Abundance Of Ammonia-oxidizing Bacteria Research Articles

Impact of Dicyandiamide (DCD) and 3,4-Dimethylpyrazole Phosphate (DMPP) on Ammonia-oxidizing Bacteria and Archaea in a Vegetable Planting Soil

Nitrification inhibitors (NIs) dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) showed significant effects in the inhibition of nitrification and the improvement of the utilization efficiency of nitrogen fertilizer in agricultural soils. However, the effects of different NIs on ammonia-oxidizing bacteria (AOB) and archaea (AOA) is still unclear. To verify the inhibitory effect of DCD and DMPP on AOB and AOA, a pot experiment was performed, including Urea, Urea+DCD, and Urea+DMPP treatments. The dynamics of NH4+-N and NO3--N and nitrification potential among different treatments were measured. In addition, real-time PCR and high-throughput sequencing approaches were applied to investigate the changes in the AOB and AOA population abundance and composition. The results revealed that the concentrations of NH4+-N in Urea+DCD and Urea+DMPP treatments were 213% and 675% higher than that in the CK treatment, respectively. However, the concentrations of NO3--N and the nitrification potentials were 13.3% and 37.2%, and 20.4% and 82.4% lower than that in CK treatment, respectively; Furthermore, the copy numbers of the bacterial and archaeal amoA gene were 51.2% and 56.5%, and 6.0% and 27.0% lower than that in the CK treatment, respectively. However, the diversity indexes of AOB and AOA communities, including evenness and richness, exhibited no significant differences after addition of DCD and DMPP. The nork-environmental-samples, unclassified-Nitrosomonadaceae, unclassified-Bacteria, and Nitrosospira, were the predominant genera of the AOB community. The no rank-Crenarchaeota, no rank-environmental-samples and Nitrososphaera were the predominant groups in the AOA community. Summarily, application of DCD and DMPP significantly delayed the transformation of NH4+-N, decreased the formation of NO3--N, inhibited the abundance and changed the composition of AOB and AOA communities. DMPP had a stronger inhibitory effect on nitrification, and on AOB and AOA than DCD. Therefore, compared with DCD, DMPP had a better application prospect regarding the improvement of the nitrogen utilization efficiency in vegetable soil.

Efficient municipal wastewater treatment by oxidation ditch process at low temperature: Bacterial community structure in activated sludge

Temperature is a key element affecting the activity of microorganisms in activated sludge. Low water temperature generally leads to decreasing wastewater treatment efficiency and destroying sludge settleability. In this study, activated sludge samples from a municipal wastewater treatment plant (WWTP) implementing oxidation ditch process was used to investigate the bacterial community characteristics of a system that operates well in a cold region (Xinjiang, China) by high-throughput 16S rRNA gene sequencing. The results showed that the influent temperature was 7–12 °C in winter and 13–17 °C in summer, while the sludge volume index (SVI) of samples was between 51 and 74 mL/g. The average removal efficiencies for chemical oxygen demand (COD), biochemical oxygen demand (BOD5), suspended solid (SS), ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) were 94%, 95%, 95%, 91%, 73% and 89%, respectively. The bacteria were distributed in 32 phyla and 559 genera. The dominant phyla were Proteobacteria (28.85–48.45%), Bacteroidetes (20.00–31.22%), Chloroflexi (3.59–12.23%), Actinobacteria (1.58–15.54%) and Firmicutes (1.38–10.49%). The dominant genera were Saprospiraceae_norank (4.41–12.23%), Comamonadaceae_unclassified (3.82–8.83%), Anaerolineaceae_norank (1.39–9.35%), Dokdonella (1.13–11.26%), Candidatus_Microthrix (0.26–7.50%), Flavobacterium (0.32–8.14%), Ferribacterium (0.36–5.19%) and Nitrospira (0.084–5.37%), which were different from those found in warm-region WWTPs. Contrary to previous studies, the relative abundance of ammonia-oxidizing bacteria (AOB; Nitrosomonas and Nitrosomonadaceae) and nitrite-oxidizing bacteria (NOB; Nitrospira) increased when the temperature decreased. The successful operation of this WWTP suggests that cold-region WWTPs can achieve good pollutants removal efficiency by simultaneously maintaining an ultra-low sludge load and high dissolved oxygen concentration in the oxidation ditch. The findings of this study provide fundamental knowledge required for an efficient and stable operation of WWTPs in cold regions.

Ammonia‐Oxidizing Bacteria and Archaea: Response to Simulated Climate Warming and Nitrogen Supplementation

Ammonia oxidation, the first and rate‐limiting step of the nitrification process, is driven by ammonia‐oxidizing archaea (AOA) and ammonia‐oxidizing bacteria (AOB). Numerous studies on the response of aboveground plant and soil microbial communities to climate change have been conducted, but the effects of climate warming and nitrogen (N) supplementation on the abundance, community composition, and diversity of AOA and AOB in arid and semiarid steppe ecosystem remain elusive. In this study, we examined these effects on soil samples from the Inner Mongolia desert steppe after 11 consecutive years of simulated climate warming and N supplementation (ammonium nitrate), using real‐time quantitative polymerase chain reaction analysis and high throughput sequencing technique. We observed that the amoA abundance of AOA outnumbered that of AOB in this desert steppe, with N supplementation having a significant effect on amoA abundance. The effect of climate warming on the amoA abundance of AOA or AOB depended on soil depth. Eleven years of simulated climate warming and N supplementation had varying effects on the amoA abundance of AOA and AOB. Nitrogen supplementation shifted ammonia‐oxidizing bacterial community structure, increased potential nitrification rates, and affected ammonia‐oxidizing microbial α diversity at topsoil. The dominating factors shaping AOB community structure among the treatments were NH4+–N, NO3−–N, and pH, whereas pH was the significant factor in shaping AOA community structure. Our results indicate that N supplementation might be the driving factor aiding oxidation of ammonia at topsoil of arid and semiarid steppe ecosystem.

The effect of peracetic acid on microbial community, water quality, nitrification and rainbow trout (Oncorhynchus mykiss) performance in recirculating aquaculture systems

Microbial biofilters control water quality and enable the overall function of recirculation aquaculture systems (RAS). Changes in environmental conditions can affect the abundance and interactions of the diverse microbial populations of the biofilter, affecting nitrification of harmful ammonium and thus fish health. Here, we examined the effect of different application frequencies (0, 1, 2 and 4 times per week) of a common disinfectant, peracetic acid (PAA, applied 1.1 mg l−1 twice per day), on biofilter microbial communities, focusing especially on nitrifying microbial groups and using a high throughput sequencing of 16S rRNA gene and quantitative PCR (qPCR). In addition, we measured biofilter nitrification rates, water quality parameters, and fish performance. Although PAA additions did not significantly change the overall microbial community composition or abundance, the abundance of ammonia-oxidizing bacteria (AOB) and nitrate-oxidizing bacteria (NOB) first decreased at the beginning of the experiment but increased in numbers towards the end of the experiment with frequent PAA applications. PAA application decreased the nitrification rate, but increased the water quality in terms of reduced ammonium levels. PAA application did not significantly affect fish growth, but higher mortality was observed with the highest PAA application level of 4 times per week. These results suggest that when applied before the fish tank, PAA can be used for temporary water quality improvement without disturbing microbial communities. However, the application frequency required for persistent water quality improvement caused increased mortality.

Nitrous oxide emissions associated with ammonia-oxidizing bacteria abundance in fields of switchgrass with and without intercropped alfalfa.

The nitrogen (N) fertilizer required to supply a bioenergy industry with sufficient feedstocks is associated with adverse environmental impacts, including loss of oxidized reactive nitrogen through leaching and the production of the greenhouse gas nitrous oxide (N2 O). We examined effects on crop yield, N fate and the response of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) to conventional fertilizer application or intercropping with N-fixing alfalfa, for N delivery to switchgrass (Panicum virgatum), a potential bioenergy crop. Replicated field plots in Prosser, WA, were sampled over two seasons for reactive nitrogen, N2 O gas emissions, and bacterial and archaeal ammonia monooxygenase gene (amoA) counts. Intercropping with alfalfa (70:30, switchgrass:alfalfa) resulted in reduced dry matter yields compared to fertilized plots, but three times lower N2 O fluxes (≤ 4 g N2 O-N ha-1 d-1 ) than fertilized plots (12.5 g N2 O-N ha-1 d-1 ). In the fertilized switchgrass plots, AOA abundance was greater than AOB abundance, but only AOB abundance was positively correlated with N2 O emissions, implicating AOB as the major producer of N2 O emissions. A life cycle analysis of N2 O emissions suggested the greenhouse gas emissions from cellulosic ethanol produced from switchgrass intercropped with alfalfa cultivation would be 94% lower than emissions from equivalent gasoline usage.

Spatial and Seasonal Variations in the Abundance of Nitrogen-Transforming Genes and the Microbial Community Structure in Freshwater Lakes with Different Trophic Statuses.

Identifying nitrogen-transforming genes and the microbial community in the lacustrine sedimentary environment is critical for revealing nitrogen cycle processes in eutrophic lakes. In this study, we examined the diversity and abundance of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), denitrifying bacteria (DNB), and anammox bacteria (AAOB) in different trophic status regions of Lake Taihu using the amoA, Arch-amoA, nirS, and hzo genes as functional markers. Quantitative Polymerase Chain Reaction (qPCR) results indicated that the abundance of the nirS gene was the highest, while the amoA gene had the lowest abundance in all regions. Except for the primary inflow area of Lake Taihu, Arch-amoA gene abundance was higher than the hzo gene in three lake bays, and the abundance of the nirS gene increased with decreasing trophic status. The opposite pattern was observed for the amoA, Arch-amoA, and hzo genes. Phylogenetic analyses showed that the predominant AOB and AOA were Nitrosomonas and Nitrosopumilus maritimus, respectively, and the proportion of Nitrosomonas in the eutrophic region (87.9%) was higher than that in the mesotrophic region (71.1%). Brocadia and Anammoxoglobus were the two predominant AAOB in Lake Taihu. Five novel unknown phylotypes of AAOB were observed, and Cluster AAOB-B was only observed in the inflow area with a proportion of 32%. In the DNB community, Flavobacterium occurred at a higher proportion (22.6–38.2%) in all regions, the proportion of Arthrobacter in the mesotrophic region (3.6%) was significantly lower than that in the eutrophic region (15.6%), and the proportions of Cluster DNB-E in the inflow area (24.5%) was significantly higher than that in the lake bay (7.3%). The canonical correspondence analysis demonstrated that the substrate concentration in sedimentary environments, such as NOx--N in the sediment, NH4+-N in the pore water, and the total organic matter, were the key factors that determined the nitrogen-transforming microbial community. However, the temperature was also a predominant factor affecting the AOA and AAOB communities.

Effect of Straw and Straw Biochar on the Community Structure and Diversity of Ammonia-oxidizing Bacteria and Archaea in Rice-wheat Rotation Ecosystems

Ammonia oxidation is the first and rate-limiting step of nitrification, driven by ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA). Straw and straw biochar retention are the popular ways to utilize the agricultural by-products in China, but their long-term effects on AOB and AOA still remain poorly understood. Based on a 7-year plot experiment, which had 4 fertilization regimes: no fertilizer (CK), regular fertilization (RT), straw retention (SR) and straw biochar retention (SB), the abundance and the composition of AOB and AOA was investigated before both the harvest of rice and wheat season by quantitative PCR and 454 high-throughput pyrosequencing, respectively. (1) Compared to RT, straw and straw biochar increased AOB abundance and diversity significantly only in wheat season (P < 0.05), and they both ranked as SB > SR > RT. Among fertilized treatments, a significant difference between SR and RT was found in AOB community composition of the winter season (R value = 0.58, P value = 0.02); (2) In contrast, AOA was almost not responsive to organic addition, except the significant enhancement of abundance by biochar in wheat season; (3) After straw and straw biochar addition, soil potential nitrification rates (PNR) was positive correlated to AOB abundance in both rice and wheat season (P < 0.01), not to AOA abundance (P = 0.211 and 0.068, respectively). This study provides scientific support for the potential of straw utilization to improve nitrification in rice-wheat rotation system with respect to soil ammonia oxidation microorganism.

Plant-driven niche differentiation of ammonia-oxidizing bacteria and archaea in global drylands.

Under controlled laboratory conditions, high and low ammonium availability are known to favor soil ammonia-oxidizing bacteria (AOB) and archaea (AOA) communities, respectively. However, whether this niche segregation is maintained under field conditions in terrestrial ecosystems remains unresolved, particularly at the global scale. We hypothesized that perennial vegetation might favor AOB vs. AOA communities compared with adjacent open areas devoid of perennial vegetation (i.e., bare soil) via several mechanisms, including increasing the amount of ammonium in soil. To test this niche-differentiation hypothesis, we conducted a global field survey including 80 drylands from 6 continents. Data supported our hypothesis, as soils collected under plant canopies had higher levels of ammonium, as well as higher richness (number of terminal restriction fragments; T-RFs) and abundance (qPCR amoA genes) of AOB, and lower richness and abundance of AOA, than those collected in open areas located between plant canopies. Some of the reported associations between plant canopies and AOA and AOB communities can be a consequence of the higher organic matter and available N contents found under plant canopies. Other aspects of soils associated with vegetation including shading and microclimatic conditions might also help explain our results. Our findings provide strong evidence for niche differentiation between AOA and AOB communities in drylands worldwide, advancing our understanding of their ecology and biogeography at the global scale.

Nonylphenol causes shifts in microbial communities and nitrogen mineralization in soil microcosms

The aims of this work was to investigate, in soil microcosms, the effects on soil microbial community structure and function of increasing concentrations of 4-Nonylphenol (NP). The lasts is a product of degradation of NPEOs (Nonylphenol polyethoxylates) with a known toxic and estrogenic capacity able to disrupt animal's hormonal systems.The effect of increasing concentrations of NP (0, 10, 30, 90, and 270 mg NP kg−1 of dry soil) in soil microcosms in three sampling dates (28, 56, and 112 days) over soil microbial activity and function were assessed. Soil microbial activity was estimated by microbial ATP content, and both bacterial and fungal communities composition were estimated using the terminal restriction fragment length polymorphism technique (T-RFLP). Abundance of ammonia-oxidizing bacteria (AOB) was estimated by qPCR of gene encoding for the bacterial ammonia-monoxygenase (amoA). Changes in biologically mediated soil properties were also assessed, namely water-soluble NH+4, NO−2 and NO−3 content, the two last allowing the assessment of mineralization rates.NP-spiking had some unexpected impacts on microbial community structure and functions, since (i) impacted both bacterial and fungal communities structure at the highest NP concentration tested, bacterial communities were resistant to lower concentrations, while fungal communities were increasingly impacted until the end of the incubation at day 112; (ii) no community structure resilience was observed in bacteria at the highest NP concentration nor for fungi at any concentration; (iii) microbial activity decreased with NP after 28 and 56 d, but increased in the last sampling at the highest concentrations tests, coupled to an enrichment in AOB taxa after 56 and 112 days, that at least partly explain also explain the observed speed up of nitrification rates.

Effects of Silver Nanoparticles and Silver Ions on Soil Nitrification Microorganisms and Ammoxidation

In order to study the effect of nanosilver on soil nitrification microorganisms and nitrogen transformation, soil culture experiments were carried out. Yellow brown soil and paddy soil were first spiked with different doses of nanosilver (10, 50, 100 mg·kg-1) and silver ions (1, 5, 10 mg·kg-1). Then, the number of nitrifying bacteria, activity of soil invertase, amoA gene abundance, NH4+-N content, NO3--N content, and soil potential ammonia oxidation rate were determined. The results showed that the number of nitrite bacteria and nitrate bacteria decreased significantly when the soils were treated with nanosilver and silver ions. Soil invertases were inhibited, and the effect on urease was greater than that on catalase. The amoA gene abundances of soil ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) decreased, and the effect on the gene abundance of AOB was greater than that of AOA. When (NH4)2SO4 was added to the soil, nanosilver and silver ion pollutants caused NH4+-N to accumulate, and the contents of NO3--N were reduced, the rate of ammonia oxidation decreased, and the transformation of ammonium nitrogen to nitrate nitrogen was inhibited. This research suggests that nanosilver and silver ions can have toxic effects on soil nitrification microorganisms and ammonium nitrogen conversion, and the degree of influence was found to be related to the soil physical and chemical properties.

Effects of sulfamethoxazole and sulfamethoxazole-degrading bacteria on water quality and microbial communities in milkfish ponds

Intensive farming practices are typically used for aquaculture. To prevent disease outbreaks, antibiotics are often used to reduce pathogenic bacteria in aquaculture animals. However, the effects of antibiotics on water quality and microbial communities in euryhaline fish culture ponds are largely unknown. The aim of this study was to investigate the interactions between sulfamethoxazole (SMX), water quality and microbial communities in milkfish (Chanos chanos) culture ponds. The results of small-scale milkfish pond experiments indicated that the addition of SMX decreased the abundance of ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB) and photosynthetic bacteria. Consequently, the levels of ammonia and total phosphorus in the fish pond water increased, causing algal and cyanobacterial blooms to occur. In contrast, the addition of the SMX-degrading bacterial strains A12 and L effectively degraded SMX and reduced the levels of ammonia and total phosphorus in fish pond water. Furthermore, the abundances of AOB, NOB and photosynthetic bacteria were restored, and algal and cyanobacterial blooms were inhibited. This study demonstrate the influences of SMX on water quality and microbial community composition in milkfish culture ponds. Moreover, the use of the bacterial strains A12 and L as dual function (bioaugmentation and water quality maintenance) beneficial bacteria was shown to provide an effective approach for the bioremediation of SMX-contaminated euryhaline milkfish culture ponds.

Responses of ammonia-oxidizers and comammox to different long-term fertilization regimes in a subtropical paddy soil

Nitrogen, including ammonium, is an essential nutrient for plant growth and heavily applied in agricultural systems via fertilization. Nitrification is a two-step microbiologically-mediated process in which ammonium is first oxidized to nitrite and then subsequently to nitrate. The objective of this study was to determine the influence of variable long-term (28 years) fertilization on the potential nitrification rate (PNR) and three prokaryotic groups involved in this process: (1) ammonium-oxidizing bacteria (AOB), (2) ammonium-oxidizing archaea (AOA), and (3) recently discovered bacteria with the capacity to perform complete nitrification (comammox). Fertilization treatments included urea ((NH2)2CO) only (N), urea ((NH2)2CO) + potassium sulfate (K2SO4) (NK), urea ((NH2)2CO) +calcium superphosphate (CaP2H4O8) +potassium sulfate (K2SO4) (NPK), and a control with no N. The PNR increased with N fertilization, indicating that N application accelerated soil nitrification. The lower AOB abundance, the highest AOA/AOB ratios and lower PNR were observed in the NK treatment compared to N and NPK treatments, suggesting that AOB may be the key driver of nitrification in this soil. Comammox had higher amoA gene abundance (2.72 × 107gene copies g−1 to 2.35 × 108 gene copies g−1 dry soil) than AOB and AOA for all treatments. The abundance of comammox clade A (7.38 × 107 gene copies g−1 -2.35 × 108 gene copies g−1 dry soil) was significantly higher than for comammox clade B (5.66 × 106 gene copies g−1 -1.42 × 107gene copies g−1 dry soil), and based on high abundance values, we suppose that comammox are non-negligible contributors to soil nitrification resulting from responsiveness to N fertilization.

The steps in the soil nitrogen transformation process vary along an aridity gradient via changes in the microbial community

Rainfall patterns are predicted to change dramatically in many terrestrial landscapes, including drylands. The most limiting resources for plant growth in arid regions is nitrogen (N) as well as water. A natural aridity gradient provides appropriate candidate conditions for predicting the impacts of changes in rainfall on soil N dynamics. To comprehensively and mechanistically examine soil N dynamics, we focused on the steps of N transformation, their microbial drivers, and the determining soil properties. We divided the N transformation process into three steps: (i) organic matter degradation, (ii) N mineralization, and (iii) nitrification, which are driven primarily by fungi, prokaryotes, and ammonia oxidizers, respectively. Soil samples were collected from three black locust forests with mean annual precipitations ranging from 449 to 606 mm. Along the aridity gradient, all three steps changed while maintaining a balance. The degradation and mineralization steps varied with changes in the soil fungal and prokaryotic communities, respectively. The compositions of these communities were determined by soil substrate quality and quantity; saprotrophs and copiotrophs decreased along the aridity gradient. On the other hand, the abundance of ammonia-oxidizing bacteria, which correlated with the rate of nitrification, was likely determined by soil moisture. Therefore, if precipitation were to decrease, changes in the nitrification step might be the first mechanism to limit plant productivity in semi-arid forests. This limitation would extend to the other steps in the N cycling process via plant–soil feedback. Thus, N cycling dynamics are predicted to achieve new stable states suited to the changed precipitation regime.

Functional relationship between ammonia-oxidizing bacteria and ammonia-oxidizing archaea populations in the secondary treatment system of a full-scale municipal wastewater treatment plant

The abundance of ammonia-oxidizing bacteria and archaea and their amoA genes from the aerobic activated sludge tanks, recycled sludge and anaerobic digesters of a full-scale wastewater treatment plant (WWTP) was determined. Polymerase chain reaction and denaturing gradient gel electrophoresis were used to generate diversity profiles, which showed that each population had a consistent profile although the abundance of individual members varied. In the aerobic tanks, the ammonia-oxidizing bacterial (AOB) population was more than 350 times more abundant than the ammonia-oxidizing archaeal (AOA) population, however in the digesters, the AOA population was more than 10 times more abundant. Measuring the activity of the amoA gene expression of the two populations using RT-PCR also showed that the AOA amoA gene was more active in the digesters than in the activated sludge tanks. Using batch reactors and ddPCR, amoA activity could be measured and it was found that when the AOB amoA activity was inhibited in the anoxic reactors, the expression of the AOA amoA gene increased fourfold. This suggests that these two populations may have a cooperative relationship for the oxidation of ammonia.

Particle-attached microorganism oxidation of ammonia in a hypereutrophic urban river.

To elucidate the importance and mechanisms of particle-attached microorganisms on ammonia oxidation, we conducted a controlled simulation experiment with samples collected from the Shunao River, an ammonia-rich hypereutrophic urban river in eastern China. The effects of particle concentration, ammonia concentration, organic carbon source and concentration, dissolved oxygen concentration, and pH were investigated on ammonia transformation rate (ammonia removal rate and NO2 - + NO3 - accumulation rate) and abundance of particle-attached ammonia-oxidizing bacteria (AOB) and archaea (AOA). All these factors significantly influenced ammonia transformation rates. Our results provided direct evidence that microorganisms attached on riverine suspended particles were associated with ammonia oxidation. Sequencing revealed that the AOA genus Nitrososphaera, and the AOB genus Nitrosomonas were the most dominant in particle-attached ammonia-oxidizing microbial communities. Further analysis showed that AOB communities had higher species richness and diversity compared with AOA communities. Additionally, AOB amoA genes were ~10-100 times more abundant than AOA amoA genes, and AOB abundance was more strongly correlated with ammonia transformation rates than AOA abundance in most experiments, indicating that particle-attached AOB were more important than AOA in the hypereutrophic urban river. This study adds to our knowledge of particle-attached microorganism oxidation of ammonia.

Low energy treatment of landfill leachate using simultaneous partial nitrification and partial denitrification with anaerobic ammonia oxidation

An up-flow anaerobic sludge blanket reactor (UASB), anoxic/oxic (A/O)–anaerobic ammonia oxidation reactor (ANAOR or anammox reactor), and anaerobic sequencing batch reactor (ASBR) were employed in the treatment of landfill leachate with partial nitrification-anammox and half-denitrification-anammox. The Chemical Oxygen Demand (COD) concentration, ammonium nitrogen (NH4+-N) concentration, and total nitrogen (TN) concentration of the basal leachate was 2200–2500 mg/L, 1200–1300 mg/L, and 1300–1400 mg/L, respectively. After a 1:2 dilution using domestic sewage, the COD, NH4+-N, and TN concentrations in the influent were 800–1000 mg/L, 400–430 mg/L, and 420–440 mg/L, respectively. After treatment, the final COD, NH4+-N, and TN were decreased to 90–100 mg/L, 13–14 mg/L, and 35–38 mg/L, respectively. In the ASBR, organic carbon sources in sewage-diluted landfill leachate were introduced for the conversion of nitrate nitrogen (NO3−-N) into nitrite nitrogen (NO2−-N). This enabled the continued reaction of NO2−-N with NH4+-N from the newly introduced sewage-diluted landfill leachate via anammox. As a result, complete TN removal was achieved in the system. Microbial diversity analysis indicated that the relative abundance of ammonia-oxidizing bacteria (AOB) was four to five times greater than nitrite-oxidizing bacteria (NOB) in the A/O reactor, showing that partial nitrification was prevalent. The relative abundance of the anammox bacterium Candidatus Kuenenia gradually increased in each reactor, reaching a maximum of 1.17%–1.39%. Using this set-up, we achieved advanced, efficient, and economical, COD reduction and nitrogen removal. Taken together, the findings provide important insights into the optimal operation of landfill leachate treatments.

Elevated temperature increased nitrification activity by stimulating AOB growth and activity in an acidic paddy soil

Global warming is predicted to alter the timing and magnitude of biogeochemical nitrogen cycling in paddy soils. However, little is known about its effect on active nitrifying populations. Here we investigated the responses of nitrification activity and active nitrifiers to elevated temperature in an acidic paddy soil. 13CO2-DNA-stable isotope probing (SIP), qPCR and high-throughput sequencing were used to determine active nitrifying phylotypes as well as difference in their abundance and community composition incubated at field temperature (15 °C) and elevated temperature (20 °C). Urea application led to significant production of nitrate and growth of ammonia-oxidizing bacteria (AOB) at both temperatures. Nitrification activity at elevated temperature was 148.3% and 18.5% higher than that of low temperature at day 28 and 56, respectively, accompanied by an increase in the extent of 13C-label incorporation by AOB. 13CO2-based SIP experiment indicated that both AOB and ammonia-oxidizing archaea (AOA) were involved in the nitrification activity and the active ammonia oxidizers changed from AOA to AOB with elevated temperature. Significant variation of AOA communities was observed under different temperatures. Dominant 13C-labeled nitrite-oxidizing bacteria (NOB) shifted from Nitrospira moscoviensis to Nitrospira japonica with higher temperature. Our findings emphasized that elevated temperature had pronounced effects on autotrophic nitrification which was mediated by altering relative abundance of active AOB and AOA, as well as the community composition of AOA and NOB. AOB were more adaptable than AOA with increasing abundance but no alteration of composition at elevated temperature.

Spatial and temporal responses of ammonia-oxidizing bacteria and archaea to organic amendments in rice-wheat rotation system

To determine the effects of organic amendment on communities of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) in rice-wheat rotation ecosystem, a long-term plot experiment with 5 treatments was conducted, and the temporal dynamics (10 growth stages) and spatial distribution (0–100 cm) of AOB and AOA abundance were determined using qPCR. The five treatments were as follows: no fertilizer control (CK), regular fertilization (RT), straw returning (SR), straw biochar returning (SB) and organic-chemical mixed fertilization (MF). The results showed the following. 1) Organic addition did not affect the temporal dynamics of AOB abundance but altered those of AOA abundance. Relative to RT, SR and MF significantly lowered AOB population sizes across the 10 sampling time points by 34.49% and 16.42%, respectively, whereas no significant differences in total AOA population size were observed among the 4 fertilization regimes. 2) Compared with the other treatments, treatments involving organic addition had higher total AOB abundance in the 0–100 cm soil layer. However, SB was the only treatment with organic addition that had a significantly higher total AOA abundance than RT (by 24.91%). 3) Under organic addition, the potential nitrification rate (PNR) was still highly correlated with AOB abundance (P < 0.01) but not AOA abundance.

Ecological Success of the Nitrosopumilus and Nitrosospira Clusters in the Intertidal Zone.

The intertidal zone is an important buffer and a nitrogen sink between land and sea. Ammonia oxidation is the rate-limiting step of nitrification, conducted by ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). However, it remains a debatable issue regarding dominant ammonia oxidizers in this region, and environmental factors driving their spatiotemporal niche differentiation have yet to be identified. In this study, intertidal and subtidal zones of Zhoushan Islands were selected for seasonal sampling. Ammonia-oxidizing activity, quantitative PCR, and 454 high-throughput sequencing were performed to study the nitrification potential, abundance, and community structure of ammonia-oxidizing archaea and bacteria. AOA and AOB amoA abundance (107-108amoA gene copies/g dry weight sediment) varied spatiotemporally independently of environmental factors. AOA surpassed AOB in most samples, driven by sediment temperature, moisture, and total nitrogen. The diversity of both AOA and AOB differed spatiotemporally. The Nitrosopumilus and Nitrosospira clusters accounted for an absolutely dominant percentage of AOA (> 99%) and AOB (> 99%) respectively, indicating a negligible contribution of other clusters to ammonia oxidation. However, there was no significant correlation between nitrification potential and the abundance of AOA or AOB. Overall, the present study showed that AOA dominated over AOB spatiotemporally in the intertidal zone of Zhoushan Islands due to fluctuations in environmental factors, and the Nitrosopumilus and Nitrosospira clusters ecologically succeeded in the intertidal zone of Zhoushan Islands.

Short term changes in the abundance of nitrifying microorganisms in a soil-plant system simultaneously exposed to copper nanoparticles and atrazine

Copper nanoparticles (NCu) may co-exist with other pollutants in agricultural soils, such as pesticides. However, this has been little evaluated yet. Thus, possible effects of the simultaneous applications of pesticides and NCu on biogeochemical cycles are expected, for example on the nitrogen cycle. Therefore, the aim of this work was to evaluate the effect of simultaneous application of the herbicide atrazine (ATZ) and NCu on the abundance of total bacteria and nitrifying communities: ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). Moreover, the ATZ dissipation was evaluated. A soil-plant system containing ATZ at field dose (3 mg a.i. kg−1) was mixed with two doses of NCu (0.05% or 0.15% w/w). Changes in the abundance of 16S rRNA and ammonia monooxygenase (amoA) genes of AOA and AOB were evaluated by real-time quantitative PCR (qPCR) at three sampling times (1, 15 and 30 days). The residual ATZ and nitrate production were also measured. The results showed significant differences in microbial composition and abundance over the 30 days of the experiment. Particularly, an initial decrease was observed in total bacterial abundance due to the presence of ATZ and NCu respect to ATZ alone (~60%). The abundance of AOA was also remarkably reduced (~85%), but these communities gradually recovered towards the end of the experiment. Conversely, AOB abundance initially increased (>100%) and remained mainly unaltered in soil exposed to ATZ and NCu 0.15% w/w, where nitrate formation was also constant. Moreover, NCu decreased the ATZ dissipation, which was translated in a 2-fold increase on the ATZ half-life values (T1/2). This study demonstrates that the simultaneous presence of NCu and ATZ may represent a risk for the total bacteria present in soil and sensitive microorganisms such as nitrifying communities, and changes in the dissipation of the pesticide could influence this process.