Ammonia Oxidation Capacity Research Articles

Insights into the response mechanisms of activated sludge system under long-term dexamethasone stress

Dexamethasone (DEX) is a hormone drug that is often detected in wastewater treatment plants, but its impact on activated sludge systems is unknown. This study explored the long-term effects of DEX on nutrient removal, microbial activities, microbial assembly, and microbial interactions in the activated sludge system. During the 90-day DEX exposure experiment, both chemical oxygen demand and total nitrogen removal efficiencies were initially inhibited and then recovered. Microbial activities, i.e., specific oxygen uptake rate and denitrification, did not differ significantly from that of the control reactor (p > 0.05), possibly due to the secretion of extracellular polymers that act as a protective barrier against excess reactive oxygen species induced by DEX. This barrier protects cell membrane integrity and ensures stable treatment performance. Analysis of microbial assembly identified the drift of stochastic processes (from 92.7 % to 51.8 %) and homogeneous selection of deterministic processes (from 1.6 % to 38.7 %) as the main driving forces of microbial community structure succession under long-term DEX stress. Although long-term exposure to 1000 μg/L DEX did not significantly increase the abundance levels of functional bacteria (Nitrosomonas and 996-1) and key genes (AmoCAB and Hao), the ammonia oxidation capacity of the activated sludge system was enhanced. Analysis of microbial interactions indicated that streamlining of functional subnetworks and increased cooperation were the primary reasons. This is the first study to explore the long-term effects of DEX on activated sludge and provide insights into microbial interaction and assembly. Moreover, the findings of this study broaden our knowledge and lay an experimental foundation for reducing risks associated with hormone drugs.

Change in Granulation Potential and Microbial Enrichment Characteristics of Sludge Induced by Microplastics

Microplastics (MPs), as a new type of pollutant, are widely detected in sewage treatment plants. Currently, research on MPs in traditional sewage treatment systems has mainly been focused on the pollution level and distribution characteristics, with a lack of studying the impact of MPs on the sludge granulation. In order to explore the effect of MPs on the granulation process, a microplastic exposure test was conducted by adding polyethylene terephthalate microplastics (PET-MPs), which are widespread in the environment. The operating performance of the system, extracellular polymeric substance (EPS) composition, and flora enrichment were analyzed on the sludge granulation. The results showed that the exposure of PET-MPs significantly accelerated the sludge granulation process, whereas the increase in EPS content dominated by PN enhanced the sludge surface hydrophobicity; the granulation rate and EPS secretion were proportional to the exposed particle size. Microplastics and EPS secretions synergistically promoted the formation of granular sludge. However, continuous microplastic exposure led to deterioration of the system decontamination performance and inhibited the degradation process of pollutants, with the most negative effect of nitrite nitrogen accumulation under 250 μm PET-MPs exposure, as high as (5.08±0.24) mg·L-1. The high-throughput sequencing revealed that the microbial community diversity fell in the experimental group. The dominant bacteria at the phylum level were Proteobacteria and Bacteroidota on the sludge granulation. Rhodocyclaceae, Sphingomonadaceae, Flavobacteriaceae, and Rhodanobacteraceae promoted flocculation by increasing EPS secretion. The decrease in Comamonadaceae and Chitinophagaceae weakened the ammonia and nitrite oxidation capacity of the system, whereas the decrease in Rhodobacteraceae, Hyphomonadaceae, and Xanthomonadaceae inhibited the removal of nitrate nitrogen.

Multidrug-resistant plasmid RP4 increases NO and N2O yields via the electron transport system in Nitrosomonas europaea ammonia oxidation

Antibiotic resistance genes (ARGs) have recently become an important public health problem and therefore several studies have characterized ARG composition and distribution. However, few studies have assessed their impact on important functional microorganisms in the environment. Therefore, our study sought to investigate the mechanisms through which multidrug-resistant plasmid RP4 affected the ammonia oxidation capacity of ammonia-oxidizing bacteria, which play a key role in the nitrogen cycle. The ammonia oxidation capacity of N. europaea ATCC25978 (RP4) was significantly inhibited, and NO and N2O were produced instead of nitrite. Our findings demonstrated that the decrease in electrons from NH2OH decreased the ammonia monooxygenase (AMO) activity, leading to a decrease in ammonia consumption. In the ammonia oxidation process, N. europaea ATCC25978 (RP4) exhibited ATP and NADH accumulation. The corresponding mechanism was the overactivation of Complex Ⅰ, ATPase, and the TCA cycle by the RP4 plasmid. The genes encoding TCA cycle enzymes related to energy generation, including gltA, icd, sucD, and NE0773, were upregulated in N. europaea ATCC25978 (RP4). These results demonstrate the ecological risks of ARGs, including the inhibition of the ammonia oxidation process and an increased production of greenhouse gases such as NO and N2O.

Investigation of Soil Microbial Communities Involved in N Cycling as Affected by the Long-Term Use of the N Stabilizers DMPP and NBPT

Both, 3,4-dimethylpyrazole phosphate (DMPP) and N-(n-butyl) thiophosphoric triamide (NBPT) are commonly used as nitrogen (N) stabilizers, and are often used in agriculture to reduce nitrogen (N) loss from soils by inhibiting soil nitrification and by slowing down urea hydrolysis, respectively. The current knowledge gap concerns how soil microbial communities involved in N cycling are affected by the long-term use of DMPP and NBPT. The present field study explored the inter-annual variation of nitrous oxide (N2O) emissions and the responses of ammonia oxidizers (AOA, AOB encoded by the amoA gene), nitrite-oxidizing bacteria (NOB, encoded by the nxrA and nxrB genes), and denitrifier (encoded by the narG and nosZ genes) populations following a long-term (8 years) addition of DMPP and NBPT. The results showed that the reduction in N2O emissions by DMPP and NBPT increased year on year. The AOB population diversity significantly increased (p < 0.05) after a long-term urea application but decreased after DMPP addition. The long-term application of urea increased the potential nitrification rate (PNR) by the enrichment of the genera with a high ammonia oxidation capacity in the AOB population. In contrast, DMPP addition weakened this effect and formed a population with a low ammonia oxidation capacity. Variations in the NOB population were mainly associated with fertilizer-induced changes in substrate NO2−, whereas DMPP and NBPT had minor impacts on the NOB population. Additionally, the change in the denitrification population was indirectly affected by the soil ammonium (NH4+) content with a long-term N stabilizer application. These findings provide a new interpretation related to the response mechanisms of the nitrifier and denitrifier populations for the long-term use of N stabilizers in soils.

An overlooked influence of reactive oxygen species on ammonia-oxidizing microbial communities in redox-fluctuating aquifers

Reactive oxygen species (ROS) are ubiquitous in O2-perturbed aquifers, but their role in shaping ammonia-oxidizing microbial communities is not clear. This study examined the dynamic responses of ammonia-oxidizing microorganisms (AOMs) in redox-fluctuating aquifers to ROS via field investigation and in-lab verification using transcriptomes/ metatranscriptome and RT-qPCR. Ammonia-oxidizing archaea (AOA) dominated recharge aquifers with lower ROS levels, whereas ammonia-oxidizing bacteria (AOB) and heterotrophic nitrifying aerobic bacteria (HNB) predominated in discharge areas with higher ROS levels. Similar succession in AOM enrichments was found in that the dominant AOMs changed from AOA Nitrosopumilus to AOB Nitrosomonas with increasing ROS. Ammonia oxidation and antioxidant capacity differed significantly among three AOM isolates exposed to ROS. ROS decreased the amoA gene expression of AOA strain Nitrososphaera viennensis PLX03, accompanied by inhibited ammonia oxidation capacity. By contrast, the catalase and superoxide dismutase activities of the AOB strain Nitrosomonas oligotropha PLL12 and HNB strain Pseudomonas aeruginosa PLL01 increased, and the antioxidant genes katG, sodA, ahpC, and ahpF were significantly upregulated. These results demonstrate that ROS exert an important influence on AOMs in redox-fluctuating aquifers. This study improves our understanding of the ecological niches of AOMs in surface/subsurface environments.

Antarctic Ardley Island terrace - An ideal place to study the marine to terrestrial succession of microbial communities.

The study of chronosequences is an effective tool to study the effects of environmental changes or disturbances on microbial community structures, diversity, and the functional properties of ecosystems. Here, we conduct a chronosequence study on the Ardley Island coastal terrace of the Fildes Peninsula, Maritime Antarctica. The results revealed that prokaryotic microorganism communities changed orderly among the six successional stages. Some marine microbial groups could still be found in near-coastal soils of the late stage (lowest stratum). Animal pathogenic bacteria and stress-resistant microorganisms occurred at the greatest level with the longest succession period. The main driving factors for the succession of bacteria, archaea, and fungi along Ardley Island terrace were found through Adonis analysis (PERMANOVA). During analysis, soil elements Mg, Si, and Na were related to the bacterial and archaeal community structure discrepancies, while Al, Ti, K, and Cl were related to the fungal community structure discrepancies. On the other hand, other environmental factors also play an important role in the succession of microbial communities, which could be different among each microorganism. The succession of bacterial communities is greatly affected by pH and water content; archaeal communities are greatly affected by ; fungal communities are affected by nutrients such as . In the analysis of the characteristic microorganisms along terrace, the succession of microorganisms was found to be influenced by complex and comprehensive factors. For instance, environmental instability, relationship with plants and ecological niches, and environmental tolerance. The results found that budding reproduction and/or with filamentous appendages bacteria were enriched in the late stage, which might be connected to its tolerance to rapid changes and barren environments. In addition, the decline in ammonia oxidation capacity of Thaumarchaeota archaeade with succession and the evolution of the fungi-plant relationship throughout classes were revealed. Overall, this research improves the understanding of the effect of the marine-to-terrestrial transition of the Ardley Island terrace on microbial communities. These findings will lay the foundation for more in-depth research regarding microbial adaptations and evolutionary mechanisms throughout the marine-terrestrial transition in the future.

Ammonia oxidation capacity of bacillus bacteria in swine wastewater after biogas treatment

Nitrogen removal with biological methods plays a crucial role in wastewater treatment technology. The treatment begins with the oxidation of ammonia to nitrite to facilitate the subsequent nitrification and denitrification. Various strains of ammonia-oxidising bacteria have been reported. In this study, we use three Bacillus bacteria isolated from swine wastewater to oxidise ammonia. Different initial densities (103, 104, 105, and 106 CFU·mL–1) of each strain were examined. The results show that the combination of all the bacteria at a ratio of 1:1:1 and a density of 105 CFU·mL–1 exhibits the most effect. The findings contribute to the diversity of ammonia-oxidising bacterial species and pose a great potential for applying these strains in wastewater treatment.

Toxicity of silver nanoparticles on Achromobacter denitrificans: effect of concentration, temperature and coexisting anions.

The indoor culture method was carried outto study the toxic effect of silver nanoparticles (AgNPs) on Achromobacter denitrificans.Specifically, the effects of AgNPsconcentration, temperature and coexisting anions were analyzed.The results showed that AgNPs exerted significant inhibition on the bacteria, which was closelycorrelated with its concentrationand temperature. Both the ammoniaoxidationand generationcapacityof Achromobacter denitrificansdecreased significantlywith an increase in AgNPsconcentration. Compared with the inhibition performance at 30 °C, NH4+-N generation rates decreased by 45.31% at 20 °C and 17.58% at 40 °C, respectively, revealing that too low or too high temperature induced toreduce the nitrogen conversion ability of Achromobacter denitrificans.While compared with temperature, the effect of coexistingions (Cl- and SO42-) was not significant(P > 0.05). Electron microscopy observations found that AgNPs non-specifically boundto the cells (content ranging from 0.04% to 0.10%) and actedon the cell surface structure, causingwrinkles,depressions, and ruptures on the surface of cell membranes, and leakage of substances in the membranes. AgNPs increasedthe rate of cell apoptosis and decreasedthe cell body volumemainly with short-term acute effects.

The protection of ammonia-oxidizing bacteria (AOB) using PDDA/GO composite materials in high salinity wastewater

Ammonia oxidation is a critical process during nitrogen removal, while the activity of ammonia oxidizing bacteria (AOB) might be impacted severely in disposing high-salinity nitrogen-containing wastewater. To protect AOB in high saline medium, layer-by-layer self-assembly using graphene oxide (GO) and poly(diallyl dimethyl ammonium chloride) (PDDA) was applied to immobilize enriched AOB. By mixing GO and AOB, it was found that 30 mg/L GO showed the best promotion on the ammonia oxidation capacity of AOB. After coating, AOB with PDDA/GO showed higher absolute value of zeta potential of −20.1 ± 1 mV and compact structure. Comparing with uncoated AOB, although NH4+-N consumption process was slightly inhibited by the PDDA/GO composite materials under low-salinity conditions (0–2 % NaCl), they presented great effective protection on the capacity of AOB in a 3 % NaCl solution. The consumption ratio of NH4+-N was 1.34 times that of uncoated AOB, and the accumulation ratio of NO2−-N of the former one was 1.40 times that of the latter. It inferred that the inhibitory to mass transferring caused by immobilizing materials was less than its positive promotion of AOB protection at 3 % NaCl concentration, and the protection of PDDA/GO composite materials was better than GO. This finding has some certain guiding significance for ammonia oxidation in high salinity.

Successional dynamics of low C/N activated sludge system under salinity shock: Performance, nitrogen removal pathways, microbial community, and assembly

Limited carbon (low C/N) and salinity stress affect the stability of wastewater treatment plants. However, the effect of salinity shock on activated sludge systems with low C/N ratio wastewater remains unclear. An anaerobic/aerobic/anoxic sequencing batch reactor treating low C/N wastewater was established to investigate the effects of salinity shock on system performance, nitrogen removal pathways, microbial community, interactions, and assembly. The results showed that the effluent COD concentration could maintain a stable level, and the average COD removal efficiency was 94.9%. However, total nitrogen removal was significantly inhibited. With the addition of salinity, efficiencies of total nitrogen removal and simultaneous nitrification and denitrification decreased from 91.4 to 73.8% to 86.7 and 39.7%, respectively; however, nitrite reduction capacity increased by 25.4%. After removing salinity, ammonia oxidation capacity further deteriorated, evidenced by the increase in effluent NH4+-N from 8.0 to 11.8 mg/L. During the salinity shock, partial nitrification became the main nitrogen removal pathway because of the inhibition of Nitrospira and high nitrite accumulation ratio (>99.0%). Molecular ecological network analysis indicated that increased competition, decreased total modules, and disappearance of keystone taxa were related to the deterioration of ammonia oxidation capacity and simultaneous nitrification and denitrification. Moreover, the abundant denitrification module and increased denitrifiers contributed to the increase in nitrite reduction capacity. Salinity shock under low C/N conditions resulted in a stronger stochastic community assembly. This study provided information that can help enable stable operations for treating low C/N wastewater.

Effect of pig manure-derived sulfadiazine on species distribution and bioactivities of soil ammonia-oxidizing microorganisms after fertilization

To evaluate the effect of pig manure-derived sulfadiazine (SDZ) on the species distribution and bioactivities of ammonia-oxidizing microorganisms (AOMs), ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA) and complete ammonia oxidizer (comammox) within the soil were investigated pre- and post-fertilization. Kinetic modeling and linear regression results demonstrated that the DT50 value of different SDZ fractions under initial SDZ concentrations of 50 and 100 mg·kg−1 exhibited the following trend: total SDZ>CaCl2-extractable SDZ>MeOH-extractable SDZ, whereas their inhibiting effect on AOMs showed an opposite trend. qPCR analysis suggested that comammox was the predominant ammonia oxidizer in soils regardless of SDZ addition, accounting for as much as 77.2–94.7% of the total amoA, followed by AOA (5.3–22.5%), whereas AOB (<0.5%) was the lowest. The SDZ exhibited a significant effect on the AOM abundance. Specifically, SDZ exerted the highest inhibitory effect on comammox growth, followed by AOA, whereas negligible for AOB. The community diversity of AOMs within the pig manure-fertilized soils was affected by SDZ, and AOA Nitrososphaera cluster 3 played a key role in potential ammonia oxidation capacity (PAO) maintenance. This study provides new insights into the inhibition mechanisms of pig manure-derived antibiotics on AOMs within the fertilized soil.

Seeding as a start-up strategy for improving the acclimation of freshwater nitrifying bioreactors to salinity stress

Recirculating aquaculture systems (RAS) for anadromous fish such as salmonids often require salinity changes during the production cycle. However, high or variable salinity can disrupt the biological nitrification process, which can be detrimental to the fish due to the accumulation of toxic ammonia or nitrite. Thus, it is vital to maintain sufficient nitrification capacity in RAS during salinity changes. This study investigated whether seeding with salinity-acclimated carriers in the freshwater start-up phase could increase the salinity tolerance of nitrifying bioreactors. Moving bed biofilm reactors (MBBR) were started with virgin carriers and seeded with mature biofilm carriers acclimated to freshwater (F), brackish water (B, 12‰ salinity), or a 1:1 mix of both (FB). All duplicate reactors were started up in freshwater and the salinity was increased to seawater (~32‰ salinity) after ~7 weeks. While F and FB had a 65–75% decrease in ammonia oxidation capacity immediately after seawater transfer, B had only a ~20% reduction. After 40 days in seawater, ammonia oxidation recovered completely and became similar in all treatments. However, nitrite accumulation was observed in all the treatments several days after the salinity increase, with the least accumulation in B and the highest in F. The type of seeding influenced the composition of the nitrifying microbial community in the new biofilms (in the freshwater phase). However, the composition in the treatments became similar after ~6 weeks in seawater. The findings indicate that seeding with brackish water biofilm carriers is a potential strategy for accelerating start-up and improving the acclimation of freshwater nitrifying bioreactors to salinity stress. However, nitrite oxidizing bacteria may require a longer period for salinity adaptation. Thus, it is important to closely monitor the nitrite concentration for a prolonged period (several days or weeks) after a salinity increase.

Enhancement on the ammonia oxidation capacity of ammonia-oxidizing archaeon originated from wastewater: Utilizing low-density static magnetic field

Enhancement on the ammonia oxidation capacity of ammonia-oxidizing archaeon originated from wastewater: Utilizing low-density static magnetic field

Biofilms remember: Osmotic stress priming as a microbial management strategy for improving salinity acclimation in nitrifying biofilms

With increasing freshwater scarcity and greater use of seawater, fluctuating salinities are becoming common in water treatment systems. This can be challenging for salinity-sensitive processes like nitrification, especially in recirculating aquaculture systems (RAS), where maintaining nitrification efficiency is crucial for fish health. This study was undertaken to determine if prior exposure to seawater (priming) could improve nitrification in moving bed biofilm reactors (MBBR) under salinity increase from freshwater to seawater. The results showed that seawater-primed freshwater MBBRs had less than 10% reduction in nitrification activity and twice the ammonia oxidation capacity of the unprimed bioreactors after seawater transfer. The primed biofilms had different microbial community composition but the same nitrifying taxa, suggesting that priming promoted physiological adaptation of the nitrifiers. Priming may also have strengthened the extrapolymeric matrix protecting the nitrifiers. In MBBRs started up in brackish water (12‰ salinity), seawater priming had no significant impact on the nitrification activity and the microbial community composition. These bioreactors were inherently robust to salinity increase, likely because they were already primed to osmotic stress by virtue of their native salinity of 12‰. The results show that osmotic stress priming is an effective strategy for improving salinity acclimation in nitrifying biofilms and can be applied to water treatment systems where salinity variations are expected.

Influence of rate of salinity increase on nitrifying biofilms

A strategy for rapid increase in salinity with minimal impact on nitrification is important for ammonia removal from saline effluents, especially in recirculating aquaculture systems with high water reuse. To study the influence of the rate of salinity increase on nitrification, continuously operated moving bed biofilm reactors were transferred from freshwater (0‰ salinity) to seawater (32‰ salinity) at five different rates of salinity change: 0 (control), 1, 2, 6, and 15‰ day−1. Each daily change was conducted gradually overnight. The results showed that at salinities higher than 4–8‰, the ammonia oxidation capacity decreased linearly with salinity and reduced by 50–90% upon complete seawater transfer, with the greatest reduction in the 1‰ day−1 treatment. Thereafter, it increased linearly with time, with little difference between treatments. Overall, the biofilm microbial communities in the control and the 15‰ day−1 treatment were highly similar, while those in the other treatments shifted significantly with time and had greater species diversity, richness, and evenness of nitrifiers. Candidatus Nitrotoga was the dominant nitrite oxidizing bacteria in all treatments throughout the study, indicating that this recently discovered group may tolerate salinities up to 32‰. The results suggest that although the rate of salinity increase influences the microbial community composition, it only weakly influences ammonia oxidation capacity, which mainly depends on salinity and seawater acclimatization time. Therefore, for rapid seawater acclimatization of freshwater nitrifying biofilms, increasing the salinity continuously in two days may be a better strategy than increasing the salinity over a month, provided an initial decrease in ammonia oxidation is acceptable. The findings can aid in the shift from net-pen fish farming to recirculating aquaculture systems, thereby lowering the ecological impacts of seafood production.

Mechanistic study of hydrothermally aged Cu/SSZ-13 catalysts for ammonia-SCR

The impact of hydrothermal ageing on the copper sites, crystalline order and critical reactions of a Cu/SSZ-13 was studied. The investigated catalyst had a low Si/Al ratio of 3.7 and was underexchanged at 65%. We propose that this catalyst had nearly saturated ion exchange positions in the 6-membered ring units (6MR) with copper ions, but still contained a significant amount of protonic sites in the large cages (8MR units). Investigation of a broad range of ageing temperatures (550–850°C) allowed us to observe that no significant number of copper ions moved from the large cages into the 6MR units. Nevertheless, the Cu ions experienced a significant increase in reducibility above ageing temperatures of 700°C. However, these changes appeared not to have a large impact on catalyst activity, which was more significantly correlated with long and short-range loss of crystallinity. Thus dealumination occurred at all temperatures above 550°C and was correlated with significantly reduced ammonia storage capacity and ammonia oxidation ability. Low-temperature SCR activity was not much affected below 850°C, but decreased significantly when total collapse of the zeolite framework occurred at this temperature. At ageing temperatures above 750°C, formation of oxidic copper species was observed and correlated partially with increased high-temperature ammonia oxidation capacity, though it is possible that oxidation in parallel occurs on non-oxidic sites in ion-exchange positions. On the other hand, low-temperature ammonia oxidation was shown to occur on ionic copper sites (likely in the 6MR units) and decrease with increasing ageing temperature. We further found some evidence that low-temperature formation of N2O during standard SCR may occur on different sites or via different mechanisms.

Characteristics of two novel cold- and salt-tolerant ammonia-oxidizing bacteria from Liaohe Estuarine Wetland

To achieve a better contaminant removal efficiency in a low-temperature and high-salt environment, two novel strains of cold- and salt-tolerant ammonia-oxidizing bacteria (AOB), i.e., Ochrobactrum sp. (HXN-1) and Aquamicrobium sp. (HXN-2), were isolated from the surface sediment of Liaohe Estuarine Wetland (LEW), China. The optimization of initial ammonia nitrogen concentration, pH, carbon–nitrogen ratio, and petroleum hydrocarbons (PHCs) to improve the ammonia-oxidation capacity of the two bacterial strains was studied. Both bacterial strains showed a high ammonia nitrogen removal rate of over 80% under a high salinity of 10‰. Even at a temperature as low as 15°C, HXN-1 and HXN-2 could achieve an ammonia nitrogen removal rate of 53% and 62%, respectively. The cold- and salt-tolerant AOB in this study demonstrated a high potential for ammonia nitrogen removal from LEW.

Contrasting response of nitrification capacity in three agricultural soils to N addition during short-term incubation

Human disturbance is a major culprit driving imbalances in the biological transformation of nitrogen from the nonreactive to the reactive pool and is therefore one of the greatest concerns for nitrogen (N) cycling. The objective of this study was to compare potential nitrification rates and the abundance of ammonia oxidizers responsible for nitrification, with the amendment of external N in different agricultural soils. Three typical Chinese agricultural soils, QiYang (QY) acid soil, ShenYang (SY) neutral soil, and FengQiu (FQ) alkaline soil, were amended with 0, 20, 150, and 300 mu g NH4 (+)-N g(-1) soil and incubated for 40 days. The abundance of ammonia oxidizing bacteria (AOB) and archaea (AOA) at the end of incubation in the soil microcosms was determined using the real-time PCR. There was a significant decrease in ammonium concentration in the QY soil from the highest to the lowest N-loading treatments, while no significant difference in ammonium concentrations was detected among the different N-loading treatments for the SY and FQ soils. A significantly higher potential nitrification rate (PNR) was observed in the FQ soil while lowest PNR was found in the QY soil. Quantitative PCR analysis of AOB amoA genes demonstrated that AOB abundance was significantly higher in the high N-loading treatments than in the control for the QY soil only, while no significant difference among treatments in the SY and FQ soils. A significant positive correlation between PNR and AOB amoA abundance, however, was found for the SY and FQ soils, but not for the QY soil. Little difference in AOA amoA abundance between different N-loading treatments was observed for all the soils. This study suggested that ammonia oxidation capacity in the FQ and SY soils was higher than those in the QY soil with the addition of ammonium fertilizer for a short-term. These findings indicated that understanding the differential responses of biological nitrification to varying input levels of ammonium fertilizer is important for maximizing N use efficiency and thereby improving agricultural fertilization management.

Response of Induced Perturbation on Replicating β-Proteobacterial Ammonia-Oxidizing Populations in Soil

The short-term response of induced perturbation by 4-ethylphenol on β-proteobacterial ammonia oxidizers (β-AOB) was investigated in two soils with initial differences in community structure. The hypotheses were that short-term effects of a disturbance of the AOB community is best monitored by specifically looking at the active populations and that soils with dissimilar active AOB populations would display different degree of resistance or resilience. Two soils from a previously characterized long-term field study fertilized with manure or sewage sludge was used. Soil microcosms were incubated in the laboratory over 15 days. The substrate-induced ammonia oxidation was measured, and the composition of β-AOB communities was determined by PCR-DGGE of specific β-AOB 16S rRNA gene fragments. Actively replicating members of the β-AOB were distinguished by the use of bromodeoxyuridine (BrdU) immunocapture. This approach demonstrated that only a minor fraction of the total AOB community was active. Exposure to 4-ethylphenol resulted in approximately 90% lowered substrate-induced ammonia oxidation rates in both soils. This activity inhibition was not accompanied by shifts in β-AOB community structure when total β-AOB DNA was studied. By contrast, changes were seen in the DGGE banding pattern of the BrdU-labeled community DNA after 4-ethylphenol addition in the manure-fertilized soil. In the sewage sludge fertilized soil, the banding pattern of the BrdU-labeled β-AOB remained unchanged, but bands were weaker after the disturbance. In conclusion, it was shown that BrdU immunocapture was applicable to detect shifts in community composition among replicating β-AOB populations in soil. However, this was not reflected by the soils' ammonia oxidation capacity to resist to or recover from the induced perturbation suggesting that rapid population shifts may not influence soil functioning in a short-term perspective.

Metabolic properties of a mixed culture of aerobic ammonia oxidizers and its optimal reaction conditions

The aerobic ammonia oxidation is an important process for nitrogen removal from wastewater with high ammonia concentration. Here, we investigated the metabolic properties of a mixed culture of aerobic ammonia oxidizers and determined its optimal reaction conditions. The maximum specific rate of NO2--N formation of the culture was 14.9mgNmg(protein)−1d−1. The ammonia oxidation capacity was positively correlated with the microbial biomass concentration. Haldane model showed that the half-saturation constant (Ks) for NH4+-N of the culture was 78.5mgL−1, and the inhibition constant (Ki) for NH4+-N was 393.4mgL−1. The acetic acid and beef extract had significant inhibitory effects on ammonia oxidation, while there was little effect of methanol and glucose on ammonia oxidation. Orthogonal experiments with range analysis, variance analysis, factor contribution analysis and response surface analysis confirmed the optimal reaction conditions for ammonia oxidation to be 30–32°C, pH 7.8–8.0, and 150–200mgL−1NH4+-N concentration.