 70 Artrobacter sp., and 79-1 Micrococcus endophyticus significantly increased the rate of mycorrhizal colonization by roughly 50%. Furthermore, co-inoculation promoted a decrease in the accumulation of Na and K extracted from plant tissue, with an increase in salt concentration, from 40 mM to 80 mM, also favoring the establishment and development of R. clarus. In addition, co-inoculation of these PGPB with R. clarus promoted maize growth and increased plant biomass through osmoregulation and protection of the photosynthetic apparatus. The tripartite symbiosis (plant-fungus-bacterium) is likely to reprogram metabolic pathways that improve maize growth and crop yield, suggesting that the AMF-PGPB consortium can minimize damages caused by saline stress.

Assuntos

Bactérias , Carbono-Carbono Liases , Micorrizas , Raízes de Plantas , Microbiologia do Solo , Zea mays , Zea mays/microbiologia , Zea mays/crescimento & desenvolvimento , Micorrizas/fisiologia , Carbono-Carbono Liases/metabolismo , Raízes de Plantas/microbiologia , Raízes de Plantas/crescimento & desenvolvimento , Bactérias/classificação , Bactérias/metabolismo , Bactérias/isolamento & purificação , Estresse Salino , Clorofila/metabolismo , Glomeromycota/fisiologia , Tolerância ao Sal , Fotossíntese , Rizosfera , Cloreto de Sódio/metabolismo , Folhas de Planta/microbiologia , Solo/química

RESUMO

Water stress is a major limiting factor for agricultural production under current and projected climate change scenarios. As a sustainable strategy, plant growth-promoting bacterial consortia have been used to reduce plant water stress. However, few studies have examined the effects of stress on multi-trait efficiency and interactivity of bacterial species. In this study, we used several in-vitro experiments, plant assays and greenhouse trials to investigate the effects of stress and bacterial consortia on 1-aminocyclopropane-1-carboxylic acid deaminase (ACCD) activities, indole-3-acetic acid (IAA) production and plant growth-promoting traits (Phosphate-solubilization, starch hydrolysis, siderophores and ammonium production). We further assessed biofilm formation and the chemotactic behaviour in response to ACC. A total of fifteen ACCD rhizobacteria with multiple growth-promoting traits from the dominant plant species from the hyperseasonal Aripo Savannas were screened in this study. Five of the isolates were further analyzed based on their ACCD activities and were tested in single and dual consortium to assess their abilities in promoting growth under simulated drought stress (-0.35 MPa) and chemically induced ACC conditions (0.03 mM). Our findings showed that bacteria which produce high concentrations of IAA affected the isolates' ability to promote growth under stress, irrespective of microbial combination with ACCD activity above the minimal threshold of 20 nmol α-ketobutyrate mg-1 h-1. Biofilm production with co-culture interaction varied greatly across treatments, however, the general trend showed an increase in biofilm under stress induce conditions. The best performing co-culture, UWIGT-83 and UWIGT-120 (Burkholderia sp.) showed enhanced growth in germination assays and in greenhouse trials with Capsicum chinense (Moruga red hot peppers) under drought stress, when compared to non-inoculated treatments. The findings highlight the importance of testing interactivity of bacterial species with multiple growth promoting traits under stress conditions; and proposed the use of ACC growth media as a novel biofilm screening method for selecting potential stress plant growth-promoting bacteria. Better screening strategies for appropriate plant growth-promoting bacteria may narrow the inconsistency observed between laboratory and field trials.

Assuntos

Bactérias , Desidratação , Desenvolvimento Vegetal , Germinação , Plantas , Raízes de Plantas/microbiologia , Carbono-Carbono Liases

RESUMO

Azospirillum is a plant-growth-promoting bacterium capable of colonizing and promoting growth in numerous crops of agronomic and horticultural significance. The objective of the present study is to develop Azospirillum brasilense CW903-acdS flocculating cells and to test their performance in promoting the growth of red pepper plants grown under salt stress. The flocculating CW903-acdS recorded 12.6, 37.3 and 91.6% higher ACCd activity at 50, 100 and 150 mM NaCl concentrations, respectively, compared to non-flocculating (normal) CW903-acdS cells. The flocculating CW903-acdS recorded 29.8 and 24.5% higher specific growth rates compared to non-flocculating CW903-acdS cells at 100 and 150 mM NaCl concentration, respectively. The flocculating CW903-acdS recorded 29.7 and 24.5% higher production of IAA-like molecule compared to the non-flocculating CW903-acdS at 100 and 150 mM NaCl concentration, respectively. Similarly, 27.5 and 25.7% higher ARA activity was observed with the flocculating CW903-acdS compared to the non-flocculating CW903-acdS type cells at 100 and 150 mM NaCl concentration, respectively. In the pot culture experiment at 50 and 100 mM NaCl concentration, CW903-acdS inoculated pepper plants recorded 9.4 and 4.7% less ethylene emission, when compared to plants inoculated with non-flocculating CW903-acdS cells. At 100 mM NaCl concentration, plants inoculated with flocculating CW903-acdS recorded 27.5% higher dry weight compared to plants inoculated with non-flocculating CW903-acdS cells. This study implied the significance of flocculating CW903-acdS with better stress amelioration and plant growth promotion in red pepper plants grown under salt-affected conditions due to the positive influence of ACCd activity.

RESUMO

Introduction: Plants interact with plant growth-promoting bacteria (PGPB), especially under stress condition in natural and agricultural systems. Although a potentially beneficial microbiome has been found associated to plants from alpine systems, this plant- PGPB interaction has been scarcely studied. Nevados de Chillán Complex hold one of the southernmost xerophytic formations in Chile. Plant species living there have to cope with drought and extreme temperatures during the growing season period, microclimatic conditions that become harsher on equatorial than polar slopes, and where the interaction with PGPB could be key for plant survival. Our goal was to study the abundance and activity of different PGPB associated to two abundant plant species of Andean xerophytic formations on contrasting slopes. Methods: Twenty individuals of Berberis empetrifolia and Azorella prolifera shrubs were selected growing on a north and south slope nearby Las Fumarolas, at 2,050 m elevation. On each slope, microclimate based on temperature and moisture conditions were monitored throughout the growing period (oct. - apr.). Chemical properties of the soil under plant species canopies were also characterized. Bacterial abundance was measured as Log CFU g-1 from soil samples collected from each individual and slope. Then, the most abundant bacterial colonies were selected, and different hormonal (indoleacetic acid) and enzymatic (nitrogenase, phosphatase, ACC-deaminase) mechanisms that promote plant growth were assessed and measured. Results and Discussion: Extreme temperatures were observed in the north facing slope, recording the hottest days (41 vs. 36°C) and coldest nights (-9.9 vs. 6.6°C). Moreover, air and soil moisture were lower on north than on south slope, especially late in the growing season. We found that bacterial abundance was higher in soils on north than on south slope but only under B. empetrifolia canopy. Moreover, the activity of plant growth-promoting mechanisms varied between slopes, being on average higher on north than on south slope, but with plant species-dependent trends. Our work showed how the environmental heterogeneity at microscale in alpine systems (slope and plant species identity) underlies variations in the abundance and plant growth promoting activity of the microorganisms present under the plant canopy of the Andean xerophytic formations and highlight the importance of PGPB from harsh systems as biotechnological tools for restoration.

RESUMO

Plant growth-promoting bacteria such as Streptomyces are an attractive alternative for increasing the sustainability of agricultural systems. In this study, Streptomyces isolates obtained from rhizosphere soil of plants in the family Fabaceae were characterized for their plant growth-promoting traits, including the production of siderophores, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, indole-3-acetic acid (IAA), and phenazines. Soybean seeds were bacterized with selected isolates to test growth promotion. All isolates produced IAA, and the isolate CLV45 was the most efficient, reaching 398.53 mg of IAA per gram of cells. CLV41, CLV45, and CLV46 showed high activity for ACC deaminase whereas CLV42, CLV44, and CLV46 were efficient in siderophore production. Pyocyanin was detected in all isolates; CLV41, CLV43, and CLV45 produced phenazine-carboxylic acid as well. Selected for IAA and ACC deaminase production combined with production of siderophores and phenazines, CLV42, CLV44, and CLV45 were tested for their growth promotion potential. Seed bacterization with CLV45 resulted in plants with increased shoot growth (36.63%) and dry mass (17.97%) compared to control plants. Results suggest that moderate or high levels of auxin and ACC deaminase production by the isolate CLV45 positively affected the growth of soybean plants, making it a strong candidate for further studies on biofertilizer formulation.

Assuntos

Glycine max/crescimento & desenvolvimento , Glycine max/microbiologia , Rizosfera , Sementes/microbiologia , Streptomyces/fisiologia , Agricultura/métodos , Raízes de Plantas/microbiologia , Microbiologia do Solo

RESUMO

Soil salinity is one of the major plant growth and yield-limiting constraints in arid and semi-arid regions of the world. In addition to the oxidative damage, increasing salt stress is associated with elevated cellular ethylene levels due to the synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC) in large amounts. The objective of the current study was to elucidate the inoculation effect of an ACC deaminase (ACCD)-producing phytobeneficial strain Achromobacter sp. FB-14 on rice plants to alleviate the salinity effects by upregulation of the stress-responsive CIPK genes. The strain FB-14 was isolated by using nutrient agar medium at 855 mM NaCl concentration and it was taxonomically identified as Achromobacter sp. with more than 99% 16S rRNA gene sequence similarity with many Achromobacter species. The strain FB-14 demonstrated substantial in vitro potential for ACCD activity, synthesis of indole compounds, and phosphate solubilization up to 100 mM NaCl concentration in the culture medium. The gene corresponding to ACCD activity (acdS) was amplified and sequenced in order to confirm the inherent enzyme activity of the strain at a molecular level. The rifampicin-resistant derivative of strain FB-14 was recovered from the rice rhizosphere on antibiotic medium up to 21 days of sowing. Moreover, the strain FB-14 was inoculated on rice plants under salinity and it not only enhanced the growth of rice plants in terms of root and shoot length, and fresh and dry weight, but also upregulated the expression of stress-responsive CIPK genes (OsCIPK03, OsCIPK12, and OsCIPK15) according to the results of qRT-PCR analysis. To the best of our knowledge, this is the first report deciphering the role of plant-beneficial Achromobacter strain relieving the rice plants from salt stress by promoting the growth and enhancing the expression of stress-responsive CIPK genes.

Assuntos

Achromobacter/enzimologia , Carbono-Carbono Liases/metabolismo , Oryza/crescimento & desenvolvimento , Oryza/microbiologia , Proteínas Serina-Treonina Quinases/genética , Estresse Salino/genética , Achromobacter/genética , Regulação da Expressão Gênica de Plantas , Oryza/genética , RNA Ribossômico 16S/genética , Solo/química , Microbiologia do Solo , Regulação para Cima

RESUMO

Introduction: The sustainable production of pastures has become a fundamental challenge for the livestock sector where research with plant growth-promoting rhizobacteria as a viable solution, has nearly not been reported. Objective: In this study, we aimed to examine the potential to stimulate growth in Pennisetum clandestinum grass using four isolated bacterial strains from soils obtained from a Colombian tropical silvopastoral system. Methods: We previously identified genetically the strains and characterized two plant growth promoting activities. In addition, we evaluated the growth-promoting effect of the strains in Kikuyo grass under greenhouse conditions. Results: We found that the four bacterial strains were phylogenetically associated with Klebsiella sp. (strains 28P and 35P), Beijerinka sp. (37L) and Achromobacter xylosoxidans (E37), based on partial 16S rRNA gene sequencing. Moreover, the in vitro biochemical assays demonstrated that the strains exhibited some plant growth promoting mechanisms such as 1-aminocyclopropane-1-carboxylic acid deaminase activity and indole compound synthesis. Notably, bacterial inoculation under greenhouse conditions showed a positive influence on P. clandestinum growth. We found a significant (P < 0.05) effect on root and shoot length and shoot dry weight. Shoot length increased by 52 % and 30 % with 37L and 35P compared to those without inoculation treatment. Similarly, the use of 37L and 28P raised shoot dry weight values by 170 % and 131 %, respectively. In root development, inoculation with strains 37L and E37 increased root length by 134 % and 100 %, respectively. Conclusion: Beijerinckia sp. 37L was the most effective of the four strains at increasing P. clandestinum biomass and length.

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Introducción: La producción sostenible de pastos se ha convertido en un desafío fundamental para el sector ganadero, donde investigaciones con bacterias promotoras de crecimiento vegetal, como una solución viable, han sido poco reportadas. Objetivo: El objetivo de este estudio fue examinar el potencial para estimular el crecimiento del pasto Pennisetum clandestinum utilizando cuatro cepas bacterianas aisladas de suelos obtenidos de un sistema silvopastoril tropical colombiano. Métodos: Anteriormente identificamos genéticamente las cepas y caracterizamos dos actividades que promueven el crecimiento de las plantas. Además, evaluamos el efecto promotor del crecimiento de las cepas en el pasto Kikuyo en condiciones de invernadero. Resultados: Encontramos que las cuatro cepas bacterianas se asociaron filogenéticamente con Klebsiella sp. (cepas 28P y 35P), Beijerinka sp. (37L) y Achromobacter xylosoxidans (E37), basados en la secuenciación parcial del gen 16S rRNA. Además, los ensayos bioquímicos in vitro demostraron que las cepas exhibían algunos mecanismos que promueven el crecimiento de las plantas tales como la actividad de la enzima desaminasa del ácido 1-aminociclopropano-1- carboxílico, y la síntesis del compuesto indol. En particular, la inoculación bacteriana bajo condiciones de invernadero mostró una influencia positiva en el crecimiento de P. clandestinum. Encontramos un efecto significativo (P < 0.05) en la longitud de la raíz y el tallo, y el peso seco del tallo. La longitud del tallo aumentó en un 52 % y 30 % con 37L y 35P, respectivamente, en comparación con aquellos sin tratamiento de inoculación. Igualmente, el uso de las cepas 37L y 28P aumentó los valores de peso seco del tallo en un 170 y un 131 %, respectivamente. En el desarrollo de la raíz, la inoculación con las cepas 37L y E37 aumentó la longitud de la raíz en 134 y 100 %, respectivamente. Conclusión: Beijerinckia sp. 37L fue la más efectiva de las cuatro cepas al aumentar la biomasa y la longitud de P. clandestinum.

RESUMO

Nine bacterial strains were previously isolated in association with pinewood nematode (PWN) from wilted pine trees. They proved to be nematicidal in vitro, and one of the highest activities, with potential to control PWN, was showed by Serratia sp. M24T3. Its ecology in association with plants remains unclear. This study aimed to evaluate the ability of strain M24T3 to colonize the internal tissues of the model plant Arabidopsis thaliana using confocal microscopy. Plant growth-promoting bacteria (PGPB) functional traits were tested and retrieved in the genome of strain M24T3. In greenhouse conditions, the bacterial effects of all nematicidal strains were also evaluated, co-inoculated or not with Bradyrhizobium sp. 3267, on Vigna unguiculata fitness. Inoculation of strain M24T3 increased the number of A. thaliana lateral roots and the confocal analysis confirmed effective bacterial colonization in the plant. Strain M24T3 showed cellulolytic activity, siderophores production, phosphate and zinc solubilization ability, and indole acetic acid production independent of supplementation with L-tryptophan. In the genome of strain M24T3, genes involved in the interaction with the plants such as 1-aminocyclopropane-1-carboxylate (ACC) deaminase, chitinolytic activity, and quorum sensing were also detected. The genomic organization showed ACC deaminase and its leucine-responsive transcriptional regulator, and the activity of ACC deaminase was 594.6 nmol α-ketobutyrate µg protein-1 µl-1. Strain M24T3 in co-inoculation with Bradyrhizobium sp. 3267 promoted the growth of V. unguiculata. In conclusion, this study demonstrated the ability of strain M24T3 to colonize other plants besides pine trees as an endophyte and displays PGPB traits that probably increased plant tolerance to stresses.

Assuntos

Arabidopsis/microbiologia , Nematoides/microbiologia , Serratia/fisiologia , Animais , Antibiose , Arabidopsis/crescimento & desenvolvimento , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Carbono-Carbono Liases/genética , Carbono-Carbono Liases/metabolismo , Pinus/parasitologia , Doenças das Plantas/parasitologia , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/microbiologia , Percepção de Quorum , Serratia/enzimologia , Serratia/genética , Serratia/isolamento & purificação , Vigna/crescimento & desenvolvimento , Vigna/microbiologia

RESUMO

Ethylene acts as a major regulator of the nodulation process of leguminous plants. Several rhizobial strains possess the ability to modulate plant ethylene levels through the expression of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase; however, rhizobia present low enzymatic activities. One possible alternative to this problem resides on the use of free-living bacteria, such as Pseudomonas, presenting high levels of ACC deaminase activity that may be used as adjuvants in the nodulation process by decreasing inhibitory ethylene levels. Nevertheless, not much is understood about the specific role of ACC deaminase in the possible role of free-living bacteria as nodulation adjuvants. Therefore, this work aims to study the effect of ACC deaminase in the plant growth-promoting bacterium, Pseudomonas fluorescens YsS6, ability to facilitate alpha- and beta-rhizobia nodulation. The ACC deaminase-producing P. fluorescens YsS6 and its ACC deaminase mutant were used in co-inoculation assays to evaluate their impact in the nodulation process of alpha- (Rhizobium tropici CIAT899) and beta-rhizobia (Cupriavidus taiwanensis STM894) representatives, in Phaseolus vulgaris and Mimosa pudica plants, respectively. The results obtained indicate that the wild-type P. fluorescens YsS6, but not its mutant defective in ACC deaminase production, increase the nodulation abilities of both alpha- and beta-rhizobia, resulting in an increased leguminous plant growth. Moreover, this is the first report of the positive effect of free-living bacteria in the nodulation process of beta-rhizobia. The modulation of inhibitory ethylene levels by free-living ACC deaminase-producing bacteria plays an important role in facilitating the nodulation process of alpha- and beta-rhizobia.

Assuntos

Alphaproteobacteria/fisiologia , Proteínas de Bactérias/metabolismo , Carbono-Carbono Liases/metabolismo , Cupriavidus/fisiologia , Mimosa/microbiologia , Phaseolus/microbiologia , Pseudomonas fluorescens/enzimologia , Inoculantes Agrícolas/fisiologia , Proteínas de Bactérias/genética , Carbono-Carbono Liases/genética , Etilenos/metabolismo , Mimosa/fisiologia , Phaseolus/fisiologia , Nodulação , Pseudomonas fluorescens/genética

RESUMO

Ethylene acts as an inhibitor of the nodulation process of leguminous plants. However, some bacteria can decrease deleterious ethylene levels by the action of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase which degrades ACC, the ethylene precursor in all higher plants. Co-inoculation of rhizobia with endophytes enhances the rhizobial symbiotic efficiency with legumes, improving both nodulation and nitrogen fixation. However, not much is understood about the mechanisms employed by these endophytic bacteria. In this regard, the role of ACC deaminase from endophytic strains in assisting rhizobia in this process has yet to be confirmed. In this study, the role of ACC deaminase in an endophyte's ability to increase Rhizobium tropici nodulation of common bean was evaluated. To assess the effect of ACC deaminase in an endophyte's ability to promote rhizobial nodulation, the endophyte Serratia grimesii BXF1, which does not encode ACC deaminase, was transformed with an exogenous acdS gene. The results obtained indicate that the ACC deaminase-overexpressing transformant strain increased common bean growth, and enhanced the nodulation abilities of R. tropici CIAT899, in both cases compared to the wild-type non-transformed strain. Furthermore, plant inoculation with the ACC deaminase-overproducing strain led to an increased level of plant protection against a seed-borne pathogen. SIGNIFICANCE AND IMPACT OF THE STUDY: In this work, we studied the effect of ACC deaminase production by the bacterial endophyte Serratia grimesi BXF1, and its impact on the nodulation process of common bean. The results obtained indicate that ACC deaminase is an asset to the synergetic interaction between rhizobia and the endophyte, positively contributing to the overall legume-rhizobia symbiosis by regulating inhibitory ethylene levels that might otherwise inhibit nodulation and overall plant growth. The use of rhizobia together with an ACC deaminase-producing endophyte is, therefore, an important strategy for the development of new bacterial inoculants with increased performance.

Assuntos

Proteínas de Bactérias/metabolismo , Carbono-Carbono Liases/metabolismo , Phaseolus/crescimento & desenvolvimento , Nodulação/fisiologia , Rhizobium tropici/metabolismo , Nódulos Radiculares de Plantas/microbiologia , Serratia/enzimologia , Inoculantes Agrícolas , Endófitos/metabolismo , Etilenos/metabolismo , Phaseolus/microbiologia , Serratia/genética , Serratia/metabolismo , Simbiose

RESUMO

Abiotic stress has a growing impact on plant growth and agricultural activity worldwide. Specific plant growth promoting rhizobacteria have been reported to stimulate growth and tolerance to abiotic stress in plants, and molecular mechanisms like phytohormone synthesis and 1-aminocyclopropane-1-carboxylate deamination are usual candidates proposed to mediate these bacterial effects. Paraburkholderia phytofirmans PsJN is able to promote growth of several plant hosts, and improve their tolerance to chilling, drought and salinity. This work investigated bacterial determinants involved in PsJN stimulation of growth and salinity tolerance in Arabidopsis thaliana, showing bacteria enable plants to survive long-term salinity treatment, accumulating less sodium within leaf tissues relative to non-inoculated controls. Inactivation of specific bacterial genes encoding ACC deaminase, auxin catabolism, N-acyl-homoserine-lactone production, and flagellin synthesis showed these functions have little influence on bacterial induction of salinity tolerance. Volatile organic compound emission from strain PsJN was shown to reproduce the effects of direct bacterial inoculation of roots, increasing plant growth rate and tolerance to salinity evaluated both in vitro and in soil. Furthermore, early exposure to VOCs from P. phytofirmans was sufficient to stimulate long-term effects observed in Arabidopsis growth in the presence and absence of salinity. Organic compounds were analyzed in the headspace of PsJN cultures, showing production of 2-undecanone, 7-hexanol, 3-methylbutanol and dimethyl disulfide. Exposure of A. thaliana to different quantities of these molecules showed that they are able to influence growth in a wide range of added amounts. Exposure to a blend of the first three compounds was found to mimic the effects of PsJN on both general growth promotion and salinity tolerance. To our knowledge, this is the first report on volatile compound-mediated induction of plant abiotic stress tolerance by a Paraburkholderia species.

RESUMO

Background: Endophytic bacteria are ubiquitous in all plant species contributing in host plant's nutrient uptake and helping the host to improve its growth. Moringa peregrina which is a medicinal plant, growing in arid region of Arabia, was assessed for the presence of endophytic bacterial strains. Results: PCR amplification and sequencing of 16S rRNA of bacterial endophytes revealed the 5 endophytic bacteria, in which 2 strains were from Sphingomonas sp.; 2 strains from Bacillus sp. and 1 from Methylobacterium genus. Among the endophytic bacterial strains, a strain of Bacillus subtilis LK14 has shown significant prospects in phosphate solubilization (clearing zone of 56.71 mm after 5 d), ACC deaminase (448.3 ± 2.91 nM α-ketobutyrate mg-1 h-1) and acid phosphatase activity (8.4 ± 1.2 nM mg-1 min-1). The endophytic bacteria were also assessed for their potential to produce indole-3-acetic acid (IAA). Among isolated strains, the initial spectrophotometry analysis showed significantly higher IAA production by Bacillus subtilis LK14. The diurnal production of IAA was quantified using multiple reactions monitoring method in UPLC/MS-MS. The analysis showed that LK14 produced the highest (8.7 uM) IAA on 14th d of growth. Looking at LK14 potentials, it was applied to Solanum lycopersicum, where it significantly increased the shoot and root biomass and chlorophyll (a and b) contents as compared to control plants. Conclusion: The study concludes that using endophytic bacterial strains can be bio-prospective for plant growth promotion, which might be an ideal strategy for improving growth of crops in marginal lands.

Assuntos

Bacillus subtilis/fisiologia , Solanum lycopersicum/crescimento & desenvolvimento , Ácidos Indolacéticos/metabolismo , Bacillus subtilis/isolamento & purificação , Bacillus subtilis/enzimologia , Bacillus subtilis/genética , Reação em Cadeia da Polimerase , Cromatografia/métodos , Solanum lycopersicum/microbiologia , Endófitos , Ácidos Indolacéticos/análise

RESUMO

Salinity is the leading abiotic stress hampering maize ( Zea mays L.) growth throughout the world, especially in Pakistan. During salinity stress, the endogenous ethylene level in plants increases, which retards proper root growth and consequent shoot growth of the plants. However, certain bacteria contain the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which converts 1-aminocyclopropane-1-carboxylic acid (an immediate precursor of ethylene biosynthesis in higher plants) into ammonia and α-ketobutyrate instead of ethylene. In the present study, two Pseudomonas bacterial strains containing ACC-deaminase were tested separately and in combinations with mineral fertilizers to determine their potential to minimize/undo the effects of salinity on maize plants grown under saline-sodic field conditions. The data recorded at 30, 50 and 70 days after sowing revealed that both the Pseudomonas bacterial strains improved root and shoot length, root and shoot fresh weight, and root and shoot dry weight up to 34, 43, 35, 71, 55 and 68%, respectively, when applied without chemical fertilizers: these parameter were enhanced up to 108, 95, 100, 131, 100 and 198%, respectively, when the strains were applied along with chemical fertilizers. It can be concluded that ACC-deaminase Pseudomonas bacterial strains applied alone and in conjunction with mineral fertilizers improved the root and shoot growth of maize seedlings grown in saline-sodic soil.

Assuntos

Desenvolvimento Vegetal , Raízes de Plantas/fisiologia , Brotos de Planta/fisiologia , Pseudomonas/crescimento & desenvolvimento , Microbiologia do Solo , Solo/química , Zea mays/fisiologia , Aminoácidos Cíclicos/metabolismo , Amônia/metabolismo , Butiratos , Carbono-Carbono Liases/metabolismo , Fertilizantes , Paquistão , Pseudomonas/enzimologia , Salinidade

RESUMO

Salinity is the leading abiotic stress hampering maize (Zea mays L.) growth throughout the world, especially in Pakistan. During salinity stress, the endogenous ethylene level in plants increases, which retards proper root growth and consequent shoot growth of the plants. However, certain bacteria contain the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which converts 1-aminocyclopropane-1-carboxylic acid (an immediate precursor of ethylene biosynthesis in higher plants) into ammonia and α-ketobutyrate instead of ethylene. In the present study, two Pseudomonas bacterial strains containing ACC-deaminase were tested separately and in combinations with mineral fertilizers to determine their potential to minimize/undo the effects of salinity on maize plants grown under saline-sodic field conditions. The data recorded at 30, 50 and 70 days after sowing revealed that both the Pseudomonas bacterial strains improved root and shoot length, root and shoot fresh weight, and root and shoot dry weight up to 34, 43, 35, 71, 55 and 68%, respectively, when applied without chemical fertilizers: these parameter were enhanced up to 108, 95, 100, 131, 100 and 198%, respectively, when the strains were applied along with chemical fertilizers. It can be concluded that ACC-deaminase Pseudomonas bacterial strains applied alone and in conjunction with mineral fertilizers improved the root and shoot growth of maize seedlings grown in saline-sodic soil.

Assuntos

Desenvolvimento Vegetal , Raízes de Plantas/fisiologia , Brotos de Planta/fisiologia , Pseudomonas/crescimento & desenvolvimento , Microbiologia do Solo , Solo/química , Zea mays/fisiologia , Aminoácidos Cíclicos/metabolismo , Amônia/metabolismo , Butiratos , Carbono-Carbono Liases/metabolismo , Fertilizantes , Paquistão , Pseudomonas/enzimologia , Salinidade

RESUMO

Salinity is the leading abiotic stress hampering maize (Zea mays L.) growth throughout the world, especially in Pakistan. During salinity stress, the endogenous ethylene level in plants increases, which retards proper root growth and consequent shoot growth of the plants. However, certain bacteria contain the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which converts 1-aminocyclopropane-1-carboxylic acid (an immediate precursor of ethylene biosynthesis in higher plants) into ammonia and α-ketobutyrate instead of ethylene. In the present study, two Pseudomonas bacterial strains containing ACC-deaminase were tested separately and in combinations with mineral fertilizers to determine their potential to minimize/undo the effects of salinity on maize plants grown under saline-sodic field conditions. The data recorded at 30, 50 and 70 days after sowing revealed that both the Pseudomonas bacterial strains improved root and shoot length, root and shoot fresh weight, and root and shoot dry weight up to 34, 43, 35, 71, 55 and 68%, respectively, when applied without chemical fertilizers: these parameter were enhanced up to 108, 95, 100, 131, 100 and 198%, respectively, when the strains were applied along with chemical fertilizers. It can be concluded that ACC-deaminase Pseudomonas bacterial strains applied alone and in conjunction with mineral fertilizers improved the root and shoot growth of maize seedlings grown in saline-sodic soil.(AU)

Assuntos

Raízes de Plantas/fisiologia , Brotos de Planta/fisiologia , Pseudomonas/crescimento & desenvolvimento , Microbiologia do Solo , Solo/química , Zea mays/fisiologia , Aminoácidos Cíclicos/metabolismo , Amônia/metabolismo , Butiratos , Carbono-Carbono Liases/metabolismo , Fertilizantes , Paquistão , Pseudomonas/enzimologia , Salinidade

RESUMO

Se aislaron bacterias rizosféricas y endófitas a partir de rizósfera y tejidos de raíz de árboles de Eucalyptus nitens con el objetivo de evaluar su capacidad de promover el crecimiento en plántulas de la misma especie en condiciones de invernadero. Los aislamientos que incrementaron el crecimiento de las plántulas fueron identificados y caracterizados por su capacidad de producir ácido indolacético (AIA), solubilizar fosfato y expresar la 1-aminociclopropano-1-carboxilato (ACC) desaminasa. Los 105 aislamientos obtenidos fueron morfológicamente diferentes y solo 15 promovieron significativamente el crecimiento de plántulas de E. nitens. Los máximos incrementos observados fueron en el peso seco aéreo (142 %) y de la raíz (135 %); también aumentaron la altura de las plantas (50 %) y el largo de raíces (45 %) de las mismas. Las rizobacterias pertenecieron a los géneros Arthrobacter, Lysinibacillus, Rahnella y Bacillus. Los aislados identificados como A. phenanthrenivorans 21 y B. cereus 113 incrementaron la emergencia de E. nitens a los 12 días en un valor promedio de 3,15 veces con relación al control. R. aquatilis aislado 78 presentó la mayor producción de AIA (97,5 ± 2,87 μg/ml) en presencia de triptófano y el mayor índice de solubilización de fósforo (2,4). B. amyloliquefaciens aislado 60 fue positivo para la actividad ACC desaminasa. Los resultados obtenidos indican el potencial de las rizobacterias estudiadas como promotoras de emergencia y crecimiento de plántulas de E. nitens y su posible uso como inoculantes, ya que presentan más de un mecanismo de acción asociado a la promoción del crecimiento.(AU)

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Rhizospheric and endophytic bacteria were isolated from the rizosphere and root tissue of Eucalyptus nitens. The objective of this work was to evaluate their capacity to promote growth in seedlings of the same species under greenhouse conditions. The isolates that improved seedling growth were identified and characterized by their capacity to produce indoleacetic acid (IAA), solubilize phosphates and increase 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. One hundred and five morphologically different strains were isolated, 15 of which promoted E. nitens seedling growth, significantly increasing the height (50%), root length (45%) as well as the aerial and root dry weight (142% and 135% respectively) of the plants. Bacteria belonged to the genus Arthrobacter, Lysinibacillus, Rahnella and Bacillus. Isolates A. phenanthrenivorans 21 and B. cereus 113 improved 3.15 times the emergence of E. nitens after 12 days, compared to control samples. Among isolated R. aquatilis, 78 showed the highest production of IAA (97.5±2.87 μg/ml) in the presence of tryptophan and the highest solubilizer index (2.4) for phosphorus, while B. amyloliquefaciens 60 isolate was positive for ACC deaminase activity. Our results reveal the potential of the studied rhizobacteria as promoters of emergence and seedling growth of E. nitens, and their possible use as PGPR inoculants, since they have more than one mechanism associated with plant growth promotion.(AU)

RESUMO

Se aislaron bacterias rizosféricas y endófitas a partir de rizósfera y tejidos de raíz de árboles de Eucalyptus nitens con el objetivo de evaluar su capacidad de promover el crecimiento en plántulas de la misma especie en condiciones de invernadero. Los aislamientos que incrementaron el crecimiento de las plántulas fueron identificados y caracterizados por su capacidad de producir ácido indolacético (AIA), solubilizar fosfato y expresar la 1-aminociclopropano-1-carboxilato (ACC) desaminasa. Los 105 aislamientos obtenidos fueron morfológicamente diferentes y solo 15 promovieron significativamente el crecimiento de plántulas de E. nitens. Los máximos incrementos observados fueron en el peso seco aéreo (142 %) y de la raíz (135 %); también aumentaron la altura de las plantas (50 %) y el largo de raíces (45 %) de las mismas. Las rizobacterias pertenecieron a los géneros Arthrobacter, Lysinibacillus, Rahnella y Bacillus. Los aislados identificados como A. phenanthrenivorans 21 y B. cereus 113 incrementaron la emergencia de E. nitens a los 12 días en un valor promedio de 3,15 veces con relación al control. R. aquatilis aislado 78 presentó la mayor producción de AIA (97,5 ± 2,87 μg/ml) en presencia de triptófano y el mayor índice de solubilización de fósforo (2,4). B. amyloliquefaciens aislado 60 fue positivo para la actividad ACC desaminasa. Los resultados obtenidos indican el potencial de las rizobacterias estudiadas como promotoras de emergencia y crecimiento de plántulas de E. nitens y su posible uso como inoculantes, ya que presentan más de un mecanismo de acción asociado a la promoción del crecimiento.

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Rhizospheric and endophytic bacteria were isolated from the rizosphere and root tissue of Eucalyptus nitens. The objective of this work was to evaluate their capacity to promote growth in seedlings of the same species under greenhouse conditions. The isolates that improved seedling growth were identified and characterized by their capacity to produce indoleacetic acid (IAA), solubilize phosphates and increase 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. One hundred and five morphologically different strains were isolated, 15 of which promoted E. nitens seedling growth, significantly increasing the height (50%), root length (45%) as well as the aerial and root dry weight (142% and 135% respectively) of the plants. Bacteria belonged to the genus Arthrobacter, Lysinibacillus, Rahnella and Bacillus. Isolates A. phenanthrenivorans 21 and B. cereus 113 improved 3.15 times the emergence of E. nitens after 12 days, compared to control samples. Among isolated R. aquatilis, 78 showed the highest production of IAA (97.5±2.87 μg/ml) in the presence of tryptophan and the highest solubilizer index (2.4) for phosphorus, while B. amyloliquefaciens 60 isolate was positive for ACC deaminase activity. Our results reveal the potential of the studied rhizobacteria as promoters of emergence and seedling growth of E. nitens, and their possible use as PGPR inoculants, since they have more than one mechanism associated with plant growth promotion.

Assuntos

Eucalyptus/microbiologia , Rhizobium/isolamento & purificação , Rhizobium/fisiologia , Plântula/crescimento & desenvolvimento , Plântula/microbiologia , Raízes de Plantas/microbiologia

RESUMO

AIM: To develop co-aggregated bacterial inoculant comprising of Methylobacterium oryzae CBMB20/Methylobacterium suomiense CBMB120 strains with Azospirillum brasilense (CW903) strain and testing their efficiency as inoculants for plant growth promotion (PGP). METHODS AND RESULTS: Biofilm formation and co-aggregation efficiency was studied between A. brasilense CW903 and methylobacterial strains M. oryzae CBMB20 and M. suomiense CBMB120. Survival and release of these co-aggregated bacterial strains entrapped in alginate beads were assessed. PGP attributes of the co-aggregated bacterial inoculant were tested in tomato plants under water-stressed conditions. Results suggest that the biofilm formation efficiency of the CBMB20 and CBMB120 strains increased by 15 and 34%, respectively, when co-cultivated with CW903. Co-aggregation with CW903 enhanced the survivability of CBMB20 strain in alginate beads. Water stress index score showed least stress index in plants inoculated with CW903 and CBMB20 strains maintained as a co-aggregated inoculant. CONCLUSIONS: This study reports the development of co-aggregated cell inoculants containing M. oryzae CBMB20 and A. brasilense CW903 strains conferred better shelf life and stress abatement in inoculated tomato plants. SIGNIFICANCE AND IMPACT OF THE STUDY: These findings could be extended to other PGP bacterial species to develop multigeneric bioinoculants with multiple benefits for various crops.

Assuntos

Alginatos/química , Azospirillum brasilense/fisiologia , Biofilmes/crescimento & desenvolvimento , Methylobacterium/fisiologia , Solanum lycopersicum/crescimento & desenvolvimento , Azospirillum brasilense/enzimologia , Azospirillum brasilense/ultraestrutura , Desidratação/prevenção & controle , Secas , Etilenos/metabolismo , Ácido Glucurônico/química , Ácidos Hexurônicos/química , Hidrólise , Peroxidação de Lipídeos , Solanum lycopersicum/microbiologia , Malondialdeído/metabolismo , Methylobacterium/enzimologia , Methylobacterium/ultraestrutura , Microscopia Eletrônica de Varredura , Microesferas , Peroxidase/metabolismo , Solo/química

RESUMO

Rhizospheric and endophytic bacteria were isolated from the rizosphere and root tissue of Eucalyptus nitens. The objective of this work was to evaluate their capacity to promote growth in seedlings of the same species under greenhouse conditions. The isolates that improved seedling growth were identified and characterized by their capacity to produce indoleacetic acid (IAA), solubilize phosphates and increase 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. One hundred and five morphologically different strains were isolated, 15 of which promoted E. nitens seedling growth, significantly increasing the height (50%), root length (45%) as well as the aerial and root dry weight (142% and 135% respectively) of the plants. Bacteria belonged to the genus Arthrobacter, Lysinibacillus, Rahnella and Bacillus. Isolates A. phenanthrenivorans 21 and B. cereus 113 improved 3.15 times the emergence of E. nitens after 12 days, compared to control samples. Among isolated R. aquatilis, 78 showed the highest production of IAA (97.5±2.87 µg/ml) in the presence of tryptophan and the highest solubilizer index (2.4) for phosphorus, while B. amyloliquefaciens 60 isolate was positive for ACC deaminase activity. Our results reveal the potential of the studied rhizobacteria as promoters of emergence and seedling growth of E. nitens, and their possible use as PGPR inoculants, since they have more than one mechanism associated with plant growth promotion.

Assuntos

Eucalyptus/microbiologia , Rhizobium/isolamento & purificação , Rhizobium/fisiologia , Plântula/crescimento & desenvolvimento , Plântula/microbiologia , Raízes de Plantas/microbiologia