Rhizobial Strains Research Articles

Development of a bioink using exopolysaccharide from Rhizobium sp. PRIM17

Biopolymers play a significant role in tissue engineering, including in the formulation of bioinks that require careful selection of the biopolymers having properties ideal for printability and supporting biological entities such as cells. Alginate is one of the most widely explored natural biopolymers for tissue engineering applications due to its biocompatibility, cross-linking ability, hydrophilic nature, and easy incorporation with other polymers. Here, a succinoglycan-like exopolysaccharide (EPS-R17) produced by a bacterial strain Rhizobium sp. PRIM17 was incorporated with alginate for the development of a bioink. The physicochemical characterization of EPS-R17 was performed before formulating the bioink with alginate. The bioink formulation was prepared by mixing different concentrations of EPS with an alginate solution at room temperature under sterile atmosphere. The prepared bioink was characterized for rheological properties, biocompatibility, and a bioplotting experiment was also conducted to mimick the extrusion bioprinting. The EPS-R17 was composed of glucose, galactose, and rhamnose with a molecular weight of 69.98 kDa. It was thermally stable up to 260 °C and showed characteristic FT-IR peaks (1723.3 cm−1) for succinyl groups. The EPS-R17 showed biocompatibility with keratinocytes (HaCaT), and fibroblasts (HDF) in vitro. The rheological properties of EPS-R17-alginate bioink at different combinations showed shear thinning behavior at 25 and 37 °C. Amplitude sweep measurements showed the gel-like nature of the polymer combinations in the solution system superior to alginate or EPS-R17 alone. The combination of 1 % EPS-R17 and 1.5 % alginate showed good compressive strength and swelling behavior. Extrusion bioprinting mimicked using a bioplotting experiment showed the sustained cell viability in the polymer matrix of EPS-R17-alginate bioink. The results indicate that the EPS-R17 can be used in combination with alginate for bioinks for bioprinting applications for providing physical properties and favorable bioactivities.

Competitiveness and Phylogenetic Relationship of Rhizobial Strains with Different Symbiotic Efficiency in Trifolium repens: Conversion of Parasitic into Non-Parasitic Rhizobia by Natural Symbiotic Gene Transfer

In Uruguayan soils, populations of native and naturalized rhizobia nodulate white clover. These populations include efficient rhizobia but also parasitic strains, which compete for nodule occupancy and hinder optimal nitrogen fixation by the grassland. Nodulation competitiveness assays using gusA-tagged strains proved a high nodule occupancy by the inoculant strain U204, but this was lower than the strains with intermediate efficiencies, U268 and U1116. Clover biomass production only decreased when the parasitic strain UP3 was in a 99:1 ratio with U204, but not when UP3 was at equal or lower numbers than U204. Based on phylogenetic analyses, strains with different efficiencies did not cluster together, and U1116 grouped with the parasitic strains. Our results suggest symbiotic gene transfer from an effective strain to U1116, thereby improving its symbiotic efficiency. Genome sequencing of U268 and U204 strains allowed us to assign them to species Rhizobium redzepovicii, the first report of this species nodulating clover, and Rhizobium leguminosarun, respectively. We also report the presence of hrrP- and sapA-like genes in the genomes of WSM597, U204, and U268 strains, which are related to symbiotic efficiency in rhizobia. Interestingly, we report here chromosomally located hrrP-like genes.

Legumes Regulate Symbiosis with Rhizobia via Their Innate Immune System.

Plant roots are constantly exposed to a diverse microbiota of pathogens and mutualistic partners. The host's immune system is an essential component for its survival, enabling it to monitor nearby microbes for potential threats and respond with a defence response when required. Current research suggests that the plant immune system has also been employed in the legume-rhizobia symbiosis as a means of monitoring different rhizobia strains and that successful rhizobia have evolved to overcome this system to infect the roots and initiate nodulation. With clear implications for host-specificity, the immune system has the potential to be an important target for engineering versatile crops for effective nodulation in the field. However, current knowledge of the interacting components governing this pathway is limited, and further research is required to build on what is currently known to improve our understanding. This review provides a general overview of the plant immune system's role in nodulation. With a focus on the cycles of microbe-associated molecular pattern-triggered immunity (MTI) and effector-triggered immunity (ETI), we highlight key molecular players and recent findings while addressing the current knowledge gaps in this area.

Effect of 24-epibrassinolide on Bradyrhizobium japonicum in pure culture and in symbiosis with Glycine max

Brassinosteroids are a group of plant steroid hormones that regulate a wide range of physiological responses, including cell elongation, photomorphogenesis, xylem differentiation, seed germination, etc. It has been proven that these hormones contribute to the formation of legume-rhizobia symbiotic systems. Applied research indicates the potentially complex role of brassinosteroids in the formation of nodules with both positive and negative effects. Therefore, research aimed at studying their role in the processes of symbiosis formation and functioning remains relevant. The aim of the study was to investigate the effect of 24-epibrassinolide on growth indicators of Bradyrhizobium japonicum in pure culture and realization of their nitrogen-fixing potential in symbiosis with soybean plants. It was found that the B. japonicum PC08 strain did not show a pronounced response to the application of concentrations 5 · 10—4, 1 · 10—5 g/L of 24-epibrassinolide.Both positive and negative effects of the tested substance on the growth dynamics this strain were weakly expressed or completely absent. The addition of this phytohormone to the growth medium of the rhizobial strain B. japonicum T21-2 led to stimulation of the growth of rhizobial cells. It was found that 24-epibrassinolide provided an increase in the number of root nodules, regardless of its concentration and the method of application. It had a significant effect on the growth of the root system of soybean plants, while its use as a component of the inoculation suspension in concentration 1 · 10—5 g/L was more effective. As a result of our research, changes in the dynamics of rhizobia growth under the influence of 24-epibrassinolide were revealed. The effect of its application was largely determined by the strain of B. japonicum that we used. We believe that the reaction to the use of 24-epibrassinolide depends on the properties and origin of the strain. The positive effect of 24-epibrasinolide on the number of formed root nodules at the late stages of the formation of the symbiotic apparatus was confirmed. Recorded changes in nitrogen-fixing activity of symbiotic systems under the influence of 24-epibrasinolide indicate that brassinosteroids have an effect on the functioning of root nodules.

Hydroponic Common-Bean Performance under Reduced N-Supply Level and Rhizobia Application.

This study aims to explore the possibility of a reduced application of inorganic nitrogen (N) fertiliser on the yield, yield qualities, and biological nitrogen fixation (BNF) of the hydroponic common bean (Phaseolus vulgaris L.), without compromising plant performance, by utilizing the inherent ability of this plant to symbiotically fix N2. Until the flowering stage, plants were supplied with a nutrient solution containing N-concentrations of either a, 100%, conventional standard-practice, 13.8 mM; b, 75% of the standard, 10.35 mM; or c, 50% of the standard, 6.9 mM. During the subsequent reproductive stage, inorganic-N treatments b and c were decreased to 25% of the standard, and the standard (100% level) N-application was not altered. The three different inorganic-N supply treatments were combined with two different rhizobia strains, and a control (no-inoculation) treatment, in a two-factorial experiment. The rhizobia strains applied were either the indigenous strain Rhizobium sophoriradicis PVTN21 or the commercially supplied Rhizobium tropici CIAT 899. Results showed that the 50-25% mineral-N application regime led to significant increases in nodulation, BNF, and fresh-pod yield, compared to the other treatment, with a reduced inorganic-N supply. On the other hand, the 75-25% mineral-N regime applied during the vegetative stage restricted nodulation and BNF, thus incurring significant yield losses. Both rhizobia strains stimulated nodulation and BNF. However, the BNF capacity they facilitated was suppressed as the inorganic-N input increased. In addition, strain PVTN21 was superior to CIAT 899-as 50-25% N-treated plants inoculated with the former showed a yield loss of 11%, compared to the 100%-N-treated plants. In conclusion, N-use efficiency optimises BNF, reduces mineral-N-input dependency, and therefore may reduce any consequential negative environmental consequences of mineral-N over-application.

Rhizobium induced modulation of growth and photosynthetic efficiency of Lens culinaris Medik. grown on fly ash amended soil by antioxidants regulation.

Rhizobium leguminosarum is a rhizospheres' nitrogen fixing microbe that improves plant growth and productivity by releasing sufficient nutrient sources from the root, by biological nitrogen fixation, solubilization of phosphorous, acquisition of iron, and enhancement of antioxidant activity in plants. On this account, a greenhouse experiment was carried out to assess the feasibility of growing lentil (Lens culinaris Medik.) on fly ash (FA) amended soil (0%, 10%, 20%, and 30%) in combination with R. leguminosarum inoculation. The data was recorded at 45day after sowing to evaluate the plant growth characteristics, photosynthetic variables (total chlorophyll and carotenoid pigments, carbonic anhydrase activity, nitrate reductase activity), damage markers (ROS, MDA, and cell viability), and defensive factors (proline and antioxidants). Among the FA-proportions tested, 20% proved most favorable in all the mentioned attributes while 30% concentration had negative repercussions on all the variables. Rhizobium inoculation had synergistic effect on all the concentrations being maximum on 20% FA. Thus, Rhizobium and 20% FA caused a significant increase on growth characteristics, photosynthetic pigments; stomatal behavior (aperture shape, size, and frequency of stomata); and activity of CA and NR, and cell viability. Application of Rhizobium on 20% FA was corroborated with decline in MDA and ROS contents and a coordinated enhancement of the activity of SOD, CAT, and POX. Therefore, 20% FA with flyash-tolerant strain of Rhizobium in Lens culinaris may be utilized as an integrated approach towards sustainable agriculture and an impulse of management of fly-ash.

Biofertilizer and NPSB fertilizer application effects on nodulation and productivity of common bean (Phaseolus vulgaris L.) at Sodo Zuria, Southern Ethiopia.

Common bean is among the vital legumes cultivated for nutrition, foreign currency earnings, and income generation. Common bean production is constrained mainly by nutrient deficiencies. A field experiment was conducted at Sodo Zuria Woreda to assess the effects of blended N-P-S-B fertilizer rates and Rhizobium strain on yield and yield traits of common bean and income of farmers. Treatments were five different rates of blended NPSB fertilizer (0, 50, 100, 150, and 200 kg ha-1) and two types of Rhizobium strains (HB-A15 and HB-429 (Rhizobia etli)) and control (without inoculation). Randomized complete block design in factorial arrangement with three replications were used. Results showed that interaction of blended NPSB rate and Rhizobium strain type had significant effect on the number of effective nodule, grain yield, and above ground dry biomass. Application of 150 kg NPSB ha-1 along with inoculation of Rhizobium etli resulted in the highest grain yield (3017.7 tons ha-1). Similarly, economic analysis indicated that the highest net return of 38298.545 ETB ha-1 was obtained from combined application of 150 kg NPSB ha-1 along with Rhizobium etli. Thus, it could be concluded that using Rhizobium etli strain with 150 kg NPSB ha-1 was found to be appropriate for common bean production in the area.

Adaptive Evolution of Rhizobial Symbiosis beyond Horizontal Gene Transfer: From Genome Innovation to Regulation Reconstruction.

There are ubiquitous variations in symbiotic performance of different rhizobial strains associated with the same legume host in agricultural practices. This is due to polymorphisms of symbiosis genes and/or largely unexplored variations in integration efficiency of symbiotic function. Here, we reviewed cumulative evidence on integration mechanisms of symbiosis genes. Experimental evolution, in concert with reverse genetic studies based on pangenomics, suggests that gain of the same circuit of key symbiosis genes through horizontal gene transfer is necessary but sometimes insufficient for bacteria to establish an effective symbiosis with legumes. An intact genomic background of the recipient may not support the proper expression or functioning of newly acquired key symbiosis genes. Further adaptive evolution, through genome innovation and reconstruction of regulation networks, may confer the recipient of nascent nodulation and nitrogen fixation ability. Other accessory genes, either co-transferred with key symbiosis genes or stochastically transferred, may provide the recipient with additional adaptability in ever-fluctuating host and soil niches. Successful integrations of these accessory genes with the rewired core network, regarding both symbiotic and edaphic fitness, can optimize symbiotic efficiency in various natural and agricultural ecosystems. This progress also sheds light on the development of elite rhizobial inoculants using synthetic biology procedures.

Bacteroid Development, Transcriptome, and Symbiotic Nitrogen-Fixing Comparison of Bradyrhizobium arachidis in Nodules of Peanut (Arachis hypogaea) and Medicinal Legume Sophora flavescens.

Bradyrhizobium arachidis strain CCBAU 051107 could differentiate into swollen and nonswollen bacteroids in determinate root nodules of peanut (Arachis hypogaea) and indeterminate nodules of Sophora flavescens, respectively, with different N2 fixation efficiencies. To reveal the mechanism of bacteroid differentiation and symbiosis efficiency in association with different hosts, morphologies, transcriptomes, and nitrogen fixation efficiencies of the root nodules induced by strain CCBAU 051107 on these two plants were compared. Our results indicated that the nitrogenase activity of peanut nodules was 3 times higher than that of S. flavescens nodules, demonstrating the effects of rhizobium-host interaction on symbiotic effectiveness. With transcriptome comparisons, genes involved in biological nitrogen fixation (BNF) and energy metabolism were upregulated, while those involved in DNA replication, bacterial chemotaxis, and flagellar assembly were significantly downregulated in both types of bacteroids compared with those in free-living cells. However, expression levels of genes involved in BNF, the tricarboxylic acid (TCA) cycle, the pentose phosphate pathway, hydrogenase synthesis, poly-β-hydroxybutyrate (PHB) degradation, and peptidoglycan biosynthesis were significantly greater in the swollen bacteroids of peanut than those in the nonswollen bacteroids of S. flavescens, while contrasting situations were found in expression of genes involved in urea degradation, PHB synthesis, and nitrogen assimilation. Especially higher expression of ureABEF and aspB genes in bacteroids of S. flavescens might imply that the BNF product and nitrogen transport pathway were different from those in peanut. Our study revealed the first differences in bacteroid differentiation and metabolism of these two hosts and will be helpful for us to explore higher-efficiency symbiosis between rhizobia and legumes. IMPORTANCE Rhizobial differentiation into bacteroids in leguminous nodules attracts scientists to investigate its different aspects. The development of bacteroids in the nodule of the important oil crop peanut was first investigated and compared to the status in the nodule of the extremely promiscuous medicinal legume Sophora flavescens by using just a single rhizobial strain of Bradyrhizobium arachidis, CCBAU 051107. This strain differentiates into swollen bacteroids in peanut nodules and nonswollen bacteroids in S. flavescens nodules. The N2-fixing efficiency of the peanut nodules is three times higher than that of S. flavescens. By comparing the transcriptomes of their bacteroids, we found that they have similar gene expression spectra, such as nitrogen fixation and motivity, but different spectra in terms of urease activity and peptidoglycan biosynthesis. Those altered levels of gene expression might be related to their functions and differentiation in respective nodules. Our studies provided novel insight into the rhizobial differentiation and metabolic alteration in different hosts.

Symbiotic effectiveness of Bradyrhizobium strains on soybean growth and productivity in Northern Mozambique

Inoculation of soybean [Glycine max(L.) Merr.] with rhizobia strains is a low-cost investment which can increase yields of smallholder farmers in Mozambique. The performance of fourBradyrhizobiumstrains was evaluated to identify the best strain to inoculate soybean grown in different agro-ecologies. Field experiments were conducted in three ecological zones in 2018 and 2019 using soybean variety Zamboane inoculated withBradyrhizobium diazoefficiensstrain USDA 110,B. japonicumstrains USDA 136, USDA 442 and WB74, and a non-inoculated control in a randomized complete block design with four replications. Indigenous rhizobia populations at the sites ranged from 9.0 x 101to 2.2 x 103cells g−1soil. All four strains increased nodulation, but USDA 110 was superior at two sites with low native rhizobia population, whereas USDA 442 and WB74 were the best at the site with relatively high native rhizobia population. On an average, the strains doubled the number of nodules and increased the dry weight up to 5.8-fold. Inoculation increased shoot dry weight and N content at podding, plant biomass, and number of pods plant−1across sites but the effects of the strains on seeds per pod, and 100-seed weight were inconsistent. Shoot N content did not differ among inoculant strains and ranged from 15.70 g kg−1in the control to 38.53 g kg−1across inoculation. All four strains increased soybean grain yield across sites in 2018 but USDA 110 outperformed the other strains and was also the best at one of the two sites in 2019. Grain yield responses associated with USDA 110 ranged from 552 kg ha−1(56%) to 1,255 kg ha−1(76%). Positive correlations between nodule dry weight plant−1and seed yield, and number of pods plant−1and grain yield were observed. The gross margin ranged from $343.50–$606.80 ha−1for the control, but it increased to $688.34–$789.36 when inoculants were applied. On an average, inoculation increased gross margin by $182.57-$395.35 ha−1over that of non-inoculated control in 2018 but drought stress in 2019 reduced the benefit. The results demonstrate that USDA 110 was the best inoculant strain and has the potential of increasing smallholder productivity and net returns.

Diversification of Sinorhizobium populations associated with Medicago polymorpha and Medicago lupulina in purple soil of China.

The double selection of environment adaptation and host specificity forced the diversification of rhizobia in nature. In the tropical region of China, Medicago polymorpha and Medicago lupulina are widely distributed, particularly in purple soil. However, the local distribution and diversity of rhizobia associated with these legumes has not been systematically investigated. To this end, root nodules of M. polymorpha and M. lupulina grown in purple soil at seven locations in Yunnan Province of China were collected for rhizobial isolation. The obtained rhizobia were characterized by RFLP of 16S-23S rRNA intergenic spacer, BOXAIR fingerprinting, and phylogeny of housekeeping and symbiosis genes. As result, a total of 91 rhizobial strains were classified into species Sinorhizobium medicae and S. meliloti, while three nodC gene types were identified among them. S. medicae containing nodC of type I was dominant in farmlands associated with M. polymorpha; while S. meliloti harboring nodC of type III was dominant in wild land nodulated by M. lupulina. For both rhizobial species, greater genetic diversity was detected in the populations isolated from their preferred host plant. A high level of genetic differentiation was observed between the two Sinorhizobium species, and gene flow was evident within the populations of the same species derived from different soil types, indicating that rhizobial evolution is likely associated with the soil features. To examine the effects of environmental features on rhizobial distribution, soil physicochemical traits and rhizobial genotypes were applied for constrained analysis of principle coordinates, which demonstrated that soil features like pH, nitrogen and sodium were the principle factors governing the rhizobial geographical distribution. Altogether, both S. medicae and S. meliloti strains could naturally nodulate with M. polymorpha and M. lupulina, but the rhizobium-legume symbiosis compatibility determined by both the host species and soil factors was also highlighted.

Members of Ensifer and Rhizobium genera are new bacterial endosymbionts nodulating Pisum sativum (L.).

A total of 84 Pisum sativum legume nodulating bacteria (LNB) were isolated from seven geographical sites from southern Tunisia. Phylogenetic analyses based on partial sequences of 16S rRNA gene and the housekeeping genes glnII, and recA grouped strains into six clusters, four of which belonged to the genus Rhizobium and two to the Ensifer genus. Among Rhizobium clusters, 41 strains were affiliated to Rhizobium leguminosarum, two strains to R. pisi, two strains to R. etli, and interestingly two strains belonged to previously undescribed Rhizobium species. The remaining two strains were closely related to Ensifer medicae (two strains) and Ensifer meliloti (two strains). A symbiotic nodC gene-based phylogeny and host specificity test showed that all Rhizobium strains nodulating pea belonged to the symbiovar viciae, whereas the Ensifer strains were associated with the symbiovar meliloti never described to date. All strains under investigation differed in the number of induced root nodules and the effectiveness of atmospheric nitrogen fixation. The R. leguminosarum PsZA23, R. leguminosarum PsGBL42, and E. medicae PsTA22a, forming the most effective symbiosis with the plant host, are potential candidates for inoculation programs.

In vitro co-inoculation of rhizobacteria from the semi-arid aiming at their implementation as bio-inoculants

The use of nitrogen fertilizers is of paramount importance for the supply of this nutrient to plants. However, the application of these fertilizers brings numerous environmental and health problems. An alternative to these chemical products would be the use of rhizobia — plant growth-promoting rhizobacteria naturally present in the rhizosphere and capable of carrying out biological nitrogen fixation. Through the present work, we propose the co-inoculation of Actinobacteria and rhizobia, aiming at the production of a new bio-inoculant that replaces, at least in part, nitrogen fertilization in legumes. It is expected that Actinobacteria, by producing exoenzymes, enable the growth of rhizobia in non-specific culture media for these microorganisms. Ten strains of Actinobacteria with statistically distinct cellulolytic and xylanolytic activity and seven strains of rhizobia without the aforementioned enzymatic activities were used. A co-inoculation of these microorganisms was performed in culture media containing carboxymethylcellulose (CMC) and xylan as sole carbon sources, and then their compatibility indexes (CI) were calculated. Actinobacteria strains A139 and A145 (both with CI = 0.857 in the medium with CMC and CI = 1 in the medium with xylan) showed remarkable facilitation of rhizobia growth, and had only one antagonistic relation each (both with rhizobia L9 in the medium with CMC). This biological interaction, called cross-feeding, occurs when microorganisms stimulate each other’s growth and is promising for prospecting a bio-inoculant, in addition to providing an overview of the ecological relationships that occur between plant growth-promoting rhizobacteria in the semi-arid region.

Produkcija indolnih jedinjenja od strane rizobijalnih bakterija

Rhizobial bacteria, besides nitrogen fixation in symbiosis with legumes, can colonize the roots of nonlegumes and promote their growth by different mechanisms, independently of N2 fixation. Owing to this, rhizobia are considered a plant growth-promoting rhizobacteria (PGPR). Some of the mechanisms of PGPR activity are phytohormone production. Selection of rhizobia which possess some of PGP traits in vitro is an important step prior to testing their effects on plants in controlled conditions or field. In this work the ability of indole-3-acid (IAA) production, one of the most important phytohormone of the auxin class, was evaluated in different rhizobial strains. The investigated rhizobial strains were isolated from alfalfa (belonged to the genera Ensifer and Rhizobium) and from soybean (Bradyrhizobium and Rhizobium). Strains of all investigated genera produced IAA in the presence of L-tryptophan as precursor, where Ensifer strains produced the highest amount of IAA (more than 200 µg ml-1 ), followed by Rhizobium, while Bradyrhizobium strains produced the least amount of IAA (with some exceptions up to 15 µg ml-1 ). With the increase of L-tryptophan concentration, the amount of IAA produced usually grew. Strains with high IAA production indicate their plant growth promoting potential and represent the candidates for evaluation of their effects in non-legumes in controlled and field conditions.

Potential of the rhizobacterium Ensifer meliloti for the phytoremediation of mixed PAH–heavy metal contamination

The potential of the rhizobial strain Ensifer meliloti P221 as a bacterium capable of degrading phenanthrene in the presence of a heavy metal (nickel) and exhibiting plant-growth promoting activity toward Sorghum bicolor under mixed contamination condition was studied. It was shown that nickel at a concentration of 0.1 mM inhibited the microbial growth and phenanthrene degradation by 43 and 34%, respectively. Analysis of the enzymes involved in the phenanthrene degradation by the rhizobium revealed the activity of the phenanthrenequinone reductase (PQR) and protocatechuate 2,3-dioxigenase (2,3-PCD). It was found that nickel at concentrations up to 0.2 mM did not affect significantly the PQR activity, but inhibited it by 30% when the metal concentration increased to 5 mM. Nickel at concentrations up to 5.0 mM did not affect significantly on the activity of 2,3-PCD. E. meliloti promoted elongation of sorghum seedling roots by 69% in medium co-contaminated with phenanthrene and nickel. The results obtained assume that the rhizobial strain studied can exhibit its PAH-degrading and plant-growth promoting activities in the environment co-contaminated with nickel and phenanthrene. This microorganism may be promising for bioremediation and phytoremediation of mixed PAH–heavy metal contamination.

Presence of rhizobia nodulating common birdsfoot trefoil (Lotus corniculatus L.) in soils of Serbia

Common birdsfoot trefoil (Lotus corniculatus L.) is a perennial forage legume tolerant to adverse environmental conditions such as low soil pH, poor drainage, various insects and plant diseases. Owing to its ability to establish a symbiosis with nitrogen-fixing bacteria, rhizobia, thrives on soils of low fertility and is used in grass mixtures to enrich the soil with nitrogen. The aim of the work was to investigate the presence of rhizobia that nodulate birdsfoot trefoil in the soils of Serbia and to perform the isolation and evaluation of their nitrogen fixation potential. The presence and abundance of birdsfoot trefoil rhizobia in 28 soil samples from different localities and types of soil in Serbia, as well as different ways of use, was tested. From positive samples the rhizobial strains were isolated and their efficiency of nitrogen fixation was tested under controlled conditions. The presence of rhizobia that nodulate birdsfoot trefoil was recorded in 23 samples, while all 5 samples where the presence of rhizobia was not recorded are characterized by the absence of the host plant. The number of rhizobia in samples where there was no host plant was significantly less than in its presence. A total of 49 rhizobial strains were isolated, and in some samples of low abundance it was not possible to isolate strains. In controlled conditions during reinoculation, 80% of the strains were active, achieving 2.5 times greater dry above-ground mass than non-inoculated plants. The percentage of nitrogen in plants ranged from 1.6% in the case of inactive strains to 4.6% in the case of highly active strains. The results of the study indicate the necessity of inoculation, that is, the application of rhizobia on the lands where the common birdsfoot trefoil is sown for the first time due to their reduced number and activity.

A Novel Rhizobium sp. Chiba-1 Strain Exhibits a Host Range for Nodule Symbiosis in Lotus Species.

Rhizobia are soil bacteria that induce the formation of nodules in the roots of leguminous plants for mutualistic establishment. Although the symbiotic mechanism between Lotus japonicus and its major symbiotic rhizobia, Mesorhizobium loti, has been extensively characterized, our understanding of symbiotic mechanisms, such as host specificity and host ranges, remains limited. In the present study, we isolated a novel Rhizobium strain capable of forming nodules on L. burttii from agricultural soil at Iwate prefecture in Japan. We conducted genomic and host range ana-lyses of various Lotus species. The results obtained revealed that the novel isolated Rhizobium sp. Chiba-1 was closely related to R. leguminosarum and had a wide host range that induced nodule development, including L. burttii and several L. japonicus wild-type accessions. However, L. japonicus Gifu exhibited an incompatible nodule phenotype. We also identified the formation of an epidermal infection threads that was dependent on the Lotus species and independent of nodule organ development. In conclusion, this newly isolated Rhizobium strain displays a distinct nodulation phenotype from Lotus species, and the results obtained herein provide novel insights into the functional mechanisms underlying host specificity and host ranges.

Synergism between rhizobium strains and soil bioactivator favor sustainable production of Arachis pintoi

Synergism between rhizobium strains and soil bioactivator favor sustainable production of Arachis pintoi

The Phylogenetic Tree Of The ‘Nod D’ Host-Specific Factor Is Incongruent With The Rhizobial Species Tree And Shows a Possible Hgt Event Between Highly Unrelated Rhizobial Bacteria

Rhizobium is a symbiotic biological nitrogen-fixing (BNF) bacteria. and has high diversity in different geographical regions worldwide. The BNF associated with the legume trees in tropical environments improves the efficiency of nitrogen and increases the soil organic matter, and soil fertility. Rhizobium consists of Mesorhizobium, Sinorhizobium, and Bradyrhizobium, the species belonging to each genera infecting a specific host. This host specificity is dictated by several factors among which Nod D was secreted by the bacterium and plays an important role. We investigated how Nod D gene sequences may have evolved to confer host specificity. We constructed phylogenetic trees of 16srRNA and Nod D trees and compared the trees with a manually built host tree. We find that the Nod D tree is incongruent with the 16srRNA tree and the topology does not show any specific pattern correlative of the host tree. We also uncover a possible HGT of the Nod D gene between highly unrelated bacterial species. This finding may have implications for the development of Rhizobium strains specific to a particular host for Agricultural purposes.

Co-inducible Catabolism of 2-Naphthol Initiated by Hydroxylase CehC1C2 in Rhizobium sp. X9 Removed Its Ecotoxicity

2-Naphthol, which originates from various industrial activities, is widely disseminated through the discharge of industrial wastewater and is, thus, harmful to the water ecosystem, agricultural production, and human health. In this study, the carbaryl degrading strain Rhizobium sp. X9 was proven to be able to degrade 2-naphthol and reduce its toxicity to rice (Oryza sativa) and Chlorella ellipsoidea. Two-component hydroxylase CehC1C2 is responsible for the initial step of degradation and generates 1,2-dihydroxynaphthalene, which is further degraded by the ceh cluster. The transcription of gene cluster cehC1C2 could be induced when both 2-naphthol and glucose were added. A bioinformatic analysis revealed that two transcriptional regulators, the inhibitor CehR2 and the activator CehR3, could be involved in this process. Our study elucidated the molecular mechanism of microbial degradation of 2-naphthol and provided an effective strategy for the in situ remediation of 2-naphthol contamination in the environment.