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Plants (Basel, Switzerland) Feb 2022Vegetables can be treated with biofertilizers as an alternative to chemical fertilizers because of their low toxicity. We investigated the effects of foliar spraying of...
Vegetables can be treated with biofertilizers as an alternative to chemical fertilizers because of their low toxicity. We investigated the effects of foliar spraying of under different levels of nitrogen (100, 150 and 200 mg/L in nutrient solution) on the growth, nutritional value, nitrate accumulation and antioxidant enzyme activities of hydroponically grown lettuce. The experiment was laid out in a completely randomized design with four replicates in a factorial combination. Plants treated with and 200 mg/L nitrogen had greater leaf area and photosynthetic pigments than plants treated with 200 mg/L nitrogen without spraying with . Increasing nitrogen levels increased leaf number, fresh and dry weights, leaf area and nitrate accumulation in lettuce plants. Peroxidase (POD) activity increased by 95.4% at a nitrogen level of 200 mg/L compared to a nitrogen level of 100 mg/L. Ascorbate peroxidase (APX) activity and leaf phosphorous (P) and potassium (K) concentrations were the highest in plants treated with a nitrogen source of 100 mg/L without foliar application of . As nitrogen levels increased in all treatments, nitrate reductase (NR) activity decreased and reached a minimum at the 200 mg/L nitrogen level. In general, foliar application of sp. can be used to promote plant growth and reduce nitrate accumulation in lettuce.
PubMed: 35161387
DOI: 10.3390/plants11030406 -
PeerJ 2023The raising trend of cultivation of ()-transgenic cotton is faced with a new challenge what effects on the growth and yield of cotton under elevated CO.
BACKGROUND
The raising trend of cultivation of ()-transgenic cotton is faced with a new challenge what effects on the growth and yield of cotton under elevated CO.
METHODS
Rhizobacteria is the significant biological regulator to increase environmental suitability and ameliorate soil-nitrogen utilization efficiency of crops, especially cotton. Pot-culture experiments investigated the effects on the yield and fiber quality components of cotton (transgenic Line SCRC 37) inoculated with (AC) under elevated CO.
RESULTS
The findings indicated that the inoculation of azotobacter significantly improved the yield and fiber quality components of cotton, the elevated CO significantly increased the soil density of and the partial yield indexes (as cottonweightper 20 bolls, lint yield per 20 bolls and boll number per plant), and non-significant decrease the fiber quality components of cotton except uniform.
DISCUSSION
Overall results obviously depicted that the inoculation of azotobacter and the elevated CO had positive effects on the yield and fiber quality components of cotton. Presumably, azotobacter inoculation can be used to stimulate plant soil-nitrogen uptake and promote plant growth for cotton under elevated CO in the future.
Topics: Bacillus thuringiensis; Carbon Dioxide; Azotobacter; Soil; Gossypium; Nitrogen
PubMed: 37576495
DOI: 10.7717/peerj.15811 -
Applied and Environmental Microbiology Sep 2022Biological nitrogen fixation requires large amounts of energy in the form of ATP and low potential electrons to overcome the high activation barrier for cleavage of the...
Biological nitrogen fixation requires large amounts of energy in the form of ATP and low potential electrons to overcome the high activation barrier for cleavage of the dinitrogen triple bond. The model aerobic nitrogen-fixing bacteria, Azotobacter vinelandii, generates low potential electrons in the form of reduced ferredoxin (Fd) and flavodoxin (Fld) using two distinct mechanisms via the enzyme complexes Rnf and Fix. Both Rnf and Fix are expressed during nitrogen fixation, but deleting either or genes has little effect on diazotrophic growth. However, deleting both and eliminates the ability to grow diazotrophically. Rnf and Fix both use NADH as a source of electrons, but overcoming the energetics of NADH's endergonic reduction of Fd/Fld is accomplished through different mechanisms. Rnf harnesses free energy from the chemiosmotic potential, whereas Fix uses electron bifurcation to effectively couple the endergonic reduction of Fd/Fld to the exergonic reduction of quinone. Different reaction stoichiometries and condition-specific differential gene expression indicate specific roles for the two reactions. This work's complementary physiological studies and thermodynamic modeling reveal how Rnf and Fix balance redox homeostasis in various conditions. Specifically, the Fix complex is required for efficient growth under low oxygen concentrations, while Rnf is presumed to maintain reduced Fd/Fld production for nitrogenase under standard conditions. This work provides a framework for understanding how the production of low potential electrons sustains robust nitrogen fixation in various conditions. The availability of fixed nitrogen is critical for life in many ecosystems, from extreme environments to agriculture. Due to the energy demands of biological nitrogen fixation, organisms must tailor their metabolism during diazotrophic growth to deliver the energy requirements to nitrogenase in the form of ATP and low potential electrons. Therefore, a complete understanding of diazotrophic energy metabolism and redox homeostasis is required to understand the impact on ecological communities or to promote crop growth in agriculture through engineered diazotrophs.
Topics: Adenosine Triphosphate; Azotobacter vinelandii; Ecosystem; Ferredoxins; NAD; Nitrogen; Nitrogen Fixation; Nitrogenase
PubMed: 36000884
DOI: 10.1128/aem.01049-22 -
Current Protocols Jan 2022
PubMed: 35034426
DOI: 10.1002/cpz1.363 -
Microbiome Oct 2021Nitrogen-fixing prokaryotes (diazotrophs) contribute substantially to nitrogen input in mangrove sediments, and their structure and nitrogen fixation rate (NFR) are...
BACKGROUND
Nitrogen-fixing prokaryotes (diazotrophs) contribute substantially to nitrogen input in mangrove sediments, and their structure and nitrogen fixation rate (NFR) are significantly controlled by environmental conditions. Despite the well-known studies on diazotrophs in surficial sediments, the diversity, structure, and ecological functions of diazotrophic communities along environmental gradients of mangrove sediment across different depths are largely unknown. Here, we investigated how biological nitrogen fixation varied with the depth of mangrove sediments from the perspectives of both NFR and diazotrophic communities.
RESULTS
Through acetylene reduction assay, nifH gene amplicon and metagenomic sequencing, we found that the NFR increased but the diversity of diazotrophic communities decreased with the depth of mangrove sediments. The structure of diazotrophic communities at different depths was largely driven by salinity and exhibited a clear divergence at the partitioning depth of 50 cm. Among diazotrophic genera correlated with NFR, Agrobacterium and Azotobacter were specifically enriched at 50-100 cm sediments, while Anaeromyxobacter, Rubrivivax, Methylocystis, Dickeya, and Methylomonas were more abundant at 0-50 cm. Consistent with the higher NFR, metagenomic analysis demonstrated the elevated abundance of nitrogen fixation genes (nifH/D/K) in deep sediments, where nitrification genes (amoA/B/C) and denitrification genes (nirK and norB) became less abundant. Three metagenome-assembled genomes (MAGs) of diazotrophs from deep mangrove sediments indicated their facultatively anaerobic and mixotrophic lifestyles as they contained genes for low-oxygen-dependent metabolism, hydrogenotrophic respiration, carbon fixation, and pyruvate fermentation.
CONCLUSIONS
This study demonstrates the depth-dependent variability of biological nitrogen fixation in terms of NFR and diazotrophic communities, which to a certain extent relieves the degree of nitrogen limitation in deep mangrove sediments. Video Abstract.
Topics: Geologic Sediments; Metagenomics; Nitrogen; Nitrogen Fixation; Soil Microbiology
PubMed: 34702367
DOI: 10.1186/s40168-021-01164-0 -
Microorganisms Sep 2022Drought stress is one of the most severe abiotic stresses affecting soil fertility and plant health, and due to climate change, it is destined to increase even further,...
Drought stress is one of the most severe abiotic stresses affecting soil fertility and plant health, and due to climate change, it is destined to increase even further, becoming a serious threat to crop production. An efficient, eco-friendly alternative is the use of plant growth-promoting bacteria (PGPB), which can promote plant fitness through direct and indirect approaches, protecting plants from biotic and abiotic stresses. The present study aims to identify bacterial consortia to promote L. cv Matador's seed germination and protect its seedlings from drought stress. Eight PGPB strains belonging to , and genera, previously characterized in physiological conditions, were analyzed under water-shortage conditions, and a germination bioassay was carried out by biopriming seeds with either individual strains or consortia. The consortia of RHF6, LMG9814, and . AGS84 displayed the capacity to positively affect seed germination and seedlings' radical development in both standard and drought conditions, ameliorating the plants' growth rate compared to the untreated ones. These results sustain using PGPB consortia as a valid ameliorating water stress strategy in the agro-industrial field.
PubMed: 36144400
DOI: 10.3390/microorganisms10091798 -
MBio Jun 2022Engineering plants to synthesize nitrogenase and assimilate atmospheric N will reduce crop dependency on industrial N fertilizers. This technology can be achieved by...
Engineering plants to synthesize nitrogenase and assimilate atmospheric N will reduce crop dependency on industrial N fertilizers. This technology can be achieved by expressing prokaryotic nitrogen fixation gene products for the assembly of a functional nitrogenase in plants. NifB is a critical nitrogenase component since it catalyzes the first committed step in the biosynthesis of all types of nitrogenase active-site cofactors. Here, we used a library of 30 distinct sequences originating from different phyla and ecological niches to restore diazotrophic growth of an Azotobacter vinelandii mutant. Twenty of these variants rescued the mutant phenotype despite their phylogenetic distance to A. vinelandii. Because multiple protein interactions are required in the iron-molybdenum cofactor (FeMo-co) biosynthetic pathway, the maturation of nitrogenase in a heterologous host can be divided in independent modules containing interacting proteins that function together to produce a specific intermediate. Therefore, functional modules composed of a variant, together with the A. vinelandii NifS and NifU proteins (for biosynthesis of NifB [FeS] clusters) and the FdxN ferredoxin (for NifB function), were expressed in Nicotiana benthamiana chloroplasts and mitochondria. Three archaeal NifB proteins accumulated at high levels in soluble fractions of chloroplasts (Methanosarcina acetivorans and Methanocaldococcus infernus) or mitochondria ( and Methanothermobacter thermautotrophicus). These NifB proteins were shown to accept [FeS] clusters from NifU and were functional in FeMo-co synthesis . The accumulation of significant levels of soluble and functional NifB proteins in chloroplasts and mitochondria is critical to engineering biological nitrogen fixation in plants. Biological nitrogen fixation is the conversion of inert atmospheric dinitrogen gas into nitrogen-reactive ammonia, a reaction catalyzed by the nitrogenase enzyme of diazotrophic bacteria and archaea. Because plants cannot fix their own nitrogen, introducing functional nitrogenase in cereals and other crop plants would reduce our strong dependency on N fertilizers. NifB is required for the biosynthesis of the active site cofactors of all nitrogenases, which arguably makes it the most important protein in global nitrogen fixation. NifB functionality is therefore a requisite to engineer a plant nitrogenase. The expression of genes from a wide range of prokaryotes into the model diazotroph Azotobacter vinelandii shows a surprising level of genetic complementation suggestive of plasticity in the nitrogenase biosynthetic pathway. In addition, we obtained NifB proteins from both mitochondria and chloroplasts of tobacco that are functional after reconstitution by providing [FeS] clusters from NifU, paving the way to nitrogenase cofactor biosynthesis in plants.
Topics: Archaeal Proteins; Azotobacter vinelandii; Bacterial Proteins; Chloroplasts; Fertilizers; Iron Compounds; Mitochondria; Nitrogen; Nitrogen Fixation; Nitrogenase; Phylogeny; Nicotiana
PubMed: 35695456
DOI: 10.1128/mbio.00268-22 -
International Journal of Molecular... Dec 2022The enzymatic transformation of various chemicals, especially using NADPH-dependent hydroxylase, into more soluble and/or high value-added products has steadily garnered...
The enzymatic transformation of various chemicals, especially using NADPH-dependent hydroxylase, into more soluble and/or high value-added products has steadily garnered increasing attention. However, the industrial application of these NADPH-dependent hydroxylases has been limited due to the high cost of the cofactor NADPH. As an alternative, enzymatic NADPH-regeneration systems have been developed and are frequently used in various fields. Here, we expressed and compared two recombinant isocitrate dehydrogenases (IDHs) from and in . Both enzymes were hyper-expressed in the soluble fraction of and were single-step purified to apparent homogeneity with yields of more than 850 mg/L. These enzymes also functioned well when paired with NADPH consumption systems. Specifically, NADPH was regenerated from NADP when an NADPH-consuming cytochrome P450 BM3 from was incorporated. Therefore, both enzymes could be used as alternatives to the commonly used regeneration system for NADPH. These enzymes also have promising potential as genetic fusion partners with NADPH-dependent enzymes due to the monomeric nature of their quaternary structure, thereby resulting in self-sufficient biocatalysts via NADPH regeneration in a single polypeptide with NADPH-dependent activity.
Topics: Azotobacter vinelandii; NADP; Isocitrate Dehydrogenase; Corynebacterium glutamicum; Escherichia coli; Cytochrome P-450 Enzyme System
PubMed: 36499645
DOI: 10.3390/ijms232315318 -
Microbiological Research Sep 2021This group has previously reported the role of ascorbic acid (AA) as an antioxidant for survivability and ability to enhancing diazotrophic efficacy in Azotobacter...
Combined application of ascorbic acid and endophytic N-fixing Azotobacter chroococcum Avi2 modulates photosynthetic efficacy, antioxidants and growth-promotion in rice under moisture deficit stress.
This group has previously reported the role of ascorbic acid (AA) as an antioxidant for survivability and ability to enhancing diazotrophic efficacy in Azotobacter chroococcum Avi2 under hydrogen peroxide (HO) stress. However, the present study showed the combined application of AA and Avi2 in drought-susceptible (IR64 and Naveen) and drought-tolerant (Ankit and Satyabhama) rice cultivars to determine their photosynthetic efficacy (chlorophyll fluorescence-imaging), antioxidants, and plant growth-promotion (PGP) under moisture deficit stress (MS, -60 kPa). The results indicated that combined application of AA and Avi2 significantly (p < 0.05) increased the total chlorophyll, relative water content, electrolytic leakage, super oxide dismutase, and catalase activities in all rice cultivars as compared to other MS treatments, whereas stress indicators like proline and HO contents were proportionally increased under MS and their concentration were normalized under combined application of AA and Avi2. Photochemical quenching, non-photochemical quenching, photosynthetic electron transport rate, and the effective quantum efficiency were found to be increased significantly (p < 0.05) in Avi2 + AA as compared to other MS treatments. Moreover, rice roots harbored significantly (p < 0.05) higher copy number of nifH gene in Avi2 + AA treatment followed by Avi2 compared to flooded control and other MS treatments. Combined application of AA and Avi2 also increased the grain yield significantly (p < 0.05) by 7.09 % and 3.92 % in drought-tolerant (Ankit and Satyabhama, respectively) and 31.70 % and 34.19 % in drought-susceptible (IR64 and Naveen, respectively) rice cultivars compared to MS treatment. Overall, the present study indicated that AA along with Avi2 could be an effective formulation to alleviate MS vis à vis enhances PGP traits in rice.
Topics: Antioxidants; Ascorbic Acid; Azotobacter; Chlorophyll; Endophytes; Nitrogen Fixation; Oryza; Oxidation-Reduction; Photosynthesis; Plant Leaves; Plant Roots; Stress, Physiological; Water
PubMed: 34146939
DOI: 10.1016/j.micres.2021.126808 -
Communications Biology Oct 2022Engineering cereals to express functional nitrogenase is a long-term goal of plant biotechnology and would permit partial or total replacement of synthetic N fertilizers...
Engineering cereals to express functional nitrogenase is a long-term goal of plant biotechnology and would permit partial or total replacement of synthetic N fertilizers by metabolization of atmospheric N. Developing this technology is hindered by the genetic and biochemical complexity of nitrogenase biosynthesis. Nitrogenase and many of the accessory proteins involved in its assembly and function are O sensitive and only sparingly soluble in non-native hosts. We generated transgenic rice plants expressing the nitrogenase structural component, Fe protein (NifH), which carries a [4Fe-4S] cluster in its active form. NifH from Hydrogenobacter thermophilus was targeted to mitochondria together with the putative peptidyl prolyl cis-trans isomerase NifM from Azotobacter vinelandii to assist in NifH polypeptide folding. The isolated NifH was partially active in electron transfer to the MoFe protein nitrogenase component (NifDK) and in the biosynthesis of the nitrogenase iron-molybdenum cofactor (FeMo-co), two fundamental roles for NifH in N fixation. NifH functionality was, however, limited by poor [4Fe-4S] cluster occupancy, highlighting the importance of in vivo [Fe-S] cluster insertion and stability to achieve biological N fixation in planta. Nevertheless, the expression and activity of a nitrogenase component in rice plants represents the first major step to engineer functional nitrogenase in cereal crops.
Topics: Fertilizers; Molybdoferredoxin; Nitrogenase; Oryza; Oxidoreductases; cis-trans-Isomerases
PubMed: 36198910
DOI: 10.1038/s42003-022-03921-9