Ammonia-oxidizing Bacteria Research Articles

Nitrifying bacteria for the remediation of organic nitrogen‐contaminated waters: a review

AbstractThe rapid growth of the world's population and its environmental impact has increased the demand for effective water treatment methods. Surface water systems, including rivers, streams, lakes, and ponds, have suffered contamination, leading to the urgent need for effective contaminant removal. Organic nitrogen compounds and nitrates are of particular concern because they pose risks to health and can cause environmental damage. However, traditional water‐treatment methods often prove ineffective for addressing these issues. For this reason, this research focuses on harnessing the capabilities of nitrifying bacteria to denitrify organic nitrogen compounds in water, exploring various bacterial strains, their functions, and their ability to obtain sources of carbon. The study also investigates innovative approaches such as biofilm systems, mixed cultures, and combined processes, which have shown stronger potential for nitrogen removal. Overall, it provides valuable insights into the use of nitrifying bacteria‐based technologies for water remediation in the face of growing environmental challenges.

Biological Nitrification Inhibition by Australian Tussock Grass and Its Impact on the Rhizosphere Ammonia-Oxidizing Microbiome

Certain plant species have developed the ability to express biological nitrification inhibition (BNI), suppressing the activity of nitrifying microbes and thereby reducing the conversion of ammonium to nitrate. This study assessed the BNI capacity and the rhizosphere ammonia-oxidizing microbiome of two grass species: the endemic Australian Barley Mitchell grass (Astrebla pectinata) and the introduced koronivia grass (Urochloa humidicola), using soils from both agricultural land and native vegetation. In agricultural soil, koronivia grass exhibited significantly higher BNI capacity compared with Barley Mitchell grass. However, in native soil, this trend was reversed, with Barley Mitchell grass demonstrating a significantly greater BNI capacity than koronivia grass (52% vs. 38%). Koronivia grass significantly altered the composition of the ammonia-oxidizing bacteria community in its rhizosphere, leading to a decrease in the Shannon index and bacteria number. Conversely, Barley Mitchell grass reduced the Shannon index (1.2 vs. 1.7) and population size (3.28 × 107 vs. 7.43 × 107 gene copy number g−1 dry soil) of the ammonia-oxidizing archaea community in its rhizosphere to a greater extent. These findings suggest that Australian Barley Mitchell grass may have evolved mechanisms to suppress soil archaeal nitrifiers, thereby enhancing its BNI capacity and adapting to Australia’s nutrient-poor soils.

Microalgae-bacteria consortia dynamics in a long term operated membrane-coupled high-rate algal pond (MHRAP)

Traditional activated sludge-based technologies have significant drawbacks, including high energy requirements and greenhouse gas emissions. Microalgae-based processes offer a promising, low-cost, and environmentally friendly alternative. However, the knowledge of treatment systems based on microalgae-bacteria consortia is limited, and even more so is their microbial composition and its relationship with operational parameters. Thus, this study explores the dynamics of microalgae-bacteria consortia in a long-term operated membrane-coupled high-rate algal pond (MHRAP) for wastewater treatment. For this, a pilot-scale MHRAP plant, located in a wastewater treatment plant in Valencia (Spain), was monitored under various hydraulic retention times (HRT) and wastewater influents: i) effluent from a primary settler and ii) effluent form pre-treatment. The biomass retention time was kept constant at 6 days. The composition of the bacterial community was studied through 16S rDNA sequencing, while 18S rDNA sequencing was used to study the microalgae. The results indicate that shorter HRTs significantly increased bacterial diversity, but not eukarya. Principal Co-ordinates Analysis (PCoA) revealed that the HRT and the incoming wastewater quality control the type of the bacterial populations. However, this effect was not observed in eukaryotic organisms. The dominant microalgae genera identified were Desmodesmus and Coelastrella, with Coelastrella becoming more prevalent at shorter HRTs. For bacteria, Verrumicrobiota dominated (18–56%) at high HRT while Proteobacteria was dominant (28–44%) at HRTs below 6 days. The changes observed in the bacterial composition, including the ammonia oxidizing bacteria (AOB) community (mainly Nitrosomonas), suggest that photo-inhibition could be taking place. The nitrite oxidizing bacteria (NOB) community was dominated by Nitrospira and Candidatus Nitrotoga. Operational parameters such as light intensity, pH, and nitrite concentration were found to significantly influence the microbial community structure. Higher light intensity and alkaline pH favored the growth of Desmodesmus, while Coelastrella thrived under lower HRTs. Bacterial diversity plays a crucial role in the treatment process, while microalgae primarily support aerobic bacterial processes by providing oxygen. These findings contribute to a deeper understanding of the complex biological processes in microalgae-bacteria consortia and offer insights into improving wastewater treatment technologies.

Impact of Drying–Wetting Cycles on Nitrification Inhibitors (DMPP and DMPSA) in a Greenhouse Experiment with Two Contrasting Mediterranean Soils

Studies of the impact of nitrification inhibitors (NIs), specifically DMPP and DMPSA, on N2O emissions during “hot moments” have produced conflicting results regarding their effectiveness after rewetting. This study aimed to clarify the effectiveness of NIs in reducing N2O emissions by assessing residual DMP concentration and its influence on ammonia-oxidizing bacteria (AOB) in two pot experiments using calcareous (Soil C, Calcic Haploxerept) and acidic soils (Soil A, Dystric Xerochrepts). Fertilizer treatments included urea (U), DMPP, and DMPSA. The experiments were divided into Phase I (water application to dry period, 44 days) and Phase II (rewetting from days 101 to 121). In both phases for Soil C, total N2O emissions were reduced by 88% and 90% for DMPP and DMPSA, respectively, compared with U alone. While in Phase I, the efficacy of NIs was linked to the regulation of AOB populations, in Phase II this group was not affected by NIs, suggesting that nitrification may not be the predominant process after rewetting. In Soil A, higher concentrations of DMP from DMPP were maintained compared to Soil C at the end of each phase. Despite this, NIs had no significant effect due to low nitrification rates and limited amoA gene abundance, indicating unfavorable conditions for nitrifiers. The study highlights the need to optimize NIs to reduce N2O emissions and improve nitrogen efficiency, while understanding their interactions with the soil. This knowledge is necessary in order to design fertilization strategies that improve the sustainability of agriculture under climate change.

Different management strategies for artificial substrates on nitrification, microbial composition, and growth of Penaeus vannamei in a super-intensive biofloc system

The aim of this study was to test the effect of different management strategies for artificial substrates on the nitrification process, microbial composition of water and biofilm, and growth of Penaeus vannamei in a super-intensive biofloc system. The research was conducted over 60 days using experimental units of 200 L and had the following treatments: T1 – artificial substrate + biofloc + shrimp + aeration (control), T2 - artificial substrate + water + aeration, T3 - artificial substrate + water, and T4 - only artificial substrate. The experiment was divided into two phases. Phase 1 involved maintaining the artificial substrates under the management strategy for 30 days. Phase 2 involved the use of substrates from phase 1 in a shrimp nursery for 30 days. Pre colonized artificial substrates (Needlona®) were employed at a ratio of 200 % of the tank's lateral area to promote biofilm growth. In the phase 1, T1 used a stocking density of 500 shrimp m−3 (9.72 ± 0.50 g). In phase 2, shrimp weighing 0.10 ± 0.05 g were stocked at a density of 1750 shrimp m−3 and all treatments included artificial substrates from phase 1, aeration, water, and shrimp. Molasses was the carbon source organic used. In phase 2, ammonia control was observed in treatments T2, T3, and T4 from the 10th day onwards. T4 had a nitrite spike, controlled from day 14 onwards, suggesting recovery of the nitrifying bacteria community. At the end of the phase 2, T2 and T4 showed higher abundance of coccoid bacteria in the biofilm compared to T1 and T3. T4 also had more bacillus. The shrimp final weight was higher in T2 compared to the other treatments. These findings suggest that maintaining the substrate submerged in water (T3) can be considered a practical management for artificial substrates and that it does not limit the nitrification process between culture cycles. Furthermore, exposure of artificial substrates to air (T4) also did not affect the nitrification process, leading to the recovery of the bacterial community, and the proliferation of various bacterial groups.

Gill-associated ammonia oxidizers are widespread in teleost fish.

Recent advances in sequencing methods have greatly expanded the knowledge of teleost-associated microorganisms. While fish-gut microbiomes are comparatively well studied, less attention has gone toward other, external organ-microbiome associations. Gills are particularly interesting to investigate due to their functions in gas exchange, osmoregulation, and nitrogen excretion. We recently discovered a branchial symbiosis between nitrogen-cycling bacteria and teleosts (zebrafish and carp), in which ammonia-oxidizing Nitrosomonas and denitrifying bacteria together convert toxic ammonia excreted by the fish into harmless dinitrogen (N2) gas. This symbiosis can function as a "natural biofilter" in fish gills and can potentially occur in all ammonotelic fish species, but it remains unknown how widespread this symbiosis is. In this study, we analyzed all publicly available gill microbiome data sets and checked for the presence of Nitrosomonas. We discovered that more than half of the described fish gill microbiomes contain 16S rRNA gene sequences of ammonia-oxidizing bacteria (AOB). The presence of gill-specific AOB was shown in both wild and aquacultured fish, as well as in marine and freshwater fish species. Based on these findings, we propose that ammonia oxidizers are widespread in teleost fish gills. These gill-associated AOB can significantly affect fish nitrogen excretion, and the widespread nature of this association suggests that the gill-associated AOB can have similar impacts on more fish species. Future research should address the contribution of these microorganisms to fish nitrogen metabolism and the fundamental characteristics of this novel symbiosis.IMPORTANCERecent advances in sequencing have increased our knowledge of teleost-associated microbiota, but the gill microbiome has received comparatively little attention. We recently discovered a consortium of nitrogen-cycling bacteria in the gills of common carp and zebrafish, which are able to convert (toxic) ammonia into harmless dinitrogen gas. These microorganisms thus function as a natural nitrogen biofilter. We analyzed all available gill microbiome data sets to determine how widespread gill-associated ammonia-oxidizing bacteria (AOB) are. More than half of the data sets contained AOB, representing both aquacultured and wild fish from freshwater and marine habitats. In total, 182 amplicon sequencing variants were obtained, of which 115 were found specifically in the gills and not the environmental microbiomes. As gill-associated AOB are apparently widespread in teleost fish, it is important to study their impact on host nitrogen excretion and the potential to reduce ammonia accumulation in (recirculating) aquaculture of relevant fish species.

Promoting effect of ammonia oxidation on sulfur oxidation during composting: Nitrate as a bridge

Ammonia (NH3) and hydrogen sulfide (H2S) are the main odor components in the composting process. Controlling their emissions is very important to reduce environmental pollution and improve the quality of composting products. This study explored the effects of functional bacteria on nitrogen and sulfur metabolism in the composting process of food waste (FW) by adding ammonia-oxidizing bacteria (AOB, A treatment), sulfur-oxidizing bacteria (SOB, S treatment), and combined AOB and SOB (AS treatment), respectively. The key bacterial species involved in nitrogen and sulfur transformation were identified, and the intrinsic mechanisms by which ammonia oxidation drove sulfur oxidation during composting were deciphered. Compared with control treatment (CK), the combined addition of functional microorganisms increased the maximum of soxB gene abundance by 1.72 times, thus resulting in the increase in the SO42- content by 44.00 %. AS treatment decreased the cumulative H2S emission and total sulfur (TS) loss by 40.24 % and 34.69 %, respectively, meanwhile lowering NH3 emission. Correlation network analysis showed that the simultaneous addition of AOB and SOB enhanced the correlation between microorganisms and sulfur oxidation genes, and Acinetobacter, Aeribacillus, Brevibacterium and Ureibacillus might be involved in the ammonia oxidation-promoted sulfur oxidation process. In summary, the optimized inoculation strategy of AOB and SOB could drive biological transformation of nitrogen and sulfur by regulating microbial community, ultimately reducing odor emissions and improving sulfur conservation.

Inoculation of ANAMMOX sludge for ultra-fast start-up of CANON process and performance optimization

The completely autotrophic nitrogen removal over nitrite (CANON) process is an economical nitrogen removal technology, but its establishment is difficult due to the coexistence of aerobic and anaerobic functional bacteria. This study rapidly started CANON process by inoculating anaerobic ammonia oxidation (ANAMMOX) sludge and adjusting aeration rate within 25 days. The key to fast start-up is adjusting the aeration to firstly enrich ammonia-oxidizing bacteria (AOB) without destroying the activity of anaerobic ammonia-oxidizing bacteria (AAOB). The aeration rate and nitrogen concentration were elevated to improve the nitrogen removal performance. Finally, the total nitrogen (TN) removal efficiency reached 82.4 % by optimizing alkalinity and the hydraulic retention time. The balance in Candidatus_Kuenenia and Nitrosomonas, which respectively accounted for ammonia nitrogen oxidation and TN removal contributed to the efficiency nitrogen removal. ANAMMOX sludge could be adopted as seed sludge for CANON process and the aeration rate was the key factor for the successful establishment.

Sludge enrichment and intermittent gradient aeration: Modulating microbial communities for start-up of partial nitrification in a sequencing batch reactor (SBR)

A novel approach has been proposed integrating sludge enrichment with intermittent gradient aeration to achieve partial nitrification (PN). Results indicated that this method suppressed nitrite-oxidizing bacteria (NOB) activity while maintained ammonia-oxidizing bacteria (AOB) activity, achieving an 82.87 % nitrite accumulation rate (NAR) during startup. During stable operation, specific ammonia oxidation rate and specific nitrite oxidation rate reached 18.44 and 2.67 mg N/g MLVSS/h, respectively. Shortening anoxic time from 30 to 20 min enhanced ammonia removal efficiency by 12.5 %, increasing NAR to 89.55 %. Further reduction to 5 min yielded 38.46 % and 91.88 %, respectively. AOB abundance enriched from 0.62 % to 22.28 %, with the AOB-to-NOB ratio jumping from 0.22 to 59.58. This research presented a rapid and effective strategy for achieving PN.

Selecting an optimal sorghum cultivar can improve nitrogen availability and wheat yield in crop rotation.

Sorghum (Sorghum bicolor L. Moench) is a cereal crop known for its biological nitrification inhibition (BNI) capacity, a plant-mediated activity limiting nitrification pathway. The use of BNI-producing plants represents an environmentally friendly and cost-effective approach to reduce nitrogen (N) losses, such as nitrate (NO3 -) leaching and nitrous oxide (N2O) gas emissions. The present study aimed to test the effectiveness of different S. bicolor cultivars in rotation to retain ammonium (NH4 +) in soils and promote N availability for the subsequent wheat crop. A two-year field rotation was established with four sorghum cultivars followed by winter wheat (Triticum aestivum L.). Urea alone or combined with the urease inhibitor N-(n-butyl) thiophosphoric triamide was applied to promote a NH4 +-based fertilization regimes. AddingN-(n-butyl) thiophosphoric triamide maintained higher soil NH4 + content and reduced ammonia-oxidizing bacteria population during sorghum cultivation. However, the benefits of the inhibitor on sorghum growth were cultivar-dependent. Notably, the further reduction in ammonia-oxidizing bacteria abundance for sorghum Voyenn and the increased soil NH4 + content for Vilomene suggested a BNI potential for these cultivars. Importantly, the Vilomene precedent enhanced wheat yield for both fertilization regimes. Overall, the present study confirms that sorghum is a suitable catch crop and emphasizes the importance of selecting the proper sorghum cultivar to maximize the yield of the target wheat crop, at the same time as minimizing N losses. Furthermore, developing combined strategies with selected sorghum cultivars and the application of urease inhibitors enables to enhance sorghum productivity as forage, achieving added value to the rotation. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Quorum sensing on the activated performances of gravity-driven membrane (GDM) system at low temperatures: Ammonia removal and flux stabilization

Gravity-driven membrane (GDM) filtration technology offers a low-energy, low-maintenance solution for water purification due to its powerful bio-cake, but faces predicament in contaminant removal under low temperatures. Quorum sensing (QS), a microbial communication process mediated by signal molecules such as C6-HSL (N-Hexanoyl-L-homoserine lactone), has been shown to influence microbial behavior and enhance biofilm formation, with promising potential for consolidation of GDM operation at low temperature. This study investigates the application of C6-HSL to enhance ammonia nitrogen and organics removal in low-temperature GDM systems. C6-HSL was administered at varying dosages (0/50/250/500 nM/d) at 5 °C, with further experiments conducted at 25 °C to assess the impact of QS regulation on GDM performance under room temperature. The results demonstrated that the optimized presence of C6-HSL (500 nM/d) improved the removal efficiency of dissolved organic carbon, ammonia nitrogen, and raised the stable flux (increase ratios at low vs. room temperature: ∼19 % vs. ∼7 %, ∼38 % vs. ∼9 %, and ∼7.9 % vs. 0.4 %, respectively). Analysis of the biofouling layer’s structural characteristics, composition, and biological activity indicated that the increased C6-HSL effectively promoted microbial growth and migration/movement, increased the production of extracellular polymeric substances (EPS) and soluble microbial products (SMP), and accelerated biofilm formation. The resulting thicker (∼172.98 vs. ∼119.21 μm), rougher (∼62.1 vs. ∼55.0 nm) cake layer, equipped with abundant channels for water penetration, contributed to increased contaminant degradation, but also stabilized the flux with slight growth (∼3.26 vs. ∼3.02 LMH) under low temperature. Notably, the enhancement effect of QS regulation was more pronounced at low temperature than at room temperature, attributing to the optimized release and diffusion of signal molecules and the more substantial stimulation of metabolic and enzymatic activity in nitrifying bacteria. This study provides valuable insights and technical support for decentralized water treatment in winter via reliable GDM process operation in challenging temperature conditions.

Comammox Nitrospira was the dominant ammonia oxidizer in an acidic biofilm reactor at pH 5.5 and pH 5.

Nitrification is a vital process in the biological removal of inorganic nitrogen compounds. In order to ensure the stability and effectiveness of this process, buffer solutions should be added to the system to maintain neutral to slightly alkaline conditions. With a focus on the newly discovered comammox Nitrospira, this research investigates the transition of the nitrifying community within a biofilm reactor under different acidic levels (initiated at pH 6 and gradually decreased to pH 5). During the 305-day continuous operation experiment, it was observed that responsible ammonia oxidizers transitioned from ammonia-oxidizing bacteria (AOB) during the initial stages (setup stage and early stage of pH 6) to comammox Nitrospira under pH 5.5 and pH 5. Further analysis using next-generation sequencing targeting both the 16S rRNA region and amoA region revealed a shift in the dominant cluster of both Nitrospirae and comammox Nitrospira under varying pH conditions. Our study identified a distinct cluster of comammox Nitrospira that is phylogenetically closed to sequences found in acidic environments, but exhibits dissimilarity from known comammox Nitrospira isolates and the majority of environmental sequences. This cluster was found to be prevalent in the acidic biofilm reactor studied and thrived particularly well at pH 5. These findings underscore the potential significance of this distinct, uncultivated group of comammox Nitrospira in performing ammonia oxidation under acidic conditions. KEY POINTS: • Ammonia was effectively removed under pH 5.5 and 5 in the biofilm reactor • The dominant ammonia oxidizer was comammox Nitrospira when pH was 5.5 and 5 • A potential acidophilic cluster of comammox Nitrospira was identified in this acidic biofilm reactor.

Effects of tourmaline on the establishment, idling, and recovery of partial nitrification: Mechanistic understanding and performance evaluation

The effects of different doses of tourmaline (Tm) on the partial nitrification (PN) system were investigated in this study. Tourmaline − Partial Nitrification sequential batch reactor (TmPNSBR) aimed to optimize the efficiency of PN for nitrogen removal in wastewater treatment. These results showed that Tm could reduce the time for PN establishment with a maximum reduction of 67.71% (Tm 8), maintained the stability of microbial community structure during the idle period, increased the ammonia oxidation rate, and promoted nitrite accumulation. Tm stimulated microorganisms to secrete more EPS (increase 7.92%–22.43% in phase I), and microorganisms adhere closely to the surface of Tm. Microbial community analysis showed that adding Tm could change the microbial community abundance and diversity, Tm increased the ammonia-oxidizing bacteria (AOB) abundance (increase 7.92%–22.43% in phase I) and decreased the nitrite-oxidizing bacteria (NOB) abundance. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt2) predicted increased content of key enzymes associated with PN and electron transport-related complexes. This study delved into the potential of Tm to mitigate environmental pollution as an efficient and environmentally friendly new material that optimizes the PN process, thereby contributing to the energy-efficient treatment of sustainable wastewater.

Growth of soil ammonia-oxidizing archaea on air-exposed solid surface.

Soil microorganisms often thrive as microcolonies or biofilms within pores of soil aggregates exposed to the soil atmosphere. However, previous studies on the physiology of soil ammonia-oxidizing microorganisms (AOMs), which play a critical role in the nitrogen cycle, were primarily conducted using freely suspended AOM cells (planktonic cells) in liquid media. In this study, we examined the growth of two representative soil ammonia-oxidizing archaea (AOA), Nitrososphaera viennensis EN76 and "Nitrosotenuis chungbukensis" MY2, and a soil ammonia-oxidizing bacterium, Nitrosomonas europaea ATCC 19718 on polycarbonate membrane filters floated on liquid media to observe their adaptation to air-exposed solid surfaces. Interestingly, ammonia oxidation activities of N. viennensis EN76 and "N. chungbukensis" MY2 were significantly repressed on floating filters compared to the freely suspended cells in liquid media. Conversely, the ammonia oxidation activity of N. europaea ATCC 19718 was comparable on floating filters and liquid media. N. viennensis EN76 and N. europaea ATCC 19718 developed microcolonies on floating filters. Transcriptome analysis of N. viennensis EN76 floating filter-grown cells revealed upregulation of unique sets of genes for cell wall and extracellular polymeric substance biosynthesis, ammonia oxidation (including ammonia monooxygenase subunit C (amoC3) and multicopper oxidases), and defense against H2O2-induced oxidative stress. These genes may play a pivotal role in adapting AOA to air-exposed solid surfaces. Furthermore, the floating filter technique resulted in the enrichment of distinct soil AOA communities dominated by the "Ca. Nitrosocosmicus" clade. Overall, this study sheds light on distinct adaptive mechanisms governing AOA growth on air-exposed solid surfaces.

Characterization of Enterobacter cloacae CAUCoF_BF_01: an autochthonous heterotrophic nitrifying strain from culture ponds for biofloc applications

The biofloc environment needs specific heterotrophic nitrifying bacteria for optimal system performance, hence screening perfect bacterial strains is crucial. Enterobacter cloacae sp. was identified as a novel heterotrophic bacterium isolated from freshwater pond sediment during July, 2022. Through high-throughput sequencing, the isolated bacterium was identified as E. cloacae CAUCoF_BF_01, which demonstrated potential nitrogen removal via heterotrophic nitrification and aerobic denitrification, as well as a preference for different C/N ratios (C/N10, 15, 20, and 25) for consuming nitrogen sources. The bacteria performed superior (p < 0.05) ammonia-N and nitrite-N removal in C/N20, with efficiencies of 91.70% and 91.0%, respectively. C/N15, on the other hand, had higher nitrate-N removal efficiency (69.20%). Furthermore, the optimum temperature for the chosen strain was determined to be 30 °C. This strain, on the other hand, can thrive in temperatures ranging from 20 to 37 °C and pH levels ranging from 6 to 10. Furthermore, the biofilm test reveals that the selected bacterial strain has the potential to form biofilm via extracellular polymeric compound secretion, besides passing ecological safety requirement. The current investigation will be helpful in the development of a successful biofloc-based probiotic for managing system generated ammonia to an optimal level, as well as floc production to maximize system efficiency.

Novel strategies for enhancing energy metabolism and wastewater treatment in algae-bacteria symbiotic system through carbon dots-induced photogenerated electrons: The definitive role of accelerated electron transport

The nitrogen removal efficiency of the algae-bacteria symbiotic system (ABSS) remains challenging due to competition for light capture and insufficient electron donors in aquaculture wastewater. To overcome this bottleneck issue, we first identified and reported the introduction of photogenerated electrons into ABSS by coupling them with carbon dots (CDs). The energy metabolism (21.52 %-56.25 %) and pollutant degradation efficiency (89.36 %-96.42 %) of ABSS/CDs surpassed the biochemical limit observed in traditional ABSS. Notably, the addtion of CDs facilitated an opening of the plastoquinone-pool (PQ-pool) valve and accelerated electron transfer rates, enabling photogenerated electrons to selectively target light-harvesting complexs as activation sites, thereby mobilizing photosynthesis and respiratory system activity to enhance nicotinamide adenine dinucleotide reduced (NADH) and adenosine triphosphate (ATP) production while promoting tricarboxylic acid (TCA) and Calvin cycle processes. In simulated swine wastewater treatment, ABSS/CDs achieved higher removal rates for the chemical oxygen demand (COD), total nitrogen (TN) and ammonium-nitrogen (NH4+-N) (100 %, 99.23 % and 98.62 % respectively) compared to pure culture systems alone. Network-based analysis revealed that ABSS/CDs improved microbial community structure stability within the photobioreactor while demonstrating efficient coupling between fungi, nitrifying bacteria, and denitrifying bacteria for enhanced performance in nitrogen removal processes. The upregulation of nitrogen metabolism and PQ-pool genes maintains efficient electron transport rates and contributes to nitrogen removal. This study expands our understanding of the physiological aptitudes of ABSS and provides valuable insights into applying CDs photoelectrons for enhanced wastewater treatment.

Understanding nitrogen removal and N2O emission mechanisms in an anaerobic-swing-anoxic-oxic (ASAO) continuous plug-flow system for low C/N municipal wastewater

This study aims to investigate effects of dissolved oxygen (DO) levels and aerated hydrodynamic retention time (HRT) on nitrogen removal and nitrous oxide (N2O) emissions in a novel anaerobic-swing-anoxic-oxic (ASAO) continuous plug-flow system for treating low carbon to nitrogen ratio municipal wastewater. The swing zones had varying DO levels and volumes, deciding the aerated HRT of the ASAO system. Results showed that low DO level (0.8–1.0 mg/L) and short aerated HRT led to high nitrogen removal performance (91.4 %–96.3 %) and low N2O emission factor (2.8 %). The simultaneous nitrification and denitrification (SND) in swing zones and endogenous denitrification in anoxic zones contributed to the nitrogen removal. Meanwhile, the SND and autotrophic denitrification processes were identified as the N2O sources. Low DO level enriched ammonia-oxidizing bacteria and enhanced the SND and autotrophic denitrification pathway. These findings suggest that the ASAO system is promising for reducing carbon emissions in municipal wastewater treatment.

Microalgae Enhance the Resistance of Pond-Dwelling Ammonia-Oxidizing Bacteria to Light Irradiation

Pond aquaculture is an important aquacultural model worldwide in which ammonia-oxidizing bacteria (AOB) are crucial for the removal of ammonia from water. The influence of light irradiation on AOB in an aquaculture pond was studied using artificial simulation wastewater under dark/light cycles of 24 h/0 h (L0), 12 h/12 h (L12), and 0 h/24 h (L24). The ammonia oxidation rates (AORs) in groups L0, L12, and L24 were 9.88 ± 0.19 mg h−1, 6.01 ± 0.32 mg h−1, and 1.85 ± 0.09 mg h−1, respectively. Long-term exposure to light had a serious impact on the AOR and decreased the abundance of Nitrosomonas spp. and their ammonia monooxygenase genes. To determine the protective effect of microalgae on AOB, different doses of freeze-dried Chlorella spp. powder were added to the nitrifying bacteria community. The photoinhibition rate of chlorophyll a (Chla) in the groups with 300 and 1300 µg L−1 of added Chlorella were 32.85% and 28.77%, respectively, while the Chla in the 2200 µg L−1 Chlorella-added group was only 0.01%, with no significant differences (p &gt; 0.05) in AOR between the dark/light treatment subgroups. Fluorescence in situ hybridization showed that AOB, nitrite-oxidizing bacteria, and algae coexist and grow together without free AOB in the nitrifying bacterial community. It was suggested that microalgae enhance the resistance of AOB to light irradiation in a pond through the shading effect provided by algal chlorophyll and the close symbiotic relationship between microalgae and AOB.

Enhancing low-temperature nitrification biofilter with Acinetobacter harbinensis HITLi7T for efficient ammonia nitrogen removal in engineering applications

Low temperature has always been a significant limitation for the biological removal of ammonia nitrogen (NH3-N) from water. Acinetobacter harbinensis HITLi7T (HITLi7T) was used to enhance the low-temperature nitrification biofilter (LTNB) with a treatment capacity of 20,000 m3/d. At 2 °C, with an empty bed contact time of 3 h, the LTNB achieved NH3-N removal levels of 1.2 ∼ 1.5 mg/L. The nitrifying bacteria (Nitrosomonas, Nitrosospira, Nitrospira and Candidatus_Nitrotoga) were significantly enriched. PICRUSt2 and FAPROTAX revealed the nitrification pathway of NH3-N conversion to hydroxylamine, then to nitrite, and finally to nitrate. The high co-occurrence of HITLi7T with the nitrifying bacteria suggested that HITLi7T might also promote the enrichment of nitrifying bacteria. Life cycle assessment showed that LTNB was an economical and environmentally friendly method for NH3-N removal. These results indicated that HITLi7T enhanced the nitrification performance of biofilters, improved the cold tolerance of nitrifying bacteria, and had potential for practical applications.

Activity of novel virus families infecting soil nitrifiers is concomitant with host niche differentiation.

Chemolithoautotrophic nitrifiers are model groups for linking phylogeny, evolution, and ecophysiology. Ammonia-oxidising bacteria (AOB) typically dominate the first step of ammonia oxidation at high ammonium supply rates, ammonia-oxidising archaea (AOA) and complete ammonia-oxidising Nitrospira (comammox) are often active at lower supply rates or during AOB inactivity, and nitrite-oxidising bacteria (NOB) complete canonical nitrification. Soil virus communities are dynamic but contributions to functional processes are largely undetermined. In addition, characterising viruses infecting hosts with low relative abundance, such as nitrifiers, may be constrained by vast viral diversity, partial genome recovery, and difficulties in host linkage. Here, we describe a targeted incubation study that aimed to determine whether growth of different nitrifier groups in soil is associated with active virus populations and if process-focussed analyses facilitate characterisation of high-quality virus genomes. dsDNA viruses infecting different nitrifier groups were enriched in situ via differential host inhibition. Growth of each nitrifier group was consistent with predicted inhibition profiles and concomitant with the abundance of their viruses. These included 61 high-quality/complete virus genomes 35-173kb in length with minimal similarity to validated families. AOA viruses lacked ammonia monooxygenase sub-unit C (amoC) genes found in marine AOA viruses but some encoded AOA-specific multicopper oxidase type 1 (MCO1), previously implicated in copper acquisition, and suggesting a role in supporting energy metabolism of soil AOA. Findings demonstrate focussed incubation studies facilitate characterisation of active host-virus interactions associated with specific processes and viruses of soil AOA, AOB and NOB are dynamic and potentially influence nitrogen cycling processes.