Aerobic N2-fixing Bacteria Research Articles

Light-Driven Ammonia Production by Azotobacter vinelandii Cultured in Medium Containing Colloidal Quantum Dots.

There is an evergrowing demand for environment-friendly processes to synthesize ammonia (NH3) from atmospheric nitrogen (N2). Although diazotrophic N2 fixation represents an undeniably "green" process of NH3 synthesis, the slow reaction rate makes it less suitable for industrially meaningful large-scale production. Here, we report the photoinduced N2 fixation using a hybrid system composed of colloidal quantum dots (QDs) and aerobic N2-fixing bacteria, Azotobacter vinelandii. Compared to the case where A. vinelandii cells are simply mixed with QDs, NH3 production increases significantly when A. vinelandii cells are cultured in the presence of core/shell InP/ZnSe QDs. During the cell culture of A. vinelandii, the cellular uptake of QDs is facilitated in the exponential growth phase. Experimental results as well as theoretical calculations indicate that the photoexcited electrons in QDs within A. vinelandii cells are directly transferred to MoFe protein, the catalytic component of nitrogenase. We also observe that the excess amount of QDs left on the outer surface of A. vinelandii disrupts the cellular membrane, leading to the decrease in NH3 production due to the deactivation of nitrogenase. The successful uptake of QDs in QD-A. vinelandii hybrid with minimal amount of QDs on the outer surface of the bacteria is key to efficient photosensitized NH3 production. The comprehensive understanding of the QD-bacteria interface paves an avenue to novel and efficient nanobiohybrid systems for chemical production.

English

Compost tea is gaining much interest due to its nutritional, biostimulation and disease suppression benefits to the plants. Four experiments were carried out to determine the effect of incubation temperature, incubation periods, dilution rate and nutritional sources on the microbial populations, physico-chemical properties and indole acetic acid (IAA) levels. Incubation at 28°C showed the highest number of bacteria and aerobic N2-fixing bacteria (ANFB), along with the highest levels of total nitrogen and IAA. All the microbial populations increased in proportion with increase in the incubation period; however, increasing the incubation more than 48 h did not show any significant improvement (P ≤ 0.05) in the physico-chemical properties or IAA levels. All microbial numbers and chemical properties decreased by increasing the dilution rate. Adding a mixture of the three used nutrients (molasses 0.5% v/v, ammonium nitrate 0.5 g/L and di-potassium phosphate 0.5 g/L) resulted in the highest microbial populations (except for ANFB) as compared to the molasses, or double the amount of each other chemical alone. This study show the optimum conditions for preparing compost tea with high microbiological and physico-chemical properties. The study includes ANFB, important for soil application, and IAA, important for foliar application, which have not been studied before in compost tea. Key words: Compost tea extraction, factors, microbiology, physico-chemical, indole acetic acid (IAA), aerobic N2-fixing bacteria (ANFB).

DNA-probing for genes coding for denitrification, N2-fixation and nitrification in bacteria isolated from different soils.

Bacteria isolated from different layers of four soils of the Cologne area were analyzed for denitrifying, nitrifying and N2-fixing isolates by colony hybridization using gene probes. In the soils tested, the percentage of denitrifying bacteria among the total population isolated was 3-8% (in one case exceptionally 15%) and thus small. Denitrifying bacteria were particularly enriched in the upper layer (depth approximately 5 cm) and were present only in low amounts at 25 cm depth in two gleysol soils. Nitrate apparently did not determine the distribution of denitrifying bacteria in these soils. The potential denitrification activity of different soil layers coincided with the distribution pattern of isolates assessed by DNA-probing. The total number of bacteria and of denitrifying isolates was considerably higher in or at the roots of plants than in the bulk, root-free soil adjacent to the plants. The percentage of the isolated aerobic N2-fixing bacteria varied between 0-3%, and these bacteria could be isolated mainly from the upper 5 cm layer. A small portion of the isolates hybridized with the probe coding for part of one subunit of ammonia monooxygenase from Nitrosomonas europaea. The investigation showed that DNA-probing can provide useful information about the relative distribution of denitrifying and N2-fixing bacteria in different soils and their layers.

Effect of chlorpyrifos on soil microbial activity

AbstractA study of the effects of the insecticide chlorpyrifos on soil microbial activity was made. Parameters included total bacterial populations, fungi, aerobic N2‐fixing bacteria, denitrifying bacteria, nitrifying bacteria, nitrogenase activity, acid and alkaline phosphatases, arylsulfatase, and dehydrogenase. The presence of 2.0, 3.5, 5.0, and 10.0 kg/ha of chlorpyrifos significantly (p < 0.05) decreased aerobic dinitrogen‐fixing bacteria and dinitrogen fixation, particularly after a second insecticide treatment The total number of bacteria increased significantly at concentrations of 2.0 to 10.0 kg/ha. Activities of acid and alkaline phosphatases and dehydrogenase significantly decreased initially at concentrations of 2.0 to 10.0 kg/ha, but recovered after 14 d to levels similar to those in control soil without chlorpyrifos. Fungal populations, nitrifying bacteria, and denitrifying bacteria were not affected as a consequence of the addition of the insecticide.

EFFECT OF CHLORPYRIFOS ON SOIL MICROBIAL ACTIVITY

A study of the effects of the insecticide chlorpyrifos on soil microbial activity was made. Parameters included total bacterial populations, fungi, aerobic N2-fixing bacteria, denitrifying bacteria, nitrifying bacteria, nitrogenase activity, acid and alkaline phosphatases, arylsulfatase, and dehydrogenase. The presence of 2.0, 3.5, 5.0, and 10.0 kg/ha of chlorpyrifos significantly (p < 0.05) decreased aerobic dinitrogen-fixing bacteria and dinitrogen fixation, particularly after a second insecticide treatment The total number of bacteria increased significantly at concentrations of 2.0 to 10.0 kg/ha. Activities of acid and alkaline phosphatases and dehydrogenase significantly decreased initially at concentrations of 2.0 to 10.0 kg/ha, but recovered after 14 d to levels similar to those in control soil without chlorpyrifos. Fungal populations, nitrifying bacteria, and denitrifying bacteria were not affected as a consequence of the addition of the insecticide.

Effect of the insecticide methidathion on agricultural soil microflora

We studied the effects of the organophosphorus insecticide methidathion, at concentrations of 10, 50, 100, 200 and 300 μg g-1 in an agricultural soil, on fungi, total bacterial populations, aerobic N2-fixing bacteria, denitrifying bacteria, nitrifying bacteria (phases I and II), and nitrogenase activity (acetylene reduction assay). The presence of 10–300 μg g-1 of methidathion significantly increased fungal populations (colony-forming units). Denitrifying bacteria, aerobic N2-fixing bacteria and N2 fixation were significantly increased at concentrations of 50–300 μg g-1. The total number of bacteria increased significantly at concentrations of 100–300 μg g-1. Nitrifying bacteria decreased initially at concentrations of 300 μg g-1, but recovered rapidly to levels similar to those in the control soil without the insecticide.

Nitrogen fixation in the rhizosphere and rhizoplane of barley

Aerobic and anaerobic N2-fixing bacteria developed in the rhizosphere of barley seedlings and exhibited N2ase activity when seedlings were grown in sterilized sand-nutrient cultures containing low levels of combined nitrogen. The source of the N2-fixing bacteria appeared to be the seed. Average daily rates up to 0.9 μmoles C2H4 h−1 g−1 dry root tissue were measured, but the intensity of the activity was affected by moisture levels and concentration of combined N in the rhizosphere. Removal and washing of the roots did not remove the activity, and roots remained active even after surface-sterilization. An unidentified aerobic N2-fixing bacterium was isolated from the rhizoplane of active barley roots. Inoculation of barley seedlings with the aerobic N2-fixing bacterium enhanced N2ase activity of excised roots 10-fold, with average rates of 0.9, 1.1 and 1.3 μmoles h−1 g−1 dry root assayed under pO2 of 0.01, 0.02 and 0.04 atm respectively. The aerobic N2-fixing bacterium also exhibited N2ase activity when inoculated into the rhizosphere of oat, rice and wheat seedlings. Microscopic observations of sterilized live and stained barley roots suggest that the aerobic N2-fixing bacterium is an endophyte which infects root tissue and metamorphoses into vesicle-like structures.

Survey of ammonium (methylammonium) transport by aerobic N2-fixing bacteria—the special case of Rhizobium

Survey of ammonium (methylammonium) transport by aerobic N2-fixing bacteria—the special case of Rhizobium

Nitrogen-Fixing (Acetylene Redution) Activity and Population of Aerobic Heterotrophic Nitrogen-Fixing Bacteria Associated with Wetland Rice

Nitrogen-fixing activity associated with different wetland rice varieties was measured at various growth stages by an in situ acetylene reduction method after the activities of blue-green algae (cyanobacteria) in the flood water and on the lower portion of the rice stem were eliminated. Nitrogen-fixing activities associated with rice varieties differed with plant growth stages. The activities increased with plant age, and the maximum was about at heading stage. The nitrogen fixed during the whole cropping period was estimated at 5.9 kg of N per ha for variety IR26 (7 days) and 4.8 kg of N per ha for variety IR36 (95 days). The population of aerobic heterotrophic N(2)-fixing bacteria associated with rice roots and stems was determined by the most-probable-number method, using semisolid glucose-yeast extract and semisolid malate-yeast extract media. The addition of yeast extract to the glucose medium increased the number and activity of aerobic heterotrophic N(2)-fixing bacteria. The glucose-yeast extract medium gave higher counts of aerobic N(2)-fixing bacteria associated with rice roots than did the malate-yeast extract medium, on which Spirillum-like bacteria were usually observed. The lower portion of the rice stem was also inhabited by N(2)-fixing bacteria and was an active site of N(2) fixation.

Acetylene reduction in artificial soil aggregates amended with cellulose, wheat straw, and xylan.

When 1-cm diameter, waterlogged, sandy clay loam soil aggregates were amended with 2% (w/w) cellulose or 2% (w/w) wheat straw, significant C2H2-reduction activity developed whether the aggregates were incubated under aerobic or anaerobic gas phases. The only N2-fixing bacteria which proliferated were anaerobes or facultative anaerobes. Aerobic N2-fixing bacteria did not proliferate in any of the aggregates, even though a few were initially present in the soil. The anaerobic bacteria in aerobically incubated, cellulose-amended aggregates proliferated more slowly than those in the anaerobically incubated aggregates, but eventually produced a higher maximum rate of C2H2-reduction. The activities of the N2-fixing bacteria in straw-amended aggregates were similar under both aerobic and anaerobic gas phases. High amendment levels (20% w/w) altered the soil structure and the requisite anaerobic microsites were not developed as rapidly under aerobic incubation conditions and so the onset of C2H2-reduction activity was delayed.

Acetylene reduction by non-symbiotic bacteria in artificial soil aggregates amended with glucose.

The C2H2-reduction assay was used to study the activity of non-symbiotic N2-fixing bacteria in glucose-amended artificial soil aggregates prepared from a sandy clay loam and a sandy loam soil. Anaerobic incubation under nitrogen resulted in significantly higher rates and greater total quantities of C2H2 reduction than did incubation in air. In the sandy clay loam soil activity under both incubation conditions was due to anaerobic N2-fixing bacteria, whereas in the sandy loam soil aerobic N2-fixing bacteria also proliferated in the aggregates. Direct observation of sectioned aggregates by fluorescence microscopy showed that peripheral zone 1 mm thick sup ported the growth of aerobic microorganisms. The anaerobic microsites in the interior of the aggregates were well protected since disruption procedures involving vigorous shaking with aerated water were required to allow O2 to penetrate and inhibit the anaerobic activity.