Activation of Rhizobium tibeticum with flavonoids enhances nodulation, nitrogen fixation, and growth of fenugreek (Trigonella foenum-graecum L.) grown in cobalt-polluted soil

Combined dynamic transcriptome and flavonoid metabolome reveal the role of Mo nanoparticles in the nodulation process in soybean

Symbiotic nitrogen fixation can reduce the impact of agriculture on the environment by reducing fertilizer input. The rapid development of nanomaterials in agriculture provides a new prospect for us to improve the biological nitrogen fixation ability of leguminous crops. Molybdenum is an important component of nitrogenase, and the potential application of MoO3NPs in agriculture is largely unexplored. In this study, on the basis of verifying that MoO3NPs can improve the nitrogen fixation ability of soybean, the effects of MoO3NPs on the symbiotic nitrogen fixation process of soybean were investigated by using dynamic transcriptome and targeted metabolome techniques. Here we showed that compared with conventional molybdenum fertilizer, minute concentrations of MoO3NPs (0.01-0.1 mg kg-1) could promote soybean growth and nitrogen fixation efficiency. The nodules number, fresh nodule weight and nitrogenase activity of 0.1 mg kg-1 were increased by 17 %, 14 % and 27 %, and plant nitrogen accumulation increased by 17 %. Compared with conventional molybdenum fertilizer, MoO3NPs had a greater effect on apigenin, kaempferol and other flavonoid, and the expression of nodulation related genes such as ENOD93, F3'H. Based on WGCNA analysis, we identified a core gene GmCHS9 that was positively responsive to molybdenum and was highly expressed during MoO3NPs induced nodulation. MoO3NPs could improve the nitrogen fixation ability of soybean by promoting the secretion of flavonoids and the expression of key genes. This study provided a new perspective for the nano-strengthening strategy of nodules development and flavonoid biosynthesis by molybdenum.

Recycling potential of cobalt metal from end-of-life new energy passenger vehicles in China

The growing demand for new energy vehicles (NEVs) has resulted in a corresponding increase in demand for cobalt as a critical material. It is crucial to estimate the cobalt resource recycling potential of China's NEV industry to ensure a balance between the supply and demand for cobalt metal minerals. This article is based on using the historical data of the new energy passenger vehicle (NEPV) sales volume from 2013 to 2022 to estimate the NEPV sales volume from 2023 to 2035. On this basis, the Weibull distribution was used to analyse the different sales scenarios (low sales and high sales) of NEPVs in China, and the recycling potential of cobalt metal in NEPVs was evaluated under three battery life scenarios (8, 10 and 12 years) from 2023 to 2035. Based on the above scenarios, in 2035, the greatest recycling potential of cobalt is predicted to be 166.9 kilotonnes, with economic values of CNY 49.01-94.60 billion. Moreover, the extent to which the recycling potential of cobalt can cover the market demand for NEPVs was analysed. Our analysis concluded that recycling cobalt as a secondary supply has emerged as a necessary solution to supplement the primary supply, which can make a significant contribution to alleviating the pressure of the supply and demand.

Biosorption and Symbiotic Potential of Horse Gram Rhizobia in Soils Contaminated with Cobalt

The current study aims evaluation of biosorption and symbiotic potential of horse gram plants associated with rhizobia inspite of Cobalt (Co) metal stress, and these rhizobia strains play a pivotal role in the phytoremediation of Co heavy metal-contaminated soils. Horse gram rhizobial isolates HGR-4, HGR-6, HGR-13 and HGR-25 were able to tolerate 1000 µg g^-1 Co supplemented in culture media and also 100 µg g^-1 in Co supplemented soil. The plants nodulated with the isolates from the study have shown higher nodulation, nitrogen and leghaemoglobin content in the potted experiment on par with the control plants. Atomic absorption spectroscopic analysis of Co content in horse gram plants inoculated with these four isolates showed maximum biosorption of Co among the bacterial root nodules. Application of these strains can be potentially aid the phytoextraction of Co from contaminated soils on association with horse gram plants.

Priming of rhizobial nodulation signaling in the mycosphere accelerates nodulation of legume hosts

The simultaneous symbiosis of leguminous plants with two root mutualists, endophytic fungi and rhizobia is common in nature, yet how two mutualists interact and co-exist before infecting plants and the concomitant effects on nodulation are less understood. Using a combination of metabolic analysis, fungal deletion mutants and comparative transcriptomics, we demonstrated that Bradyrhizobium and a facultatively biotrophic fungus, Phomopsis liquidambaris, interacted to stimulate fungal flavonoid production, and thereby primed Bradyrhizobial nodulation signaling, enhancing Bradyrhizobial responses to root exudates and leading to early nodulation of peanut (Arachis hypogaea), and such effects were compromised when disturbing fungal flavonoid biosynthesis. Stress sensitivity assays and reactive oxygen species (ROS) determination revealed that flavonoid production acted as a strategy to alleviate hyphal oxidative stress during P. liquidambaris-Bradyrhizobial interactions. By investigating the interactions between P. liquidambaris and a collection of 38 rhizobacteria, from distinct bacterial genera, we additionally showed that the flavonoid-ROS module contributed to the maintenance of fungal and bacterial co-existence, and fungal niche colonization under soil conditions. Our results demonstrate for the first time that rhizobial nodulation signaling can be primed by fungi before symbiosis with host plants and highlight the importance of flavonoid in tripartite interactions between legumes, beneficial fungi and rhizobia.

Carbon Nanofiber Double Active Layer and Co-Incorporation as New Anode Modification Strategies for Power-Enhanced Microbial Fuel Cells

Co-doped carbon nanofiber mats can be prepared by the addition of cobalt acetate to the polyacrylonitrile/DMF electrospun solution. Wastewater obtained from food industries was utilized as the anolyte as well as microorganisms as the source in single-chamber batch mode microbial fuel cells. The results indicated that the single Co-free carbon nanofiber mat was not a good anode in the used microbial fuel cells. However, the generated power can be distinctly enhanced by using double active layers of pristine carbon nanofiber mats or a single layer Co-doped carbon nanofiber mat as anodes. Typically, after 24 h batching time, the estimated generated power densities were 10, 92, and 121 mW/m2 for single, double active layers, and Co-doped carbon nanofiber anodes, respectively. For comparison, the performance of the cell was investigated using carbon cloth and carbon paper as anodes, the observed power densities were smaller than the introduced modified anodes at 58 and 62 mW/m2, respectively. Moreover, the COD removal and Columbic efficiency were calculated for the proposed anodes as well as the used commercial ones. The results further confirm the priority of using double active layer or metal-doped carbon nanofiber anodes over the commercial ones. Numerically, the calculated COD removals were 29.16 and 38.95% for carbon paper and carbon cloth while 40.53 and 45.79% COD removals were obtained with double active layer and Co-doped carbon nanofiber anodes, respectively. With a similar trend, the calculated Columbic efficiencies were 26, 42, 52, and 71% for the same sequence.

Efficacy of fenugreek plant for ascorbic acid assisted phytoextraction of copper (Cu); A detailed study of Cu induced morpho-physiological and biochemical alterations

Phytoremediation via phyto-extraction is well recognized and sustainable principle for the economical removal of heavy metals from contaminated water and soil. The twofold objective of the present research work was to investigate the remediation potential of fenugreek for Cu under the influence of ascorbic acid (AA). The effect of copper-ascorbic acid chelation on the growth regulation of fenugreek (Trigonella foenum-graceum L.) and its potential to accumulate Cu was investigated in hydroponic medium to optimize concentration with complete randomized design (CRD). Juvenile fenugreek plants were treated with different treatments of AA (5 mM) and Cu (100, 250 and 500 μM). The different morpho-physiological parameters of fenugreek plant such as growth, biomass and chlorophylls were significantly reduced under Cu stress. However, the activities of antioxidant enzymes, electrolyte leakage and reactive oxygen species enhanced with increasing concentration of applied Cu. Results indicated significant increase in plant growth, biomass, physiology and antioxidant enzymes and decrease in reactive oxygen species and electrolyte production in AA mediated fenugreek plants compared to controls and Cu only treated plants. However, it was also found that AA enhanced Cu concentration maximum up to 42% in leaf, 18% in stem and 45% in roots as compared to Cu treated only plants. Moreover, application of AA signified the research results revealing to act as growth regulator and chelator under Cu stress.

Metabolism-mediated induction of zinc tolerance in Brassica rapa by Burkholderia cepacia CS2-1

Brassica rapa (Chinese cabbage) is an essential component of traditional Korean food. However, the crop is often subject to zinc (Zn⁺) toxicity from contaminated irrigation water, which, as a result, compromises plant growth and production, as well as the health of human consumers. The present study investigated the bioaccumulation of Zn⁺ by Burkholderia cepacia CS2-1 and its effect on the heavy metal tolerance of Chinese cabbage. Strain CS2-1 was identified and characterized on the basis of 16S rRNA sequences and phylogenetic analysis. The strain actively produced indole-3-acetic acid (3.08 ± 0.21 μg/ml) and was also able to produce siderophore, solubilize minerals, and tolerate various concentrations of Zn⁺. The heavy metal tolerance of B. rapa plants was enhanced by CS2-1 inoculation, as indicated by growth attributes, Zn⁺ uptake, amino acid synthesis, antioxidant levels, and endogenous hormone (ABA and SA) synthesis. Without inoculation, the application of Zn⁺ negatively affected the growth and physiology of B. rapa plants. However, CS2-1 inoculation improved plant growth, lowered Zn⁺ uptake, altered both amino acid regulation and levels of flavonoids and phenolics, and significantly decreased levels of superoxide dismutase, endogenous abscisic acid, and salicylic acid. These findings indicate that B. cepacia CS2-1 is suitable for bioremediation against Zn⁺-induced oxidative stress.

Rhizobium tibeticum activated with a mixture of flavonoids alleviates nickel toxicity in symbiosis with fenugreek (Trigonella foenum graecum L.)

The objective of this study is to explore the response of an activated Rhizobium tibeticum inoculum with a mixture of hesperetin (H) and apigenin (A) to improve the growth, nodulation, and nitrogen fixation of fenugreek (Trigonella foenum graecum L.) grown under nickel (Ni) stress. Three different sets of fenugreek seed treatments were conducted, in order to investigate the activated R. tibeticum pre-incubation effects on nodulation, nitrogen fixation and growth of fenugreek under Ni stress. Group (I): uninoculated seeds with R. tibeticum, group (II): inoculated seeds with uninduced R. tibeticum group (III): inoculated seeds with induced R. tibeticum. The present study revealed that Ni induced deleterious effects on rhizobial growth, nod gene expression, nodulation, phenylalanine ammonia-lyase (PAL) and glutamine synthetase activities, total flavonoids content and nitrogen fixation, while the inoculation with an activated R. tibeticum significantly improved these values compared with plants inoculated with uninduced R. tibeticum. PAL activity of roots plants inoculated with induced R. tibeticum and grown hydroponically at 75 and 100 mg L(-1) Ni and was significantly increased compared with plants receiving uninduced R. tibeticum. The total number and fresh mass of nodules, nitrogenase activity of plants inoculated with induced cells grown in soil treated up to 200 mg kg(-1) Ni were significantly increased compared with plants inoculated with uninduced cells. Plants inoculated with induced R. tibeticum dispalyed a significant increase in the dry mass compared with those treated with uninduced R. tibeticum. Activation of R. tibeticum inoculum with a mixture of hesperetin and apigenin has been proven to be practically important in enhancing nodule formation, nitrogen fixation and growth of fenugreek grown in Ni contaminated soils.