Nitrogen (N2) fixation activity under different oxygen concentration of methanotrophic bacteria isolated from rice fields and their molecular identification

Rice fields are a significantly sources of atmospheric methane. Methanotrophic bacteria are unique in their ability to utilize methane as a sole carbon source and their ability to fix N2. This research successfully characterized N2 fixation activity under different oxygen concentrations of methanotrophic bacteria isolated from rice fields. From 19 tested isolates, four isolates performed activity to fix N2. They could fix N2 on different concentration of air saturation (10 % up to 100%). The growth of methanotrophs is not directly corelated with the N2 fixation activity, and their N2 fixation activities are affected by O2 concentrations. The BGM 3 and BGM 9 isolates had very good N2 fixation activity. Their activities were increased by increasing air saturation up to 50% (approximately 10% O2), but then decrease by increasing air saturation from 50% (approximately 10% O2) to 100% (approximately 20% O2). However, the highest N2 fixation activity was performed by the BGM 9 isolate at 30% air saturation (approximately 6% O2), and the isolate was identified as Methylococcus capsulatus. This information can support application of the isolates to achieve sustainable and environmentally friendly agricultural system.

Rhamnolipid Enhances the Nitrogen Fixation Activity of Azotobacter chroococcum by Influencing Lysine Succinylation

The enhancement of nitrogen fixation activity of diazotrophs is essential for safe crop production. Lysine succinylation (KSuc) is widely present in eukaryotes and prokaryotes and regulates various biological process. However, knowledge of the extent of KSuc in nitrogen fixation of Azotobacter chroococcum is scarce. In this study, we found that 250 mg/l of rhamnolipid (RL) significantly increased the nitrogen fixation activity of A. chroococcum by 39%, as compared with the control. Real-time quantitative reverse transcription PCR (qRT-PCR) confirmed that RL could remarkably increase the transcript levels of nifA and nifHDK genes. In addition, a global KSuc of A. chroococcum was profiled using a 4D label-free quantitative proteomic approach. In total, 5,008 KSuc sites were identified on 1,376 succinylated proteins. Bioinformatics analysis showed that the addition of RL influence on the KSuc level, and the succinylated proteins were involved in various metabolic processes, particularly enriched in oxidative phosphorylation, tricarboxylic acid cycle (TCA) cycle, and nitrogen metabolism. Meanwhile, multiple succinylation sites on MoFe protein (NifDK) may influence nitrogenase activity. These results would provide an experimental basis for the regulation of biological nitrogen fixation with KSuc and shed new light on the mechanistic study of nitrogen fixation.

Biological Nitrogen Fixation and Denitrification in Rhizosphere of Potato Plants in Response to the Fertilization and Inoculation

The study aim was to evaluate the potential nitrogen fixation and denitrification in the rhizosphere soil of potato plants, crop yield and output quality in response to the different fertilization systems and the inoculation with Azospirillum brasilense 410. Field stationary experiment was conducted between 2016 and 2019 with potato in a crop rotation system on leached chernozem soil. Farmyard manure, 40 t/ha, applied prior to potatoes planting promotes nitrogen fixation (0.8–2.0 times compared to control). However, it has also affected denitrification (in 1.4–2.2 times higher compared to control). The lowest rate of mineral fertilizers used in the experiment, N40P40K40, was shown as most environmentally feasible. Under its use the increase of soil nitrogenase activity and low denitrification levels were observed. Same trends were also noted for the medium fertilizer rate, N80P80K80. The highest doses of mineral fertilizers, N120P120K120, substantially affected the denitrification process and reduced the nitrogen fixation activity (in 1.9–2.2 times). The combination of manure with the medium fertilizers rate has also resulted in high denitrification levels, while the soil nitrogen fixation activity has restored only at flowering stage. Crop inoculation with A. brasilense combined with the manure application, has not affected studied processes. However, crop inoculation after the green manure intercropping has shown the growth of nitrogenase activity. Used on the mineral fertilizers background inoculation has activated nitrogen fixation and has ensured the decrease of denitrification levels, subject to the fertilization background. High fertilizer rates have hampered the inoculation efficiency. Inoculation has promoted crop yields on unfertilized and mineral backgrounds or following green manure. Crop inoculation following organic and the organo-mineral backgrounds had no significant effect, probably due to the competition for A. brasilense from microorganisms that have created a competitive environment for A. brasilense. Despite its environmental expediency, inoculation combined with the low fertilizer doses underperforms the action of inoculation combined with the medium fertilizer rates showing the latter as the compromise between the environmental requirements and crop productivity. The use of inoculation has promoted the accumulation of starch and ascorbic acid and has contributed to the reduction of nitrate contents in the tubers of inoculated plants.

Study on Interactive Effects of Different Levels of Lead and Mercury on Nitrogen Fixation of Some Diazotrophs

Researchers have studied the effects of addition of metal elements in combination with nitrogen fixing organisms as inoculants on the plants (growth) predominantly in legumes, however there is a major gap because responses and effects of these proposed micronutrients on the nitrogen fixation activity of these microbes both free living and symbiotic remains sketchy at best. Therefore, the effect of supplementation of lead and Mercury (bioaugmentation) on the nitrogen fixation potential of two (2) diazotrophs was evaluated in this study. Aims: To evaluate the interactive effects of different levels of Lead and Mercury on Nitrogen fixation of both Rhizobium and Xanthobactersppin-vitro. Place and Duration of Study: Sample organisms where collected from Groundnut rhizospheric soil of a farm in Cross River state, Nigeria. The microorganism isolation and nitrogen fixation analysis was further carried out at MacCliff General services Laboratory, Owerri, Nigeria for a duration of 3 months. Study Design: The interactive plots serve to show the effect of one variable (lead) on the value of mercury (the other) and is derived by selecting high and low values for lead (Pb) and entering them into the equation along with the range of values for Mercury (Hg). The values of independent variables (lead and mercury levels) used in the plots were selected by observing the highest concentration (+1) and lowest concentration (-1) values which are able to support nitrogen fixation independently in Rhizobium and Xanthobacter. Methodology: The soil samples were collected from groundnut rhizosphere at a 20 cm depth using sterile soil corer (sterilized with 95% ethanol) and matured Groundnut plants were uprooted with care. From these samples, both Rhizobium and Xanthobacterspp were isolated. The isolated organisms were re-vitalized in Jensen’s nitrogen free broth and standardized to 0.5 McFarland standards. To determine nitrogen fixation, the broth cultures were examined for nitrate nitrogen (NO3-N) and amino nitrogen (Amino-N) levels after ten days of the experiment under continuous airflow using the Jensen’s nitrogen free broth containing the metal salts, Mercury (II) chloride HgCl2 and Lead (II) acetate trihydratePb (CH3COO)2.3H2O). Nitrate nitrogen and amino Nitrogen was obtained using cataldo and ninhydrins methods respectively. The data obtained was made in triplicates and reported as mean values. Interactive effect plots and statistical analysis were done using Minitab 17 software at 5% level of significance (p<0.05). Results: The main effect plots illustrate that to maximize nitrogen fixation in Xanthobacterspthrough the utilization of the selected metals as micronutrient, we should use lead at 6.25 mg/L and mercury at 25mg/L yielding 0.508 mg/L for nitrogen fixation response. The plot also suggests that if lead metals are used at a higher concentration than stated nitrogen fixation will decline. On the interaction plots, the slopes indicate that an interference or antagonistic interaction effect (crossed lines) exist between lead and mercury in the nitrogen fixation activity of Xanthobacter. The R-squared adjusted value suggests that 70.87% of the variations in nitrogen fixation response is explained by the interaction of lead and mercury, hence the model likely fits the data. However, the P-value was not significant at 0.102. For Rhizobium sp. mercury also has a higher fixation magnitude than Lead but relatively at 0.554 mg/L. However, the interaction plot showed parallel lines indicating that there was no interaction effect. Therefore, one can say that the relationship between lead and nitrogen fixation does not depend on the concentration of mercury and vice versa. The model was also statistically insignificant at 0.981. Conclusion: Interactive effect only occurred in the nitrogen fixation of Xanthobactersp. This raises a need for further study combination of metal elements which could be utilized to stimulate nitrogen, phosphorus and potassium production in Diazotrophs both in the field and in-vitro.

Efficiency of formation and functioning of the symbiotic soybean system with glyphosate treatment

The efficiency of the formation and functioning of the soybean symbiotic system during the crops treatment with glyphosate and pre-sowing seed inoculation with different strains of Bradyrhizobium in the field studied. It is known, that glyphosate can affect symbiotic nitrogen fixation through direct action on rhizobia and symbiotic formations, we took plant samples for analysis after four weeks of glyphosate treatment and determined the aboveground mass of plants and symbiotic apparatus formation evaluated by the number of nodules, their mass and nitrogen fixation activity. It was shown that the late treatment (35 days after sowing) with glyphosate does not provide a sufficient level of weed control and under such conditions inhibits the development and growth of soybean plants, reduces the growth of aboveground and root mass. Treatment of plants with glyphosate before the formation of symbiotic apparatus (21 days after sowing) reduces nitrogen fixation activity by 3550%, but it does not have a significant effect on the formation of soybean yield. The obtained results confirmed the hypothesis of intensification of the nitrogen complex during late treatment of plants with glyphosate in plants inoculated with Bradyrhizobium japonicum strain EL-35 and the composition of strains of B. japonicum EM-24 and B. japonicum EL-35. The most effective for inoculation of soybean plants was a mixture of the studied strains of B. japonicum EM-24 and B. japonicum EL-35, which provides high nitrogen fixation activity and productivity. Therefore, to reduce the negative impact of glyphosate on the nitrogen fixation activity of symbiotic systems and to obtain high soybean productivity, it is necessary to select rhizobia strains with a high rate of symbiotic system formation, because even a slight decrease in nitrogen fixation can have long-term negative consequences.

Understanding of Hierarchical Behavior of Bi2WO6 with Enhanced Photocatalytic Nitrogen Fixation Activity

Hierarchical Bi2WO6 nanostructures self-assembled with planar arranged nanosheets and dispersed Bi2WO6 nanosheets were synthesized with different dosages of EG via a simple hydrothermal route. The Bi2WO6 photocatalysts were analyzed by...