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Biophysical Chemistry Oct 2021The MoFe protein component of the nitrogenase enzyme complex is the substrate reducing site and contains two sets of symmetrically arrayed metallo centers called the P...
The MoFe protein component of the nitrogenase enzyme complex is the substrate reducing site and contains two sets of symmetrically arrayed metallo centers called the P (FeS) and the FeMoco (MoFeS-C-homocitrate) centers. The ATP-binding Fe protein is the specific reductant for the MoFe protein. Both symmetrical halves of the MoFe protein are thought to function independently during nitrogenase catalysis. Forming [AlF] transition-state complexes between the MoFe protein and the Fe protein of Azotobacter vinelandii ranging from 0 to 2 Fe protein/MoFe protein produced a series of complexes whose specific activity decreases with increase in bound Fe protein/MoFe protein ratio. Reduction of 2H to H was inhibited in a linear manner with an x-intercept at 2.0 with increasing Fe protein binding, whereas acetylene reduction to ethylene decreased more rapidly with an x-intercept near 1.5. H reduction is a distinct process occurring independently at each half of the MoFe protein but acetylene reduction decreases more rapidly than H reduction with increasing Fe protein/MoFe protein ratio, suggesting that a response is transmitted between the two αβ halves of the MoFe protein for acetylene reduction as Fe protein is bound. A mechanistic model is derived to investigate this behavior. The model predicts that each site functions independently for 2H reduction to H. For acetylene reduction, the model predicts positive (synchronous) not negative cooperativity arising from acetylene binding to both sites before substrate reduction occurs. When this model is applied to inhibition by Cp2 and modified Av2 protein (L127∆) that form strong, non-dissociable complexes, positive cooperativity is absent and each site acts independently. The results suggest a new paradigm for the catalytic function of the MoFe protein during nitrogenase catalysis.
Topics: Acetylene; Azotobacter vinelandii; Nitrogenase
PubMed: 34242995
DOI: 10.1016/j.bpc.2021.106650 -
Frontiers in Bioengineering and... 2020Poly-(3-hydroxyalkanoates) (PHAs) are bacterial carbon and energy storage compounds. These polymers are synthesized under conditions of nutritional imbalance, where a... (Review)
Review
Poly-(3-hydroxyalkanoates) (PHAs) are bacterial carbon and energy storage compounds. These polymers are synthesized under conditions of nutritional imbalance, where a nutrient is growth-limiting while there is still enough carbon source in the medium. On the other side, the accumulated polymer is mobilized under conditions of nutrient accessibility or by limitation of the carbon source. Thus, it is well known that the accumulation of PHAs is affected by the availability of nutritional resources and this knowledge has been used to establish culture conditions favoring high productivities. In addition to this effect of the metabolic status on PHAs accumulation, several genetic regulatory networks have been shown to drive PHAs metabolism, so the expression of the PHAs genes is under the influence of global or specific regulators. These regulators are thought to coordinate PHAs synthesis and mobilization with the rest of bacterial physiology. While the metabolic and biochemical knowledge related to the biosynthesis of these polymers has led to the development of processes in bioreactors for high-level production and also to the establishment of strategies for metabolic engineering for the synthesis of modified biopolymers, the use of knowledge related to the regulatory circuits controlling PHAs metabolism for strain improvement is scarce. A better understanding of the genetic control systems involved could serve as the foundation for new strategies for strain modification in order to increase PHAs production or to adjust the chemical structure of these biopolymers. In this review, the regulatory systems involved in the control of PHAs metabolism are examined, with emphasis on those acting at the level of expression of the enzymes involved and their potential modification for strain improvement, both for higher titers, or manipulation of polymer properties. The case of the PHAs producer is taken as an example of the complexity and variety of systems controlling the accumulation of these interesting polymers in response to diverse situations, many of which could be engineered to improve PHAs production.
PubMed: 32426348
DOI: 10.3389/fbioe.2020.00386 -
Ecotoxicology and Environmental Safety Dec 2022Elevated atmospheric carbon dioxide (eCO) concentrations can alter the carbon:nitrogen ratio and palatability of host plants for herbivorous insects, but rhizobacteria...
Elevated atmospheric carbon dioxide (eCO) concentrations can alter the carbon:nitrogen ratio and palatability of host plants for herbivorous insects, but rhizobacteria likely mitigate the alteration and influence physiological adaptation of insects. In this study, we conducted transcriptomic analysis of maize (Zea mays) response to Azotobacter chroococcum (AC) inoculation under eCO conditions in contrast to ambient CO (aCO), and studied the effects of plant-defense change of maize under eCO on the oriental armyworm, Mythimna separata. Results showed that there were 16, 14, 16 and 135 differentially expressed genes that were associated with plant-defense response in maize leaves between aCO-CK and aCO-AC, eCO-CK and eCO-AC, aCO-CK and eCO-CK, aCO-AC and eCO-AC, respectively. Moreover, A. chroococcum inoculation and eCO influenced plant hormone signal transduction of maize. Interestingly, A. chroococcum inoculation significantly decreased the contents of JA (jasmonic acid) and JA-Ile (isoleucine conjugate of JA) in leaves, but eCO markedly increased contents of JA-Ile, JA and SA (salicylic acid). Compared to aCO, eCO significantly decreased activity of protective enzyme (catalase), and increased activities of digestive (lipase and protease), protective (peroxidase) and detoxifying enzymes (carboxylesterase, Mixed-functional oxidase and glutathione s-transferase), prolonged developmental time, and decreased survival rate and body weight of larvae (P < 0.05). A. chroococcum inoculation significantly increased the activity of protective enzyme (catalase), and decreased the activities of detoxifying enzymes (carboxylesterase, glutathione s-transferase and mixed-functional oxidase), thus increased the growth rate and body weight of larvae in comparison with no-inoculation of A. chroococcum (P < 0.05). The indices of M. separata were significantly correlated with the foliar contents of JA, JA-Ile and SA (|r| = 0.44-0.85, P < 0.05), indicating that A. chroococcum inoculation altered the physiological adaptation of M. separata under eCO by disturbing defense substances in maize. Our results in understanding effects of A. chroococcum inoculation on maize resistance to herbivorous insects will be valuable for agricultural pest control in the future at eCO conditions.
Topics: Animals; Zea mays; Catalase; Carbon Dioxide; Spodoptera; Glutathione Transferase; Carboxylic Ester Hydrolases
PubMed: 36399994
DOI: 10.1016/j.ecoenv.2022.114296 -
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 -
Journal of Fungi (Basel, Switzerland) Apr 2022Antifungal efficacy of against trichothecene-producing spp. was investigated in maize, sorghum, and wheat. The three cereals were subjected to four treatments as...
Antifungal efficacy of against trichothecene-producing spp. was investigated in maize, sorghum, and wheat. The three cereals were subjected to four treatments as control (T1), alone (T2), combination of and treatment (T3), and only (T4). All the treatments were evaluated for total mass of seedlings, root and shoot length, seed germination, and vigor index (VI), and extent of rhizoplane colonization by was investigated. Further, greenhouse studies were conducted to learn the efficacy of in vivo conditions. Antifungal efficacy was tested by the dual-culture method which resulted in significant reduction in growth. Infection by was reduced up to 50% in treated cereals such as maize, sorghum, and wheat, and there was also significant increase in seedling mass in the three hosts. Maize showed the highest VI (1859.715), followed by sorghum (1470.84), and wheat (2804.123) with treatment. In addition, seed germination was enhanced to 76% in maize, 69% in sorghum, and 68% in wheat, respectively. Efficacy of rhizoplane colonization showed successful isolation of with high CFU rate, and furthermore, significant colonization inhibition by spp. was observed. In the greenhouse conditions, on the 45th day of the experimental set-up, the highest shoot length/root length recorded in maize was 155.70/70.0 cm, in sorghum 165.90/48.0 cm, and in wheat 77.85/56.0 cm, and the maximum root mass recorded was 17.53 g in maize, 4.52 g in sorghum, and 1.90 g in wheat. Our present study showed that seed treatment by may be used as an alternate biocontrol method against infection in maize, sorghum, and wheat.
PubMed: 35628729
DOI: 10.3390/jof8050473 -
Foods (Basel, Switzerland) Sep 2022The use of microbial biostimulants such as plant growth-promoting rhizobacteria (PGPB) and arbuscular mycorrhizal fungi (AMF) has gained popularity in recent years as a... (Review)
Review
The use of microbial biostimulants such as plant growth-promoting rhizobacteria (PGPB) and arbuscular mycorrhizal fungi (AMF) has gained popularity in recent years as a sustainable approach to boost yield as well as the quality of produce. The beneficial effects of microbial biostimulants have been reported numerous times. However, information is missing concerning quantitative assessment of the overall impact of microbial biostimulants on the yield and quality of vegetable crops. Here we provide for the first time a comprehensive, semi-systematic review of the effects of microbial biostimulants allowed by Regulation (EU) 2019/1009, including microorganisms belonging to the AMF (phylum Glomeromycota), or to , and genera, on vegetable crops' quality and yield, with rigorous inclusion and exclusion criteria based on the PRISMA method. We identified, selected and critically evaluated all the relevant research studies from 2010 onward in order to provide a critical appraisal of the most recent findings related to these EU-allowed microbial biostimulants and their effects on vegetable crops' quality and yield. Moreover, we highlighted which vegetable crops received more beneficial effects from specific microbial biostimulants and the protocols employed for plant inoculation. Our study is intended to draw more attention from the scientific community to this important instrument to produce nutrient-dense vegetables in a sustainable manner. Finally, our semi-systematic review provides important microbial biostimulant application guidelines and gives extension specialists and vegetable growers insights into achieving an additional benefit from microbial biostimulant application.
PubMed: 36076841
DOI: 10.3390/foods11172656 -
Methods in Molecular Biology (Clifton,... 2019The biological reduction of nitrogen gas to ammonia is limited to a select group of nitrogen-fixing prokaryotes. While nitrogenase is the catalyst of nitrogen fixation...
The biological reduction of nitrogen gas to ammonia is limited to a select group of nitrogen-fixing prokaryotes. While nitrogenase is the catalyst of nitrogen fixation in these biological systems, a consortium of additional gene products is required for the synthesis, activation, and catalytic competency of this oxygen-sensitive metalloenzyme. Thus, the biochemical complexity of this process often requires functional studies and isolation of gene products from the native nitrogen-fixing organisms. The strict aerobe Azotobacter vinelandii is the best-studied model bacterium among diazotrophs. This chapter provides a description of procedures for targeted genomic manipulation and isolation of A. vinelandii strains. These methods have enabled identification and characterization of gene products with roles in nitrogen fixation and other related aspects of metabolism. The ability to modify and control expression levels of targeted sequences provides a biotechnological tool to uncover molecular details associated with nitrogen fixation, as well as to exploit this model system as a host for expression of oxygen-sensitive proteins.
Topics: Azotobacter vinelandii; Bacterial Proteins; Gene Expression Regulation, Bacterial; Genetic Engineering; Metalloproteins; Nitrogen Fixation; Nitrogenase; Phenotype
PubMed: 30317476
DOI: 10.1007/978-1-4939-8864-8_6 -
International Journal of Biological... Aug 2023This study involved the extraction of an exopolysaccharide (EPS) from Azotobacter salinestris AZ-6, which was isolated from soil cultivated with leguminous plants. In a...
This study involved the extraction of an exopolysaccharide (EPS) from Azotobacter salinestris AZ-6, which was isolated from soil cultivated with leguminous plants. In a medium devoid of nitrogen, the AZ-6 strain displayed a maximum EPS yield of 1.1 g/l and the highest relative viscosity value of 3.4. The homogeneity of the polymer was demonstrated by the average molecular weight of 1.61 × 10 Da and a retention time of 17.211 min for levan. The presence of characteristic functional groups and structural units of carbohydrate polymers has been confirmed through spectroscopic analyses utilizing Fourier-transform infrared (FT-IR) and nuclear magnetic resonance (NMR) techniques. Thermogravimetric analysis (TGA) revealed a noteworthy decrease in weight (74 %) in the temperature range spanning from 260 to 350 °C. X-ray diffraction (XRD) was utilized to verify the crystalline and amorphous characteristics of EPS-AZ-6. The EPS-AZ-6 exhibited significant cytotoxicity against the MCF-7 tumor cell line, as evidenced by an IC value of 6.39 ± 0.05 μg/ml. It also demonstrated a moderate degree of cytotoxicity towards HepG-2 cell line, as indicated by an IC value of 29.79 ± 0.41 μg/ml. EPS-AZ-6 exhibited potent antioxidant and in vitro antibacterial properties. These characteristics suggest the potential application value of EPS-AZ-6 in the food industry and pharmaceutical applications.
Topics: Spectroscopy, Fourier Transform Infrared; Azotobacter; Antioxidants; Molecular Weight; Polysaccharides, Bacterial
PubMed: 37390994
DOI: 10.1016/j.ijbiomac.2023.125594 -
PeerJ 2021Organic and biological fertilizers are considered as a very important source of plant nutrients. A field experiment was conducted during 2017-2018 in paddy soil to...
Organic and biological fertilizers are considered as a very important source of plant nutrients. A field experiment was conducted during 2017-2018 in paddy soil to investigate the effect of vermicomposting of cattle manure mixture with and rice straw on soil microbial activity, nutrient uptake, and grain yield under inoculation of N-fixing bacteria. Experimental factors consisted of organic amendments at six levels (vermicomposts prepared from manure (VM); manure + rice straw (VRM); manure + mixture (VAM); manure + rice straw + mixture (VRAM); raw manure without vermicomposting (M), and a control) and N-fixing bacteria at three levels (, , and non-inoculation). The results showed that, vermicompost treatments compared to control and raw manure significantly increased the number and biomass-C of soil microorganisms, urease activity, number of tillers hill, phosphorus (P) and potassium (K) uptake, and grain and protein yield. Inoculation of plants with N-fixing bacteria, especially increased the efficiency of organic amendments, so that the maximum urease activity, soil microbial activity, P and N uptake, and grain yield (4,667 (2017) and 5,081 (2018) kg/h) were observed in vermicompost treatments containing (VAM and VRAM) under inoculation with . The results of the study suggested that, using an organic source along with inoculation with appropriate N-fixing bacteria for vermicompost has a great effect on enzyme activity, soil biology, nutrient uptake and grain yield has a synergistic interaction on agronomic traits under flooded conditions. Therefore, this nutrient method can be used as one of the nutrient management strategies in the sustainable rice production.
PubMed: 34557340
DOI: 10.7717/peerj.10833 -
Applied Microbiology and Biotechnology Sep 2023Reductive soil disinfestation (RSD) is an effective bioremediation technique to restructure the soil microbial community and eliminate soilborne phytopathogens. Yet we...
Reductive soil disinfestation (RSD) is an effective bioremediation technique to restructure the soil microbial community and eliminate soilborne phytopathogens. Yet we still lack a comprehensive understanding of the keystone taxa involved and their roles in ecosystem functioning in degraded soils treated by RSD. In this study, the bacteriome network structure in RSD-treated soil and the subsequent cultivation process were explored. As a result, bacterial communities in RSD-treated soil developed more complex topologies and stable co-occurrence patterns. The richness and diversity of keystone taxa were higher in the RSD group (module hub: 0.57%; connector: 23.98%) than in the Control group (module hub: 0.16%; connector: 19.34%). The restoration of keystone taxa in RSD-treated soil was significantly (P < 0.01) correlated with soil pH, total organic carbon, and total nitrogen. Moreover, a strong negative correlation (r = -0.712; P < 0.01) was found between keystone taxa richness and Fusarium abundance. Our results suggest that keystone taxa involved in the RSD network structure are capable of maintaining a flexible generalist mode of metabolism, namely with respect to nitrogen fixation, methylotrophy, and methanotrophy. Furthermore, distinct network modules composed by numerous anti-pathogen agents were formed in RSD-treated soil; i.e., the genera Hydrogenispora, Azotobacter, Sphingomonas, and Clostridium_8 under the soil treatment stage, and the genera Anaerolinea and Pseudarthrobacter under the plant cultivation stage. The study provides novel insights into the association between fungistasis and keystone or sensitive taxa in RSD-treated soil, with significant implications for comprehending the mechanisms of RSD. KEY POINTS: • RSD enhanced bacteriome network stability and restored keystone taxa. • Keystone taxa richness was negatively correlated with Fusarium abundance. • Distinct sensitive OTUs and modules were formed in RSD soil.
Topics: Soil; Bacteria; Microbiota; Fusarium; Firmicutes; Soil Microbiology
PubMed: 37450017
DOI: 10.1007/s00253-023-12676-0