Rhizobium Bacteria Research Articles

Zinc and Phosphate Solubilizing by Rhizobacteria Promotes Lettuce (Lactuca sativa L.) Growth in Salty Conditions

Due to climate change, the world is negatively affected by drought, temperature, salinity, and flood stress, leading to a significant decline in crop production. Lettuce is particularly significant when considering salt stress. To increase plant tolerance to salinity, various strategies are employed to support the development of agriculture. Rhizobacteria play a key role in regulating phosphorus (P) and zinc (Zn) homeostasis in plants. According to the study results, Rhizobium bacteria supported plant growth by improving the solubility of zinc and phosphate. These findings highlight the beneficial effects of plant growth-promoting rhizobacteria (PGPR) on the antioxidant system, which helps detoxify reactive oxygen species. The relationship between proline accumulation and antioxidant enzyme activities showed that PGPR inoculation enhanced the plant's defense mechanism against salt stress. In establishing this tolerance, increases in chlorophyll content, repair of membrane repair, and higher leaf relative humidity under salt stress were observed. PGPR also improved seedling height, diameter, and fresh and dry weight under stress by 70%, 51.4%, 55%, and 109%, respectively, due to the stress-mitigating effects of P and Zn. In conclusion, it is predicted that there will be a need to develop fertilization programs containing different rhizobacteria and Zn+P combinations. These programs would activate the antioxidant mechanism in saline soils, stabilize physiological processes, and positively impact plant growth.

Alleviation of Fe-induced chlorosis of soybean plants grown in calcareous soil by a freeze-dried iron fertilizer containing siderophores produced by Rhizobium radiobacter

The concerns about the unsustainability of traditional synthetic Fe chelates lead to the search for new environmentally friendly alternatives, such as siderophores-based fertilizers. In this work, the focus was on the evaluation of a bio-based Fe-chelate fertilizer obtained from the culture of the siderophore-producer bacterium Rhizobium radiobacter. The suitability of a freeze-dried fertilizer formulated from a R. radiobacter culture labeled with 57Fe to alleviate Fe chlorosis in soybean plants cultivated in calcareous soil was analyzed and the new potential Fe fertilizer was evaluated in comparison to the traditional synthetic chelate o,oEDDHA/57Fe3+. This natural chelate was able to maintain chlorophyll content stable during all the pot trials and presented greater Fe concentration in the remaining soil fractions serving as an Fe pool for a long time whereas o,oEDDHA/57Fe3+ could supply Fe quickly. The new bio-based Fe siderophore fertilizer, derived from R. radiobacter culture, could be a green substitute to conventional synthetic chelates to address Fe chlorosis in calcareous soil conditions.

Cultural and Biochemical Characteristics of Rhizobium Present in Nodule of Pongamia Pinnata (l.) Pierre

The present investigation is an attempt to study the impact of rocky terrain on Rhizobium bacteria of root nodules isolated from legume trees. To study the morphological, cultural, and biochemical characteristics of bacterial strain the bacteria obtained from nodules of selected legume i.e. Pongamia pinnata. Rhizobia inhabited in root nodules of plant, grown in Kota university campus, rhizobia were isolated and inoculated on Yeast Extract Mannitol Agar (YEMA) medium and it’s morphological, cultural and biochemical characteristics were studied. It was observed that colonies were circular or irregular; light creamish, glistering, gelatinous, convex with entire margins. The bacteria were gram negative, rod shaped, aerobic, non-spore forming and slow-moving bacteria arranged single, in pairs and in clusters. It showed negative chemical reaction for indole, while showed positive reaction for citrate utilization, catalase, urease. By the help of bio chemical characteristics it was confirmed that isolated bacterial culture may be of Rhizobium pongamie and rocky terrain with high temperature of environment does not have any negative effect on the characters of Rhizobium, our findings was supported by many earlier investigations.

Seed inoculation with Rhizobium japonium bacteria improved fatty acid composition of different soybean (Glycine max L.) genotypes

BackgroundSoybean is an important crop for food security as it fulfills global oil requirements. Seed inoculation with bacteria is frequently used to increase its production; however, it could change the seed composition. Nevertheless, the genotypes respond differently to the bacteria. Therefore, it is necessary to assess the impact of Rhizobium bacteria on the seed composition. MethodsThis two-year (2018 and 2019) study investigated the effects of seed inoculation with Rhizobium japonicum on fatty acid composition of different soybean genotypes. Three frequently cultivated soybean genotypes, i.e., ‘Gapsoy16′, ‘Traksoy’, and ‘İlksoy’ were included in the study. The seeds were either inoculated with R. japonicum or sown without inoculation. The fatty acid profile, i.e., saturated fatty acids (palmitic and stearic acid) and unsaturated fatty acids (oleic, linoleic, linolenic, and arachidic acids) was determined, and the collected data were analyzed by single and multivariate analysis. ResultsSeed inoculation with R. japonicum significantly altered the fatty acid composition of different genotypes; however, varied effects were recorded for the genotype. Linoleic acid, oleic acid, and palmitic acid made up ∼ 33 % of total fatty acids in seeds. Linoleic acid contents varied between 30.78–34.02 %, whereas oleic acid contents ranged between 27.85–31.04 %. Similarly, palmitic acid contents differed between 15.53–16.93 %. The ‘İlksoy’ and ‘Gapsoy’ had the highest contents of palmitic and oleic acids, respectively. Overall, inoculation of bacteria increased the composition of unsaturated fatty acids and lowered saturated fatty acids. ConclusionSeed inoculation with R. japonicum increased the essential fatty acid composition in ‘Traksoy’ genotype. However, ‘İlksoy’ genotype recorded a decrease in unsaturated fatty acids. Therefore, ‘Traksoy’ can be inoculated with R. japonicum to improve fatty acid profile.

Response of Integrated Nutrient Management (INM) Practice on Growth, Yield and Quality Parameters of Fenugreek (Trigonella corniculate L.)

Integrated nutrient management methods assist improve fenugreek (Trigonella corniculate L.) development and yield by integrating the use of organic and inorganic fertilizers. These methods enhance soil fertility, increase nutrient availability, and improve plant health, all of which lead to increased crop yield, growth and quality. Future policies must place a high priority on the economical, sustainable, and efficient use of nutrient resources for the purpose to increase agricultural output. Thus, proper crop, water, soil, and land management along with integrated nutrient management are necessary for sustainable agriculture. Improved soil qualities and increased nutrient availability for agricultural plants come from the use of organic manures in conjunction with inorganic fertilizers. This enhances fenugreek growth, yield, and quality measures. The synthesis of carbohydrates, phytohormones, and even biofertilizers is enhanced by a nutritious diet. It also builds up the soil's organic status, which raises the availability of other nutrients and contributes to the maximum growth of crops. Vermicompost, farmyard manure, rhizobium, phosphorus- and potassium-soluble bacteria (PSB) are among the materials used in methi cultivation that support sustainable agriculture by enhancing soil fertility, nutrient availability, and general crop health, all of which lead to higher methi yields and quality. Organic matter is a storehouse of nutrients; applying both organic and inorganic fertilizer together can boost yields, improve soil fertility, raise crop input-use efficiency, and reduce the need for expensive fertilizers. This crop responds effectively to N provided through a combination of organic and inorganic sources. Majority of the nitrogen applied from different sources is not used by the first crop and is always reflected in the crop that follows. Therefore, it is necessary to assess how integrated nutrition management affected fenugreek's yield and nutrient uptake.

Rhizobial and passenger endophytes alleviates moisture stress in groundnut (Arachis hypogaea)

Moisture stress poses a significant threat to global agriculture, compromising crop yields and food security. In the quest for sustainable solutions, endophytic microorganisms have emerged as promising candidates for enhancing plant resilience to drought. The study's primary goal was to analyse the significance of bacterial endophytes, both rhizobial and passenger endophytes, in alleviating the effects of moisture stress. Here, PEG 6000 was used to test the drought endurance of the ten identified rhizobial and passenger endophytes. Rhizobium pusense S6R2, Enterobacter cloacae S23 and Bacillus tequilensis NBB13 were selected as best performing endophytes as they showed high tolerance of poly ethylene glycol (PEG) and maximum plant growth promoting traits like Indole Acetic Acid, exopolysaccharide production, biofilm formation, 1-aminocyclopropane1-carboxylate (ACC) deaminase activity, siderophore, zinc and phosphorous solubilisation even in PEG induced moisture stress condition. Metabolite analysis revealed that twenty-four significant compounds mostly belong to fatty acyls, amino acids, peptides, polyketides, and benzenoids were found in the root exudates of groundnut treated with endophytes. The best-performing endophytes were used in a pot culture experiment, with groundnut as the test crop. The current study found that co-inoculation of Rhizobium pusense S6R2 and Enterobacter cloacae S23 significantly increased nodule number, growth, photosynthetic pigment, anti-oxidant enzymes, and osmolyte under moisture stressed conditions when compared to other treatments. As a result, co-inoculation of Rhizobium and entophytic bacteria may be recommended as a bio-inoculant for groundnut for moisture stress alleviation after confirming the results in field evaluation.

Enhancing Bio-Fertilization Potential of Introduced Hedysarum Species Through Indirect Root Inoculation: Implications for Agro-Ecological Sustainability in Arid Lands

Saharan soils are devoid of Rhizobium bacteria specific to the Sulla plants which is indispensable for nitrogen fixation and soil fertility. The present study aims to test the possibility of formation nodules on the roots of some species of Hedysarum (Sulla) genus introduced in Ghardaïa region with indirect inoculation in the reason to optimize the use of nitrogen fertilizers. Three soil samples were chosen from three different districts of Algeria (Tizi-Ouzou, Sétif and El-Tarf) to be used as substrate and source of bacterial strains for three different species of Sulla (Hedysarum coronarium, Hedysarum carnosum, Hedysarum flexuosum). The results showed the formation of a considerable number of nodules in all treatments. The effect of species and samples of soils on the studied parameter was highly significant (p<0.000) at the 5% significance level. All cultivated species in the soil of Sétif could form significant more nodules compared to other soils. The disparity in the average number of nodules formed in the soil of Sétif represents a rate of 78.75% compared to the soil of Tizi-Ouzou. This study could contribute to improve fodder production of Sulla species cultivated in Ghardaïa region and also provides a forage rich in protein for local livestock.

The Effects of Frass and Vermicompost Fertilization on the Biometrical Parameters of Plant and Soil Quality, and the Rhizobiome, in Red Beet (Beta vulgaris L.) Cultivation

Insect frass and vermicompost hold potential applications as fertilizers, with their abilities to improve plant resilience against unfavorable environmental conditions and increase their resistance to pests and diseases. In this study, we explored the effects of vermicompost fertilization, mealworm frass, and superworm frass as potential plant fertilizers for red beet cultivation. We analyzed the connections among chemical parameters, rhizobiome structure and function, and the biometrics of fertilizer-treated plants. In general, soils enriched with vermicompost and superworm frass exhibited the highest macroelement contents. Dry superworm frass fertilization was characterized by the increased availabilities of total nitrogen, NH4-N, and NO3-N. The use of vermicompost and mealworm frass resulted in significantly higher red beet biomass values. The presence of the highest N-fixation potential and key hormonal substances involved in plant development, such as auxins and gibberellins, was demonstrated using wet superworm frass. The results indicated that wet superworm frass, similar to vermicompost and dry superworm frass, exhibits high chemoheterotrophic potential. This suggests an r-type strategy and high adaptive flexibility of rhizobial bacteria. As a consequence, both life in the root zone and the microbiome itself may be better adapted to sudden, unfavorable environmental changes or attacks by plant pathogens.

The microbial-driven nitrogen cycle and its relevance for plant nutrition.

Nitrogen (N) is a vital nutrient and an essential component of biological macromolecules such as nucleic acids and proteins. Microorganisms are major drivers of N-cycling processes in all ecosystems, including the soil and plant environment. The availability of N is a major growth-limiting factor for plants and it is significantly affected by the plant microbiome. Plants and microorganisms form complex interaction networks resulting in molecular signaling, nutrient exchange, and other distinct metabolic responses. In these networks, microbial partners influence growth and N use efficiency of plants either positively or negatively. Harnessing the beneficial effects of specific players within crop microbiomes is a promising strategy to counteract the emerging threats to human and planetary health due to the overuse of industrial N fertilizers. However, in addition to N-providing activities (e.g. the well-known symbiosis of legumes and Rhizobium spp.), other plant-microorganism interactions must be considered to obtain a complete picture of how microbial-driven N transformations might affect plant nutrition. For this, we review recent insights into the tight interplay between plants and N-cycling microorganisms, focusing on microbial N-transformation processes representing N sources and sinks that ultimately shape plant N acquisition.

Biological, physiological and economic characteristics of Onobrychis chorasanica Bunge ex Bois. (Sainfoin) under sowing conditions

Onobrychis chorasanica Bunge ex Bois. (Sainfoin) is a valuable pasture plant that is resistant to drought, produces high biomass and is not inferior to alfalfa in terms of nutrient content. It is urgent to research the possibilities of cultivation of this plant for the purpose of growing hay in hilly conditions. The presence of nitrogen-fixing Rhizobium bacteria in the roots of plants is important in increasing the fertility of desert soils and this feature increases its role in the creation of artificial grasslands in hilly conditions. In the experiments, it was shown that it is possible to reach 100 % germination by mechanical scarification of the seeds isolated from O. chorasanica pods using sandpaper. Germination of unscarred seeds in field conditions depends on the year and the depth of planting them in the soil. In a dry year, the highest fertility was observed to be 13.3-15.0 % in the options where the seeds were buried at a depth of 3-4 cm, and in years with abundant rainfall, this indicator was 35.3 % in the option where the seeds were buried at a depth of 3 cm. The viability of lawns in the 2nd year of life was 72-95 % in different options. Hay productivity of O. chorasanica was found to be 41 centners per ha in hilly conditions and seed yield was up to 250 kg. The results obtained in the research are promising for the intensification of feed production of O. chorasanica in local conditions. The obtained results serve to increase the biomass yield of pasture plants and the variety of used feeds in farms specializing in animal husbandry.

Development of approaches for genome editing of pea plants using CRISPR/Cas9 prime-editing technique

Mitogen-activated protein kinases (MAPKs) play an important role as intracellular regulators of signal pathways in plants. Some MAPKs have been shown to be induced in the roots of legume plants during symbiosis with nitrogen-fixing rhizobial bacteria. One of such signal regulators, MAPK6, was shown to be involved in the development of symbiosis between Pisum sativum L. pea plants and rhizobia. Using genetic engineering approaches, we overexpressed the MAPK6 gene in transgenic roots, that resulted in an increase in the number of nodules and the biomass of pea plants. New approaches for genome editing of pea plants have been designed using the CRISPR/Cas9 prime-editing technique, when the MAPK6 gene was used as a target. We have analyzed the transgenic roots of pea transformants and observed the presence of the gene encoding Cas9 the pegRNA sequence in the genome of transformants. Therefore, the possibility of using genetic engineering methods to obtain plants with increased efficiency of symbiosis will be investigated in future experiments.

Optimization of Rhizobium rhizogenes-mediated transformation, regeneration and characterization of Malus domesticaBorkh. Ri lines

This study explored the establishment and optimization of Ri (root inducing) technology for apple breeding, using the bacterium Rhizobium rhizogenes to obtain Ri lines with compact shoots and stronger root systems. The transformation and shoot regeneration for Malus domestica cultivars was studied in detail. Various R. rhizogenes strains, scion and rootstock genotypes, explant types, wounding methods and explant orientations were tested for hairy root induction. Most of the 16 tested strains, especially those with plasmid type III, induced hairy roots in the rootstock genotype ‘M26’. Although apple genotypes differed in response, in most of them roots were successfully induced using strains ATCC 15834, LMG 63 and LMG 150, with leaf blades outperforming petioles as explants. Wounding by scratching or sonication further improved transformation efficiency, as did placing leaf blades with their abaxial side upward on root induction medium. The majority (94%) of roots formed in one transformation experiment were tested PCR-positive for at least one T-DNA gene. Shoot regeneration experiments investigated salt concentrations, gelling agents, cytokinin types, concentrations, and a resting period on hormone-free medium. Shoot regeneration was highly genotype-dependent varying between 0 and 83%, whereas only minor, non-significant effects were observed for the treatments tested. Copy numbers of T-DNA genes were estimated using digital PCR for the first time in apple Ri lines. In the greenhouse, two Ri lines showed compact shoots and shorter leaves, but no enhanced root system. The improved protocol provides a valuable tool for breeders and scientists to obtain and further use Ri lines.

Probing the active site of Class 3 L-asparaginase by mutagenesis. I. Tinkering with the zinc coordination site of ReAV.

ReAV, the inducible Class-3 L-asparaginase from the nitrogen-fixing symbiotic bacterium Rhizobium etli, is an interesting candidate for optimizing its enzymatic potential for antileukemic applications. Since it has no structural similarity to known enzymes with this activity, it may offer completely new ways of approach. Also, as an unrelated protein, it would evade the immunological response elicited by other asparaginases. The crystal structure of ReAV revealed a uniquely assembled protein homodimer with a highly specific C135/K138/C189 zinc binding site in each subunit. It was also shown before that the Zn2+ cation at low and optimal concentration boosts the ReAV activity and improves substrate specificity, which indicates its role in substrate recognition. However, the detailed catalytic mechanism of ReAV is still unknown. In this work, we have applied site-directed mutagenesis coupled with enzymatic assays and X-ray structural analysis to elucidate the role of the residues in the zinc coordination sphere in catalysis. Almost all of the seven ReAV muteins created in this campaign lost the ability to hydrolyze L-asparagine, confirming our predictions about the significance of the selected residues in substrate hydrolysis. We were able to crystallize five of the ReAV mutants and solve their crystal structures, revealing some intriguing changes in the active site area as a result of the mutations. With alanine substitutions of Cys135 or Cys189, the zinc coordination site fell apart and the mutants were unable to bind the Zn2+ cation. Moreover, the absence of Lys138 induced atomic shifts and conformational changes of the neighboring residues from two active-site Ser-Lys tandems. Ser48 from one of the tandems, which is hypothesized to be the catalytic nucleophile, usually changes its hydration pattern in response to the mutations. Taken together, the results provide many useful clues about the catalytic mechanism of the enzyme, allowing one to cautiously postulate a possible enzymatic scenario.

Response of green gram [Vigna radiata (L) Wilczek] to application of biofertilizers and phosphorus

The present study was carried out at the Crop Research Centre, Carrier Point University, Kota (Rajasthan), during the kharif season of 2020 and 2021 to assess the effect of phosphorus, rhizobium and phosphate solubilizing bacteria on growth and yield attributes of green gram. Significantly increase in growth, yield attributes and yield of green gram were recorded with the application of phosphorus 50 kg P2 O5 /ha. In case of biofertilizers (PSB, Rhizobium and PSB + Rhizobium), all growth and yield attributes and yield were increased significantly. However, among treatment combinations, the maximum values of these parameters were observed with 50 kg P2 O5 /ha + biofertilizers (PSB + Rhizobium) in comparison to all other treatment combinations. The net returns and B: C ratio were also higher under 50 kg P2 O5 /ha + biofertilizers (PSB + Rhizobium).

Cattle dry manure fertilization increases forage yield of grass‐legume mixtures, while maintaining the legume proportion and root‐associated microbiota

AbstractThe aim of this study was to find ways to improve the forage yield of grass‐legume mixtures without compromising soil biodiversity. In Argentinean Patagonia, the effects of applying cattle dry manure (M) and urea (U) (0, 60, 120, or 240 kg N ha−1 year−1) were assessed on herbage production of irrigated fescue‐lotus mixtures, as well as on the activity/abundance of autochthonous arbuscular mycorrhizal fungi and N‐fixing rhizobium bacteria. We hypothesised that manure has advantages over urea in increasing forage yields while maintaining the proportion of legumes and root‐associated microbiota. The 120 U, 240 U, and 240 M resulted in the greatest forage production; however, yield varied depending on the source applied. The high productivity of the 120 U and 240 U was probably due to the fast grass growth immediately after fertilization, which resulted in a depressed growth of the legume. The high yield of the swards fertilized with 240 M was probably due to slight and delayed growth of grass without legume yield decline. The highest radiation interception was found in swards with a low legume proportion, suggesting a light competition from grass fertilized with the highest urea doses, which were also consistent with the highest N and P nutritional status. The microbial activity/abundance were not affected by fertilization, but the final number of nodules was positively associated with the legume proportion. In conclusion, manure fertilization increased forage yield of the mixtures, while preserving the legume proportion and the root‐associated microbiota. Our findings aid in reducing synthetic‐N fertilizers applied in pasture‐based livestock systems.

The evolutionary genomics of adaptation to stress in wild rhizobium bacteria

Microbiota comprise the bulk of life's diversity, yet we know little about how populations of microbes accumulate adaptive diversity across natural landscapes. Adaptation to stressful soil conditions in plants provides seminal examples of adaptation in response to natural selection via allelic substitution. For microbes symbiotic with plants however, horizontal gene transfer allows for adaptation via gene gain and loss, which could generate fundamentally different evolutionary dynamics. We use comparative genomics and genetics to elucidate the evolutionary mechanisms of adaptation to physiologically stressful serpentine soils in rhizobial bacteria in western North American grasslands. In vitro experiments demonstrate that the presence of a locus of major effect, the nre operon, is necessary and sufficient to confer adaptation to nickel, a heavy metal enriched to toxic levels in serpentine soil, and a major axis of environmental soil chemistry variation. We find discordance between inferred evolutionary histories of the core genome and nreAXY genes, which often reside in putative genomic islands. This suggests that the evolutionary history of this adaptive variant is marked by frequent losses, and/or gains via horizontal acquisition across divergent rhizobium clades. However, different nre alleles confer distinct levels of nickel resistance, suggesting allelic substitution could also play a role in rhizobium adaptation to serpentine soil. These results illustrate that the interplay between evolution via gene gain and loss and evolution via allelic substitution may underlie adaptation in wild soil microbiota. Both processes are important to consider for understanding adaptive diversity in microbes and improving stress-adapted microbial inocula for human use.

Isolation and screening of stress tolerant and plant growth promoting root nodulating rhizobial bacteria from some wild legumes of Nagaland, India

Wild legumes are widely distributed and better adapted to extreme agro-climatic conditions because of their soil microbiota. In the present study, Root Nodulating Bacteria (RNB) were isolated from wild legumes and analysed for their abiotic stress tolerant and Plant Growth Promoting Traits (PGPT). Rhizobial strains were identified based on their 16S rRNA sequences. A total of 14 rhizobial species were characterized based, of which six were Rhizobium (AIS3, AIS9, AIR14, LUMCR3, LUMVRW4, LUMVRW8), four belongs to Burkholderia (AIS12, MOLKCS15, CHMP9, CHMP10) and one each of genera Cupriavidus (LUMMD12), Herbaspirillum (LUMVRW4), Paraburkholderia (CHMP1) and Ralstonia (LUMDes9). Stress tolerance analysis found most of the strains are to be tolerant to alkaline pH (9–11) where highest tolerance exhibited by Rhizobium sp. (strain AIS9) and Burkholderia territorii (strain MOKCS15). Seven Rhizobial strains were able to thrive at lower temperature stress (10 and 20 °C); while, strains AIS9, CHMP1 and LUMMD21 were able to grow at higher temperature (40 and 50 °C). Most of the isolate could tolerate salinity stress up to 1.5 %; but, only isolates AIS9, AIS12 and LUMMD12 could tolerate 2 and 2.5 % salt concentrations. The PGPT analyses found LUMCR3 having the highest IAA production potentiality (102.5 µg/ml); while, isolate MOKCS15 exhibited highest phosphate solubilizing activity (4.1 Phosphate Solubilization Index). The RNB isolates in the present study exhibited both stress tolerance and PGP traits indicating their potential use as biofertilizer under extreme agronomic conditions to improve productivity.

The influence of metal nanocarboxylates on the nitrogen-fixing activity of symbiotic soybean systems grown under field conditions

Background. Numerous scientific and industrial studies have proven the high effectiveness of using micronutrients in nanoscale form in agricultural crop cultivation technologies. Among them, special attention is drawn to soybeans, which hold a leading position in terms of sown areas among other leguminous crops in the country. They can provide up to 70 % of their own nitrogen needs through the fixation of its molecular form from the atmosphere in symbiosis with Bradyrhizobium japonicum nodulating bacteria. New methods of molecular biology, biotechnology, and genetic engineering, along with classical methods of microbiology, plant physiology, genetics, and agrochemistry, allow for addressing both fundamental questions regarding the characteristics of formation and functioning of legume-rhizobial systems, and practical approaches to correcting the interactions between symbiotic partners with the aim of creating highly effective symbioses. Therefore, research aimed at significant increasing the current level of biological nitrogen fixation and adapting symbiotic systems to negative environmental factors is currently relevant. The use of nanotechnology, in particular, the study of the effect of iron, germanium, and cobalt nanocarboxylates on the formation and functioning of the soybean-rhizobial symbiosis under field conditions in combination with seed inoculation with rhizobial bacteria may be promising. Materials and Methods. The objects of the investigation were symbiotic systems created with the participation of the Almaz variety of soybean and the Bradyrhizobium japonicum B1-20 rhizobacteria, and with the introduction of nanocarboxylates of iron (Fe), germanium (Ge) and cobalt (Co) into their cultivation medium. Physiological, microbiological, biochemical, and statistical research methods were used. Results. It was found that under field conditions, before the pod formation stage, the vegetative mass of soybean plants inoculated with rhizobial bacteria with the introduction of nanoparticles of carboxylates of iron, germanium, or cobalt into their cultivation medium was at the level of control plants or slightly exceeded them. It has been shown that under the effects of chelated micronutrients, the number of root nodules increased compared to control plants during the flowering and pod formation stages, and their mass was greater from the three trifoliate leaf stage, which ensured efficient functioning of the legume-rhizobial symbiosis. It has been noted that the used metal nanocarboxylates promote active functioning of the symbiotic apparatus in soybean plants, as an increase in nitrogen-fixing activity was observed at the stages of three trifoliate leaf development and flowering, ranging from 26–70 % depending on the microelement used. Conclusions. During field cultivation of soybeans, the effectiveness of pre-sowing seed inoculation with Bradyrhizobium japonicum B1-20 rhizobia was demonstrated through the introduction of iron, germanium, or cobalt nanocarboxylates into their cultivation medium. This opens up opportunities for increasing the efficiency of symbiotic systems of soybeans.

Prevalent role of homologous recombination in the repair of specific double-strand breaks in Rhizobium etli.

Double-strand breaks (DSBs) are the most dangerous injuries for a genome. When unrepaired, death quickly ensues. In most bacterial systems, DSBs are repaired through homologous recombination. Nearly one-quarter of bacterial species harbor a second system, allowing direct ligation of broken ends, known as Non-Homologous End Joining (NHEJ). The relative role of both systems in DSBs repair in bacteria has been explored only in a few cases. To evaluate this in the bacterium Rhizobium etli, we used a modified version of the symbiotic plasmid (264 kb), containing a single copy of the nifH gene. In this plasmid, we inserted an integrative plasmid harboring a modified nifH gene fragment containing an I-SceI site. DSBs were easily inflicted in vivo by conjugating a small, replicative plasmid that expresses the I-SceI nuclease into the appropriate strains. Repair of a DSB may be achieved through homologous recombination (either between adjacent or distant repeats) or NHEJ. Characterization of the derivatives that repaired DSB in different configurations, revealed that in most cases (74%), homologous recombination was the prevalent mechanism responsible for repair, with a relatively minor contribution of NHEJ (23%). Inactivation of the I-SceI gene was detected in 3% of the cases. Sequence analysis of repaired derivatives showed the operation of NHEJ. To enhance the number of derivatives repaired through NHEJ, we repeated these experiments in a recA mutant background. Derivatives showing NHEJ were readily obtained when the DSB occurred on a small, artificial plasmid in a recA mutant. However, attempts to deliver a DSB on the symbiotic plasmid in a recA background failed, due to the accumulation of mutations that inactivated the I-SceI gene. This result, coupled with the absence of derivatives that lost the nonessential symbiotic plasmid, may be due to an unusual stability of the symbiotic plasmid, possibly caused by the presence of multiple toxin-antitoxin modules.

Yield Test of Shade-Tolerant Maize Using the Intercropping Method of Maize-Soybean Under Coconut Trees

Maize is a light-dependent crop, but new varieties have been developed that can tolerate shade. This allows farmers to grow maize as an intercrop between coconut trees, making more efficient use of their land. Farmers can also intercrop with legume plants, which provide additional nitrogen through Rhizobium bacteria, leading to increased maize productivity. The aim of this study was to obtain the best intercropping pattern for maize and soybeans under coconut trees that results high yields in maize. The study was conducted in Padang Pariaman Regency of West Sumatra, at an altitude of approximately 150 meters, from February to July 2022. The experimental design was a Split Plot Design with Randomized Block Design, consisting of three main plot levels (planting time) and four subplot levels (planting model). The results of the study indicate that intercropping maize and soybeans under coconut trees has no effect on the weight of maize cobs, but there is a positive correlation between ear weight, cob length, cob diameter, number of rows per cob, and the weight of 1000 maize seeds.