Symbiotic Nitrogen Fixation System Research Articles

Temporal dynamics of rhizosphere bacterial community in the Robinia pseudoacacia–Mesorhizobium loti symbiotic system for remediation of cadmium-contaminated soils

Rhizobia can be used to enhance the phytoremediation of cadmium-contaminated soils by legumes, and a symbiotic nitrogen-fixing system has been shown to reshape the structure of rhizosphere microbiota in a mining area. However, little is known about the temporal dynamics and possible roles of rhizosphere microbiota in rhizobia-enhanced phytoremediation. A rhizobox experiment was conducted using Robinia pseudoacacia alone or inoculated with Mesorhizobium loti HZ76 under greenhouse conditions. Rhizosphere bacterial communities were characterized over a 90-day period at three levels of cadmium (determined by the distance from the mining area; uncontaminated: 0.08 mg kg−1, contaminated: 0.39 and 1.72 mg kg−1). Rhizobial inoculation considerably improved the phytoremediation efficiency, such as increasing plant biomass and cadmium accumulation by approximately two times at 90 days after planting. The bacterial community structure shifted remarkably with increasing duration of remediation. Bacterial diversity exhibited a decreasing trend in the first 60 days and then recovered at 90 days. Despite having no discernible impact on the bacterial community structure in the rhizosphere, rhizobial inoculation enabled the enrichment of potentially beneficial taxa (e.g., Microvirga, Mesorhizobium, Diaphorobacter, Steroidobacter, Brevundimonas) with resistance to heavy metals and involvement in nutrient cycling. The bacterial co-occurrence networks of low and high cadmium-contaminated soils showed the highest average degree and clustering coefficient at 60 and 30 days, respectively. Some bacterial taxa involved in nitrogen fixation (e.g., Rhizobacter, Mesorhizobium), denitrification (e.g., Niastella, Nitrospira), and carbon turnover (e.g., Solirubrobacter, Brevundimonas) were found to be potential keystone taxa. The collective findings clarify possible mechanisms by which rhizosphere bacteria participate in phytoremediation of cadmium-contaminated mining soils using the R. pseudoacacia–M. loti symbiotic system.

Computationally Reconstructed Interactome of Bradyrhizobium diazoefficiens USDA110 Reveals Novel Functional Modules and Protein Hubs for Symbiotic Nitrogen Fixation.

Symbiotic nitrogen fixation is an important part of the nitrogen biogeochemical cycles and the main nitrogen source of the biosphere. As a classical model system for symbiotic nitrogen fixation, rhizobium-legume systems have been studied elaborately for decades. Details about the molecular mechanisms of the communication and coordination between rhizobia and host plants is becoming clearer. For more systematic insights, there is an increasing demand for new studies integrating multiomics information. Here, we present a comprehensive computational framework integrating the reconstructed protein interactome of B. diazoefficiens USDA110 with its transcriptome and proteome data to study the complex protein-protein interaction (PPI) network involved in the symbiosis system. We reconstructed the interactome of B. diazoefficiens USDA110 by computational approaches. Based on the comparison of interactomes between B. diazoefficiens USDA110 and other rhizobia, we inferred that the slow growth of B. diazoefficiens USDA110 may be due to the requirement of more protein modifications, and we further identified 36 conserved functional PPI modules. Integrated with transcriptome and proteome data, interactomes representing free-living cell and symbiotic nitrogen-fixing (SNF) bacteroid were obtained. Based on the SNF interactome, a core-sub-PPI-network for symbiotic nitrogen fixation was determined and nine novel functional modules and eleven key protein hubs playing key roles in symbiosis were identified. The reconstructed interactome of B. diazoefficiens USDA110 may serve as a valuable reference for studying the mechanism underlying the SNF system of rhizobia and legumes.

FORMATION AND FUNCTIONING OF SYMBIOTIC SYSTEMS OF SOYA – BRADYRHIZOBIUM JAPONICUM FOR THE INFLUENCE OF COMPLEXES OF NANOPARTICLES OF CARBOXYLATES OF MICROELEMENTS

Objective. To study the effect of combined preparations based on highly active strains of Brad-yrhizobium japonicum and complexes of carboxylates of trace elements germanium, molybdenum, and ferrum on a symbiotic apparatus of soybean plants, in order to increase the efficiency of bacte-rial inoculants. Methods. Gas chromatography, microbiological, physiological. Results. The com-bination of a microbiological preparation based on efficient strains of nodule bacteria with complexes of nanoparticles of carboxylates Mo, Fe, Ge was found to promote the enhancement of nodulation activity, provide growth of mass of root nodules, activate the nitrogen-fixing activity of symbiotic soybean systems. When use the preparation combined with germanium and molyb-denum compounds, nitrogenase activity increases by 23–63 %, in combination with inoculum with germanium and ferrum nanocarboxylates — by 14–21 % depending on the phases of soybean or-ganogenesis. The complex application of biological and abiotic factors influencing the formation and functioning of symbiotic nitrogen-fixing systems contributes to the improvement of plant mor-phometric parameters and provides high yields of this crop. At the same time, it was established that germanium carboxylate complexes with molybdenum carboxylate, as well as germanium nanocarboxylates, should be used as effective stimulants for the formation of seed productivity of soybean plants and nitrogen-fixing activity of symbiotic systems created with their participation. In the experiment, soybean yield under the combination of B. japonicum with germanium and molyb-denum nanocarboxylates increased by 10 %, and by 13 % — under the complex application of bac-terial inoculum with germanium and ferrum carboxylate nanoparticles. Conclusion. Application of these complexes of nanocomponents in microbiological production technologies will allow plants to be supplied with additional nutritional elements, forming effective plant-microbial systems and ob-taining high and stable crops of environmentally safe food and feed protein.

Growth of Ormosia henryi seedlings and photosynthetic and physiological characteristics with rhizobia inoculation.

To screen the growth-promoting strains of rhizobia for Ormosia henryi and to establish a good symbiotic nitrogen-fixing system, root nodules of O. henryi collected from Guizhou, Zhejiang, Anhui, Fujian, and Jiangxi Provinces were isolated and identified. Using randomized block design, 20 strains of rhizobia that passed reinoculation and 16SrDNA sequence analysis were inoculated into one-year-old aseptic potted O. henryi seedlings followed by measurement of the photosynthetic rate, transpiration rate, chlorophyll fluorescence parameters, growth indexes, and nodulation indexes. Results showed that the nodulation rates of the 20 strains were above 90.0%, the nodule number and nodule weight of strain No. 7 was the highest. Compared to the control which was not been inoculated, inoculation rhizobium significantly (P < 0.05) increased photosynthetic rate, transpiration rate and chlorophyll fluorescence parameters of O. henryi seedlings. Rhizobium also promoted the growth of above ground and underground parts as well as accumulation of total biomass. Seedlings with different rhizobium strains increased the photosynthetic rate (41.6%-197.4%), transpiration rate (3.2%-512.9%), actual photosynthetic quantum yield (4.8%-95.2%), total root surface area (3.4%-866.1%), average root diameter (6.7%-193.3%), root number (0.5%-92.1%), seedling height growth (6.3%-273.8%), diameter growth (10.7%-185.7%), and biomass (37.9%-310.3%). The comprehensive evaluation showed that the best five strains for promoting growth of O. henryi seedlings were No. 15, 16, 7, 18, and 17, and these could be used as excellent strains for inoculation of O. henryi seedlings.

Characterization of Diversity of Bradyrhizobia on Cowpea in Iraq Reveals Unusual Strain Characteristics

Rhizobium-legume symbiosis is considered as one of the most well established symbiotic nitrogen fixing system for agronomic studies. Association between legumes and rhizobia results in the formation of root nodules where symbiotic nitrogen fixation occurs. The current study aimed to authenticate 110 isolates from 20 sites belonging to 10 governorates in Iraq, tested their capacity of nodulation with cowpea and classified them depending on the phenotype and genotype presented by sequence analysis of 16S rRNA. To fulfill these goals, many approaches have been implemented such as Authentication Tests, Bromothymol Blue Reaction, Colony Size and Morphology, Antibiotic Test, Sequencing of 16S rRNA and Phylogenetic analysis. This study provides an easy way to classify the Bradyrhizobia sp. strains by genotype analysis depending on the phenotypes (i.e. motility and colony size) by sample preservation and high quality DNA isolation from environmental soil samples followed by 16S rRNA sequencing. This molecular technique has demonstrated the usefulness of these methods, easy technologies, and their applications to microbiome analysis and environmental science. Interestingly, a group of Bradyrhizobia identified in the current study was able to secrete acidic products before switching and starting to secrete alkali products after 1, 2 and 3 days. This is an unusual phenotype observed within rhizobia strains.

FUNCTIONING OF NITROGEN FIXATION SYMBIOSIS AND PEAS PRODUCTIVITY UNDER THE APPLICATION OF DIFFERENT TYPES AND DOSES OF FERTILIZERS

The efficiency of different types and doses of fertilizers and pre-sowing bacterization of pea seeds (Starter variety) on the formation and functioning of symbiotic nitrogen fixation system, crop productivity and protein content in grain was studied in long-term field experiment on the typical black soil for five years. It was shown that fertilizer doses not exceeding N60P60K60 were the most appropriate to use in the cultivation technology of pea. The use of manure, compost and organic-mineral fertilizer in crop rotation had positively affected the productivity of peas. Pre-sowing seed bacterization was proved to be an important agricultural practice as its application increases crop productivity and improves product quality.

Nodule formation, distribution and symbiotic efficacy of Vigna unguiculata L. under different soil salinity regimes

Rhizobium-legume symbiosis is one of the most well-established symbiotic nitrogenfixing system for agronomic studies. The current study aimed to test the hypothesis that screeningfor salt-tolerant rhizobial strains or salt-tolerant cultivar does not necessarily promise a salttolerantsymbiotic system, as the symbiotic system is more sensitive to salt stress than thebacterium and/or the plant. In fact, the current study reveals that there is a decrease in salttolerance of the symbiotic system by 1 dS/m , and also that there is a gradual shift in the spatialdistribution of the nodules from the primary roots to the secondary roots under increased saltlevels, and is time-dependant. Thus, the current study confirms that there is a need to screen forsalt-tolerant symbiotic Rhizobium-legume system for producing efficient root nodules, thereby anefficient repository for nitrogen fixation

Search for genes that confer acid tolerance to plants

To remediate the worldwide-spreading acid sulphate soil area and utilize it for human beings, acid tolerant leguminous plants are expected to be useful as crops and pioneer plants. The purpose of this study is to produce symbiotic nitrogen fixing systems tolerant to acid sulfate soils, through the identification of the genes that confer acid tolerance on plants and the isolation of acid-tolerant rhizobia. We identified acid tolerant genes by two approaches. One approach is functional screening of a soybean cDNA library and their characterization in planta. E. coli cells were transformed with a cDNA library of soybean and cultured on a LB medium adjusted to pH 4 or pH 5. Selected six tolerant clones were introduced into Arabidopsis thaliana using a plant expression vector. The overexpressors grew better than the wild type under the acid and aluminium stresses. The other one is molecular genetic analysis of the candidate genes identified by previous studies: a gene for a key enzyme of sulfur assimilation, cysteine synthase. The candidate gene was ectopically overexpressed in A. thaliana under the control of the cauliflower mosaic virus 35S promoter. All the genes tested were shown to confer acid tolerance on the model plants.

The Diversity of Biological Nitrogen Fixing Systems in Kenya

This paper outlines efforts to utilize Biological Nitrogen Fixation (BNF) technology through the utilization of microbial and plant components of symbiotic nitrogen-fixing systems that are encountered in a tropical environment. It underscores the immense potential that exists in the application of BNF research in tropical farming systems using the diverse array of nitrogen fixing systems found in Kenya and some of the factors that influence BNF such as the prevalent stress conditions (acid stress, nutritional needs) that exist between rhizobia at the genera, species, and strain levels. The contribution of non-leguminous systems such as Frankia, and the free-living and associative nitrogen fixing systems have also been considered as have the other symbiotic nitrogen fixing systems: Azolla, and Blue green algae. Key Words: Rhizobium, Bradyrhizobium, Sinorhizobium, Azorhizobium, Legumes, Nitrogen Fixation Journal of Tropical Microbiology Vol.3 2004: 35-47

Future directions for biological nitrogen fixation research

Enormous progress has been made in the last decade in understanding the physiology and genetics of nitrogen-fixing microorganisms, but relatively little has been done to translate theory into practice. The object of this note is to define strategies for research on applied nitrogen fixation and thus to help increase food and energy production and contribute to the restoration of soil fertility. Attention is given here to the symbiotic nitrogenfixing systems, legumes and actinorhizal plants, because of their unquestionable importance in tropical agriculture, agroforestry and forestry (National Research Council, 1979; Dawson, 1986). No attempt is made to evaluate the priorities for research on Azolla, non-symbiotic Cyanobacteria or non-symbiotic nitrogen-fixing bacteria in plant litter (Hill et al., 1988) or in the rhizosphere of cereals and pasture grasses (associative nitrogen fixation). Problems related to nitrogen fixation by Cyanobacteria have already been extensively explored and carefully reviewed (IRRI, 1979; Lumpkin and Plucknett, 1980; Roger and Kulasooriya, 1980; Roger and Reynaud, 1982; Roger and Watanabe, 1986). Generally the ecosystem received little nitrogen from non-symbiotic rhizospheric nitrogen-fixing microorganisms because they do not get enough energy to fix appreciable amounts of nitrogen and are often hindered in their activity in the field (Alexander, 1982; Barraquio et al., 1984; Beringer and Hirsch, 1984). However recent experiments based on the use of "N suggest that the nitrogen-fixing bacteria associated with the roots of several tropical crops, including wetland rice, sugar cane and some forage grasses, can fix significant amounts of nitrogen (Boddey and Dobereiner, 1987). Rhizospheric microorganisms can also contribute to plant growth through other

Differential phosphorus requirements ofAzollaspecies and strains in phosphorus-limited continuous culture

Abstract Phosphorus represents a major limiting factor in the field for the growth of the Azolla-Anabaena symbiotic nitrogen-fixing system. The yield of fresh matter increased up to 5 ppm P in batch culture, following a quadratic type of relationship. However, the tissue phosphorus content increased with each incremental increase in phosphorus concentration. The threshold concentration of the phosphorus in Azolla appeared to be 0.2 to 0.3%. Below that, plant growth was proportional to the phosphorus content. A continuous-flow device for determining the minimum phosphorus level was developed. Azolla pinnata from Bangkok grew normally at 0.06 ppm P. At 0.03 ppm P, the biomass, contents of phosphorus, nitrogen, and chlorophyll, and the acetylene-reduction activity were decreased. Further phosphorus increases of more than 0.06 up to 0.12 ppm in the medium had no impact on the growth of Azolla. Eleven Azolla strains, including A. pinnata, A. mexicana, A. caroliniana, and A. filiculoides, were compared at the limiting concentration of phosphorus (0.03 ppm) in continuous-flow culture. Substantial differences among the species and strains were noted. For healthy growth, different species required widely differing phosphorus concentrations in the water medium. A. pinnata from Bangkok produced maximum yield and maximum frond area, and exhibited the better nitrogen-fixing capacity in the phosphorus limiting condition than did the other species compared. Other A. pinnata strains grew better in the phosphorus limited condition than the New World Azolla species.

Compatibility of the components of nitrogenase from soybean bacteroids and free-living nitrogen-fixing bacteria

The ability of the components of nitrogenase from free-living nitrogen-fixing bacteria to cross-react and form active enzyme complexes with the components of the enzyme isolated from a symbiotic nitrogen-fixing system was tested. Nitrogenase components of Azotobacter vinelandii, Bacillus polymyxa cross-reacted with components of nitrogenase from Rhizobium japonicum bacteroids. No evidence of a cross reaction was obtained in the case of Clostridium pasteurianum.