The Synergistic Impact of Arbuscular Mycorrhizal Fungi and Compost Tea to Enhance Bacterial Community and Improve Crop Productivity under Saline-Sodic Condition.

Soil salinity has a negative impact on the biochemical properties of soil and on plant growth, particularly in arid and semi-arid regions. Using arbuscular mycorrhizal fungi (Glomus versiform) and foliar spray from compost tea as alleviating treatments, this study aimed to investigate the effects of alleviating salt stress on the growth and development of maize and wheat grown on a saline-sodic soil during the period of 2022/2023. Six treatments were used in the completely randomized factorial design experiment. The treatments included Arbuscular mycorrhizal fungus (AMF0, AMF1) and varied concentrations of compost tea (CT0, CT50, and CT100). AMF colonization, the bacterial community and endosphere in the rhizosphere, respiration rate, growth parameters, and the productivity were all evaluated. The application of AMF and CT, either separately or in combination, effectively mitigated the detrimental effects caused by soil salinity. The combination of AMF and CT proved to be highly efficient in improving the infection rate of AMF, the bacterial community in the rhizosphere and endosphere, growth parameters, and grain yield of maize and wheat. Therefore, it can be proposed that the inoculation of mycorrhizal fungi with compost tea in saline soils is an important strategy for enhancing salt tolerance in maize and wheat plants through improving microbial activity, the infection rate of AMF, and overall maize and wheat productivity.

Nitrogen fertilization regulates crosstalk between marandu palisadegrass and Herbaspirillum seropedicae: An investigation based on 15N isotopic analysis and root morphology.

Strategies seeking to increase the use efficiency of nitrogen (N) fertilizers and that benefit plant growth through multiple mechanisms can reduce production costs and contribute to more sustainable agriculture free of polluting residues. Under controlled conditions, we investigated the compatibility between foliar inoculation with an endophytic diazotrophic bacterium (Herbaspirillum seropedicae HRC54) at control and low, medium and high N fertilization levels (0, 25, 50 and 100 mg of N kg-1 as urea, respectively) in Marandu palisadegrass. Common procedures in our research field (biometric and nutritional assessments) were combined with isotopic techniques (natural abundance - δ15N‰ and 15N isotope dilution) and root scanning to determine the contribution of fixed N and recovery of N fertilizer by the grass. Overall, the combined use of 15N isotopic techniques revealed that inoculation not only improved the recovery of applied N-urea from the soil but also provided fixed nitrogen to Marandu palisade grass, resulting in an increase in the total accumulated N. When inoculated plants grew at control and low levels of N, a positive cascade effect encompassing root growth stimulation (nodes of smaller diameter roots), better soil and fertilizer resource exploitation and increased forage production was observed. In contrast, increasing N reduced the contributions of N fixed by H. seropedicae from 21.5% at the control level to 8.6% at the high N level. Given the minimal to no observed growth promotion, this condition was deemed inhibitory to the positive effects of H. seropedicae. We discuss how to make better use of H. seropedicae inoculation in Marandu palisadegrass, albeit on a small scale, thus contributing to a more rational and efficient use of N fertilizers. Finally, we pose questions for future investigations based on 15N isotopic techniques under field conditions, which have great applicability potential.

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 55 days. 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.

The outstanding diversity of rhizobia microsymbionts of common bean (Phaseolus vulgaris L.) in Mato Grosso do Sul, central-western Brazil, revealing new Rhizobium species.

Common bean is considered a legume of great socioeconomic importance, capable of establishing symbioses with a wide variety of rhizobial species. However, the legume has also been recognized for its low efficiency in fixing atmospheric nitrogen. Brazil is a hotspot of biodiversity, and in a previous study, we identified 13 strains isolated from common bean (Phaseolus vulgaris) nodules in three biomes of Mato Grosso do Sul state, central-western Brazil, that might represent new phylogenetic groups, deserving further polyphasic characterization. The phylogenetic tree of the 16S rRNA gene split the 13 strains into two large clades, seven in the R. etli and six in the R. tropici clade. The MLSA with four housekeeping genes (glnII, gyrB, recA, and rpoA) confirmed the phylogenetic allocation. Genomic comparisons indicated eight strains in five putative new species and the remaining five as R. phaseoli. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) comparing the putative new species and the closest neighbors ranged from 81.84 to 92.50% and 24.0 to 50.7%, respectively. Other phenotypic, genotypic, and symbiotic features were evaluated. Interestingly, some strains of both R. etli and R. tropici clades lost their nodulation capacity. The data support the description of the new species Rhizobium cerradonense sp. nov. (CNPSo 3464T), Rhizobium atlanticum sp. nov. (CNPSo 3490T), Rhizobium aureum sp. nov. (CNPSo 3968T), Rhizobium pantanalense sp. nov. (CNPSo 4039T), and Rhizobium centroccidentale sp. nov. (CNPSo 4062T).

Biochar amendment reduces biological nitrogen fixation and nitrogen use efficiency in cadmium-contaminated paddy fields.

Cadmium (Cd) contamination poses a considerable threat to human health through grain enrichment and limits biological nitrogen fixation (BNF) in paddy fields. Biochar has shown great potential for agricultural soil remediation because it inactivates Cd, but uncertainties remain as to how biochar amendments affect BNF and grain N use efficiency in paddies. To elucidate these issues, we investigated the effects of biochar amendment on the structure and function of diazotrophic bacterial communities in different rice growth stages in Cd-contaminated paddy fields, and evaluated the contribution of BNF to grain N use efficiency under biochar amendment. The results showed that biochar amendment significantly increased the abundance of diazotrophic bacteria in the tillering and jointing stages. Furthermore, the community structure of soil diazotrophic bacteria markedly changed with biochar amendment, with a significant reduction in the abundances of Euryarchaeota, Desulfobacterales (Proteobacteria), and Sphingomonadales (Bacteroidetes) in the tillering stage. Changes in the soil carbon/nitrogen (C/N) ratio was the main factor driving diazotrophic microbial community characteristics caused by the release of available C from biochar at the tillering stage, rather than the Cd. Moreover, biochar amendment increased the efficiency of BNF (especially for autotrophic N2 fixation) in the vegetative phase of rice growth. Notably, biochar amendment significantly decreased BNF efficiency during the filling stage and reduced grain N use efficiency. The limited available nutrients in biochar and the toxicity of polycyclic aromatics and phenols in biochar-derived dissolved organic matter were responsible for the varied impacts of biochar on BNF in different rice growth stages. For the first time, we report that biochar amendment in paddy soils reduces Cd toxicity but also inhibits BNF and thereby decreases N use efficiency. Therefore, before applying biochar to inactivate Cd in paddy fields, there should be a trade-off between agricultural production and ecological safety to achieve sustainable agriculture.

Presence and activity of nitrogen-fixing bacteria in Scots pine needles in a boreal forest: a nitrogen-addition experiment.

Endophytic nitrogen-fixing bacteria have been detected and isolated from the needles of conifer trees growing in North American boreal forests. Because boreal forests are nutrient-limited, these bacteria could provide an important source of nitrogen for tree species. This study aimed to determine their presence and activity in a Scandinavian boreal forest, using immunodetection of nitrogenase enzyme subunits and acetylene-reduction assays of native Scots pine (Pinus sylvestris L.) needles. The presence and rate of nitrogen fixation by endophytic bacteria were compared between control plots and fertilized plots in a nitrogen-addition experiment. In contrast to the expectation that nitrogen-fixation rates would decline in fertilized plots, as seen, for instance, with nitrogen-fixing bacteria associated with bryophytes, there was no difference in the presence or activity of nitrogen-fixing bacteria between the two treatments. The extrapolated calculated rate of nitrogen fixation relevant for the forest stand was 20 g N ha-1 year-1, which is rather low compared with Scots pine annual nitrogen use but could be important for the nitrogen-poor forest in the long term. In addition, of 13 colonies of potential nitrogen-fixing bacteria isolated from the needles on nitrogen-free media, 10 showed in vitro nitrogen fixation. In summary, 16S rRNA sequencing identified the species as belonging to the genera Bacillus, Variovorax, Novosphingobium, Sphingomonas, Microbacterium and Priestia, which was confirmed by Illumina whole-genome sequencing. Our results confirm the presence of endophytic nitrogen-fixing bacteria in Scots pine needles and suggest that they could be important for the long-term nitrogen budget of the Scandinavian boreal forest.

Agronomic performance and quality of baby corn in response to the inoculation of seeds with Azospirillum brasilense and nitrogen fertilization in the summer harvest.

The association with Azospirillum brasilense promotes better growth and development in corn plants due to biological N fixation, the capacity to help in the synthesis of phytohormones and to improve the use of nutrients by crop plants. However, there aren't specific recommendations for the use of inoculation in baby corn crop. Thus, this study aimed to evaluate the effects of seed inoculation with A. brasilense, associated with nitrogen fertilization management, on the agronomic performance and chemical quality of baby corn grown in three summer growing seasons (2014/2015; 2015/2016 and 2016/2017). The evaluated treatments consisted of combination of five levels of seed inoculation (0.0, 50, 100, 150 and 200 mL 60,000 seeds-1) based on Azospirillum brasilense, two levels of nitrogen fertilization at sowing time (0.0 and 30.0 kg of N ha-1) and two levels of nitrogen in topdressing (0.0 and 110.0 kg of N ha-1), applied at the V4 stage of the popcorn hybrid IAC 125. The characteristics evaluated were: leaf area index (LAI), leaf nitrogen content (LNC), total husked spikelets yield (HSY) and commercial spikelets yield (CSY), and the chemical characteristics of the commercial spikelets: crude protein content (CPC), starch content (STC) and total sugar content (TSC). The inoculation, when combined with nitrogen fertilization, provided positive responses for LAI and provided an average increment of 6 kg ha-1 to CSY for every 10 mL 60,000 seeds-1 of inoculant added to the seeds. The LNC, CPC, STC and TSC weren't affected by seed inoculation. Nitrogen fertilization provided increments for all characteristics evaluated, except for TSC, which was negatively affected by nitrogen topdressing. The baby corn crop responded positively to seed inoculation with Azospirillum brasilense, combined with Nitrogen fertilization.

Genetic engineering for enhanced biological nitrogen fixation in cereal crops.

Enhancing biological nitrogen (N) fixation in cereal crops has been a long-sought objective. Recently, Yan et al. identified plant compounds that induce biofilm production of diazotrophic bacteria and then performed genetic engineering in order to improve nitrogen fixation in rice plants. These findings hold promise for sustainable agriculture.

Molecular and biochemical responses of sesame (Sesame indicum L.) to rhizobacteria inoculation under water deficit.

Introduction: Water scarcity is a challenge for sesame cultivation under rainfed conditions. In this scenario, a potential strategy to alleviate the water deficit is the application of plant growth-promoting bacteria. The objective of this study was to analyze the interaction of rhizobacteria with sesame cultivation under water deficit conditions. Methods: An experiment was conducted in pots in a greenhouse using the BRS Morena sesame cultivar. The experimental design was completely randomized in a factorial scheme: 2 (irrigation regimes - daily irrigation and water deficit by suspending irrigation until 90% stomatal closure) x 6 (treatments with nitrogen or inoculants), with 5 replications. The types of fertilization were characterized by the addition of nitrogen (ammonium sulfate; 21% N), inoculants based on Bacillus spp. (pant001, ESA 13, and ESA 402), Agrobacterium sp. (ESA 441), and without nitrogen (control). On the fifth day after the suspension of irrigation, plant material was collected for gene expression analysis (DREB1 and HDZ7), activities of antioxidant enzymes (superoxide dismutase and catalase), relative proline content, and photosynthetic pigments. At the end of the crop cycle (about 85 days), production characteristics (root dry matter, aboveground dry matter, number of capsules, and thousand seed weight), as well as leaf nitrogen (N) and phosphorus (P) content, were evaluated. Results and Discussion: There was a positive effect on both production and biochemical characteristics (proline, superoxide dismutase, catalase, and photosynthetic pigments). Regarding gene expression, most of the inoculated treatments exhibited increased expression of the DREB1 and HDZ7 genes. These biological indicators demonstrate the potential of rhizobacteria for application in sesame cultivation, providing nutritional supply and reducing the effects of water deficit.

Simple and sensitive spectrophotometric method for estimating the nitrogen-fixing capacity of bacterial cultures.

Biological nitrogen fixation (BNF) is a process through which a group of microorganisms called diazotrophs convert unassimilable atmospheric nitrogen into ammonia. In aqueous media, ammonia yields ammonium ions that can be assimilated by microorganisms and plants. To reduce the application of nitrogen fertilizers and their environmental effects, an alternative approach toward sustainable agriculture is the induction of artificial associations between diazotrophs and plants. This has led to increased interest in the search for microorganisms capable of supplying nitrogen to crops. This article presents a simple, economical, and sensitive spectrophotometric method for estimating the BNF capacity of bacteria cultured in a liquid NFb medium, based on the variation of absorbance caused by the change in color of bromothymol blue in the culture medium. The structure and color of this indicator are modified by pH shifts, which depend on the concentration of fixed ammonium ions.•The nitrogen concentration (estimated from the ammonium in the culture medium) showed a positive correlation (R 2 = 0.984) with the absorbance measured at 610 nm. The regression equation obtained through the origin was y = 0.009682140x, where y is the absorbance and x is the nitrogen concentration in the culture medium.•The methods used at present to measure the efficiency of BNF require expensive equipment, which may not be affordable for many laboratories or companies working in this field.•This technique can be used for pure bacterial strains and microbial consortia from soil or commercial products.

Sugarcane Genotypes with Contrasting Biological Nitrogen Fixation Efficiencies Differentially Modulate Nitrogen Metabolism, Auxin Signaling, and Microorganism Perception Pathways.

Sugarcane is an economically important crop that is used for the production of fuel ethanol. Diazotrophic bacteria have been isolated from sugarcane tissues, without causing visible plant anatomical changes or disease symptoms. These bacteria can be beneficial to the plant by promoting root growth and an increase in plant yield. Different rates of Biological Nitrogen Fixation (BNF) were observed in different genotypes. The aim of this work was to conduct a comprehensive molecular and physiological analysis of two model genotypes for contrasting BNF efficiency in order to unravel plant genes that are differentially regulated during a natural association with diazotrophic bacteria. A next-generation sequencing of RNA samples from the genotypes SP70-1143 (high-BNF) and Chunee (low-BNF) was performed. A differential transcriptome analysis showed that several pathways were differentially regulated among the two BNF-contrasting genotypes, including nitrogen metabolism, hormone regulation and bacteria recognition. Physiological analyses, such as nitrogenase and GS activity quantification, bacterial colonization, auxin response and root architecture evaluation, supported the transcriptome expression analyses. The differences observed between the genotypes may explain, at least in part, the differences in BNF contributions. Some of the identified genes might be involved in key regulatory processes for a beneficial association and could be further used as tools for obtaining more efficient BNF genotypes.

Exploiting the Potential of Bioreactors for Creating Spatial Organization in the Soil Microbiome: A Strategy for Increasing Sustainable Agricultural Practices.

Industrial production of synthetic nitrogen fertilizers and their crop application have caused considerable environmental impacts. Some eco-friendly alternatives try to solve them but raise some restrictions. We tested a novel method to produce a nitrogen bioinoculant by enriching a soil microbial community in bioreactors supplying N2 by air pumping. The biomass enriched with diazotrophic bacteria was diluted and applied to N-depleted and sterilized soil of tomato plants. We estimated microbial composition and diversity by 16S rRNA metabarcoding from soil and bioreactors at different run times and during plant uprooting. Bioreactors promoted the N-fixing microbial community and revealed a hided diversity. One hundred twenty-four (124) operational taxonomic units (OTUs) were assigned to bacteria with a greater Shannon diversity during the reactor's steady state. A total of 753 OTUs were found in the rhizospheres with higher biodiversity when the lowest concentration of bacteria was applied. The apparent bacterial abundance in the batch and continuous bioreactors suggested a more specific functional ecological organization. We demonstrate the usefulness of bioreactors to evidence hidden diversity in the soil when it passes through bioreactors. By obtaining the same growth of inoculated plants and the control with chemical synthesis fertilizers, we evidence the potential of the methodology that we have called directed bioprospecting to grow a complex nitrogen-fixing microbial community. The simplicity of the reactor's operation makes its application promising for developing countries with low technological progress.

Resource Allocation During the Transition to Diazotrophy in Klebsiella oxytoca.

Free-living nitrogen-fixing bacteria can improve growth yields of some non-leguminous plants and, if enhanced through bioengineering approaches, have the potential to address major nutrient imbalances in global crop production by supplementing inorganic nitrogen fertilisers. However, nitrogen fixation is a highly resource-costly adaptation and is de-repressed only in environments in which sources of reduced nitrogen are scarce. Here we investigate nitrogen fixation (nif) gene expression and nitrogen starvation response signaling in the model diazotroph Klebsiella oxytoca (Ko) M5a1 during ammonium depletion and the transition to growth on atmospheric N2. Exploratory RNA-sequencing revealed that over 50% of genes were differentially expressed under diazotrophic conditions, among which the nif genes are among the most highly expressed and highly upregulated. Isotopically labelled QconCAT standards were designed for multiplexed, absolute quantification of Nif and nitrogen-stress proteins via multiple reaction monitoring mass spectrometry (MRM-MS). Time-resolved Nif protein concentrations were indicative of bifurcation in the accumulation rates of nitrogenase subunits (NifHDK) and accessory proteins. We estimate that the nitrogenase may account for more than 40% of cell protein during diazotrophic growth and occupy approximately half the active ribosome complement. The concentrations of free amino acids in nitrogen-starved cells were insufficient to support the observed rates of Nif protein expression. Total Nif protein accumulation was reduced 10-fold when the NifK protein was truncated and nitrogenase catalysis lost (nifK 1 - 1 203), implying that reinvestment of de novo fixed nitrogen is essential for further nif expression and a complete diazotrophy transition. Several amino acids accumulated in non-fixing ΔnifLA and nifK 1 - 1203 mutants, while the rest remained highly stable despite prolonged N starvation. Monitoring post-translational uridylylation of the PII-type signaling proteins GlnB and GlnK revealed distinct nitrogen regulatory roles in Ko M5a1. GlnK uridylylation was persistent throughout the diazotrophy transition while a ΔglnK mutant exhibited significantly reduced Nif expression and nitrogen fixation activity. Altogether, these findings highlight quantitatively the scale of resource allocation required to enable the nitrogen fixation adaptation to take place once underlying signaling processes are fulfilled. Our work also provides an omics-level framework with which to model nitrogen fixation in free-living diazotrophs and inform rational engineering strategies.

Herbaspirillum seropedicae strain HRC54 expression profile in response to sugarcane apoplastic fluid.

Bacterial transcriptome profiling in the presence of plant fluids or extracts during microbial growth may provide relevant information on plant-bacteria interactions. Here, RNA sequencing (RNA-Seq) was used to determine the transcriptomic profile of Herbaspirillum seropedicae strain HRC54 at the early stages of response to sugarcane apoplastic fluid. Differentially expressed gene (DEG) analysis was performed using the DESeq2 and edgeR packages, followed by functional annotation using Blast2GO and gene ontology enrichment analysis using the COG and KEGG databases. After 2 h of sugarcane apoplastic fluid addition to the H. seropedicae HRC54 culture, respectively, 44 and 45 genes were upregulated and downregulated. These genes were enriched in bacterial metabolism (e.g., oxidoreductase and transferase), ABC transporters, motility, secretion systems, and signal transduction. RNA-Seq expression profiles of 12 genes identified in data analyses were verified by RT-qPCR. The results suggested that H. seropedicae HRC54 recognized sugarcane apoplastic fluid as the host signal, and some DEGs were closely involved at the early stages of the establishment of plant-bacteria interactions. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13205-021-02848-y.

The potential of extracellular biopolymer production by Mesorhizobium sp. from monosaccharide constituents of lignocellulosic biomass.

OBJECTIVE: The effects of monosaccharide constituents of lignocellulosic materials on exopolysaccharide (EPS) production by Mesorhizobium sp. Semia 816 were studied. RESULTS: According to the results, by using sugars commonly found in lignocellulosic biomass as carbon sources (glucose, arabinose and xylose), no significant differences were observed in the production of EPS, reaching 3.39 g/L, 3.33 g/L and 3.27 g/L, respectively. Differences were observed in monosaccharide composition, mainly in relation to rhamnose and glucuronic acid contents (1.8 times higher when arabinose was compared with xylose). However, the biopolymers showed no differences in relation to rheological properties, with EPS aqueous-based suspensions (1.0% w/v) presenting pseudoplastic behavior, and a slight difference in degradation temperatures. Using soybean hulls hydrolysate as carbon source, slightly higher values were obtained (3.93 g/L). CONCLUSION: The results indicate the potential of the use of lignocellulosic hydrolysates containing these sugars as a source of carbon in the cultivation of Mesorhizobium sp. Semia 816 for the production of EPS with potential industrial applications.

Initial development of upland rice plants inoculated with the MAY12 strain of Azospirillum spp / Desenvolvimento inicial de plantas de arroz de terras altas inoculadas com a estirpe MAY12 de Azospirillum spp

ABSTRACT: The purpose of this study was to evaluate the contribution of the inoculation of the strain Azospirillum MAY12 to the development of rice plants of the cultivar BRS Esmeralda. A completely randomized experiment was performed in a greenhouse, with 8 treatments and 6 repetitions, namely, commercial inoculant (CI) containing strains of Azospirillum brasilense ABV5 and ABV6 (T1), MAY12 (T2), nitrogen control with 50 mg of N or full dose (T3), CI + 30% of N (percentage referring to full dose) (T4), CI + 60% N (T5), MAY12 + 30% N (T6), MAY12 + 60% N (T7) and absolute control (T8). There was a significant increase in the fresh and dry mass of the shoot and roots, height, root volume, and the number of tillers and leaves of plants with the MAY12 inoculation (with and without N added) compared to T8. Treatments containing MAY12 + N increased the total dry mass by ~920% compared to T8, matching the T3 yield. The inoculation of MAY12 in isolation was as efficient as the application of the full dose of N, resulting in an increase of ~115% in height and 373% in root volume of the plants compared to T8. The MAY12 strain demonstrated good performance in the development of the cultivar, which was comparable to the CI in the variables tested. Therefore, inoculation with the MAY12 strain is promising for the partial reduction of nitrogen fertilizers in upland rice cultivation.

RESUMO: O objetivo deste trabalho foi avaliar a contribuição da inoculação da estirpe de Azospirillum MAY12 no desenvolvimento de plantas de arroz da cultivar BRS Esmeralda. Foi realizado um experimento inteiramente casualizado em casa de vegetação, tendo oito tratamentos e seis repetições: inoculante comercial (IC) contendo as estirpes de Azospirillum brasilense AbV5 e AbV6 (T1), MAY12 (T2), testemunha nitrogenada com 50 mg de N ou dose cheia (T3), IC + 30% de N (percentual referente à dose cheia) (T4), IC + 60% de N (T5), MAY12 + 30% de N (T6), MAY12 + 60% de N (T7) e testemunha absoluta (T8). Houve aumento significativo da massa fresca e seca da parte aérea e de raízes, altura, volume de raízes e do número de perfilhos e de folhas das plantas com a inoculação de MAY12 (com e sem adição de N) em relação a T8. Os tratamentos contendo MAY12 + N aumentaram em torno de 920% a massa seca total em relação a T8, equiparando-se ao rendimento T3. A inoculação de MAY12, isoladamente, foi tão eficiente quanto a aplicação da dose cheia de N para o aumento em torno de 115% da altura e de 373% do volume de raízes das plantas em relação a T8. A estirpe MAY12 apresentou bom desempenho no desenvolvimento da cultivar equiparando-se com o IC nas variáveis testadas. Portanto, a inoculação com a estirpe MAY12 mostra-se promissora para a redução parcial de fertilizantes nitrogenados no cultivo de arroz de terras altas.

Phosphate solubilizing bacteria stimulate wheat rhizosphere and endosphere biological nitrogen fixation by improving phosphorus content.

Phosphate (P) availability often limits biological nitrogen fixation (BNF) by diazotrophic bacteria. In soil, only 0.1% of the total P is available for plant uptake. P solubilizing bacteria can convert insoluble P to plant-available soluble P (ionic P and low molecular-weight organic P). However, limited information is available about the effects of synergistic application of diazotrophic bacteria and P solubilizing bacteria on the nitrogenase activity of rhizosphere and nifH expression of endosphere. In this study, we investigated the effects of co-inoculation with a diazotrophic bacterium (Paenibacillus beijingensis BJ-18) and a P-solubilizing bacterium (Paenibacillus sp. B1) on wheat growth, plant and soil total N, plant total P, soil available P, soil nitrogenase activity and the relative expression of nifH in plant tissues. Co-inoculation significantly increased plant biomass (length, fresh and dry weight) and plant N content (root: 27%, shoot: 30%) and P content (root: 63%, shoot: 30%). Co-inoculation also significantly increased soil total N (12%), available P (9%) and nitrogenase activity (69%) compared to P. beijingensis BJ-18 inoculation alone. Quantitative real-time PCR analysis showed co-inoculation doubled expression of nifH genes in shoots and roots. Soil nitrogenase activity and nifH expression within plant tissues correlated with P content of soil and plant tissues, which suggests solubilization of P by Paenibacillus sp. B1 increased N fixation in soils and the endosphere. In conclusion, P solubilizing bacteria generally improved soil available P and plant P uptake, and considerably stimulated BNF in the rhizosphere and endosphere of wheat seedlings.

Seasonal variation of epiphytic bacteria in the phyllosphere of Gingko biloba, Pinus bungeana and Sabina chinensis.

Phyllosphere harbors diverse microorganisms, which influence plant growth and health. In order to understand the extent to which environmental factors affect epiphytic microbial communities, we characterized microbial communities on leaves of three separate tree species present on the college campus, and also present within a forest park over two seasons. Quantitative PCR analysis showed the quantity of 16S rRNA genes was lower in May compared with October, while the abundances of functional genes (nifH and bacterial amoA genes) were extremely high in May. High-throughput sequencing revealed a large variation in the diversity and composition of bacterial and diazotrophic communities over the two seasons, and showed the abundance of functional genera, such as Nocardioides, Bacillus and Zoogloea were significantly elevated in May. In addition, xenobiotic biodegradation pathways of bacterial communities were clearly elevated in May. Network analysis showed the correlations between phyllospheric bacteria in May were more complex than that in October and showed greater negative correlations. These results were consistent in all tree species in this study. This study showed that phyllospheric bacteria varied greatly in different seasons, which implies that different growing seasons should be considered in the exploitation of the interactions between phyllospheric microorganisms and host plants.

Inoculation of plant growth-promoting bacteria attenuates the negative effects of drought on sorghum.

Microbial inoculants are suitable cost-effective technology to help plants endure drought. For the development of commercial inoculants, screening of efficient plant growth-promoting bacteria (PGPB) is a crucial step. The aim of this study was to evaluate the performance of PGPB to modulate drought resistance in Sorghum bicolor. A pot experiment with sorghum was conducted to access the role of previously selected PGPB strains. In addition, two non-inoculated control treatments (with and without urea fertilization) were also evaluated. For comparison, a fully irrigated treatment (FIT) was also assessed. All plants were fully irrigated for 47 days when the water supply was completely suspended for the drought-stressed treatments. When the soil moisture was close to zero, the irrigation was resumed. During dehydration and rehydration process, the leaf gas exchange (LGE) was evaluated. The parameters of plant growth and nitrogen nutrition were assessed 8 days after reirrigation. Comparing to the FIT, all treatments reduced the LGE rates, but in the presence of Bacillus sp. ESA 402 photosynthesis rate was less reduced. Some inoculation treatments promoted better recovery of photosynthesis, comparable to the FIT, 6 days after rehydration. The plant growth and nitrogen nutrition were negatively affected by the drought, but the inoculation of different bacteria reduced some negative effects. The nitrogen accumulation in the shoots was increased by all strains, suggesting their diazotrophic ability even under drought. Overall, the inoculation of Bacillus sp. ESA 402 was the best bacterium with potential for future field trials.

Development of a bacterial consortium comprising oil-degraders and diazotrophic bacteria for elimination of exogenous nitrogen requirement in bioremediation of diesel-contaminated soil.

The purpose of this study was to develop an effective bacterial consortium and determine their ability to overcome nitrogen limitation for the enhanced remediation of diesel-contaminated soils. Towards this, various bacterial consortia were constructed using oil-degrading and nitrogen-fixing microbes. The diesel removal efficiency of various developed consortia was evaluated by delivering the bacterial consortia to the diesel-contaminated soils. The consortium Acinetobacter sp. K-6 + Rhodococcus sp. Y2-2 + NH4NO3 resulted in the highest removal (85.3%) of diesel from the contaminated soil. The consortium containing two different oil-degrading microbes (K-6 + Y2-2) and one nitrogen-fixing microbe Azotobacter vinelandii KCTC 2426 removed 83.1% of the diesel from the soil after 40 days of treatment. The total nitrogen content analysis revealed higher amounts of nitrogen in soil treated with the nitrogen-fixing microbe when compared with that of the soil supplemented with exogenous inorganic nitrogen. The findings in this present study reveal that the consortium containing the nitrogen-fixing microbe degraded similar amounts of diesel to that degraded by the consortium supplemented with exogenous inorganic nitrogen. This suggests that the developed consortium K-6 + Y2-2 + KCTC 2426 compensated for the nitrogen limitation and eliminated the need for exogenous nitrogen in bioremediation of diesel-contaminated soils.