Missing lithotroph identified as new planctomycete

Niche Differentiation of Aerobic and Anaerobic Ammonia Oxidizers in a High Latitude Deep Oxygen Minimum Zone

To elucidate the potential for nitrification and denitrification processes in a high latitude deep oxygen minimum zone (OMZ) we determined the abundance and community composition of the main microbial players in the aerobic and anaerobic (anammox) ammonium oxidation and denitrification processes in the Gulf of Alaska throughout the water column. Within the dominant bacterial groups, Flavobacterales, Rhodobacterales, Actinomarinales, and SAR86 were more abundant in epipelagic waters and decreased with depth, whereas SAR11, SAR324, Marinimicrobia, and Thiomicrospirales increased their contribution to the bacterial community with depth. Nitrosopumilaceae also increased with depth and dominated the OMZ and bathypelagic archaeal communities. Euryarchaeota Marine Group II exhibited an opposite depth pattern to Nitrosopumilaceae, whereas Marine Group III and Woesearchaeota were more abundant in the bathypelagic realm. Candidatus Brocadia contributed 70-100% of the anammox bacterial community throughout the water column. Archaeal ammonia oxidizers (AOA) dominated the microbial community involved in the nitrogen cycle. Two AOA ecotypes, the high ammonia (HAC) and low ammonia (LAC)-AOA, characterized by distinct genes for aerobic ammonia oxidation (amoA) and for denitrification (nirK), exhibited a distinct distribution pattern related to depth and ammonia concentrations. HAC-AOA dominated in epipelagic (80.5 ± 28.3% of total AOA) oxygenated and ammonia-rich waters, and LAC-AOA dominated in the OMZ (90.9 ± 5.1%) and bathypelagic waters (85.5 ± 13.5%), characterized by lower oxygen and ammonia concentrations. Bacterial denitrifiers (3.7 ± 6.9 bacterial nirK gene mL-1) and anaerobic ammonia oxidizers (78 ± 322 anammox 16S rRNA genes L-1) were low in abundance under the oxygen conditions in the Gulf of Alaska throughout the water column. The widespread distribution of bacterial denitrifiers and anaerobic ammonia oxidizers in low abundances reveals a reservoir of genetic and metabolic potential ready to colonize the environment under the predicted increase of OMZs in the ocean. Taken together, our results reinforce the niche partitioning of archaeal ammonia oxidizers based on their distinct metabolic characteristics resulting in the dominance of LAC-AOA in a high latitude deep OMZ. Considering the different ecological roles and functions of the two archaeal ecotypes, the expansion of the zones dominated by the LAC-ecotype might have implications for the nitrogen cycle in the future ocean.

Nitrogen removal performance of marine anammox bacteria treating nitrogen-rich saline wastewater under different inorganic carbon doses: High inorganic carbon tolerance and carbonate crystal formation

With different inorganic carbon (IC) doses, nitrogen removal performance of marine anammox bacteria (MAB) treating nitrogen-rich saline wastewater was investigated in a sequencing batch reactor. Ammonium removal efficiency (ARE) was above 99% at 108-3600 mg/L IC, which indicated MAB had a good tolerance to high IC dose. When IC was 108-1200 mg/L, ARE reached 90% within 2.5 h. MAB activity was greatly promoted by providing adequate IC. Besides, the maximal substrate conversion rate (3.4 kg/(m³ d)) was achieved at 180 mg/L IC. Both the modified Logistic and Boltzmann models were appropriate to describe nitrogen removal at low IC doses, while the modified Gompertz model was more accurate at high IC doses. Calcium carbonate crystal was formed on the surface of MAB granule at high IC doses, which resulted in a significant deterioration of nitrogen removal performance.

Exploring the effects of operational mode and microbial interactions on bacterial community assembly in a one-stage partial-nitritation anammox reactor using integrated multi-omics

BACKGROUND

The metabolic capacities of anammox bacteria and associated microbial community interactions in partial-nitritation anammox (PNA) reactors have received considerable attention for their crucial roles in energy-efficient nitrogen removal from wastewater. However, a comprehensive understanding of how abiotic and biotic factors shape bacterial community assembly in PNA reactors is not well reported.

RESULTS

Here, we used integrated multi-omics (i.e., high-throughput 16S rRNA gene, metagenomic, metatranscriptomic, and metaproteomic sequencing) to reveal how abiotic and biotic factors shape the bacterial community assembly in a lab-scale one-stage PNA reactor treating synthetic wastewater. Analysis results of amplicon sequences (16S rRNA gene) from a time-series revealed distinct relative abundance patterns of the key autotrophic bacteria, i.e., anammox bacteria and ammonia-oxidizing bacteria (AOB), and the associated heterotrophic populations in the seed sludge and the sludge at the new stable state after deterioration. Using shotgun metagenomic sequences of anammox sludge, we recovered 58 metagenome-assembled genomes (MAGs), including 3 MAGs of anammox bacteria and 3 MAGs of AOB. The integrated metagenomic, metatranscriptomic, and metaproteomic data revealed that nitrogen metabolism is the most active process in the studied PNA reactor. The abundant heterotrophs contribute to the reduction of nitrate to nitrite/ammonium for autotrophic bacteria (anammox bacteria and AOB). Genomic and transcriptomic data revealed that the preference for electron donors of the dominant heterotrophs in different bacterial assemblages (seed and new stable state) varied along with the shift in anammox bacteria that have different metabolic features in terms of EPS composition. Notably, the most abundant heterotrophic bacteria in the reactor were more auxotrophic than the less abundant heterotrophs, regarding the syntheses of amino acids and vitamins. In addition, one of the abundant bacteria observed in the bacterial community exhibited highly transcribed secretion systems (type VI).

CONCLUSIONS

These findings provide the first insight that the bacterial communities in the PNA reactor are defined by not only abiotic factors (operating mode) but also metabolic interactions, such as nitrogen metabolism, exchange of electron donors, and auxotrophies.

Geochemical and Metagenomic Characterization of Jinata Onsen, a Proterozoic-Analog Hot Spring, Reveals Novel Microbial Diversity including Iron-Tolerant Phototrophs and Thermophilic Lithotrophs

Hydrothermal systems, including terrestrial hot springs, contain diverse geochemical conditions that vary over short spatial scales due to progressive interactions between reducing hydrothermal fluids, the oxygenated atmosphere, and, in some cases, seawater. At Jinata Onsen on Shikinejima Island, Japan, an intertidal, anoxic, iron-rich hot spring mixes with the oxygenated atmosphere and seawater over short spatial scales, creating diverse chemical potentials and redox pairs over a distance of ~10 m. We characterized geochemical conditions along the outflow of Jinata Onsen as well as the microbial communities present in biofilms, mats, and mineral crusts along its traverse using 16S rRNA gene amplicon and genome-resolved shotgun metagenomic sequencing. Microbial communities significantly changed downstream as temperatures and dissolved iron concentrations decreased and dissolved oxygen increased. Biomass was more limited near the spring source than downstream, and primary productivity appeared to be fueled by the oxidation of ferrous iron and molecular hydrogen by members of Zetaproteobacteria and Aquificae. The microbial community downstream was dominated by oxygenic Cyanobacteria. Cyanobacteria are abundant and active even at ferrous iron concentrations of ~150 μM, which challenges the idea that iron toxicity limited cyanobacterial expansion in Precambrian oceans. Several novel lineages of Bacteria are also present at Jinata Onsen, including previously uncharacterized members of the phyla Chloroflexi and Calditrichaeota, positioning Jinata Onsen as a valuable site for the future characterization of these clades.

Enhancing biotreatment of incineration leachate by applying an electric potential in a partial nitritation-Anammox system

An electric potential (EP) was applied to enhance biotreatment of anaerobically-treated leachate from municipal solid waste incineration plants using a partial nitritation-Anammox system. At an optimal EP difference of 0.06 V, total nitrogen removal efficiency reached 71.9%, 17.3% higher than the control system without an EP. Removal of organic matter was also stimulated with the EP, particularly macromolecules with molecular weight >20 kDa in the leachate. Applying EP also promoted production of extracellular polymeric substances and improved the protein/polysaccharide ratio. High-throughput DNA sequencing revealed that Anammox bacteria in the genus Candidatus Kuenenia were enriched for on electrodes with the applied EP. Heterotrophic denitrifiers, which potentially could degrade organic macromolecules, were also more abundant on the electrodes with EP compared with the control reactor. These results show that applying an EP could be a useful strategy in Anammox technologies treating real wastewater high in ammonia and refractory organic compounds.

NanoSIMS reveals unusual enrichment of acetate and propionate by an anammox consortium dominated by Jettenia asiatica

Anaerobic ammonium-oxidizing (anammox) bacteria convert ammonium and nitrite into N₂ in a chemolithoautotrophic way, meaning that they utilize CO₂/HCO₃ solely as their carbon sources. Such autotrophic behavior limits their competitiveness with heterotrophic microorganisms in both natural environments and engineered systems. Recently, environmental metagenomic results have indicated the capability of anammox bacteria to metabolize short-chain fatty acids, further confirmed by limited experimental evidence based on highly enriched cultures. However, clear evidence is difficult to get because of the limits of traditional methodologies which rely on the availability of a pure anammox culture. In this study, we identified and quantified the uptake of acetate and propionate, on a single-cell level, by an anammox consortium that was dominated by Candidatus Jettenia asiatica (relative abundance of 96%). The consortium, growing in granular form with an average relative abundance of anammox bacteria of 96.0%, was firstly incubated in a¹³C-labelled acetate or propionate medium; then microtome sections were scanned by a nanometer-scale secondary ion mass spectrometer (NanoSIMS). The NanoSIMS scannings revealed that the consortium enriched acetate and propionate at a >10 times higher efficiency than bicarbonate incorporation. Our results also suggest that acetate or propionate was likely not assimilated by J. asiatica directly, but firstly oxidized to CO₂, which then served as carbon sources for the follow-up autotrophy in J. asiatica cells. Furthermore, more [¹⁵N]ammonium was enriched by the propionate-fed consortium than the acetate-fed consortium despite that exactly the same amount of ¹³C atoms were supplied. Our study strongly indicates an alternative lifestyle, namely organotrophy, in addition to chemolithoautotrophy of anammox bacteria, making it more versatile than often expected. It suggests that the niche of anammox bacteria in both natural and engineered ecosystems can be much broader than usual assumed. Recognising this is important for their role in wastewater treatment and the global nitrogen turn-over rates.

Anammox microbial community and activity changes in response to water and dissolved oxygen managements in a paddy-wheat soil of Southern China

Anammox are unusual members of the microbial community contributing to N losses via anaerobic ammonium oxidation. Anammox use nitrite as a substrate and produce hydrazine as an intermediate product. Up to date, the effects of dissolved oxygen and moisture dynamics on anammox potential and microbial community in agricultural soils were poorly understood. In this study, we investigated the interaction of dissolved oxygen and moisture contents as factors affecting the soil anammox process. The experiment had four fertilization treatments i.e. Control (CK), Chemical fertilizer (CF), Pig composted manure plus chemical fertilizer (PMCF), and Straw returned to soil plus chemical fertilizer (SRCF) with different water contents, 70%-FC, Alternate wetting and drying (AWD), Flooding I (D.O 5.8 mg L^-1), and Flooding II (D.O 2.6 mg L^-1). ¹⁵N-isotopic tracer technique was used to evaluate the anammox and denitrification rates. The results showed that the anammox rate ranged from the lowest 0.56 nmol N₂·g^-1·h^-1 in CF (with 70% FC water) to the highest rate of 1.47 nmol N₂·g^-1·h^-1 in SRCF (with flooding II). In water treatments, the average lowest and highest anammox rates were in the 70% FC (0.61 nmol N₂·g^-1·h^-1) and Flooding II (1.14 nmol N₂·g^-1·h^-1), respectively. Moreover, under soil treatments, the minimum average anammox rate was found in the PMCF (0.76 nmol N₂·g^-1·h^-1) and maximum in the SRCF (1.01 nmol N₂·g^-1·h^-1). Interestingly, anammox genes copy numbers were highest in alternate wetting and drying conditions under all fertilizer treatments rather than in continuous flooding. The phylogenetic analysis showed that Ca. Brocadia was dominating while some of Ca. Jettenia was also present. In conclusion, alternate wetting and drying could increase the number of anammox bacteria and microbial diversity.

Effects of Ca2+ Concentration on Anaerobic Ammonium Oxidation Reactor Microbial Community Structure

The anaerobic ammonium oxidation (anammox) reaction removes nitrogen from wastewater, the performance of which is influenced by Ca2+; however, the effect of Ca2+ on microbial community structure is unclear. Therefore, the effects of Ca2+ concentration on the treatment performance of an anammox reactor and microbial community structure of anammox sludge were investigated. Ca2+ concentration minimally influenced the removal efficiency of NO2−–N and NH4+–N, but substantially influenced total N removal. Changing the Ca2+ concentration (between 25 and 125 mg/L) caused the average removal rate of total nitrogen to fluctuate by 3.3 percentage points. There were five major bacterial phyla in the anammox sludge: Proteobacteria, Chloroflexi, Acidobacteria, Planctomycete, and Chlorobi. Microbiological analysis revealed that the genera Acidobacterium, Anaerolinea, and Denitratisoma were positively correlated with Ca2+ concentration, and improved treatment performance of the anammox reactor. Moreover, uncultured Chlorobi bacterium clone RUGL1-218 (GQ421108.1) and uncultured sludge bacterium A21b (KT182572.1) may be key microorganisms for the immobilization of anammox bacteria. These findings offer a theoretical basis for improved wastewater treatment using the anammox process.

Accomplishing a N-E-W (nutrient-energy-water) synergy in a bioelectrochemical nitritation-anammox process

This study reports an investigation of the concept, application and performance of a novel bioelectrochemical nitritation-anammox microbial desalination cell (MDC) for resource-efficient wastewater treatment and desalination. Two configurations of anammox MDCs (anaerobic-anammox cathode MDC (AnA_moxMDC) and nitration-anammox cathode MDC (NiA_moxMDC)) were compared with an air cathode MDC (CMDC), operated in fed-batch mode. Results from this study showed that the maximum power density produced by NiA_moxMDC (1,007 mW/m³) was higher than that of AnA_moxMDC (444 mW/m³) and CMDC (952 mW/m³). More than 92% of ammonium-nitrogen (NH₄⁺-N) removal was achieved in NiA_moxMDC, significantly higher than AnA_moxMDC (84%) and CMDC (77%). The NiA_moxMDC performed better than CMDC and AnA_moxMDC in terms of power density, COD removal and salt removal in desalination chamber. In addition, cyclic voltammetry analysis of anammox cathode showed a redox peak centered at -140 mV Vs Ag/AgCl confirming the catalytic activity of anammox bacteria towards the electron transfer process. Further, net energy balance of the NiA_moxMDC was the highest (NiA_moxMDC-0.022 kWh/m³ >CMDC-0.019 kWh/m³ >AnA_moxMDC-0.021 kWh/m³) among the three configurations. This study demonstrated, for the first time, a N-E-W synergy for resource-efficient wastewater treatment using nitritation-anammox process.

Interactions between anaerobic ammonium- and methane-oxidizing microorganisms in a laboratory-scale sequencing batch reactor

The reject water of anaerobic digestors still contains high levels of methane and ammonium that need to be treated before these effluents can be discharged to surface waters. Simultaneous anaerobic methane and ammonium oxidation performed by nitrate/nitrite-dependent anaerobic methane-oxidizing(N-damo) microorganisms and anaerobic ammonium-oxidizing(anammox) bacteria is considered a potential solution to this challenge. Here, a stable coculture of N-damo archaea, N-damo bacteria, and anammox bacteria was obtained in a sequencing batch reactor fed with methane, ammonium, and nitrite. Nitrite and ammonium removal rates of up to 455 mg N-NO₂^- L^-1 day^-1 and 228 mg N-NH₄⁺ L^-1 were reached. All nitrate produced by anammox bacteria (57 mg N-NO₃^- L^-1 day^-1) was consumed, leading to a nitrogen removal efficiency of 97.5%. In the nitrite and ammonium limited state, N-damo and anammox bacteria each constituted about 30-40% of the culture and were separated as granules and flocs in later stages of the reactor operation. The N-damo archaea increased up to 20% and mainly resided in the granular biomass with their N-damo bacterial counterparts. About 70% of the nitrite in the reactor was removed via the anammox process, and batch assays confirmed that anammox activity in the reactor was close to its maximal potential activity. In contrast, activity of N-damo bacteria was much higher in batch, indicating that these bacteria were performing suboptimally in the sequencing batch reactor, and would probably be outcompeted by anammox bacteria if ammonium was supplied in excess. Together these results indicate that the combination of N-damo and anammox can be implemented for the removal of methane at the expense of nitrite and nitrate in future wastewater treatment systems.

Strategy of rapid start-up and the mechanism of de-nitrogen in landfill bioreactor

Nitrogen removal from landfill leachate via anaerobic ammonium oxidation (Anammox) process has been considered as an innovative and sustainable approach to the traditional nitrification and denitrification process. However, the various technologies for rapid start-up of Anammox are still being explored. In this study, two strategies (inoculating anaerobic sludge and without inoculation) were applied to treat landfill leachate based on biological nitrogen removal processes. The start-up and mechanism of de-nitrogen process in landfill bioreactor was explored using ¹⁵N stable isotopic tracing, quantitative polymerase chain reaction (qPCR) and high-throughput sequencing methods. Results showed that inoculating anaerobic sludge was beneficial to enhance the nitrogen removal at the initial stage (from day 10 to day 25), but no significant increase was found during days 25-55 (p > 0.05). ¹⁵N stable isotopic tracing demonstrated that the inoculation of sludge accelerated by denitrification other than Anammox. Inoculation of sludge was conducive to increase of ammonia-oxidizing bacteria (AOB)- amoA and niK genes. Thauera was the dominant genus for nitrogen removal due to inoculation of sludge in landfill bioreactor, whereas the abundance of Candidatus Kuenenia did not increase by inoculating the sludge. Moreover, seeding anaerobic sludge could not provide Anammox's ecological niches. The results will provide a scientific basis for the selection of suitable operational condition for the rapid start-up in the landfill bioreactor.

Nitrifier abundance and diversity peak at deep redox transition zones

More than half of the global ocean floor is draped by nutrient-starved sediments characterized by deep oxygen penetration and a prevalence of oxidized nitrogen. Despite low energy availability, this habitat hosts a vast microbial population, and geochemical characteristics suggest that nitrogen compounds are an energy source critical to sustaining this biomass. However, metabolic rates of nitrogen transformation and their link to microbial survival in this global-scale ecosystem remain virtually unknown. Here we provide quantitative constraints on microbial nitrogen cycling in open ocean oligotrophic sediments from seafloor to basement, spanning approximately 8 million years. We find active microbial nitrogen transformation throughout the sediment column but at very low rates. Local peaks in diversity and abundance of nitrifiers and denitrifiers occur at redox transition zones deep within the sediments, strongly indicating that these microbes are revived from their maintenance state and start growing again after millions of years of attrition.

Identification of quorum sensing signal AHLs synthases in Candidatus Jettenia caeni and their roles in anammox activity

Acyl-homoserine lactone (AHL)-based quorum sensing (QS) in the anaerobic ammonium oxidizing (anammox) consortia has attracted increasing attention. However, AHL synthase in anammox bacteria and the relationship between AHL synthetic genes and anammox activity are still not clear because anammox bacteria have not been isolated from the consortia. Two novel synthases of AHLs (JqsI-1 and JqsI-2), which are HdtS-type rather than the widely studied LuxI-type, were identified in anammox bacteria Candidatus Jettenia caeni and synthesized four AHLs. There was a correlation between AHL concentration, in situ transcriptional expression of the AHL synthase genes (jqsI-1 and jqsI-2) and genetic marker of anammox activity (hydrazine synthase gene, hzsA). And AHL add-back studies demonstrated that AHL influence the expression of hzsA to regulate anammox bacterial activity. This study provides insight into the QS communication pathway of anammox bacteria for wastewater treatment.

Dual nitrogen and oxygen isotope fractionation during anaerobic ammonium oxidation by anammox bacteria

Natural abundance of stable nitrogen (N) and oxygen (O) isotopes are invaluable biogeochemical tracers for assessing the N transformations in the environment. To fully exploit these tracers, the N and O isotope effects (¹⁵ε and ¹⁸ε) associated with the respective nitrogen transformation processes must be known. However, the N and O isotope effects of anaerobic ammonium oxidation (anammox), one of the major fixed N sinks and NO₃^- producers, are not well known. Here, we report the dual N and O isotope effects associated with anammox by three different anammox bacteria including "Ca. Scalindua japonica", a putative marine species, which were measured in continuous enrichment culture experiments. All three anammox species yielded similar N isotope effects of NH₄⁺ oxidation to N₂ (¹⁵ε_NH4→N2) ranging from 30.9‰ to 32.7‰ and inverse kinetic isotope effects of NO₂^- oxidation to NO₃^- (¹⁵ε_NO2→NO3 = -45.3‰ to -30.1‰). In contrast, ¹⁵ε_NO2→N2 (NO₂^- reduction to N₂) were significantly different among three species, which is probably because individual anammox bacteria species might possess different types of nitrite reductase. We also report the combined O isotope effects for NO₂^- oxidation (¹⁸E_NO2→NO3) by anammox bacteria. These obtained dual N and O isotopic effects could provide significant insights into the contribution of anammox bacteria to the fixed N loss and NO₂^- reoxidation (N recycling) in various natural environments.

Sweating the assets - The role of instrumentation, control and automation in urban water systems

Instrumentation, control and automation (ICA) are currently applied throughout the urban water system at water treatment plants, in water distribution networks, in sewer networks, and at wastewater treatment plants. However, researchers and practitioners specialising in respective urban water sub-systems do not frequently interact, and in most cases to date the application of ICA has been achieved in silo. Here, we review start-of-the-art ICA throughout these sub-systems, and discuss the benefits achieved in terms of performance improvement, cost reduction, and more importantly, the enhanced capacity of the existing infrastructure to cope with increased service demand caused by population growth and continued urbanisation. We emphasise the importance of integrated control within each of the sub-systems, and also across the entire urban water system. System-wide ICA will have increasing importance with the growing complexity of the urban water environment in cities of the future.

Abundance and diversity of nitrogen-removing microorganisms in the UASB-anammox reactor

Anaerobic ammonium oxidation is considered to be the most economical and low-energy biological nitrogen removal process. So far, anammox bacteria have not yet been purified from cultures. Some nitrogen-removing microorganisms cooperate to perform the anammox process. The objective of this research was to analyze the abundance and diversity of nitrogen-removing microorganisms in an anammox reactor started up with bulking sludge at room temperature. In this study, the ammonia-oxidizing archaea phylum Crenarchaeota was enriched from 9.2 to 53.0%. Nitrosomonas, Nitrosococcus, and Nitrosospira, which are ammonia-oxidizing bacteria, increased from 3.2, 1.7, and 0.1% to 12.8, 20.4, and 3.3%, respectively. Ca. Brocadia, Ca. Kuenenia, and Ca. Scalindua, which are anammox bacteria, were detected in the seeding sludge, accounting for 77.1, 11.5, and 10.6%. After cultivation, the dominant genus changed to Ca. Kuenenia, accounting for 82.0%. Nitrospirae, nitrite oxidation bacteria, decreased from 2.2 to 0.1%, while denitrifying genera decreased from 12.9 to 2.1%. The results of this study contribute to the understanding of nitrogen-removing microorganisms in an anammox reactor, thereby facilitating the improvement of such reactors. However, the physiological and metabolic functions of the ammonia-oxidizing archaea community in the anammox reactor need to be investigated in further studies.

Enhancing mainstream nitrogen removal by employing nitrate/nitrite-dependent anaerobic methane oxidation processes

Due to serious eutrophication in water bodies, nitrogen removal has become a critical stage for wastewater treatment plants (WWTPs) over past decades. Conventional biological nitrogen removal processes are based on nitrification and denitrification (N/DN), and are suffering from several major drawbacks, including substantial aeration consumption, high fugitive greenhouse gas emissions, a requirement for external carbon sources, excessive sludge production and low energy recovery efficiency, and thus unable to satisfy the escalating public needs. Recently, the discovery of anaerobic ammonium oxidation (anammox) bacteria has promoted an update of conventional N/DN-based processes to autotrophic nitrogen removal. However, the application of anammox to treat domestic wastewater has been hindered mainly by unsatisfactory effluent quality with nitrogen removal efficiency below 80%. The discovery of nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) during the last decade has provided new opportunities to remove this barrier and to achieve a robust system with high-level nitrogen removal from municipal wastewater, by utilizing methane as an alternative carbon source. In the present review, opportunities and challenges for nitrate/nitrite-dependent anaerobic methane oxidation are discussed. Particularly, the prospective technologies driven by the cooperation of anammox and n-DAMO microorganisms are put forward based on previous experimental and modeling studies. Finally, a novel WWTP system acting as an energy exporter is delineated.

Resuscitation of anammox bacteria after >10,000 years of dormancy

Water is essential for life on Earth, and an important medium for microbial energy and metabolism. Dormancy is a state of low metabolic activity upon unfavorable conditions. Many microorganisms can switch to a metabolically inactive state after water shortage, and recover once the environmental conditions become favorable again. Here, we resuscitated dormant anammox bacteria from dry terrestrial ecosystems after a resting period of >10 ka by addition of water without any other substrates. Isotopic-tracer analysis showed that water induced nitrate reduction yielding sufficient nitrite as substrate and energy for activating anammox bacteria. Subsequently, dissimilatory nitrate reduction to ammonium (DNRA) provided the substrate ammonium for anammox bacteria. The ammonium and nitrite formed were used to produce dinitrogen gas. High throughput sequencing and network analysis identified Brocadia as the dominant anammox species and a Jettenia species seemed to connect the other community members. Under global climate change, increasing precipitation and soil moisture may revive dormant anammox bacteria in arid soils and thereby impact global nitrogen and carbon cycles.

Investigation of COD and COD/N ratio for the dominance of anammox pathway for nitrogen removal via isotope labelling technique and the relevant bacteria

This study aimed to investigate the importance of COD (chemical oxygen demand) and ratio of COD and nitrogen (COD/N) in influencing the dominance of anammox pathway to N-removal in anammox systems, which had been widely researched and results were not yet conclusive. Results showed that N-removal efficiency increased with increasing organic substrate, while the anammox contribution to N-removal decreased as confirmed by isotope labelling technique. Excessively high TN (total nitrogen) concentrations were detrimental to N-removal, and TN of 600 mg L^-1 was optimized. Specific COD of 300 mg L^-1 (a threshold value above which anammox was less active) was synergistic for N-removal. Moreover, Illumina sequencing and qPCR techniques uncovered that while the microbial community composition was relatively stable for all treatments, abundances of denitrifier were positively correlated with increase of COD, which was counter-productive for anammox abundance. Structure equation model indicated that COD was more important with respect to maintain the anammox stability than the COD/N ratio. Furthermore, experiment and model fittings revealed that anammox contributed more than 80% of N-removal when COD was below 55.7 mg L^-1, and approximately 50% at 220-300 mg L^-1 COD, respectively. These data formed a reference for regulation of anammox systems in real-world applications.

Quick start-up and stable operation of a one-stage deammonification reactor with a low quantity of AOB and ANAMMOX biomass

In this study, a quick start-up of one-stage deammonification in an immobilized aerobic ammonium oxidizing bacteria (AOB) and anoxic ammonium oxidizing (ANAMMOX) bacteria up-flow reactor (IAAR) was successfully achieved. With the aid of gel layers, AOB and ANAMMOX bacteria had excellent spatial distribution, theoretically meeting dissolved oxygen requirements for the simultaneous processes of aerobic and anaerobic ammonium oxidizing. The results indicated that an IAAR containing 0.4 g-VSS L^-1 immobilized biomass achieved a nitrogen removal rate (NRR) of 0.53 kg-N m^-3 d^-1 after only 10 days of operation and subsequently reached a maximum nitrogen removal rate (NRR_max) of 3.73 kg-N m^-3 d^-1. The micro-profiles of DO and pH were measured using microelectrodes to help understand the stratification of the microbial processes inside the gel layers. The distribution of AOB and ANAMMOX bacteria within the gel layers was verified using fluorescence in situ hybridization (FISH) analysis. The community distribution in the FISH three-dimensional images closely corresponded to the micro-profiles of DO concentration and pH, enabling rapid adaptation and stable operation of the reactor seeded with a quite low quantity of biomass.

The revolution of performance, sludge characteristics and microbial community of anammox biogranules under long-term NiO NPs exposure

Given the increasing applications of NiO nanoparticles (NPs) in battery products, the potential effects of NiO NPs on anaerobic ammonium oxidation (anammox) systems were studied for the first time. The results showed that the anammox system performance obviously differed under the stresses of different NiO NPs concentrations. After the withdrawal of NiO NPs, the nitrogen removal performance of the anammox reactor returned to nearly that of the initial phase within 35 days. Compared with 0 mg L^-1 NiO NPs, the specific anammox activity first increased and then decreased to the minimum value of 116.8 ± 13.8 mg TN g^-1 VSS d^-1 at 60 mg L^-1 NiO NPs. The variations in the heme c contents and extracellular polymeric substance amounts were similar to the variations in the specific anammox activity throughout the whole experiment. Additionally, the relative abundance of the dominant bacteria (Candidatus kuenenia) increased from 20.44% at 60 mg L^-1 NiO NPs to 23.14% at the end of the last phase. Thus, the potential effects of NiO NPs on anammox systems should be a cause for great concern.

Piggery wastewater treatment by aerobic granular sludge: Granulation process and antibiotics and antibiotic-resistant bacteria removal and transport

The aim of this work was to study the responses of aerobic granulation process to antibiotics and investigate the antibiotics and antibiotic-resistant bacteria (ARB) removal and transport. Results showed that aerobic granular sludge (AGS) was dominant in the bioreactor at day 45, and the relatively high protein content from tightly bound extracellular polymeric substances (TB-EPS) facilitated aerobic granulation and maintained biomass stabilization. The protein contents in EPS and TB-EPS were positively correlated with relative hydrophobicity, thereby improving the adsorption capacity among hydrophobic particles. The chemical oxygen demand (COD), NH₃-N, and total N removal efficiencies were 98.0%, 97.0%, and 92.4%, respectively. Five antibiotics, including kanamycin, tetracycline, ciprofloxacin, ampicillin, and erythromycin, were examined in piggery wastewater, with concentrations up to the concentration range of 29.4-44.1 µg/l, and the total antibiotics removal rate reached up to 88.4% ± 4.5%. A total of 5.2% of the total antibiotics were discharged from bioreactor, and 62.5% of the total antibiotics were degraded, and 32.3% of total antibiotics were adsorbed by aerobic granules. The presence of antibiotics rarely exhibited an influence on AGS formation, and the relatively high microbial activity of aerobic granules was beneficial to antibiotics removal. The ARB removal rate increased up to 89.4% ± 3.3%, but a large amount of ARB was enriched in aerobic granules.

Effect of temperature on nitrogen removal and biological mechanism in an up-flow microaerobic sludge reactor treating wastewater rich in ammonium and lack in carbon source

Previous study has demonstrated that microaerobic process is effective in nitrogen removal from the wastewater with high ammonium and low carbon to nitrogen ratio. In the microaerobic system, synergistic action of anammox, ammonia oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB) and denitrifiers was the key issues to remove nitrogen from the wastewater rich in ammonium. Temperature has a significant effect on specific growth rate and activity of various nitrogen removal functional bacteria. In this study, the effect of temperature (35 °C-15 °C) on nitrogen removal were investigated in an up-flow microaerobic sludge reactor (UMSR) at the HRT of 8 h and reflux ratio of 45. Above 71.2% of total nitrogen (TN) and 80.7% of NH₄⁺ removal efficiencies were observed at the temperature no less than 17 °C. With the temperature further decreasing to 15 °C, denitrifiers still dominant the UMSR, but AOB, NOB and Candidatus Brocadia as the predominant anammox bacteria were inhibited revealed by high throughput sequencing, resulting in the decrease of TN and NH₄⁺ removal to 39.7% and 61.8%, respectively. Fortunately, when the temperature rebounded to 20 °C, a higher TN and NH₄⁺ removal of 81.2% and 97.3% were obtained again in the UMSR.

Anaerobic ammonium oxidation coupled to iron reduction in constructed wetland mesocosms

Acidimicrobiaceae sp. A6 (referred to as A6) was recently identified as playing a key role in the Feammox process (ammonium oxidation coupled to iron reduction). Two constructed wetlands (CW) were built and bioaugmented with A6 to determine if, under the right conditions, Feammox can be enhanced in CWs by having strata with higher iron content. Hence, the solid stratum in the CWs was sand, and one CW was augmented with ferrihydrite. Vertical ammonium (NH₄⁺) concentration profiles in the CW mesocosms were monitored regularly. After four months of operation, when reducing conditions were established in the CWs, they were inoculated with an enrichment culture containing A6 and monitored for an additional four months, after which they were dismantled and analyzed. During the four-month period after the A6 enrichment culture injection, 25.0 ± 7.3% of NH₄⁺ was removed from the CW with the high iron substrate whereas 11.0 ± 9.7% was removed from the CW with the low iron substrate on average. Since the CW with high NH₄⁺ removal had the same plant density, same bacterial biomass, same fraction of ammonium oxidizing bacteria (AOB), a higher biomass of A6, and a higher pH (NH₄⁺ oxidation by Feammox raises pH, whereas NH₄⁺ oxidation by aerobic AOB decreases pH), this difference in NH₄⁺ removal is attributed to the Feammox process, indicating that wetlands can be constructed to take advantage of the Feammox process for increased NH₄⁺ removal.

The microbial community structure change of an anaerobic ammonia oxidation reactor in response to decreasing temperatures

In anaerobic ammonium oxidation (anammox) systems, temperature may regulate the activity of functional bacteria (e.g., anammox bacteria) and the composition of the microbial population, ultimately determining the performance of the anammox reactor. Knowledge of the dynamic changes in nitrogen removal rates and the microbial anammox community at low and/or ambient temperature is still limited. This study explored the response of an anammox sequencing batch reactor (SBR) to a gradient of decreasing temperature (33, 25, 20, 15, 10 °C), followed by recovery to 22 °C, over 360 days. Particularly, the specific anammox activity (SAA) and microbial community were assessed. The anammox reaction in the SBR remained stable and efficient at 20-33 °C, with a total nitrogen removal load of 0.4 g-N L^-1 day^-1 and an SAA of > 0.32 g-N g-VSS^-1 day^-1; 10 °C was the turning point for the anammox bacterial metabolic activity, at which the SAA decreased by 91% compared with that at 33 °C. After the temperature was returned to 22 °C, the anammox activity recovered to 0.24 g-N g-VSS^-1 day^-1. The apparent activation energy for the anammox reaction was 68.4 kJ mol^-1 at 10-33 °C and 152.9 kJ mol^-1 at 10-20 °C. High-throughput sequencing results revealed that Kuenenia was the dominant species of anammox bacteria, and Kuenenia had a higher tolerance to low temperature than Candidatus Brocadia and Candidatus Jettenia. This study clearly shows the effectiveness of anammox bioreactors for treatment of wastewater at ambient temperatures of 15-33 °C.

Effects of gibberellin on the activity of anammox bacteria

The enhancement of gibberellin (GA) on the activity of anaerobic ammonium oxidation(anammox) bacteria in short-term batch experiments(500 mL serum bottle) was studied in this paper. To make sure the accuracy of the data, each experiment group was conducted some statistical analysis. The results showed that GA played an important role in improving anammox activity when the GA dosage ranged from 0.1 to 1.5 mg L^-1, and the total nitrogen removal rate (NRR) was increased by 34% when the GA dosage was 1 mg L^-1. The monitoring results of extracellular polymeric substances (EPS) and biomass of anammox bacteria indicated that GA addition improved the secretion of EPS and the biomass increasing, whose amount achieved maximum under the GA dose of 1 mg L^-1. Compared to the control test, the maximum improvement ratio of the EPS and biomass was 28.6% and 34%, respectively. In addition, the cloning results also indicated that the anammox bacterial community structure shifted in species level of Candidatus Brocadia genus during the experiment, and the most dominant anammox bacteria were Candidatus Brocadia fulgid.

Aggregation ability of three phylogenetically distant anammox bacterial species

Anaerobic ammonium-oxidizing (anammox) bacteria are well known for their aggregation ability. However, very little is known about cell surface physicochemical properties of anammox bacteria and thus their aggregation abilities have not been quantitatively evaluated yet. Here, we investigated the aggregation abilities of three different anammox bacterial species: "Candidatus Brocadia sinica", "Ca. Jettenia caeni" and "Ca. Brocadia sapporoensis". Planktonic free-living enrichment cultures of these three anammox species were harvested from the membrane bioreactors (MBRs). The physicochemical properties (e.g., contact angle, zeta potential, and surface thermodynamics) were analyzed for these anammox bacterial species and used in the extended DLVO theory to understand the force-distance relationship. In addition, their extracellular polymeric substances (EPSs) were characterized by X-ray photoelectron spectroscopy and nuclear magnetic resonance. The results revealed that the "Ca. B. sinica" cells have the most hydrophobic surface and less hydrophilic functional groups in EPS than other anammox strains, suggesting better aggregation capability. Furthermore, aggregate formation and anammox bacterial populations were monitored when planktonic free-living cells were cultured in up-flow column reactors under the same conditions. Rapid development of microbial aggregates was observed with the anammox bacterial population shifts to a dominance of "Ca. B. sinica" in all three reactors. The dominance of "Ca. B. sinica" could be explained by its better aggregation ability and the superior growth kinetic properties (higher growth rate and affinity to nitrite). The superior aggregation ability of "Ca. B. sinica" indicates significant advantages (efficient and rapid start-up of anammox reactors due to better biomass retention as granules and consequently stable performance) in wastewater treatment application.

Trending topics and open questions in anaerobic ammonium oxidation

Anaerobic ammonium-oxidizing (anammox) bacteria are major players in the biological nitrogen cycle and can be applied in wastewater treatment for the removal of nitrogen compounds. Anammox bacteria anaerobically convert the substrates ammonium and nitrite into dinitrogen gas in a specialized intracellular compartment called the anammoxosome. The anammox cell biology, physiology and biochemistry is of exceptional interest but also difficult to study because of the lack of a pure culture, standard cultivation techniques and genetic tools. Here we review the most important recent developments regarding the cell structure - anammoxosome and cell envelope - and anammox energy metabolism - nitrite reductase, hydrazine synthase and energy conversion - including the trending topics electro-anammox, extracellular polymeric substances and ladderane lipids.

Genome-Centered Metagenomics Analysis Reveals the Symbiotic Organisms Possessing Ability to Cross-Feed with Anammox Bacteria in Anammox Consortia

Although using anammox communities for efficient wastewater treatment has attracted much attention, the pure anammox bacteria are difficult to obtain, and the potential roles of symbiotic bacteria in anammox performance are still elusive. Here, we combined long-term reactor operation, genome-centered metagenomics, community functional structure, and metabolic pathway reconstruction to reveal multiple potential cross-feedings during anammox reactor start-up according to the 37 recovered metagenome-assembled genomes (MAGs). We found Armatimonadetes and Proteobacteria could contribute the secondary metabolites molybdopterin cofactor and folate for anammox bacteria to benefit their activity and growth. Chloroflexi-affiliated bacteria encoded the function of biosynthesizing exopolysaccharides for anammox consortium aggregation, based on the partial nucleotide sugars produced by anammox bacteria. Chlorobi-affiliated bacteria had the ability to degrade extracellular proteins produced by anammox bacteria to amino acids to affect consortium aggregation. Additionally, the Chloroflexi-affiliated bacteria harbored genes for a nitrite loop and could have a dual role in anammox performance during reactor start-up. Cross-feeding in anammox community adds a different dimension for understanding microbial interactions and emphasizes the importance of symbiotic bacteria in the anammox process for wastewater treatment.

A critical review of one-stage anammox processes for treating industrial wastewater: Optimization strategies based on key functional microorganisms

The one-stage nitritation/anammox (anaerobic ammonium oxidation) process is an energy-saving technology, which has been successfully developed and widely applied to treat industrial wastewaters. For the one-stage nitritation/anammox process, key functional microbes generally include anaerobic ammonia oxidation bacteria (AnAOB), ammonia-oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB), and heterotrophic bacteria (HB). Cooperation and competition among the key functional microbes are critical to the stability and performance of anammox process. Based upon key functional microorganisms, this review summarizes and discusses the optimized strategies that promote the operation of one-stage nitritation/anammox process. In particular, the review focuses on strategies related to: (1) the retention of anammox biomass through granular sludge or biofilm, (2) the balanced relationship between AOB and AnAOB, (3) the NOB suppression and (4) the HB management by controlling the influent organic matter. In addition, the review proposes further research to address the existing challenges.

Microbial community dynamics in an ANAMMOX reactor for piggery wastewater treatment with startup, raising nitrogen load, and stable performance

Bacterial community dynamics of the ANAMMOX reactor of an integrated “UASB + SHARON + ANAMMOX” system for treating piggery wastewater were investigated using the Illumina MiSeq method with samples obtained at ~ 2-week intervals during a 314-day period. With aerobic activated sludge as seeds and low content artificial wastewater (NH₄⁺–N 50 mg/L; NO₂⁻–N 55 mg/L) as influent for the ANAMMOX reactor, nitrogen removal was initially observed on day 38 with a removal rate 1.3 mg N L⁻¹ day⁻¹, and increased to 90.4 mg N L⁻¹ day⁻¹ on day 55 with almost complete removal of ammonia and nitrite, indicating a successful startup of the reactor. Increasing influent load stepwise to NH₄⁺–N 272.7 mg/L/NO₂⁻–N 300 mg/L, nitrogen removal rate increased gradually to 470 mg N L⁻¹ day⁻¹ on day 228, and maintained a stable level (~ 420 mg N L⁻¹ day⁻¹) following introduction of SHARON effluent since day 229. Correlation between microbial community dynamics and nitrogen removal capability was significant (r = 0.489, p < 0.001). Microbial community composition was determined by influent ammonia, influent nitrite, effluent nitrate and some undefined factors. Anammox bacteria, accounting for ~ 98.7% of Planctomycetes, became detectable (0.03% relative abundance) since day 38 and increased to 0.9% on day 58, well consistent with nitrogen removal performance of the reactor. Relative abundance of anammox bacteria gradually increased to 38.4% on day 140 with stepwise increased influent load; decreased to 0.4% on day 169 because of nitrite inhibition; increased to 19.24% on day 233 when the influent load was dropped; kept at ~ 9.0% with SHARON effluent used as influent and dropped to 3.3% finally. Anammox bacteria, only Candidatus Brocadia and Ca. Kuenenia detected, were the most abundant at genus level. Ca. Brocadia related taxa were enriched firstly under low load and detectable during the entire experimental period. Three main groups represented by Ca. Brocadia related OTUs were enriched or eliminated at different loads, but Ca. Kuenenia related taxa were enriched only under high load (NO₂⁻–N > 300 mg/L), suggesting their different niches and application for different loads. These findings improve the understanding of relationships among microbial community/functional taxa, running parameters and reactor performance, and will be useful in optimizing running parameters for rapid startup and high, stable efficiency.

Evidence of differential adaptation to decreased temperature by anammox bacteria

Low temperature is recognized as one of the major barriers for the application of the anaerobic ammonium oxidation (anammox) process to treat mainstream wastewater. Studies are yet to reveal the underlying biological limitations and molecular mechanisms associated with the inhibition of low temperature on the anammox process. In this study, metaproteomics was used to examine proteome modulation patterns of the anammox community occurring at different temperatures. The anammox community remarkably altered their proteomes when the temperature decreased from 35 °C to 20 °C. This was especially for proteins involved in energy conversion, transcription and translation and inorganic ion transport. However, at 15 °C the anammox activities became distinctly inhibited, and there was evidence of energy limitations and severe stress in Candidatus Kuenenia and to a lesser degree in Candidatus Brocadia. Candidatus Jettenia exhibited more changes in its proteome at 15 °C. From the proteomes, at the lower temperatures there was evidence of stress caused by toxic nitrogen compounds or reactive oxygen species in the anammox bacteria. Hydroxylamine oxidoreductase (HAO)-like proteins and an oxidative stress response protein (a catalase) were in high abundance to potentially ameliorate these inhibitory effects. This study offers metaproteomic insight into the anammox community-based physiological response to decreasing temperatures.

Anaerobic Ammonium Oxidation in Acidic Red Soils

Anaerobic ammonium oxidation (anammox) has been proven to be an important nitrogen removal process in terrestrial ecosystems, particularly paddy soils. However, the contribution of anammox in acidic red soils to nitrogen loss has not been well-documented to date. Here, we investigated the activity, abundance, and distribution of anammox bacteria in red soils collected from nine provinces of Southern China. High-throughput sequencing analysis showed that Candidatus Brocadia dominates the anammox bacterial community (93.03% of sequence reads). Quantification of the hydrazine synthase gene (hzsB) and anammox 16S rRNA gene indicated that the abundance of anammox bacteria ranged from 6.20 × 10⁶ to 1.81 × 10⁹ and 4.81 × 10⁶ to 4.54 × 10⁸ copies per gram of dry weight, respectively. Contributions to nitrogen removal by anammox were measured by a ¹⁵N isotope-pairing assay. Anammox rates in red soil ranged from 0.01 to 0.59 nmol N g⁻¹ h⁻¹, contributing 16.67–53.27% to N₂ production in the studied area, and the total amount of removed nitrogen by anammox was estimated at 2.33 Tg N per year in the natural red soils of southern China. Pearson correlation analyses revealed that the distribution of anammox bacteria significantly correlated with the concentration of nitrate and pH, whereas the abundance and activity of anammox bacteria were significantly influenced by the nitrate and total nitrogen concentrations. Our findings demonstrate that Candidatus Brocadia dominates anammox bacterial communities in acidic red soils and plays an important role in nitrogen loss of the red soil in Southern China.

Abundance and Diversity of Aerobic/Anaerobic Ammonia/Ammonium-Oxidizing Microorganisms in an Ammonium-Rich Aquitard in the Pearl River Delta of South China

Natural occurring groundwater with abnormally high ammonium concentrations was discovered in the aquifer-aquitard system in the Pearl River Delta, South China. The community composition and abundance of aerobic/anaerobic ammonia/ammonium-oxidizing microorganisms (AOM) in the aquitard were investigated in this study. The alpha subunit of ammonia monooxygenase gene (amoA) was used as the biomarker for the detection of aerobic ammonia-oxidizing archaea (AOA) and bacteria (AOB), and also partial 16S rRNA gene for Plantomycetes and anaerobic ammonium-oxidizing (anammox) bacteria. Phylogenetic analysis showed that AOA in this aquitard were affiliated with those from water columns and wastewater treatment plants; and AOB were dominated by sequences among the Nitrosomonas marina/Nitrosomonas oligotropha lineage, which were affiliated with environmental sequences from coastal eutrophic bay and subtropical estuary. The richness and diversity of both AOA and AOB communities had very little variations with the depth. Candidatus Scalindua-related sequences dominated the anammox bacterial community. AOB amoA gene abundances were always higher than those of AOA at different depths in this aquitard. The Pearson moment correlation analysis showed that AOA amoA gene abundance positively correlated with pH and ammonium concentration, whereas AOB amoA gene abundance negatively correlated with C/N ratio. This is the first report that highlights the presence with low diversity of AOM communities in natural aquitard of rich ammonium.

Status, Challenges, and Perspectives of Mainstream Nitritation-Anammox for Wastewater Treatment

  The nitritation-anammox process is an efficient and cost-effective approach for biological nitrogen removal, but its application in treating mainstream wastewater remains a great challenge. Mainstream nitritation-anammox processes could create opportunities for achieving energy self-sufficient, or energy-generating water resource recovery facilities. Significant advancements have been achieved via pilot- and full-scale trials to overcome the major obstacles under mainstream conditions, such as repression of nitrite-oxidizing bacteria, limiting the overgrowth of denitrifiers, and effective selection and retention of ammonia-oxidizing bacteria and anammox bacteria. This review paper intends to provide a detailed update of research progress on mainstream nitritation-anammox processes, discuss metabolic interactions, and examine major challenges and possible solutions towards the future development.

The role of COD/N ratio on the start-up performance and microbial mechanism of an upflow microaerobic reactor treating piggery wastewater

This study investigated the role of COD/N ratio on the start-up and performance of an upflow microaerobic sludge reactor (UMSR) treating piggery wastewater at 0.5 mgO₂/L. At high COD/N ratio (6.24 and 4.52), results showed that the competition for oxygen between ammonia-oxidizing bacteria, nitrite-oxidizing bacteria and heterotrophic bacteria limited the removal of nitrogen. Nitrogen removal efficiency was below 40% in both scenarios. Decreasing the influent COD/N ratio to 0.88 allowed achieving high removal efficiencies for COD (∼75%) and nitrogen (∼85%) due to the lower oxygen consumption for COD mineralization. Molecular biology techniques showed that nitrogen conversion at a COD/N ratio 0.88 was dominated by the anammox pathway and that Candidatus Brocadia sp. was the most important anammox bacteria in the reactor with a relative abundance of 58.5% among the anammox bacteria. Molecular techniques also showed that Nitrosomonas spp. was the major ammonia-oxidiser bacteria (relative abundance of 86.3%) and that denitrification via NO₃^- and NO₂^- also contributed to remove nitrogen from the system.

Microbial Nitrogen Cycle Hotspots in the Plant-Bed/Ditch System of a Constructed Wetland with N2O Mitigation

Artificial microbial nitrogen (N) cycle hotspots in the plant-bed/ditch system were developed and investigated based on intact core and slurry assays measurement using isotopic tracing technology, quantitative PCR and high-throughput sequencing. By increasing hydraulic retention time and periodically fluctuating water level in heterogeneous riparian zones, hotspots of anammox, nitrification, denitrification, ammonium (NH₄⁺) oxidation, nitrite (NO₂^-) oxidation, nitrate (NO₃^-) reduction and DNRA were all stimulated at the interface sediments, with the abundance and activity being about 1-3 orders of magnitude higher than those in nonhotspots. Isotopic pairing experiments revealed that in microbial hotspots, nitrite sources were higher than the sinks, and both NH₄⁺ oxidation (55.8%) and NO₃^- reduction (44.2%) provided nitrite for anammox, which accounted for 43.0% of N-loss and 44.4% of NH₄⁺ removal in riparian zones but did not involve nitrous oxide (N₂O) emission risks. High-throughput analysis identified that bacterial quorum sensing mediated this anammox hotspot with B.fulgida dominating the anammox community, but it was B. anammoxidans and Jettenia sp. that contributed more to anammox activity. In the nonhotspot zones, the NO₂^- source (NO₃^- reduction dominated) was lower than the sink, limiting the effects on anammox. The in situ N₂O flux measurement showed that the microbial hotspot had a 27.1% reduced N₂O emission flux compared with the nonhotspot zones.

The hunt for the most-wanted chemolithoautotrophic spookmicrobes

Microorganisms are the drivers of biogeochemical methane and nitrogen cycles. Essential roles of chemolithoautotrophic microorganisms in these cycles were predicted long before their identification. Dedicated enrichment procedures, metagenomics surveys and single-cell technologies have enabled the identification of several new groups of most-wanted spookmicrobes, including novel methoxydotrophic methanogens that produce methane from methylated coal compounds and acetoclastic 'Candidatus Methanothrix paradoxum', which is active in oxic soils. The resultant energy-rich methane can be oxidized via a suite of electron acceptors. Recently, 'Candidatus Methanoperedens nitroreducens' ANME-2d archaea and 'Candidatus Methylomirabilis oxyfera' bacteria were enriched on nitrate and nitrite under anoxic conditions with methane as an electron donor. Although 'Candidatus Methanoperedens nitroreducens' and other ANME archaea can use iron citrate as an electron acceptor in batch experiments, the quest for anaerobic methane oxidizers that grow via iron reduction continues. In recent years, the nitrogen cycle has been expanded by the discovery of various ammonium-oxidizing prokaryotes, including ammonium-oxidizing archaea, versatile anaerobic ammonium-oxidizing (anammox) bacteria and complete ammonium-oxidizing (comammox) Nitrospira bacteria. Several biogeochemical studies have indicated that ammonium conversion occurs under iron-reducing conditions, but thus far no microorganism has been identified. Ultimately, iron-reducing and sulfate-dependent ammonium-oxidizing microorganisms await discovery.

Keeping a Completely Autotrophic Nitrogen Removal over Nitrite System Effective in Treating Low Ammonium Wastewater by Adopting an Alternative Low and High Ammonium Influent Regime

An alternative low and high ammonium influent regime was proposed and adopted to keep a completely autotrophic nitrogen removal over nitrite (CANON) effective when treating low ammonium wastewater. Results show that, by cyclic operating at an alternative low and high ammonium concentration for 10 days and 28 days, the CANON system could effectively treat low ammonium wastewater. Excessive proliferation of nitrite oxidizing bacteria (NOB) under low ammonium environment was still the challenge for the stable CANON operation; but with 28 days of a high ammonium treatment combined with a sludge retention time control, the NOB overproliferated in the low ammonium operational period could be under control. Specifically, when the nitrite oxidation rate reached 8 g N/m³/h, the CANON system should enter the high ammonium influent operating mode. 16S rDNA high-throughput sequencing results show that the appropriate sludge discharging provided an environment favoring Candidatus Jettenia.

Practical applications of PCR primers in detection of anammox bacteria effectively from different types of samples

Research on anammox (anaerobic ammonium oxidizing) bacteria is important due to their biogeochemical and industrial application significance since the first discovery made over two decades ago. By coupling NH₄⁺ and NO₂^- biochemically to form N₂ gas, anammox bacteria contribute significantly to global marine and terrestrial nitrogen balance (responsible for 50, 9~40, and 4~37% of the nitrogen loss for marine, lakes, and paddy soil) and are also useful in energy-conserving nitrogen removal in wastewater treatment. PCR-based detection and quantification of anammox bacteria are an easy, essential, and widely accessible technique used ubiquitously for studying them in many environmental niches. In this article, we make a summary on practical applications of 16S rRNA and functional gene PCR primers, including hydrazine dehydrogenase (Hzo), nitrite reductase (NirS), hydrazine synthase (Hzs), and cytochrome c biogenesis proteins (Ccs) in detection of them. PCR primer performances in both practical applications and tests in silico are also presented for comparison. For detecting general and specific anammox bacterial groups, selection of appropriate PCR primers for different environmental samples and practical application guidance on choice of appropriate primer pairs for different purposes are also offered. This article provides practical information on selection and application of PCR technique in detection of anammox bacteria from the diverse environments to further promote convenient applications of this technique in research and other purposes.

Performance and mechanism of free nitrous acid on the solubilization of waste activated sludge

Free nitrous acid (FNA) is a promising chemical reagent for excess sludge reduction. The distinctive properties of FNA treatment on waste activated sludge (WAS) disposal have previously been demonstrated, however, the cellular response, permeabilization, and disruption caused by low-concentration FNA and the direct cell solubilization of WAS using concentrated FNA should be better understood. In this study, the parameters that influence the sludge solubilization efficiency were optimized over a wide range of FNA concentrations. The sludge solubilization efficiency was found to be superior when the sludge was exposed to FNA (when the dosage of NaNO2 was 0.12 g g-1 TSS and the pH was 3.0, FNA = 20.94 mg L-1) for 10 h at 25 °C, and the TSS removal and COD dissolution efficiencies were found to be prominent at 38% and 7%, respectively. In the FNA treatment of WAS, some FNA-tolerable cells increased the K+, Ca2+, and H+ effluxes under low concentrations of FNA, and finally achieved ion homeostasis based on the results using a scanning ion-selective electrode measurement technique. This could cause the cells in WAS to maintain cytoactivity and integrity under a low-concentration FNA treatment. Furthermore, flow cytometry was used to assess the permeabilization and disruption of sludge cells toward a concentration gradient of FNA. Flow cytometry results indicated that cells in sludge flocs were disrupted within 30 minutes when the FNA concentration was above 8 mg L-1.

Microbial pathways for nitrogen loss in an upland soil

The distribution and importance of anaerobic ammonium oxidation (anammox) and nitrite-dependent anaerobic methane oxidation (n-damo) have been identified in aquatic ecosystems; their role in agricultural upland soils however has not yet been well investigated. In this study, we examined spatio-temporal distributions of anammox and n-damo bacteria in soil profiles (300 cm depth) from an agricultural upland. Monitoring nitrogen (N) conversion activity using isotope-tracing techniques over the course of one year showed denitrification (99.0% N-loss in the winter and 85.0% N-loss in the summer) predominated over anammox (1.0% N-loss in the winter and 14.4% N-loss in the summer) and n-damo (0.6% N-loss in the winter) in surface soils (0-20 cm). While below 20 cm depth, N-loss was dominated by anammox (79.4 ± 14.3% in the winter and 65.4 ± 12.5% in the summer) and n-damo was not detected. Phylogenetic analysis showed that Candidatus Brocadia anammoxidans dominated the anammox community in the surface soil and Candidatus Brocadia fulgida dominated below 20 cm depth. Dissimilatory nitrate reduction to ammonium (DNRA), another nitrite reduction process, was found to play a limited role (4.9 ± 3.5%) in the surface soil compared with denitrification; below 80 cm DNRA rates were much higher than rates of anammox and denitrification. Ammonium oxidation was the main source of NO2- above 80 cm (70.9 ± 23.3%), the key influencing factor on anammox rates, and nitrate reduction (100%) was the main NO2- source below 80 cm. Considering the anammox, n-damo and denitrification rates as a whole in the sampled soil profile, denitrification is still the main N-loss process in upland soils.