Ammonia-oxidizing Bacteria Research Articles

Insights into the influence of organic and salinity on the two-stage partial nitritation/anammox process in treating food waste digestate

ABSTRACT Food waste digestate (FWD), which contains significant levels of ammonium, organic matter, and salinity, can interfere with treatment performance of the anammox process. In this study, a two-stage partial nitritation/anammox (PN/A) process was established to investigate nitrogen removal and microbial response in treating FWD at a nitrogen loading rate (NLR) of 0.27 ± 0.02 gN/L/d. High concentrations of free ammonia (58 mg/L) and free nitrous acid (0.3 mg/L) facilitated the initiation of the partial nitritation (PN) process, achieving an average NO2 −/NH4 + ratio of 1.28 ± 0.08. For the anammox process, a nitrogen removal rate (NRR) of 0.72 ± 0.13 gN/L/d was achieved. Free ammonia (NH3) stripping, Anammox pathway, and denitrification pathway contributed 4.1 ± 0.3%, 5.1 ± 0.2%, and 84.0 ± 1.5% of the total nitrogen removal, respectively. Nitrosomonas, a salt-tolerant ammonia-oxidizing bacteria (AOB), was enriched to 1.0%, while Nitrospira, a nitrite-oxidizing bacteria (NOB), was effectively suppressed to 0.003%. The salt-tolerant anammox genera unclassified_f__Brocadiaceae (13.9%) and Candidatus_Kuenenia (4.8%) dominated the nitrogen removal pathway. The high enrichment of unclassified_f__Brocadiaceae ensured stable operation of the anammox process at 0.62 ± 0.11% salinity, even with a high initial FA inhibition concentration of 40 mg/L. Additionally, norank_f_A4b (1.34%) and norank_f_norank_o_SBR1031 (52.1%) facilitated the hydrolysis of refractory organic matter. Denitrifying bacteria, including Hyphomicrobium, Truepera, and unclassified_c__Alphaproteobacteria, played significant roles in nitrate removal, with a CODconsumed/NO3 − removed ratio of 2.7 ± 0.2. This study highlights the application of a two-stage PN/A process for rapid startup and effective nitrogen removal from FWD.

Enhancing simultaneous nitrogen and phosphorus removal using partial nitritation/anammox with an airlift inner-circulation partition bioreactor

The partial nitritation/anammox (PNA)-hydroxyapatite (HAP) process for synchronized nitrogen (N) and phosphorus (P) removal has attracted much attention; however, its use has been restricted by the limited availability of optimal bioreactor configuration and its operational conditions. In the present study, a new single-stage PNA reactor, the airlift inner-circulation partition bioreactor (AIPBR), was continuously operated for 261 days at a fixed hydraulic retention time of 6 h. The results showed that the optimal removal performance (ammonia, 92.77 ± 0.72 %; total N, 76.92 ± 1.78 %; %, total P, 86.57 ± 2.84 %) was achieved at a Ca/P ratio of 4.0 during the operation period; the influent ammonia and P concentrations were maintained at 250 mg/L and 20 mg/L, respectively. The P removal efficiency was 10 % higher than that reported in similar studies, indicating that a highly efficient PNA-HAP process can be successfully achieved using the AIPBR. By enhancing the circulation of the mixture between the inner and outer layers, accelerating the accumulation of ammonia-oxidizing and anaerobic ammonia-oxidizing bacteria, and promoting simultaneous biological autotrophic denitrification and phosphorization, the sludge granulation and HAP crystallization were gradually strengthened by the pH increase inside the sludge particles. Our findings provide a scientific basis for developing next-generation technologies for synchronized N and P removal from wastewater.

Nitrogen metabolic responses of non-rhizosphere and rhizosphere microbial communities in constructed wetlands under nanoplastics disturbance

Constructed wetlands (CWs) serve as crucial sinks for nanoplastics, making them a significant research hotspot regarding the impacts of nanoplastics on the nitrogen metabolism within microbial communities. However, there has been a lack of comparative analysis between rhizosphere and non-rhizosphere microbial communities under nanoplastics disturbance. This study analyzes the nitrogen metabolic responses of these microbial communities in CWs following repeated nanoplastics disturbance. Results indicated that repeated nanoplastics disturbances led to a 17.72% decrease in the relative abundance of nitrifying bacteria in rhizosphere microbial community, while the relative abundance of Polaromonas increased by 5.24% in non-rhizosphere community. Microbial network revealed that rhizosphere microbial community primarily contributed to nitrogen metabolism by forming a tightly connected network. In contrast, non-rhizosphere microbes dominated nitrogen cycling by promoting energy and information exchange among microbes. Furthermore, rhizosphere and non-rhizosphere microbial communities exhibited distinct resistance and adaptation to nanoplastics disturbance. Rhizosphere microbes responded by activating antioxidant systems, whereas non-rhizosphere microbes could develop adaptive growth and metabolism, using nanoplastics as a carbon source. The adaptation strategies of non-rhizosphere community proved more advantageous for coping with persistent nanoplastics disturbance. This study comprehensively investigated the differences of nitrogen metabolism between rhizosphere and non-rhizosphere microorganisms in CWs under nanoplastics disturbance.

Biological and ecological consequences of combined biofilm, shellfish and phytoremediation along a wastewater treatment system from shrimp aquafarm

Biological treatments have been widely applied to remove wastewater nutrients, while single biological treatment is insufficient to achieve desired efficiency. Moving beyond removal of nutrient, equivalent focus on ecological consequences and biotic pollutants (e.g., pathogens) along the decontamination procedures is lacking. Herein, we established an efficient biological treatment system by integrating biofilm, shellfish and Spartina, which efficiently reduced the levels of wastewater nutrients (> 62.7 %) and sediment antibiotics (> 84.6 %) before discharge, with unsatisfied removal of total phosphorus and diversified potential pathogens. Our biological treatments potentiated C storage and ammoxidation process, and mitigated CH4 emission, of which are conjointly governed by the direct effect of nutrient pollutions and the indirect effect of antibiotics. In contrast, denitrification potential in wastewater and sediment was divergent, resulting in an uncertainty on net N2O emission. We identified diverse ammonia-oxidizing bacteria assistors that were candidates for improving ammoxidation. Intriguingly, bacterial biomakers could quantitatively and accurately diagnose wastewater entropy water quality index and sediment multi-nutrient cycling index, with overall 81.9 % and 91.1 % accuracy, respectively. The combined biological treatments can be a double-edged sword between water quality improvement and mitigating pathogenicity. These findings greatly deepen our understanding of the biological and ecological consequences of a biofilm-shellfish-phytoremediation system, and accordingly some strategies are informed for improving decontamination efficiency.

Unravelling depth layers of microbial communities, nitrogen transformation rate, and extracellular polymeric substances in anammox granules

Anammox granules harbor a variety of bacteria, with each granule layer providing a niche for bacteria with specific metabolic functions. To investigate microbial distribution, nitrogen transformation rates, and extracellular polymeric substance (EPS) content across the depth layers of anammox granules, granules sized 0.9–2.0 mm were sheared into seven layers. The outer layers exhibited higher anammox bacterial abundance (9.9 %) than the inner layers (8.1 %). In contrast, the abundance of denitrifying bacteria increased from 25.0 % in outer layers to 34.9 % in inner layers. Nitrifying bacteria, along with heterotrophic nitrifying and aerobic denitrifying bacteria, were predominantly found in outer layers. Despite the higher EPS content in inner layers, denitrification rates remained low across all layers, likely due to limited carbon availability from microbial lysis or EPS. These findings offer valuable insights into the niche distribution of microbial communities within anammox granules.

Effects of a Vegetable Eel Co-Culture System on the Soil Ammonia-Oxidizing Microbial Community

(1) Background: A vegetable eel co-culture system is an economically efficient way of agricultural cultivation, which can have an impact on the soil microbial environment and play a pivotal role in the soil nutrient cycle, but there is little research on its impact on soil ammonia-oxidizing microorganisms. (2) Methods: NovaSeq platform sequencing was employed to investigate the richness, structure, and diversity of soil ammonia-oxidizing microbial communities, exploring the effects of a vegetable eel co-culture system on soil nitrogen cycling. Four different planting treatments were set up: unfertilized without vegetable eel (CCK), fertilized without vegetable eel (CRT), unfertilized with vegetable eel (ICK), and fertilized with vegetable eel (IRT). (3) Results: A vegetable eel co-culture system significantly increased soil pH and decreased bulk density under fertilization conditions. The soil nitrification potential rate was enhanced by a vegetable eel co-culture system to an average of 26.3%. A vegetable eel co-culture system significantly altered the community structure of all ammonia-oxidizing microorganisms, with a significant increase in the richness and diversity of ammonia-oxidizing bacteria (AOB) and comammox clade-A, while fertilization significantly increased the diversity of all ammonia-oxidizing microbial communities. Structural equation modeling (SEM) analysis showed that the main environmental factors affecting the structure of the ammonia-oxidizing microbial community were nitrate and total nitrogen. The number of amoA genes in AOB and comammox clade-B was significantly positively correlated with the soil potential N nitrification rate (PNR), which played a leading role in the nitrification of alkaline vegetable soil. The network analysis revealed that a vegetable eel co-culture system improved the modularity of AOB and comammox clade-B by 13.14% and 5.66%. (4) Conclusions: This study showed that the vegetable eel co-culture system stimulated the evolution of ammonia-oxidizing microbial communities by changing the physicochemical properties, which in turn promoted the soil nitrification reaction.

Integrated impacts of mariculture on nitrogen cycling processes in the coastal groundwater of Beihai, southern China

Groundwater nitrogen (N) contamination in coastal zones is becoming an increasingly serious global issue. Mariculture, as a major anthropogenic activity, has profound impacts on coastal groundwater and constitutes an important source of coastal N contamination. However, a comprehensive understanding of the impact of mariculture on N cycling (especially N removal) is still lacking. Taking the Daguansha mariculture region in southern China as the study area, we aimed to investigate the environmental impact of mariculture on coastal groundwater and identify N cycling processes influenced by mariculture using hydrogeochemistry, multiple isotopes, coupled with 16S rRNA gene sequencing, and the quantitative polymerase chain reaction (qPCR) experiments. The results showed that the combined effects of seawater intrusion and seepage from land-based mariculture ponds have led to localized groundwater salinization in the region. Meanwhile, mariculture promotes nitrification and anammox processes in groundwater. The dominance of ammonia-oxidizing and anammox bacteria in the upper aquifer is attributable to local salinization, N and organic carbon input, as well as anoxic to suboxic conditions induced by seepage from aquaculture ponds. In addition, the gene abundances of ammonia oxidation (dominated by AOA) and denitrification were positively correlated, indicating their cooperative interaction. This study provides deeper insight into N cycling in coastal groundwater systems affected by extensive mariculture.

Distribution and key influential factors of comammox in drained and waterlogged soils of zoige plateau peatland

Peatlands are important carbon and nitrogen reservoirs, playing crucial roles in nitrogen cycling. During microbially-driven nitrogen cycling, nitrous oxide (N2O, 298 times global warming potential of CO2) can be emitted, exacerbating global warming. Complete ammonia-oxidizing bacteria (comammox), a newly discovered group of prokaryotes, can independently oxidize ammonia directly to nitrate, bypassing the nitrite stage, and thereby reducing N2O production associated with the traditional two-step nitrification process. However, information on comammox distribution and its key influential factors in plateau peatlands remains scarce. Thus, this study chose Zoige plateau peatland in China to collect soil samples from different soil types (drained and waterlogged), across different seasons (non-growing and growing), and at various depth (0–100 cm) to assess comammox abundance and community composition. Additionally, soil properties were analyzed and correlated with comammox abundance and community composition to identify the key factors affecting comammox distribution. Comammox abundance varied significantly across soil types, depth, and sampling seasons. Waterlogged soils demonstrated higher comammox abundance than drained soils. In waterlogged soils, comammox abundance showed higher during growing season than non-growing season, while the opposite trend was observed in drained soils. Regardless of soil types, comammox abundance decreased with increasing soil depth. In soils of Zoige plateau peatland, comammox clades A.1, A.2, A.3 and B.1 were identified, with clade B.1 dominating the comammox community. Both Nitrospira sp. CG24A (clade B.1) and Candidatus Nitrospira nitrificans (clade A.1) showed great seasonal variations. Soil properties, including moisture, pH, carbon, and nutrients, collectively influenced comammox abundance and diversity. Among these factors, NH4+-N was the main factor affecting comammox abundance, while moisture primarily drove community distribution. These findings provide valuable insights into comammox distribution, enhancing our understanding of its potential role in mitigating N2O emissions and thus nitrogen cycling in plateau peatland soils.

The Effects of Predominantly Chemoautotrophic Versus Heterotrophic Biofloc Systems on Nitrifying Bacteria, Planktonic Microorganisms, and Growth of Penaeus vannamei, and Oreochromis niloticus in an Integrated Multitrophic Culture

The aim of this study was to evaluate the effect of predominantly chemoautotrophic and heterotrophic biofloc systems on ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), and planktonic microorganisms in an integrated Penaeus vannamei and Oreochromis niloticus integrated multitrophic culture. Shrimp and tilapia were stocked at a density of 400 shrimp m−2 and 45 fish m−3, respectively. The trial consisted of two biofloc treatments, with three replicates each: chemoautotrophic and heterotrophic. The identification and quantification of the planktonic microorganisms (ciliates, flagellates, microalgae, and total bacteria) and nitrifying bacteria were carried out through direct counting and fluorescence in situ hybridization, respectively. At the end of the trial, heterotrophic treatment had resulted in higher total abundance of bacteria. The relative abundance of AOB and NOB in relation to the total abundance was less than 0.1% for both treatments. The system was dominated by flagellates in both treatment groups. The abundance of microalgae and ciliates was higher with chemoautotrophic treatment. After 43 days, the shrimp weights were higher in the chemoautotrophic group, while the final weights of the tilapia were not significantly different between the two treatments. The type of biofloc system (Chemoautotrophic vs. Heterotrophic) did not significantly alter the establishment of AOB and NOB in a Penaeus vannamei and Oreochromis niloticus integrated multitrophic culture. The two treatments proved to be equally efficient for maintaining good water quality, but the chemoautotrophic treatment resulted in better shrimp growth. Thus, our study demonstrated that chemoautotrophic biofloc is a promising approach in integrated multitrophic aquaculture.

Efficient ammonia oxidation by Pseudomonas citronellolis strain YN-21 under strongly acidic conditions: Performance and mechanism

Ammonia oxidation microorganisms generally tend to have low rates of ammonia oxidation under acidic conditions, as the protonated ammonia is not a substrate for ammonia monooxygenase. In this work, heterotrophic ammonia oxidation bacteria (HAOB) Pseudomonas citronellolis strain YN-21 showed high efficiency in removing NH4+ (12.7 mg/L/h) even at initial pH 4.5. The potential acid resistance mechanisms (H+ efflux, H+ consumption, and production of alkaline substances) maintained intracellular pH neutrality. Transcriptome analysis showed that genes involved in amino acid metabolism, carbohydrate metabolism, ABC transporter and nitrogen metabolism were significantly up-regulated, which facilitated the rapid removal of NH4+ in an acidic environment. Moreover, urea could be used as an alternative nitrogen source for YN-21 in a strongly acidic environment, and the production of NH3 from urea hydrolysis provided a substrate for ammonia oxidation. These results provide new insights into efficient ammonia oxidation in acidic environments.

Effect of Pseudomonas Fluorescens on Isofetamid Dissipation and Soil Microbial Activity

The aim of this study was to assess the effect of Pseudomonas fluorescens (P) application on isofetamid (IS) dissipation; the number of specific genes of archaea, bacteria and ammonia-oxidizing bacteria (AOB); and the activity of β-Glucosidase, phosphomonoesterase, N-acetyl-glucosaminidase and arylsulfatase. It was observed that the IS concentration was lower in the P+IS than in IS throughout the entire study period, which indicates the potential of P. fluorescens to decompose isofetamid faster. IS+P application significantly influenced N-acetyl-glucosaminidase, arylsulfatase and phosphomonoesterase activity in soil compared to the control by approximately 29%, 72% and 6.5%, respectively. Moreover, it was observed that on day 21 in IS+P, the number of bacterial genes was significantly higher than in the control and IS and than on day 1, by 10% and 20%, respectively. On day 21, the number of archaea was significantly higher in all variants and ranged from 3.61 (control) to 6.88 log10 gene copies/g dm (IS+P). Correlation analysis showed a positive correlation between IS and TOC, while there was a negative correlation between IS and β-Glu and the number of archaea and AOB genes. The tested strain has the potential to be a biofertilizer and an agent in the bioremediation of contaminated soils.

Biocrusts Mediate the Niche Distribution and Diversity of Ammonia-Oxidizing Microorganisms in the Gurbantunggut Desert, Northwestern China

Biological soil crusts (biocrusts) play pivotal ecological roles in regulating nitrogen cycling within desert ecosystems. While acknowledging the essential role played by ammonia-oxidizing microorganisms in nitrogen transformation, there remains a paucity of understanding concerning how disturbances to biocrusts impact the diversity and spatial distribution patterns among ammonia oxidizer communities within temperate deserts. This investigation delved into assessing how 4 years’ worth of removing biocrust influenced niche differentiation between nitrifying archaea and bacteria while also examining its effects on shaping community structures of predominant ammonia-oxidizing archaea (AOA) within the Gurbantunggut Desert soils. Despite notable variations in abundance of ammonia-oxidizing microbes across distinct soil depths throughout different seasons, it became apparent that removing biocrust significantly altered both the abundance and niche pattern for AOA alongside their bacterial counterparts during winter and summer periods. Notably dominating over their bacterial counterparts within desert soils, AOA displayed their highest archaeal to bacterial amoA gene copy ratio (6549-fold higher) at a soil depth of 5–10 cm during summer. Moreover, substantial impacts were observed upon AOA diversity along with compositional changes following such perturbation events. The aftermath saw an emergence of more diffuse yet dynamic AOA communities, especially noticeable amidst winter when nitrogen and water limitations were relatively alleviated. In summary, our findings underscore how interactions between biocrust coverages alongside factors like soil temperature, total carbon content, or NO3−_N concentrations govern niches occupied by ammoxidation communities whilst influencing assemblage processes too. The sensitivity shown by dominant AOAs towards biocrust removal further underscores how biocrust coverage influences nitrogen transformation processes while potentially involving other communities and functions in desert ecosystems.

Biochar and neem seed cake co-amendment effects on soil nitrogen cycling and NH3 volatilization in contrasting soils

In a 28-day incubation study, ball milling technologies were applied to enhance the sorptive and functional properties of pristine biochar. The effect of ball-milled (BM) biochar, neem seed cake, and their co-amendment was evaluated on nitrification, ammonia (NH3) volatilization, and the abundance of nitrifying microbial communities in three contrasting tropical soils of different pH (acidic, neutral, and alkaline). The amendments were applied at 2% dry w/w to soils fertilized with ammonium chloride (NH4Cl). Results showed that in neutral and alkaline soils, the co-amendment led to a 40% and 64% increase in NH3 volatilization, respectively, compared to control due to significant ammonium (NH4+) retention and temporary nitrification inhibition. Conversely, in acidic soil, BM biochar and neem seed cake amplified nitrification by 23% and 62%, respectively, compared to sole amendments, while neem seed cake increased NH3 volatilization by 56% compared to BM biochar + neem seed cake due to NH4+ retention, altered soil pH, and changes in nitrifying microbial community. The abundance of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and complete ammonia oxidizers (Comammox) was altered by changes in soil pH and N availability modulated by BM biochar and neem seed cake. Correlation analysis revealed significant relationships between soil organic matter (SOM), NH4+, and NO3− on the abundance of nitrifying microorganisms. The study affirms the efficacy of BM biochar-neem seed cake co-amendment on nitrification inhibition but indicates potential N losses by NH3 volatilization depending on soil type, highlighting the need for soil type-specific management strategies to optimize N retention while minimizing environmental impacts.

Thermodynamic characteristics of nitrifiers reveal the potential NOB inhibition strategies at low temperatures

Nitrification is a highly temperature-sensitive biological process, yet relatively little research has explored thermodynamic characteristics of enzyme-catalyzed nitrification processes in wastewater treatment systems. In this study, a variety of thermodynamic models were employed to evaluate thermodynamic characteristics of four activated sludge samples cultivated under various temperatures (10, 15, and 20 °C) and ammonia nitrogen concentration (40 mg/L and 300 mg/L). Results revealed a higher maximum temperature (Tmax) for ammonia oxidizing bacteria (AOB) compared to nitrite oxidizing bacteria (NOB), suggesting the robust resistance to high temperatures of AOB. Conversely, the lower minimum temperature (Tmin) of NOB indicated its stronger tolerance to low temperatures. Notably, both low temperatures and high-ammonia nitrogen concentrations are conducive to the competition of Nitrotoga over Nitrospira, resulting in Nitrotoga emerging as the dominant NOB within 10∼15 °C. Moreover, heat capacity (ΔCpǂ) of enzymes exhibited a similar trend across all samples, i.e. HAO > AMO > NOR, indicating that HAO exhibited the strongest thermodynamic stability, followed by AMO, and NOR has the worst thermodynamic stability. Additionally, the difference in optimal temperature (Topt) between dominant AOB-Nitrosomonas and dominant NOB-Nitrotoga cultivated at high nitrogen concentration and low temperature could reach up to +8.13 °C, enabling selective inactivation of NOR through thermal treatment at Topt,AOB ∼ Topt,NOB. However, despite insignificant differences in Topt,AOB and Topt,NOB under low-temperature and low-ammonia nitrogen concentration, the smaller the difference between Tmax and Top (Tmax-Topt) of NOB and smaller D-value of NOR made NOB more susceptible to inhibition than AOB. However, the presence of low-abundance Nitrospira renders thermal treatment alone inadequate for complete NOB inhibition, combing it with other strategies is necessary for effective inhibition. Therefore, the fundamental differences in thermodynamic characteristics of AOB and NOB determine the potential of NOB inhibition strategies at low temperatures.

Both AOA and AOB contribute to nitrification and show linear correlation with nitrate leaching in purple soils with a wide nitrogen gradient

Ammonia oxidizers play an important role in nitrification that forms nitrate, the main form of leaching nitrogen (N). However, little is known about how ammonia oxidizers bridge long-term N fertilization levels and soil nitrate leaching. We conducted a field experiment in purple soil, investigating the interactions among soil physico-chemical parameters, ammonia-oxidizing microbial communities, and N leaching under 0, 90, 180, 270, and 360 kg N ha−1 yr−1 fertilization levels. We found that soil inorganic N leaching increased exponentially with increasing N application rate. N fertilization enhanced the abundances of the amoA gene in ammonia-oxidizing archaea (AOA) and bacteria (AOB), while partial least squares regression analysis revealed that AOA and AOB abundances were correlated with pH and soil organic carbon (SOC). Compared with no N fertilization, N application reduced AOA alpha diversity and increased AOB alpha diversity. AOA alpha diversity was associated with pH and bulk density, whereas soil SOC and inorganic N content were more important in predicting changes in AOB alpha diversity. A linear relationship was established between soil NO3−-N leaching, the potential nitrification rate (PNR), and the abundances of AOA and AOB. The association of soil NO3−-N leaching and PNR with both AOA and AOB abundances were further corroborated by Mantel test, random forest regression, and partial least squares path modelling. Furthermore, alterations in the AOB alpha diversity, soil pH and NH4+-N content also contribute to the increasing soil NO3−-N leaching along the N application rate. Our results suggest that AOA, which previous studies have found to be active only under low N conditions, can also contribute to nitrification and support soil NO3−-N leaching at a wide range of N gradients. Overall, this finding advances the current understanding of the relationship between soil N leaching and microbial functional properties to some extent.

Biological Nitrification Inhibitors with Antagonistic and Synergistic Effects on Growth of Ammonia Oxidisers and Soil Nitrification

Biological nitrification inhibition (BNI) refers to the plant-mediated process in which nitrification is inhibited through rhizospheric release of diverse metabolites. While it has been assumed that interactive effects of these metabolites shape rhizosphere processes, including BNI, there is scant evidence supporting this claim. Hence, it was a primary objective to assess the interactive effects of selected metabolites, including caffeic acid (CA), vanillic acid (VA), vanillin (VAN), syringic acid (SA), and phenylalanine (PHE), applied as single and combined compounds, against pure cultures of various ammonia-oxidising bacteria (AOB, Nitrosomonas europaea, Nitrosospira multiformis, Nitrosospira tenuis, Nitrosospira briensis) and archaea (AOA, Nitrososphaera viennensis), as well as soil nitrification. Additionally, benzoic acid (BA) was examined as a novel biological nitrification inhibitor. All metabolites, except SA, tested as single compounds, achieved varied levels of inhibition of microbial growth, with CA exhibiting the highest inhibitory potential. Similarly, all metabolites applied as single compounds, except PHE, inhibited soil nitrification by up to 62%, with BA being the most potent. Inhibition of tested nitrifying microbes was also observed when compounds were assessed in combination. The combinations VA + PH, VA + CA, and VA + VAN exhibited synergism against N. tenuis and N. briensis, while others showed antagonism against N. europaea, N. multiformis, and N. viennensis. Although all combinations suppressed soil nitrification, their interactions against soil nitrification revealed antagonism. Our findings indicate that both antagonism and synergism are possible in rhizospheric interactions involving BNI metabolites, resulting in growth inhibition of nitrifiers and suppression of soil nitrification.

Nitrifying and denitrifying microbes exhibit distinct community structure and activity responses to different crop rotation systems in subtropical paddy soils

The adverse impacts of double-season rice cultivation on soil health and crop yield can be alleviated by crop rotation. However, the mechanisms by which biotic and abiotic factors influence microbial nitrogen cycling under different crop rotation systems remain unclear. Here, we evaluated the impact of crop rotation in paddy soils on the community abundance, composition, and activity of nitrifying microbes (ammonia-oxidizing archaea and bacteria (AOA and AOB)) and denitrifying microbes (nirK- and nirS-denitrifiers). A 6-year field experiment was performed with four crop rotation systems: (1) double rice as a control, (2) middle-season rice–fallow rotation (MR), (3) middle-season rice–oilseed rape rotation (MROR), and (4) middle-season rice–pak choi–oilseed rape rotation (MRPOR). AOB abundance increased significantly in MROR and MRPOR treatments, whereas AOA abundance decreased significantly in MROR. nirS gene abundance was significantly lower in MROR and MRPOR treatments, whereas nirK gene abundance was significantly lower in MR and MRPOR treatments. AOB and nirK gene community structures were significantly altered by crop rotation; this relationship was closely correlated with soil water content and NO3−-N concentration. For MROR and MRPOR treatments, potential nitrification activity was significantly increased and positively correlated with AOB abundance, whereas denitrification enzyme activity was significantly decreased and correlated with nirK and nirS community structure. Therefore, nitrifiers and denitrifiers exhibit distinct responses to crop rotation in paddy soils, which may influence microbial nitrogen cycling. These findings have practical implications for selecting appropriate cropping regimes.

Long-term effects of film mulching and fertilization regimes on gross N transformations in calcareous dryland soils

Plastic film mulching (PM) and nitrogen (N) fertilization regimes significantly affect crop yield, N supply capacity, and N losses. However, the long-term effects and the underlying mechanisms, like the belowground N transformations, call for in-depth investigation. Here, a 15N tracing study was conducted to quantify the gross N transformation rates of the calcareous soil subjected to 12 years of PM and various fertilization regimes. We found that autotrophic nitrification (ONH4) and mineralization (M) were the predominant soil N conversion processes, while dissimilatory nitrate reduction to ammonium (DNRA) and nitrate immobilization (INO3) were negligible in the calcareous soil, leading to the accumulation of nitrate. Long-term PM significantly decreased the rates of M, recalcitrant organic-N mineralization (MNrec), ONH4, and NH4+ immobilization to labile organic-N (INH4_Nlab) due to the negative effect on the abundances of fungi and ammonia-oxidizing bacteria (AOB) amoA gene compared to control soil. Relative to no N control, different fertilization regimes significantly increased the AOB amoA gene abundance, decreased fungal abundance and ITS:16S ratio, thus increasing ONH4 and M, decreasing NH4+ immobilization rates to labile and recalcitrant organic-N. Compared to normal N rate (F225), high N rate (F380) and normal N plus manure (F225+M) markedly increased ONH4 and INO3. Regression analyses revealed that M and AOB amoA gene abundance affected ONH4, and in turn N2O production. The findings provide an improved understanding of the long-term effects of PM and N managements on soil N supply capacity and potential N losses based on internal N cycling and molecular biology.

Multi-stage anoxic/oxic sequencing batch reactor realizes shortcut nitrogen removal for anaerobically co-digested liquor of municipal sludge and urban organic wastes

ABSTRACT Nitrogen removal from the combined anaerobic digestion dehydration liquor (CADDL) of municipal sludge and urban organic wastes is challenging due to high ammonium concentrations, low C/N ratio, and poor biodegradability. This study proposes a multi-stage anoxic/oxic (A/O) sequencing batch reactor with step feeding to realize partial nitrification and denitrification for shortcut nitrogen removal from the CADDL. We investigated the effects of external carbon source (acetate), dissolved oxygen (DO), A/O duration ratio, and A/O stage number on biological nitrogen removal. Moreover, we assessed the microbial community structure and nitrogen removal pathway. The results showed that the C/N consumption ratio for nitrite reduction to dinitrogen was 3.0 mg COD/mg N, and denitrifying bacteria yielded about 0.43. The optimal dosage of acetate was 2.2 mg COD/mg N. High DO concentration (1.5∼3.0 mg/L) in the aerobic stage improved the ammonia-oxidizing bacteria activity and nitrogen removal rather than worsening the nitritation. A high A/O duration ratio (50 min/60 min) was conducive to complete denitrification of nitrite. The three-stage A/O had an excellent nitrogen removal performance. Under optimal conditions, the nitrite accumulation ratio of nitritation and the total inorganic nitrogen removal reached 100% and 90.1%, respectively. The dominant ammonia-oxidizing bacteria was the genus Nitrosomonas (0.76% abundance), and the dominant denitrifying bacteria was Thauera (0.24% abundance). The nitrite-oxidizing bacteria were not detected, confirming that the biological nitrogen removal pathway was partial nitrification and denitrification. These findings provide a feasible option for the low-carbon nitrogen removal treatment for the CADDL of municipal sludge and urban organic wastes.

Sulfamethoxazole removal in nitrifying membrane aerated biofilms: Physiological responses and antibiotic resistance genes

Efficient removal of ammonia nitrogen and sulfamethoxazole (SMX) from wastewater has become increasingly critical due to their detrimental effects on aquatic ecosystems and public health. This study aimed to investigate the nitrogen transformation and SMX removal in a membrane aerated biofilm reactor (MABR) under different SMX concentrations (0–200 μg L−1) with a nitrifying membrane bioreactor (MBR) as a control. Results suggested that SMX removal in MABR was better than that of MBR with SMX addition (50–200 μg L−1). Membrane aerated biofilms tended to secrete more extracellular polymeric substances (EPS) and generate less antioxidant enzymes in response to SMX stress when compared with nitrifying sludge in MBR. Metagenomic analysis indicated that distinct succession of microbial community was observed in both systems after SMX addition, and the relative abundance of nitrifying bacteria (Nitrosomonas, Nitrospira, and Nitrobacter) evidently decreased under SMX concentration of 200 μg L−1. The proliferation of predominant antibiotic resistance gene (ARG) sul2 was suppressed more obviously in MABR than that in MBR. Thus, this study provided extensive insights into the advantages of nitrifying MABR in simultaneous removal of ammonium and antibiotics with less risk of associated ARGs spread.