Fixation Of Atmospheric Nitrogen Research Articles

Potential Role and Utilization of Plant Growth Promoting Microbes in Plant Tissue Culture.

Plant growth promoting microbes (PGPMs) play major roles in diverse ecosystems, including atmospheric nitrogen fixation, water uptake, solubilization, and transport of minerals from the soil to the plant. Different PGPMs are proposed as biofertilizers, biostimulants, and/or biocontrol agents to improve plant growth and productivity and thereby to contribute to agricultural sustainability and food security. However, little information exists regarding the use of PGPMs in micropropagation such as the in vitro plant tissue culture. This review presents an overview of the importance of PGPMs and their potential application in plant micropropagation. Our analysis, based on published articles, reveals that the process of in vitro classical tissue culture techniques, under strictly aseptic conditions, deserves to be reviewed to allow vitroplants to benefit from the positive effect of PGPMs. Furthermore, exploiting the potential benefits of PGPMs will lead to lessen the cost production of vitroplants during micropropagation process and will make the technique of plant tissue culture more efficient. The last part of the review will indicate where research is needed in the future.

Diversity and Physiological Characteristics of Antarctic Lichens-Associated Bacteria.

The diversity of lichen-associated bacteria from lichen taxa Cetraria, Cladonia, Megaspora, Pseudephebe, Psoroma, and Sphaerophorus was investigated by sequencing of 16S rRNA gene amplicons. Physiological characteristics of the cultured bacterial isolates were investigated to understand possible roles in the lichen ecosystem. Proteobacteria (with a relative abundance of 69.7–96.7%) were mostly represented by the order Rhodospirillales. The 117 retrieved isolates were grouped into 35 phylotypes of the phyla Actinobacteria (27), Bacteroidetes (6), Deinococcus-Thermus (1), and Proteobacteria (Alphaproteobacteria (53), Betaproteobacteria (18), and Gammaproteobacteria (12)). Hydrolysis of macromolecules such as skim milk, polymer, and (hypo)xanthine, solubilization of inorganic phosphate, production of phytohormone indole-3-acetic acid, and fixation of atmospheric nitrogen were observed in different taxa. The potential phototrophy of the strains of the genus Polymorphobacter which were cultivated from a lichen for the first time was revealed by the presence of genes involved in photosynthesis. Altogether, the physiological characteristics of diverse bacterial taxa from Antarctic lichens are considered to imply significant roles of lichen-associated bacteria to allow lichens to be tolerant or competitive in the harsh Antarctic environment.

Diversity of Insect Fauna Associated with Summer and Monsoon Cowpea [Vigna unguiculata (L.) Walp.

Background: Cowpea [Vigna unguiculata (L.) Walp.], is one of an important pulse grown throughout the world. The cowpea crop helps in fixation of atmospheric nitrogen; besides, it supports the natural enemies’ population. The study on diversity of pestiferous insect associated with cowpea crop help to understand the population dynamics of these pests depending on location and seasons. These diversity studies are useful to formulate management practices which are area specific.Methods: An extensive survey was conducted at different locations (Udaipur, Bhilwara, Banswara, Chittorgarh and Pratapgarh) of southern Rajasthan during summer (Zaid) and monsoon (Kharif) seasons of 2019 and 2020. The randomly selected plants were observed for pestiferous insect population to calculate different diversity indices.Result: The insect pest complex of cowpea categorized into 5 orders viz., Hemiptera, Thysanoptera, Coleoptera, Diptera and Lepidoptera comprising 14 families. The pestiferous fauna includes population of flea beetle, jassids, whiteflies, sap sucking bugs, leaf miner, thrips, aphids, spotted pod borer and lycaenid caterpillar. During the study, it was found that overall species richness was more during the monsoon season as compared to that during the summer. The relative diversity of aphids was the maximum on account of the clumped distribution and exponential growth. In 2019, the maximum diversity was recorded in Banswara (Simpson index= 6.49 and Shannon index= 2.04) during monsoon; whereas, in 2020, the maximum diversity was recorded in Bhilwara (Simpson index= 4.03 and Shannon index= 1.81) during summer.

Regulation of superoxide dismutase activity in soybean plants by inoculating seeds with rhizobia containing nanoparticles of metal carboxylates under conditions of different water supply

Soybean is one of the most profitable advanced crops in agricultural production in Ukraine and the world as a whole. Therefore, studies of means of regulation and increase in the adaptive capacity of soybeans in symbiosis with nodule bacteria under the action of unfavourable environmental factors are relevant and should be aimed at the use of complex bacterial compositions involving modern nanotechnological approaches. Nanocarboxylates of ferrum, molybdenum and germanium metals were used as components of rhizobia inoculation suspension for soybean seed treatment to study the effectiveness of their complex effect on the regulation of the activity of the key antioxidant enzyme superoxide dismutase in plants under drought. Various symbiotic systems were used, which included soybean plants and inoculation suspensions based on the active, virulent Tn5-mutant Bradyrhizobium japonicum B1-20 by adding nanoparticles of ferrum, germanium and molybdenum carboxylates to the culture medium in a ratio of 1: 1000. Citric acid was the chelator. A model drought lasting 14 days was created during the period of active fixation of atmospheric molecular nitrogen by root nodules of soybeans in the budding and flowering stages, by means of controlled watering of plants to 30% of the total moisture content. In the stage of bean formation, watering of plants was resumed to the optimal level – 60% of the total moisture content. The control was soybean plants, the seeds of which were inoculated with a suspension of rhizobia without the addition of chelated metals. The following research methods were used in the work – microbiological, physiological and biochemical. According to the results, it was found that when nanoparticles of carboxylates of ferrum, molybdenum and germanium were added to the inoculation suspension of rhizobia, there was an increase in superoxide dismutase activity in root nodules and a decrease in soybean leaves under optimal water supply conditions of plants. This indicates the initial changes in the activity of the antioxidant enzyme in these symbiotic systems, induced by the influence of chelated metals in combination with the rhizobia of the active Tn5-mutant B. japonicum B1-20. Prolonged drought induced an increase in the overall level of superoxide dismutase activity in soybean nodules and leaves, compared to plants grown under optimal watering conditions. The symbiotic system formed by soybeans and B. japonicum with molybdenum carboxylate nanoparticles was the most sensitive to long-term drought exposure, compared to two other soybean-rhizobial symbioses using ferrum and germanium nanocarboxylates. This was manifested in the unstable reaction of the enzyme to the action of drought – suppression or intensification of the level of its activity in the root nodules and leaves of soybeans inoculated with rhizobia containing molybdenum carboxylate nanoparticles. In symbiotic systems with the participation of germanium and ferrum nanocarboxylates, slight changes were revealed in superoxide dismutase activity in root nodules and leaves of plants during drought and restoration of enzyme activity to the level of plants with optimal watering after water stress. It is concluded that the addition to the culture medium of rhizobia Tn5-mutant B1-20 of nanocarboxylates of germanium or ferrum is an effective means of regulating the activity of the antioxidant enzyme superoxide dismutase in soybean root nodules and leaves, which can contribute to an increase in the protective properties and adaptation of plants to the action of dehydration.

Radiation interception and radiation use efficiency in mixtures of winter cover crops

Abstract Context Cover crops are sown in autumn after harvest of a main crop to capture residual nitrogen and to build biomass that will contribute to soil organic matter after being ploughed under. Mixtures are purportedly more productive than pure stands of single species. Research problem Dry matter accumulation in field crops can be separated in the processes of resource capture and resource conversion. Here we apply this conceptual approach to analyse whether and how pure stands of single species and stands of species mixtures differ in radiation capture and radiation use efficiency. Methods cover crops were sown as pure stands (12 treatments) or mixtures (11 treatments) at two years in four sites, three in the Netherlands and one in northern Germany. Ground cover was measured throughout a growing period of up to twelve weeks to quantify radiation capture while final biomass was determined at harvest. The ratio of biomass and cumulative radiation capture was used to calculate radiation use efficiency. Results Oats and crucifers were the most productive species. Crucifers covered the soil quickly and their radiation capture was consequently high (517 MJ m−2) but their radiation use efficiency was low (0.80 g MJ-1). Oats intercepted less radiation (459 MJ m−2) than crucifers but had a higher radiation use efficiency (1.15 g MJ-1). Legumes had low radiation interception (332 MJ m−2) combined with low radiation use efficiency (0.64 MJ m−2) while the group of forb species belonging to other plant families (e.g. Linaceae, Boraginaceae and Asteraceae) had intermediate radiation capture (371 MJ m−2) and radiation use efficiency (0.84 g MJ-1). The radiation capture and radiation use efficiency of mixtures was similar to that of the dominant species in the mixtures, in all cases a crucifer or oats. Conclusions and implications The analysis of radiation capture and radiation use efficiency in this study indicates that mixture performance was governed by species dominance within the mixture, with the species capturing most of the light determining to a large extent the radiation use efficiency of the mixture as a whole. Results show the importance of including one or more productive species in a species mixture used for cover cropping, i.e. oats or a crucifer. If species with slow initial growth or low radiation use efficiency are included in a mixture to provide particular services, such as flower resources, atmospheric nitrogen fixation or antibiosis against pests, these species should be included in a large enough proportion to enable their establishment in the mixture.

Setting ambitious goals for agriculture to meet environmental targets

Setting ambitious goals for agriculture to meet environmental targets

Symbiotic Nitrogen Fixation by Legumes in Alpine Ecosystems: a Vegetation Experiment

The natural nitrogen-15 abundance method does not always make it possible to calculate the rate of symbiotic nitrogen fixation by legumes and needs to be improved. Five legume species typical for the alpine belt of the Teberda Nature Reserve (Anthyllis vulneraria, Astragalus levieri, Hedysarum caucasicum, Oxytropis kubanensis, and Trifolium polyphyllum) have been grown from seeds under conditions of laboratory vegetation experiment. The results show that nodules on the roots of these plants are formed at early stages of their development; Trifolium polyphyllum does not form nodules either under high-mountain conditions or during growth in the laboratory. The natural 15N abundance in the leaves of legume plants in alpine ecosystems makes it possible to calculate the contribution of atmospheric N2 to nitrogen nutrition as early as the first year of their development, while the isotopic nitrogen composition of the roots does not allow this parameter to be determined. The calculation of atmospheric nitrogen fixation rate should take into account isotope fractionation between symbiotic bacteria (nodules) and the host plant; otherwise, the proportion of fixed nitrogen in plant nutrition may be underestimated.

A novel energy efficient path for nitrogen fixation using a non-thermal arc.

Plasma-assisted nitrogen fixation is a promising sustainable and clean alternative to the classical Haber–Bosch process. However, the high energy consumption and low production rate of plasma-assisted nitrogen fixation limit its application. This study shows that the non-thermal (non-equilibrium) enhancement of the arc plasma significantly reduces the energy consumption of nitrogen fixation. The highest energy efficiency with high NO selectivity is observed with a low specific energy input (SEI). However, the highest production rate is reached at a high SEI. The studied process offers high NO selectivity (up to 95%) with low energy consumption (∼48 GJ per tN) at 0.1 kJ L−1 SEI, which is much lower than the previously reported value of plasma-assisted atmospheric nitrogen fixation and is close to that of the Haber–Bosch process.

Agroecological modeling of nitrogen and carbon transfers between decomposer micro-organisms, plant symbionts, soil and atmosphere in an intercropping system

The modeling of continuous transfers of carbon (C) and nitrogen (N) previously published in the literature has paid little attention to the functional role of micro-organisms. In general, only monoculture systems have been modeled. Furthermore, there have been few experiments under field conditions at farm scale, where clear evidence for the benefits of intercropping is lacking. This work focus on mechanistic modeling approaches based on the ecological functioning of the microbial biomass, to quantify the daily exchange of C and N between plant organs, micro-organisms, rhizobial symbionts, soil compartments and the atmosphere in an arable intercropping system. The MOMOS model was validated on C and N data collected from a common bean (Phaseolus vulgaris L. cv. El Djadida) and maize (Zea mays L. cv. Filou) intercropping system. The experiment was performed at two field sites that were chosen with farmers to represent both high and low soil P availability. The results show that all C and N exchanges were successfully predicted at 5% significance and that they depend on the phenological stage, especially the flowering stage. Increased C allocation from photosynthesis to roots contributed to increasing both grain yield and N grain for intercropped maize. C and N stocks in the common bean nodules were lower in intercropping than in monocultures, and this is associated with the decrease of total atmospheric nitrogen (N2) fixation by intercropped common beans, in particular with a high soil P. However, the rate of N2 fixation was higher in the intercrops than in the monoculture when the soil is P-deficient. Micro-organisms were responsible for most of the C losses from the soil to the atmosphere but intercropping significantly reduced the C losses by improving micro-organism C use efficiency. These results uncover the strong link between N and C stocks, confirming the robustness of the newly formulated MOMOS equations that are validated in this paper. This agroecological modeling experiment demonstrated the functional role of microbial biomass, in both the growth of the intercrops crop and their symbiosis, improving the prediction of the daily C and N flows between plant organs, soil compartments and the atmosphere.

Analysis of the Interaction between Pisum sativum L. and Rhizobium laguerreae Strains Nodulating This Legume in Northwest Spain.

Pisum sativum L. (pea) is one of the most cultivated grain legumes in European countries due to the high protein content of its seeds. Nevertheless, the rhizobial microsymbionts of this legume have been scarcely studied in these countries. In this work, we analyzed the rhizobial strains nodulating the pea in a region from Northwestern Spain, where this legume is widely cultivated. The isolated strains were genetically diverse, and the phylogenetic analysis of core and symbiotic genes showed that these strains belong to different clusters related to R. laguerreae sv. viciae. Representative strains of these clusters were able to produce cellulose and cellulases, which are two key molecules in the legume infection process. They formed biofilms and produced acyl-homoserine lactones (AHLs), which are involved in the quorum sensing regulation process. They also exhibited several plant growth promotion mechanisms, including phosphate solubilization, siderophore, and indole acetic acid production and symbiotic atmospheric nitrogen fixation. All strains showed high symbiotic efficiency on pea plants, indicating that strains of R. laguerreae sv. viciae are promising candidates for the biofertilization of this legume worldwide.

Decline of Black Alder Alnus glutinosa (L.) Gaertn. along the Narewka River in the Białowieża Forest District

Abstract Black Alder Alnus glutinosa (L.) Gaertn. is an important tree commonly growing in Poland. Alders are actinorhizal plants that play an important ecological role in riparian ecosystems through atmospheric nitrogen fixation, filtration and purification of waterlogged soils as well as providing a refuge for terrestrial and aquatic organisms thus helping to stabilize stream banks. Black alder used to be considered a very pest and disease resistant species but, the situation changed in 2000, when an unprecedented decline of Alders was observed in Poland. In the Białowieża Forest District, this decline has been observed on wet meadow habitats and along rivers or watercourses. Currently, there are several hypotheses explaining Alder dieback, among them climatic changes and Phytophthora infections. In terms of climate, Black Alder requires a high atmospheric humidity during all phases of its reproductive cycle. It tolerates neither long-term summer flooding nor a significant decrease in the groundwater level. In terms of pests, oomycete pathogens of the genus Phytophthora are the most destructive plant pathogens known and many of them are present in forests and nurseries all over Europe. The aim of this study was to evaluate the health of Black Alder along the Narewka River in the Białowieża Forest District. Selected areas were monitored in 2012 and 2018, but no relationship between drought and alder health was found. A preliminary analysis of soil and water samples by real time PCR revealed the presence of two Phytophthora species: P. alni and P. cactorum. Further and more detailed research is required to elucidate the role of these pathogens in Alder dieback.

Environmental factors and thresholds for nitrogen fixation by phytoplankton in tropical reservoirs

AbstractIn theory, the phytoplankton community of freshwater ecosystems with low concentrations of dissolved inorganic nitrogen (DIN) can obtain this element by atmospheric nitrogen (N2) fixation. This process could explain the dominance of cyanobacteria in tropical reservoirs, yet is rarely quantified in these systems. Assessing the factors related to N2fixation can assist in the management of cyanobacterial blooms. Our study characterized environmental factors related to N2fixation in Brazilian tropical reservoirs with contrasting trophic states, and defined quantitative thresholds for water chemistry and physical characteristics that stimulated N2fixation. We used field assays with15N for estimating N2fixation rates by phytoplankton. The highest rates normalized by chlorophyll‐a(maximum of 143 × 10−4 μg‐N μg‐Chl‐a−1 h−1) coincided with eutrophic conditions and presence of diazotrophs. Receiver operating characteristic (ROC) analysis provided significant thresholds for water temperature (≥22°C), soluble reactive phosphorus (SRP) (≥3.0 μg‐P L−1), total phosphorus (TP) (≥20.5 μg‐P L−1), DIN:SRP (≤487) and DIN:TP (≤82) molar ratios, chlorophyll‐a(≥12 μg L−1), and total suspended solids (≥4 mg L−1). Censored regressions confirmed that temperature, chlorophyll‐a, and phosphorus were important predictors of N2fixation rates. In general, the N2fixation rates determined in this study were lower than those found for temperate reservoirs. However, the temperature threshold of 22°C or above, identified in our analysis, suggests that phytoplankton have the potential to fix N2throughout the year in tropical reservoirs. Our results suggested that phosphorus is the main nutrient controlling the rates of N2fixation when N2‐fixing cyanobacteria were present. Phosphorus abatement is, thus, crucial for managing the trophic state and controlling N2‐fixing cyanobacteria in these ecosystems.

Monitoring the Return of Marine-Derived Nitrogen to Riparian Areas in Response to Dam Removal on the Elwha River, Washington

Two sources of nitrogen to Pacific Northwest riparian areas are marine-derived nitrogen (MDN) via anadromous Pacific salmon (Oncorhynchus spp.) and atmospheric nitrogen fixation via red alder (Alnus rubra). The recent removal of two large dams on the Elwha River, WA, opened up about 60 km of previously inaccessible river habitat for anadromous salmon. We used naturally abundant stable nitrogen isotopes to establish baseline data to monitor the influx of MDN to riparian zones of Elwha River tributaries post dam removal. We sampled riparian soil, overstory, and understory vegetation in sites with nitrogen-fixing A. rubra and sites with bigleaf maple (Acer macrophyllum) at an undammed reference site, and along three tributaries, one between the former dams (accessible to anadromous salmon since 2012) and the others upstream of the former dams (no anadromous salmon). Based on δ15N measurements of soil and vegetation, we did not detect MDN at any of the tributaries, including the reference tributary. However, the understory riparian vegetation between the former dams had a higher δ15N than the other tributaries, which may be due to upstream anthropogenic nitrogen sources. Although A. rubra foliage was isotopically distinct from A. macrophyllum, and A. rubra litter had higher total nitrogen, soil and understory vegetation in A. rubra and A. macrophyllum sites did not differ isotopically. Monitoring of these areas and those further upstream on the Elwha River will allow us to trace the return of MDN to the watershed, and help to clarify the role that anadromous fish play in riparian ecosystems.

A Nod factor- and type III secretion system-dependent manner for Robinia pseudoacacia to establish symbiosis with Mesorhizobium amorphae CCNWGS0123.

Under nitrogen-limiting conditions, symbiotic nodulation promotes the growth of legume plants via the fixation of atmospheric nitrogen to ammonia by rhizobia in root nodules. The rhizobial Nod factor (NF) and type III secretion system (T3SS) are two key signaling pathways for establishing the legume-rhizobium symbiosis. However, whether NF signaling is involved in the nodulation of Robinia pseudoacacia and Mesorhizobium amorphae CCNWGS0123, and its symbiotic differences compared with T3SS signaling remain unclear. Therefore, to elucidate the function of NF signaling in nodulation, we mutated nodC in M. amorphae CCNWGS0123, which aborted NF synthesis. Compared with the plants inoculated with the wild type strain, the plants inoculated with the NF-deficient strain exhibited shorter shoots with etiolated leaves. These phenotypic characteristics were similar to those of the plants inoculated with the T3SS-deficient strain, which served as a Nod- (non-effective nodulation) control. The plants inoculated with both the NF- and T3SS-deficient strains formed massive root hair swellings, but no normal infection threads were detected. Sections of the nodules showed that inoculation with the NF- and T3SS-deficient strains induced small, white bumps without any rhizobia inside. Analyzing the accumulation of 6 plant hormones and the expression of 10 plant genes indicated that the NF- and T3SS-deficient strains activated plant defense reactions while suppressing plant symbiotic signaling during the perception and nodulation processes. The requirement for NF signaling appeared to be conserved in two other leguminous trees that can establish symbiosis with M. amorphae CCNWGS0123. In contrast, the function of the T3SS might differ among species, even within the same subfamily (Faboideae). Overall, this work demonstrated that nodulation of R. pseudoacacia and M. amorphae CCNWGS0123 was both NF and T3SS dependent.

Alcaligenes aquatilis GTE53: Phosphate solubilising and bioremediation bacterium isolated from new biotope “phosphate sludge enriched-compost”

The isolation and identification of beneficial bacteria from the active phase of composting is considered to be a key bio-quality parameter for the assessment of the process. The aim of this work was the selection and identification of beneficial bacteria from a co-composting experiment of vegetable waste (VW), olive oil mill waste (O2MW), and phosphate sludge (PS). Phosphate-solubilizing strains were isolated from the thermophilic phase using Pikovskaya (PVK) solid medium supplemented with tricalcium phosphate Ca3(PO4) (TCP) as the sole source of phosphorus (P). Therefore, the selected isolate Alcaligenes aquatilis GTE53 was tested to tolerate abiotic stresses (different levels of temperature, variable pH, high salinity and water stress). The isolate was also assessed for indole acetic acid (IAA) and siderophores synthesis, nitrogen fixation, phenol degradation and pathogens inactivation. The quality of the co-composting process was also investigated by monitoring the physico-chemical parameters. The obtained results showed that A. aquatilis GTE53 displayed a higher solubilization index of 2.4 and was efficiently dissolved, up to 162.8 and 247.4 mg·mL−1 of inorganic phosphate from PS and phosphate rock (PR), respectively. A. aquatilis GTE53 exhibited siderophores and IAA release, along with atmospheric nitrogen fixation. In addition to that, A. aquatilis GTE53 showed a high resistance to heat and tolerance to acidic and alkaline pH, high salinity and water stress. Moreover, A. aquatilis GTE53 could degrade 99.2% of phenol from a high-concentrated medium (1100 mg·L−1 of phenol) and can inactivate the most abundant pathogens in industrial wastes: Escherichia coli, Streptococcus sp., Salmonella sp., and Fusarium oxysporum albedinis. Analysis of temperature, pH, electrical conductivity, carbon/nitrogen (C/N) ratio, indicated successful co-composting. An efficient transformation of P to the available form and a great abatement of polyphenols, were also recorded during the process. The findings of this study will help to advance the understanding of A. aquatilis GTE53 functions and will facilitate its application to promote beneficial microbial organisms during composting, thus obtaining a high-quality product.

Lichenicola cladoniae gen. nov., sp. nov., a member of the family Acetobacteraceae isolated from an Antarctic lichen.

Two Gram-stain-negative, facultative anaerobic, chemoheterotrophic, pink-coloured, rod-shaped and non-motile bacterial strains, PAMC 26568 and PAMC 26569T, were isolated from an Antarctic lichen. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strains PAMC 26568 and PAMC 26569T belong to the family Acetobacteraceae and the most closely related species are Gluconacetobacter takamatsuzukensis (96.1 %), Gluconacetobacter tumulisoli (95.9 %) and Gluconacetobacter sacchari (95.7 %). Phylogenomic and genomic relatedness analyses showed that strains PAMC 26568 and PAMC 26569T are clearly distinguished from other genera in the family Acetobacteraceae by average nucleotide identity values (<72.8 %) and the genome-to-genome distance values (<22.5 %). Genomic analysis revealed that strains PAMC 26568 and PAMC 26569T do not contain genes involved in atmospheric nitrogen fixation and utilization of sole carbon compounds such as methane and methanol. Instead, strains PAMC 26568 and PAMC 26569T possess genes to utilize nitrate and nitrite and certain monosaccharides and disaccharides. The major fatty acids (>10 %) are summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c; 40.3-40.4 %), C18 : 1 2OH (22.7-23.7 %) and summed feature 2 (C14 : 0 3OH and/or C16 : 1 iso I; 12.0 % in PAMC 26568). The major respiratory quinone is Q-10. The genomic DNA G+C content of PAMC 26568 and PAMC 26569T is 64.6 %. Their distinct phylogenetic position and some physiological characteristics distinguish strains PAMC 26568 and PAMC 26569T from other genera in the family Acetobacteraceae supporting the proposal of Lichenicola gen. nov., with the type species Lichenicola cladoniae sp. nov. (type strain, PAMC 26569T=KCCM 43315T=JCM 33604T).

Phylogeny of Plant Growth-Promoting Actinobacteria Isolated from Legume Nodules in Turkey

Actinobacteria are a biotechnologically important group of microorganisms utilized for their high capacity to synthesize many bioactive substances as well as agriculturally important compounds. In the present study, a culture-dependant approach was employed to isolate actinobacteria from wild legume nodules and their plant growth-promoting activities for indole-3-acetic acid production, atmospheric nitrogen fixation and inorganic phosphate solubilisation was investigated. A molecular approach based on 16S rRNA gene sequence analysis was employed to identify the isolates. After pairwise sequence analysis, six isolates were identified as members of the genera Streptomyces and Micromonospora. All isolates could produce indole-3-acetic acid and utilize atmospheric nitrogen while only one isolate was able to solubilize inorganic phosphate. The isolated actinobacteria are considered to be promising candidates for biological fertilizers especially because of their ability to use atmospheric nitrogen and produce high level of indole-3-acetic acid.

Evidence for Succession and Putative Metabolic Roles of Fungi and Bacteria in the Farming Mutualism of the Ambrosia Beetle Xyleborus affinis.

The bacterial and fungal community involved in ambrosia beetle fungiculture remains poorly studied compared to the famous fungus-farming ants and termites. Here we studied microbial community dynamics of laboratory nests, adults, and brood during the life cycle of the sugarcane shot hole borer, Xyleborus affinis We identified a total of 40 fungal and 428 bacterial operational taxonomic units (OTUs), from which only five fungi (a Raffaelea fungus and four ascomycete yeasts) and four bacterial genera (Stenotrophomonas, Enterobacter, Burkholderia, and Ochrobactrum) can be considered the core community playing the most relevant symbiotic role. Both the fungal and bacterial populations varied significantly during the beetle's life cycle. While the ascomycete yeasts were the main colonizers of the gallery early on, the Raffaelea and other filamentous fungi appeared after day 10, at the time when larval hatching happened. Regarding bacteria, Stenotrophomonas and Enterobacter dominated overall but decreased in foundresses and brood with age. Finally, inferred analyses of the putative metabolic capabilities of the bacterial microbiome revealed that they are involved in (i) degradation of fungal and plant polymers, (ii) fixation of atmospheric nitrogen, and (iii) essential amino acid, cofactor, and vitamin provisioning. Overall, our results suggest that yeasts and bacteria are more strongly involved in supporting the beetle-fungus farming symbiosis than previously thought.IMPORTANCE Ambrosia beetles farm their own food fungi within tunnel systems in wood and are among the three insect lineages performing agriculture (the others are fungus-farming ants and termites). In ambrosia beetles, primary ambrosia fungus cultivars have been regarded essential, whereas other microbes have been more or less ignored. Our KEGG analyses suggest so far unknown roles of yeasts and bacterial symbionts, by preparing the tunnel walls for the primary ambrosia fungi. This preparation includes enzymatic degradation of wood, essential amino acid production, and nitrogen fixation. The latter is especially exciting because if it turns out to be present in vivo in ambrosia beetles, all farming animals (including humans) are dependent on atmospheric nitrogen fertilization of their crops. As previous internal transcribed spacer (ITS) metabarcoding approaches failed on covering the primary ambrosia fungi, our 18S metabarcoding approach can also serve as a template for future studies on the ambrosia beetle-fungus symbiosis.

Nitrate reductases and hemoglobins control nitrogen-fixing symbiosis by regulating nitric oxide accumulation.

The interaction between legumes and rhizobia leads to the establishment of a symbiotic relationship between plant and bacteria. This is characterized by the formation of a new organ, the nodule, which facilitates the fixation of atmospheric nitrogen (N2) by nitrogenase through the creation of a hypoxic environment. Nitric oxide (NO) accumulates at each stage of the symbiotic process. NO is involved in defense responses, nodule organogenesis and development, nitrogen fixation metabolism, and senescence induction. During symbiosis, either successively or simultaneously, NO regulates gene expression, modulates enzyme activities, and acts as a metabolic intermediate in energy regeneration processes via phytoglobin-NO respiration and the bacterial denitrification pathway. Due to the transition from normoxia to hypoxia during nodule formation, and the progressive presence of the bacterial partner in the growing nodules, NO production and degradation pathways change during the symbiotic process. This review analyzes the different source and degradation pathways of NO, and highlights the role of nitrate reductases and hemoproteins of both the plant and bacterial partners in the control of NO accumulation.

Artificial, Photoinduced Activation of Nitrogenase Using Directed and Mediated Electron Transfer Processes

Nitrogenase, a bacteria-based enzyme, is the sole enzyme that is able to generate ammonia by atmospheric nitrogen fixation. Thus, improved understanding of its utilization and developing methods to artificially activate it may contribute to basic research, as well as to the design of future artificial systems. Here, we present methods to artificially activate nitrogenase using photoinduced reactions. Two nitrogenase variants originating from Azotobacter vinelandii were examined using photoactivated CdS nanoparticles (NPs) capped with thioglycolic acid (TGA) or 2-mercaptoethanol (ME) ligands. The effect of methyl viologen (MV) as a redox mediator of hydrogen and ammonia generation was tested and analyzed. We further determined the NPs conductive band edges and their effect on the nitrogenase photoactivation. The nano-biohybrid systems comprising CdS NPs and nitrogenase were further imaged by transmission electron microscopy, visualizing their formation for the first time. Our results show that the ME-capped CdS NPs–nitrogenase enzyme biohybrid system with added MV as a redox mediator leads to a five-fold increase in the production of ammonia compared with the non-mediated biohybrid system; nevertheless, it stills lag behind the natural process rate. On the contrary, a maximal hydrogen generation amount was achieved by the αL158C MoFe-P and the ME-capped CdS NPs.