Missing lithotroph identified as new planctomycete

Enhancing nitrogen removal through directly integrating anammox into mainstream wastewater treatment: Advantageous, issues and future study

Anaerobic ammonium oxidation (anammox) has great potential to be applied to the process of nitrogen removal from mainstream wastewater. However, directly applying complete anammox to the mainstream is typically hindered by low temperatures, a low ammonia concentration, and high organic matter concentrations. Directly integrating anammox into mainstream treatment by enhancing the in-situ enrichment of anammox bacteria in wastewater treatment plants (WWTPs) could effectively improve the nitrogen removal efficiency and reduce the treatment cost. A certain anammox bacteria abundance in full-scale WWTPs provides the feasibility of directly integrating anammox into mainstream treatment and realizing partial mainstream anammox. The technical development status of partial anammox and the mechanisms of achieving partial mainstream anammox by aeration and organic control are summarized. This review provides an enhanced understanding of this novel technical route of partial mainstream anammox treatment for improving the quality, performance, and prospects for this technology to be used in upgrading WWTPs.

Unveiling the effect of acetate on the interactions of functional bacteria in an anammox biofilm system

Biodegradable organics make an important impact on anaerobic ammonium oxidation (anammox) system. In this study, acetate was selected as a typical biodegradable organic, and its effect on the anammox biofilm system was comprehensively discussed from the macro and micro perspectives. Under a low influent concentration of acetate (<240 ± 10 mg/L), the best total nitrogen (TN) removal performance was 96%, but it decreased to 83% when the acetate concentration increased to 350 ± 20 mg/L. With the addition of acetate, the relative abundance of the family Brocadiaceae, which contains all known anammox bacteria, gradually increased from 7.97% to 12.79%, indicating that the presence of acetate promoted enrichment of anammox bacteria in the biofilm. Metagenomic analysis further demonstrated that an appropriate concentration of acetate helps to increase the abundances of the key enzymes related to nitrogen removal and enhance the metabolism of anammox and denitrification, thereby promoting the synergy of anammox and denitrifying bacteria. Hydrazine synthase (hzs), which is unique to the anammox process, was detected in association with the genera Candidatus Kuenenia, Candidatus Jettenia and Candidatus Brocadia, with its abundance increasing from 13268 (with no addition of acetate) to 19186 (with acetate addition of 240 ± 10 mg/L). This work provides a deeper understanding of the intrinsic interactions between functional bacteria in an anammox biofilm system.

Integrated moving bed biofilm reactor with partial denitrification-anammox for promoted nitrogen removal: Layered biofilm structure formation and symbiotic functional microbes

Partial denitrification/anaerobic ammonia oxidation (anammox) (PD/A) is currently an advanced nitrogen removal process. This study developed a PD/A system in a moving bed biofilm reactor. Results showed that the nitrogen removal efficiency reached 76.60% with a COD/NO₃-N of 2.0, and the contribution of anammox was 88.01%. Further analysis showed that the biocarriers could form layered pH and dissolved oxygen structures to promote the aggregation of different functional bacteria at various depths, thus stabilizing the coupled process. Microbial structure analysis showed that the abundance of Saccharimonadales, responsible for denitrification, increased from 0% to 36.27% between day 0 and day 120, while the abundance of Candidatus Jettenia, responsible for anammox, decreased from 10.41% to 2.20%. The synergistic effect of Saccharimonadales and Candidatus Jettenia enabled stable and efficient removal of nitrogen. This study proposed a novel configuration of the PD/A process and provided a theoretical basis for its promotion and application.

Enhanced cycling of nitrogen and metals during rapid infiltration: Implications for managed recharge

We present results from a series of plot-scale field experiments to quantify physical infiltration dynamics and the influence of adding a carbon-rich, permeable reactive barrier (PRB) for the cycling of nitrogen and associated trace metals during rapid infiltration for managed aquifer recharge (MAR). Recent studies suggest that adding a bio-available carbon source to soils can enhance denitrification rates and associated N load reduction during moderate-to-rapid infiltration (≤1 m/day). We examined the potential for N removal during faster infiltration (>1 m/day), through coarse and carbon-poor soils, and how adding a carbon-rich PRB (wood chips) affects subsurface redox conditions and trace metal mobilization. During rapid infiltration, plots amended with a carbon-rich PRB generally demonstrated modest increases in subsurface loads of dissolved organic carbon, nitrite, manganese and iron, decreases in loads of nitrate and ammonium, and variable changes in arsenic. These trends differed considerably from those seen during infiltration through native soil without a carbon-rich PRB. Use of a carbon-rich soil amendment increased the fraction of dissolved N species that was removed at equivalent inflowing N loads. There is evidence that N removal took place primarily via denitrification. Shifts in microbial ecology following infiltration in all of the plots included increases in the relative abundances of microbes in the families Comamonadaceae, Pseudomonadaceae, Methylophilaceae, Rhodocyclaceae and Sphingomonadaceae, all of which contain genera capable of carrying out denitrification. These results, in combination with studies that have tested other soil types, flow rates, and system scales, show how water quality can be improved during infiltration for managed recharge, even during rapid infiltration, with a carbon-rich soil amendment.

Free Nitrous Acid Inhibits Atenolol Removal during the Sidestream Partial Nitritation Process through Regulating Microbial-Induced Metabolic Types

Limited studies have attempted to evaluate pharmaceutical removal during the sidestream partial nitritation (PN) process. In this work, atenolol biodegradation by PN cultures was investigated by maintaining ammonium and pH at different levels. For the first time, free nitrous acid (FNA), other than ammonium, pH, and free ammonia, was demonstrated to inhibit atenolol removal, with biodegradation efficiencies of ∼98, ∼67, and ∼28% within 6 days at average FNA levels of 0, 0.03, and 0.19 mg-N L^-1, respectively. Ammonia-oxidizing bacteria (AOB)-induced metabolism was predominant despite varying FNA concentrations. In the absence of ammonium/FNA, atenolol was mostly biodegraded via AOB-induced metabolism (65%) and heterotroph-induced metabolism (33%). AOB-induced metabolism was largely inhibited (down to 29%) at 0.03 mg-N L^-1 FNA, while ∼27 and ∼11% were degraded via heterotroph-induced metabolism and AOB-induced cometabolism, respectively. Higher FNA (0.19 mg-N L^-1) substantially reduced atenolol biodegradation via heterotroph-induced metabolism (4%), AOB-induced metabolism (16%), and AOB-induced cometabolism (8%). Newly identified products and pathways were related to metabolic types and FNA levels: (i) deamination and decarbonylation (AOB-induced cometabolism, 0.03 mg-N L^-1 FNA); (ii) deamination from atenolol acid (heterotrophic biodegradation); and (iii) nitro-substitution (reaction with nitrite). This suggests limiting FNA to realize simultaneous nitrogen and pharmaceutical removal during the sidestream process.

Identification and characterization of a novel hydroxylamine oxidase, DnfA, that catalyzes the oxidation of hydroxylamine to N2

Nitrogen (N₂) gas in the atmosphere is partially replenished by microbial denitrification of ammonia. Recent study has shown that Alcaligenes ammonioxydans oxidizes ammonia to dinitrogen via a process featuring the intermediate hydroxylamine, termed “Dirammox” (direct ammonia oxidation). However, the unique biochemistry of this process remains unknown. Here, we report an enzyme involved in Dirammox that catalyzes the conversion of hydroxylamine to N₂. We tested previously annotated proteins involved in redox reactions, DnfA, DnfB, and DnfC, to determine their ability to catalyze the oxidation of ammonia or hydroxylamine. Our results showed that none of these proteins bound to ammonia or catalyzed its oxidation; however, we did find DnfA bound to hydroxylamine. Further experiments demonstrated that, in the presence of NADH and FAD, DnfA catalyzed the conversion of ¹⁵N-labeled hydroxylamine to ¹⁵N₂. This conversion did not happen under oxygen (O₂)-free conditions. Thus, we concluded that DnfA encodes a hydroxylamine oxidase. We demonstrate that DnfA is not homologous to any known hydroxylamine oxidoreductases and contains a diiron center, which was shown to be involved in catalysis via electron paramagnetic resonance experiments. Furthermore, enzyme kinetics of DnfA were assayed, revealing a K_m of 92.9 ± 3.0 μM for hydroxylamine and a k_cat of 0.028 ± 0.001 s⁻¹. Finally, we show that DnfA was localized in the cytoplasm and periplasm as well as in tubular membrane invaginations in HO-1 cells. To the best of our knowledge, we conclude that DnfA is the first enzyme discovered that catalyzes oxidation of hydroxylamine to N₂.

Activation of N-acyl-homoserine lactone-mediated quorum sensing system improves long-term preservation of anammox microorganisms by vacuum lyophilization

The long-term preservation of anaerobic ammonium oxidation (anammox) microorganisms via vacuum lyophilization process would help commercialize the technique. In this study, vacuum lyophilization was evaluated for the cost-effective long-term preservation of such microorganisms. Skim milk was found to be the most effective cryoprotectant for maintaining the physiological properties (heme c, EPS, and the PN/PS ratio) of anammox microorganisms. Conversely, the vacuum lyophilization technique was shown to cause serious damage to the quorum sensing (QS) system of anammox, so that anammox activity was not adequately recovered afterwards. To overcome this limitation, activation of the AHL-mediated QS system were applied to the vacuum lyophilization process. Endogenous (i.e., fresh anammox sludge of 10%) and exogenous (i.e., C6-HSL of 60 mg/L) QS autoinducers significantly increased anammox activity to 88.2 ± 12.2 and 130.0 ± 12.2 mgTN/gVSS/d, respectively, after 56 d of reactivation. In addition, nitrogen removal potentials were estimated to be 123.5 and 87.5 gTN/m³/d, respectively. The effect of the exogenous QS autoinducer on anammox reactivation was reconfirmed through the comparison experiment. The results of this study will be greatly significant to this field since they improve the feasibility of the once-underestimated vacuum lyophilization technique.

Micron-scale biogeography reveals conservative intra anammox bacteria spatial co-associations

Micron-scale resolution can help to reliably identify true taxon-taxon interactions in complex microbial communities. Despite widespread recognition of the critical role of metabolic interactions in anaerobic ammonium oxidation (anammox) system performance, no studies have examined microbial interactions at the micron-scale in anammox consortia. To fill this gap, we extensively sampled (totally 242 samples) the consortia of a lab-scale anammox reactor at different length scales, including bulk-scale (∼cm), macro-scale (300-500 µm) and micron-scale (70-100 µm). We firstly observed evident micron-scale heterogeneity in anammox consortia, with the relative abundance of anammox bacteria fluctuated greatly across individual clusters (2.0%-79.3%), indicating that the biotic interactions play a significant role in the assembly of anammox communities under well-controlled and well-mixed condition. Importantly, by mapping the spatial associations in anammox consortia at micron-scale, we demonstrated that the conserved co-associations for anammox bacteria were restricted to three different Brocadia species over time, and their co-associations with heterotrophs were random, implying that there was no statistically significant symbiotic interaction between anammox bacteria and other heterotrophic populations. Further metagenomic binning revealed that the quorum sensing with secondary messenger c-di-GMP potentially holding on the conservative metabolic cooperation among Brocadia species. These results shed new light on the social behavior of the anammox community. Overall, delineating of biological structures at micron-scale opens a new way of monitoring the microbial spatial structure and interactions, paving the way for improved community engineering of biotreatment systems.

Stratification patterns of anammox granular sludge bed: Linking particle size distribution to microbial activity and community

Anammox granular sludge processes are an attractive and efficient biotechnology in the field of wastewater treatment. In this study, the stratification patterns of anammox granular sludge bed (GSB) at steady states were illustrated and its relationship to microbial activity and community were systematically investigated under different nitrogen loading rates (NLRs). Morphological observation and quantitive particle size distribution analysis demonstrated that the GSB at low NLR was mainly composed of micro and fine granules with a big difference between bottom and top sludge layers. But at high NLR, the volumetric mean diameter (VMD) of GSB increased with the size distribution width (Span) declined forming a more homogeneous and coarse granules population. The particle size distribution parameters of GSB could be fast characterized by the optical lightness (L*) parameter (r = -0.771, p < 0.01, n = 16) and held a significant correlation with the nitrogen removal rate (NRR) of anammox system (r > 0.9, p < 0.05). The microbial spatial distribution patterns of different sludge layers were further investigated by high-throughput sequencing. The microbial community α-diversity index and microbial abundance matrix proved that the community structure tend to coverage at high NLR. Significant difference of the relative abundance of microbial community was detected under different NLRs. The VMD of GSB held a significant correlation with the relative abundance of AnAOB (r = 0.556, p < 0.01, n = 16) and other common accompanying bacteria (Denitratisoma and Chloroflexi). This study proved that the apparent particle size distribution patterns of GSB could be a potential auxiliary indicator to reflect the microbial activity and community, which can facilitate the innovative process monitor of anammox system based on visual features.

Microbial response on the first full-scale DEMON® biomass transfer for mainstream deammonification

Sidestream partial nitritation and deammonification (pN/A) of high-strength ammonia wastewater is a well-established technology. Its expansion to the mainstream is, however mainly impeded by poor retention of anaerobic ammonia oxidizing bacteria (AnAOB), insufficient repression of nitrite oxidizing bacteria (NOB) and difficult control of soluble chemical oxygen demand and nitrite levels. At the municipal wastewater treatment plant in Strass (Austria) the microbial consortium was exhaustively monitored at full-scale over one and a half year with regular transfer of sidestream DEMON® biomass and further retention and enrichment of granular anammox biomass via hydrocyclone operation. Routine process parameters were surveyed and the response and evolution of the microbiota was followed by molecular tools, ex-situ activity tests and further, AnAOB quantification through particle tracking and heme measurement. After eight months of operation, the first anaerobic, simultaneous depletion of ammonia and nitrite was observed ex-situ, together with a direction to higher nitrite generation (68% of total NO_x-N) as compared to nitrate under aerobic conditions. Our dissolved oxygen (DO) scheme allowed for transient anoxic conditions and had a strong influence on nitrite levels and the NOB community, where Nitrobacter eventually dominated Nitrospira. The establishment of a minor but stable AnAOB biomass was accompanied by the rise of Chloroflexi and distinct emergence of Chlorobi, a trend not seen in the sidestream system. Interestingly, the most pronounced switch in the microbial community and noticeable NOB repression occurred during unfavorable conditions, i.e. the cold winter season and high organic load. Further abatement of NOB was achieved through bioaugmentation of aerobic ammonia oxidizing bacteria (AerAOB) from the sidestream-DEMON® tank. Performance of the sidestream pN/A was not impaired by this operational scheme and the average volumetric nitrogen removal rate of the mainstream even doubled in the second half of the monitoring campaign. We conclude that a combination of both, regular sidestream-DEMON® biomass transfer and granular SRT increase via hydrocyclone operation was crucial for AnAOB establishment within the mainstream.

Isolation, diversity and antimicrobial activity of planctomycetes from the Tejo river estuary (Portugal)

The discovery of new bioactive compounds is an invaluable aid to the development of new drugs. Strategies for finding novel molecules can focus on the exploitation of less studied organisms and ecosystems such as planctomycetes and brackish habitats. The unique cell biology of the underexplored Planctomycetota mean it is of particular interest. In this study, we aimed to isolate planctomycetes from the estuary of the Tejo river (Portugal). To reach this goal, macroalgae, water and sediments were sampled and diverse media and isolation techniques applied. Sixty-nine planctomycetal strains were brought into pure culture. An analysis of the 16S rRNA genes found that the majority of the isolates were affiliated to the genus Rhodopirellula. Putative novel taxa belonging to genera Stieleria and Rhodopirellula were also isolated and characterized morphologically. Enterobacterial Repetitive Intergenic Consensus fingerprinting analyses showed higher diversity and different genotypes within close strains. Relevant biosynthetic gene clusters were found in most isolates and acetone extracts from representative strains exhibited mild antimicrobial activities against Escherichia coli and Staphylococcus aureus. Our work has not only enlarged the number and diversity of cultured planctomycetes but also shown the potential for the discovery of bioactive compounds from the novel taxa.

Low-Temperature Isolation of a Labile Silylated Hydrazinium-yl Radical Cation, [(Me3 Si)2 N-N(H)SiMe3 ]

The oxidation of silylated hydrazine, (Me3 Si)2 N-N(H)SiMe3 , with silver salts led to the formation of a highly labile hydrazinium-yl radical cation, [(Me3 Si)2 N-N(H)SiMe3 ].+ , at very low temperatures (decomposition > -40 °C). EPR, NMR, DFT and Raman studies revealed the formation of a nitrogen-centered radical cation along the N-N unit of the hydrazine. In the presence of the weakly coordinating anion [Al{OCH(CF3 )2 }4 ]- , crystallization and structural characterization in the solid state were achieved. The hydrazinium-yl radical cation has a significantly shortened N-N bond and a nearly planar N2 Si3 framework, in contrast to the starting material. According to DFT calculations, the shortened N-N bond has a total bond order of 1.5 with a π-bond order of 0.5. The π bond can be regarded as a three-π-electron, two-center bond.

Community Structure and Microbial Associations in Sediment-Free Methanotrophic Enrichment Cultures from a Marine Methane Seep

Syntrophic consortia of anaerobic methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB) consume large amounts of methane and serve as the foundational microorganisms in marine methane seeps. Despite their importance in the carbon cycle, research on the physiology of ANME-SRB consortia has been hampered by the slow growth and complex physicochemical environment the consortia inhabit. Here, we report successful sediment-free enrichment of ANME-SRB consortia from deep-sea methane seep sediments in the Santa Monica Basin, California. Anoxic Percoll density gradients and size-selective filtration were used to separate ANME-SRB consortia from sediment particles and single cells to accelerate the cultivation process. Over a 3-year period, a subset of the sediment-associated ANME and SRB lineages, predominantly comprised of ANME-2a/2b ("Candidatus Methanocomedenaceae") and their syntrophic bacterial partners, SEEP-SRB1/2, adapted and grew under defined laboratory conditions. Metagenome-assembled genomes from several enrichments revealed that ANME-2a, SEEP-SRB1, and Methanococcoides in different enrichments from the same inoculum represented distinct species, whereas other coenriched microorganisms were closely related at the species level. This suggests that ANME, SRB, and Methanococcoides are more genetically diverse than other members in methane seeps. Flow cytometry sorting and sequencing of cell aggregates revealed that Methanococcoides, Anaerolineales, and SEEP-SRB1 were overrepresented in multiple ANME-2a cell aggregates relative to the bulk metagenomes, suggesting they were physically associated and possibly interacting. Overall, this study represents a successful case of selective cultivation of anaerobic slow-growing microorganisms from sediments based on their physical characteristics, introducing new opportunities for detailed genomic, physiological, biochemical, and ecological analyses. IMPORTANCE Biological anaerobic oxidation of methane (AOM) coupled with sulfate reduction represents a large methane sink in global ocean sediments. Methane consumption is carried out by syntrophic archaeal-bacterial consortia and fuels a unique ecosystem, yet the interactions in these slow-growing syntrophic consortia and with other associated community members remain poorly understood. The significance of this study is the establishment of sediment-free enrichment cultures of anaerobic methanotrophic archaea and sulfate-reducing bacteria performing AOM with sulfate using selective cultivation approaches based on size, density, and metabolism. By reconstructing microbial genomes and analyzing community composition of the enrichment cultures and cell aggregates, we shed light on the diversity of microorganisms physically associated with AOM consortia beyond the core syntrophic partners. These enrichment cultures offer simplified model systems to extend our understanding of the diversity of microbial interactions within marine methane seeps.

Technologies for Biological and Bioelectrochemical Removal of Inorganic Nitrogen from Wastewater: A Review

Water contamination due to various nitrogenous pollutants generated from wastewater treatment plants is a crucial and ubiquitous environmental problem now-a-days. Nitrogen contaminated water has manifold detrimental effects on human health as well as aquatic life. Consequently, various biological treatment processes are employed to transform the undesirable forms of nitrogen in wastewater to safer ones for subsequent discharge. In this review, an overview of various conventional biological treatment processes (viz. nitrification, denitrification, and anammox) have been presented along with recent novel bioelectrochemical methods (viz. microbial fuel cells and microbial electrolysis cells). Additionally, nitrogen is an indispensable nutrient necessary to produce artificial fertilizers by fixing dinitrogen gas from the atmosphere. Thus, this study also explored the potential capability of various nitrogen recovery processes from wastewater (like microalgae, cyanobacteria, struvite precipitation, stripping, and zeolites) that are used in industries. Further, the trade-offs, challenges posed by these processes have been dwelt on along with other biological processes like CANON, SHARON, OLAND, and others.

Metagenomic Insights Into Competition Between Denitrification and Dissimilatory Nitrate Reduction to Ammonia Within One-Stage and Two-Stage Partial-Nitritation Anammox Bioreactor Configurations

Anaerobic ammonia oxidizing bacteria (Anammox) are implemented in high-efficiency wastewater treatment systems operated in two general configurations; one-stage systems combine aerobic ammonia oxidizing bacteria (AOB) and Anammox within a single aerated reactor, whereas two-stage configurations separate these processes into discrete tanks. Within both configurations heterotrophic populations that perform denitrification or dissimilatory nitrate reduction to ammonia (DNRA) compete for carbon and nitrate or nitrite and can impact reactor performance because DNRA retains nitrogen in the system. Therefore, it is important to understand how selective pressures imposed by one-stage and two-stage reactor configurations impact the microbial community structure and associated nitrogen transforming functions. We performed 16S rRNA gene and metagenomic sequencing on different biomass fractions (granules, flocs, and suspended biomass) sampled from two facilities treating sludge dewatering centrate: a one-stage treatment facility (Chambers Creek, Tacoma, WA) and a two-stage system (Rotterdam, Netherlands). Similar microbial populations were identified across the different samples, but relative abundances differed between reactor configurations and biomass sources. Analysis of metagenome assembled genomes (MAGs) indicated different lifestyles for abundant heterotrophic populations. Acidobacteria, Bacteroidetes, and Chloroflexi MAGs had varying capacity for DNRA and denitrification. Acidobacteria MAGs possessed high numbers of glycosyl hydrolases and glycosyl transferases indicating a role in biomass degradation. Ignavibacteria and Phycosphaerae MAGs contributed to the greater relative abundance of DNRA associated nrf genes in the two-stage granules and contained genomic features suggesting a preference for an anoxic or microoxic niche. In the one-stage granules a MAG assigned to Burkholderiales accounted for much of the abundant denitrification genes and had genomic features, including the potential for autotrophic denitrification using reduced sulfur, that indicate an ability to adapt its physiology to varying redox conditions. Overall, the competition for carbon substrates between denitrifying and DNRA performing heterotrophs may be impacted by configuration specific selective pressures. In one-stage systems oxygen availability in the bulk liquid and the oxygen gradient within granules would provide a greater niche space for heterotrophic populations capable of utilizing both oxygen and nitrate or nitrite as terminal electron acceptors, compared to two-stage systems where a homogeneous anoxic environment would favor heterotrophic populations primarily adapted to anaerobic metabolism.

Dirammox Is Widely Distributed and Dependently Evolved in Alcaligenes and Is Important to Nitrogen Cycle

Nitrogen cycle is an essential process for environmental health. Dirammox (direct ammonia oxidation), encoded by the dnfT1RT2ABCD cluster, was a novel pathway for microbial N2 production defined in Alcaligenes ammonioxydans HO-1. Here, a copy of the cluster dnfT1RT2ABCD as a whole was proved to have existed and very conserved in all Alcaligenes genomes. Phylogenetic analyses based on 16S rRNA gene sequences and amino acid sequences of DnfAs, together with G + C content data, revealed that dnf cluster was evolved associated with the members of the genus Alcaligenes. Under 20% O2 conditions, 14 of 16 Alcaligenes strains showed Dirammox activity, which seemed likely taxon-related. However, the in vitro activities of DnfAs catalyzing the direct oxidation of hydroxylamine to N2 were not taxon-related but depended on the contents of Fe and Mn ions. The results indicated that DnfA is necessary but not sufficient for Dirammox activity. The fact that members of the genus Alcaligenes are widely distributed in various environments, including soil, water bodies (both freshwater and seawater), sediments, activated sludge, and animal-plant-associated environments, strongly suggests that Dirammox is important to the nitrogen cycle. In addition, Alcaligenes species are also commonly found in wastewater treatment plants, suggesting that they might be valuable resources for wastewater treatment.

Metagenomic evidence of a novel family of anammox bacteria in a subsea environment

Bacteria in the order 'Candidatus Brocadiales' within the phylum Planctomycetes (Planctomycetota) have the remarkable ability to perform anaerobic ammonium oxidation (anammox). Two families of anammox bacteria with different biogeographical distributions have been reported, marine Ca. Scalinduaceae and freshwater Ca. Brocadiaceae. Here we report evidence of three new species within a novel genus and family of anammox bacteria, which were discovered in biofilms of a subsea road tunnel under a fjord in Norway. In this particular ecosystem, the nitrogen cycle is likely fuelled by ammonia from organic matter degradation in the fjord sediments and the rock mass above the tunnel, resulting in the growth of biofilms where anammox bacteria can thrive under oxygen limitation. We resolved several metagenome-assembled genomes (MAGs) of anammox bacteria, including three Ca. Brocadiales MAGs that could not be classified at the family level. MAGs of this novel family had all the diagnostic genes for a full anaerobic ammonium oxidation pathway in which nitrite was probably reduced by a NirK-like reductase. A survey of published molecular data indicated that this new family of anammox bacteria occurs in many marine sediments, where its members presumably would contribute to nitrogen loss.

Multidisciplinary characterization of nitrogen-removal granular sludge: A review of advances and technologies

Nitrogen-removal granular sludge (NRGS) is a promising technology in wastewater treatment, with advantages of efficient nitrogen removal, less footprint, lower sludge production and energy consumption, and is a way for wastewater treatment plants to achieve carbon-neutrality. Aerobic granular sludge (AGS) and anammox granular sludge (AnGS) are two typical NRGS technologies that have attracted extensive attention. Mounting evidence has shown strong associations between NRGS properties and the status of NRGS systems; however, a holistic view is still missing. The aim of this article is to provide an overview of NRGS with an emphasis on characterization. Specifically, the integrated nitrogen transformation pathways inside NRGS and the performance of NRGS treating various wastewaters are discussed. NRGS properties are categorized as physical-, chemical-, biological- and systematical ones, presenting current advances and corresponding characterization technologies. Finally, the future prospects for furthering the mechanistic understanding and engineering application of NRGS are proposed. Overall, the technological advancements in characterization have greatly contributed to understanding NRGS properties, which are potential factors for optimizing the performance and evaluating the working status of NRGS. This review will provide guidance in characterizing NRGS properties and boost the introduction of novel characterization technologies.

Ammonia-oxidizing archaea and complete ammonia-oxidizing Nitrospira in water treatment systems

Nitrification, the oxidation of ammonia to nitrate via nitrite, is important for many engineered water treatment systems. The sequential steps of this respiratory process are carried out by distinct microbial guilds, including ammonia-oxidizing bacteria (AOB) and archaea (AOA), nitrite-oxidizing bacteria (NOB), and newly discovered members of the genus Nitrospira that conduct complete ammonia oxidation (comammox). Even though all of these nitrifiers have been identified within water treatment systems, their relative contributions to nitrogen cycling are poorly understood. Although AOA contribute to nitrification in many wastewater treatment plants, they are generally outnumbered by AOB. In contrast, AOA and comammox Nitrospira typically dominate relatively low ammonia environments such as drinking water treatment, tertiary wastewater treatment systems, and aquaculture/aquarium filtration. Studies that focus on the abundance of ammonia oxidizers may misconstrue the actual role that distinct nitrifying guilds play in a system. Understanding which ammonia oxidizers are active is useful for further optimization of engineered systems that rely on nitrifiers for ammonia removal. This review highlights known distributions of AOA and comammox Nitrospira in engineered water treatment systems and suggests future research directions that will help assess their contributions to nitrification and identify factors that influence their distributions and activity.

NH2OH Disproportionation Mediated by Anaerobic Ammonium-oxidizing (Anammox) Bacteria

Anammox bacteria produce N₂ gas by oxidizing NH₄⁺ with NO₂^–, and hydroxylamine (NH₂OH) is a potential intermediate of the anammox process. N₂ gas production occurs when anammox bacteria are incubated with NH₂OH only, indicating their capacity for NH₂OH disproportionation with NH₂OH serving as both the electron donor and acceptor. Limited information is currently available on NH₂OH disproportionation by anammox bacteria; therefore, the stoichiometry of anammox bacterial NH₂OH disproportionation was examined in the present study using ¹⁵N-tracing techniques. The anammox bacteria, Brocadia sinica, Jettenia caeni, and Scalindua sp. were incubated with the addition of ¹⁵NH₂OH, and the production of ¹⁵N-labeled nitrogenous compounds was assessed. The anammox bacteria tested performed NH₂OH disproportionation and produced ^15-15N₂ gas and NH₄⁺ as reaction products. The addition of acetylene, an inhibitor of the anammox process, reduced the activity of NH₂OH disproportionation, but not completely. The growth of B. sinica by NH₂OH disproportionation (–240.3‍ ‍kJ mol NH₂OH^–1 under standard conditions) was also tested in 3 up-flow column anammox reactors fed with 1) 0.7‍ ‍mM NH₂OH only, 2) 0.7‍ ‍mM NH₂OH and 0.5‍ ‍mM NH₄⁺, and 3) 0.7‍ ‍mM NH₂OH and 0.5‍ ‍mM NO₂^–. NH₂OH consumption activities were markedly reduced after 7‍ ‍d of operation, indicating that B. sinica was unable to maintain its activity or biomass by NH₂OH disproportionation.

Partnering of anammox and denitrifying bacteria benefits anammox's recovery from starvation and complete nitrogen removal

The cooperative metabolic activity of anammox and denitrifying bacteria could speed up anammox's recovery and reduce nitrate generated from the anammox reaction. In this study, a laboratory-scale model system containing a defined anammox culture AMX and a simultaneous nitrification and denitrification (SND) bacterium - Thauera sp. strain SND5 was established and investigated. Several lines of evidence revealed that strain SND5 consumed soluble microbial products (SMPs) generated by culture AMX (as high as 1.5 mg/L), stimulating anammox activity after long-term starvation. At low C/N ratios with an optimal C/N of 1, SND5 completely consumed organic carbon first at anoxic condition, storing carbon intracellularly as poly-β-hydroxybutyrate (PHB) (as high as 0.6 mg/L biomass), thereby creating a favorable environment for the growth of anammox bacteria. The anammox reaction and nitrate reduction supported by PHB catabolism could then proceed simultaneously, resulting in enhanced nitrogen removal. Cooperative interactions between anammox and denitrifying bacteria involving SMPs consumption and PHB synthesis may play a significant role in nitrogen cycling at nitrite- and carbon-limited environments.

Sustainable Intensification of Maize in the Industrial Revolution: Potential of Nitrifying Bacteria and Archaea

Sustainable intensification is a means that proffer a solution to the increasing demand for food without degrading agricultural land. Maize is one of the most important crops in the industrial revolution era, there is a need for its sustainable intensification. This review discusses the role of maize in the industrial revolution, progress toward sustainable production, and the potential of nitrifying bacteria and archaea to achieve sustainable intensification. The era of the industrial revolution (IR) uses biotechnology which has proven to be the most environmentally friendly choice to improve crop yield and nutrients. Scientific research and the global economy have benefited from maize and maize products which are vast. Research on plant growth-promoting microorganisms is on the increase. One of the ways they carry out their function is by assisting in the cycling of geochemical, thus making nutrients available for plant growth. Nitrifying bacteria and archaea are the engineers of the nitrification process that produce nitrogen in forms accessible to plants. They have been identified in the rhizosphere of many crops, including maize, and have been used as biofertilizers. This study's findings could help in the development of microbial inoculum, which could be used to replace synthetic fertilizer and achieve sustainable intensification of maize production during the industrial revolution.

Effects of marine produced organic matter on the potential estuarine capacity of NOx- removal

Dissolved inorganic nitrogen (DIN) is very high in the Pearl River Estuary (PRE) and nitrate (NO_x^-) removal processes such as denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA) are important for determining export of DIN to coastal waters. However, fluxes of NO_x^- removal and influencing factors in the PRE are still unclear. We conducted 4 cruises at 11 sites in the PRE to investigate potential NO_x^- removal rates, their contributions, and corresponding gene abundances, and controlling factors in surface sediments (0-5 cm). The results showed that the potential rates of denitrification, anammox, and DNRA as well as their contributions varied spatially and seasonally. Denitrification (1.98 ± 1.7 μg N g^-1 d^-1) was the major NO_x^- removal processes (68.43 ± 14.61%) while DNRA (0.45 ± 0.28 μg N g^-1 d^-1) contributed 22.61 ± 14.89% in NO_x^- removal. The NO_x^- removal processes and corresponding gene abundances were correlated with the chlorophyll concentrations in both overlying water and sediment, indicating that marine-produced organic matter was the major driver for benthic NO_x^- removal processes. In addition, water column turbidity had important effects on primary production, which affects benthic N processes. Our study provides evidences for that the turbidity-regulated primary production in overlying water is the primary driver for benthic NO_x^- removal processes. The contribution of sediment NO_x^- removal fluxes to water column NO_x^- concentration was low in the upper estuary and increased in the lower estuary where marine produced chlorophyll a was higher. However, daily fluxes of NO_x^- removal were estimated to account for only 0.18-7.22% (mean 1.85 ± 1.62%) of NO_x^- in the whole overlying water column. This suggests that most riverine NO_x^- was exported out into the adjacent coastal waters.

Long-Term Limitation Effects of Se(VI), Zn(II), and Ni(II) on Start-Up of the Anammox Process Using Gel Carrier

Anaerobic ammonia oxidation (anammox) bacteria are inhibited by heavy metals at high concentrations but require trace amounts of some heavy-metal elements for growth and activity maintenance. The present study evaluates the long-term limitation effects of Se(VI), Zn(II), and Ni(II) on the start-up period of an anammox reactor. To strictly limit the levels of heavy metals in the reactor, all tests used ultrapure water as the influent synthetic wastewater and all reactors were installed in a clean booth. The anammox biomass was maintained through the gel entrapment technique. In the absence of Se(VI) and Ni(II), the anammox reactor start-up was 18.9 kg-N (m³-carrier d)⁻¹ (nitrogen conversion rate (NCR) per gel carriers), indicating that Se(VI) and Ni(II) are not required or need not be continuously added to maintain the anammox process. Under Zn(II) limitation, the anammox process failed to start-up and the NCR tended to decrease rapidly. After readdition of 0.005 mg L⁻¹ of Zn(II), the NCR did not decline further and instead partially recovered at a very slow rate. The NCR was completely recovered after adding 0.020 mg L⁻¹ of Zn(II). These results reveal that Zn(II) limitation seriously affects the start-up of the anammox process while Se(VI) and Ni(II) are not required or need not be continuously added to the anammox process.

The removal of ammonia nitrogen via heterotrophic assimilation by a novel Paracoccus sp. FDN-02 under anoxic condition

A novel strain FDN-02 was isolated from a sequencing batch biofilm reactor. FDN-02 was identified as Paracoccus sp., and the Genbank Sequence_ID was MW652628. Comparing with the removal efficiency of ammonia nitrogen (NH₄⁺-N) by bacterium FDN-02 under different growth conditions, the optimal initial pH, carbon source, and C/N ratio were 7.0, sucrose, and 16, respectively. The maximum removal efficiency and rate of NH₄⁺-N were respectively 96.2% and 10.06 mg-N/L/h within 8 h under anoxic condition when the concentration of NH₄⁺-N was 44.87 mg/L. Specifically, 71.9% of NH₄⁺-N was utilized by strain FDN-02 through heterotrophic assimilation to synthetize organic nitrogen, and approximately 24.1% of NH₄⁺-N was lost in the form of gaseous nitrogen without the emission of nitrous oxide. Bacterium FDN-02 was also found to be a denitrifying organism, and nitrate nitrogen and nitrite nitrogen of lower concentrations were removed by denitrification after the enlargement of biomass. Further investigation showed that the biomass after the removal of NH₄⁺-N by strain FDN-02 had resource utilization potential, and the contents of proteins and amino acids were 635 and 192.97 mg/g, respectively, especially for the usage as an alternative nutrient source for livestock and organic fertilizers. This study provided a promising environmentally friendly biological treatment method for the removal of NH₄⁺-N in the wastewater.

Metabolic Diversity and Aero-Tolerance in Anammox Bacteria from Geochemically Distinct Aquifers

Anaerobic ammonium oxidation (anammox) is important for converting bioavailable nitrogen into dinitrogen gas, particularly in carbon-poor environments. However, the diversity and prevalence of anammox bacteria in the terrestrial subsurface-a typically oligotrophic environment-are little understood. To determine the distribution and activity of anammox bacteria across a range of aquifer lithologies and physicochemistries, we analyzed 16S rRNA genes and quantified hydrazine synthase genes and transcripts sampled from 59 groundwater wells and metagenomes and metatranscriptomes from an oxic-to-dysoxic subset. Data indicate that anammox and anammox-associated bacteria (class "Candidatus Brocadiae") are prevalent in the aquifers studied, and that anammox community composition is strongly differentiated by dissolved oxygen (DO), but not ammonia/nitrite. While "Candidatus Brocadiae" diversity decreased with increasing DO, "Candidatus Brocadiae" 16S rRNA genes and hydrazine synthase (hzsB) genes and transcripts were detected across a wide range of bulk groundwater DO concentrations (0 to 10 mg/L). Anammox genes and transcripts correlated significantly with those involved in aerobic ammonia oxidation (amoA), potentially representing a major source of nitrite for anammox. Eight "Candidatus Brocadiae" genomes (63 to 95% complete), representing 2 uncharacterized families and 6 novel species, were reconstructed. Six genomes have genes characteristic of anammox, all for chemolithoautotrophy. Anammox and aerotolerance genes of up to four "Candidatus Brocadiae" genomes were transcriptionally active under oxic and dysoxic conditions, although activity was highest in dysoxic groundwater. The coexpression of nrfAH nitrite reductase genes by "Candidatus Brocadiae" suggests active regeneration of ammonia for anammox. Our findings indicate that anammox bacteria contribute to loss of fixed N across diverse anoxic-to-oxic aquifer conditions, which is likely supported by nitrite from aerobic ammonia oxidation. IMPORTANCE Anammox is increasingly shown to play a major role in the aquatic nitrogen cycle and can outcompete heterotrophic denitrification in environments low in organic carbon. Given that aquifers are characteristically oligotrophic, anammox may represent a major route for the removal of fixed nitrogen in these environments, including agricultural nitrogen, a common groundwater contaminant. Our research confirms that anammox bacteria and the anammox process are prevalent in aquifers and occur across diverse lithologies (e.g., sandy gravel, sand-silt, and volcanic) and groundwater physicochemistries (e.g., various oxygen, carbon, nitrate, and ammonium concentrations). Results reveal niche differentiation among anammox bacteria largely driven by groundwater oxygen contents and provide evidence that anammox is supported by proximity to oxic niches and handoffs from aerobic ammonia oxidizers. We further show that this process, while anaerobic, is active in groundwater characterized as oxic, likely due to the availability of anoxic niches.

Effects of sludge morphology on the anammox process: Analysis from the perspectives of performance, structure, and microbial community

The nitrogen removal characteristics, physicochemical properties, and microbial community composition of four different anaerobic ammonium oxidation (anammox) sludge morphologies were investigated. The morphologies considered in this study, namely suspended sludge (Rs), biofilm (Rm), granular sludge (Rg), and encapsulated biomass (Re), were prepared from floc sludge. The results show that Re exhibited the maximum anammox activity, followed by Rg, Rm, and Rs. Additionally, the anammox contribution rate was higher in Rg and Re. The higher extracellular polymer content in Rg promoted sludge accumulation, and tryptophan was observed in Rm and Rg, which was replaced by humic acids in Rs. Re showed the largest specific surface area, hydrophobicity and strength, and its good structure ensured enrichment of anammox bacteria (AnAOB). In terms of the microbial community, the functional bacterium Candidatus Kuenenia accounted for the highest proportion in Rm (39.27%), but the presence of both anaerobic and aerobic regions led to increased community complexity with more nitrifying bacteria. In contrast, Rg and Re had a more specific microbial community. In addition, denitrifying bacteria tended to grow in Rs, while nitrifying bacteria were retained in Rm. The AnAOB were more likely to be enriched in sludge aggregates (both Rm and Rg) and carriers (Re). Through correlation analysis, the potential relationship involving bacterial flora evolution of each sample was clarified. Finally, the structural models of different morphologies of sludge were proposed. This study deepens the understanding of various anammox sludge morphologies as well as provides useful information for the cultivation of AnAOB and further application of anammox.

Diversity and Distribution of Anaerobic Ammonium Oxidation Bacteria in Hot Springs of Conghua, China

Anaerobic ammonium oxidation (anammox) is an important process of the nitrogen cycle, and the anammox bacteria have been studied in a wide variety of environments. However, the distribution, diversity, and abundance of anammox bacteria in hot springs remain enigmatic. In this study, the anammox process was firstly investigated in hot springs of Conghua, China. Anammox-like bacterial sequences that closely affiliated to “Candidatus Brocadia,” “Candidatus Kuenenia,” “Candidatus Scalindua,” “Candidatus Anammoxoglobus,” and “Candidatus Jettenia” were detected. Several operational taxonomic units (OTUs) from this study shared low sequence identities to the 16S rRNA gene of the known anammox bacteria, suggesting that they might be representing putative novel anammox bacteria. A quantitative PCR analysis of anammox-specific 16S rRNA gene confirmed that the abundance of anammox bacteria ranged from 1.60 × 10⁴ to 1.20 × 10⁷ copies L^–1. Nitrate was a key environmental factor defining the geographical distribution of the anammox bacterial community in the hot spring ecosystem. Dissolved inorganic carbon had a significant influence on anammox bacterial biodiversity. Our findings for the first time revealed that the diverse anammox bacteria, including putative novel anammox bacterial candidates, were present in Conghua hot spring, which extended the existence of anammox bacteria to the hot springs in China and expands our knowledge of the biogeography of anammox bacteria. This work filled up the research lacuna of anammox bacteria in Chinese hot spring habitat and would guide for enrichment strategies of anammox bacteria of Conghua hot springs.

Granular activated carbon promoting re-granulation of anammox-hydroxyapatite granules for stable nitrogen removal at low phosphate concentration

Anaerobic ammonium oxidation (anammox) coupled with hydroxyapatite (HAP) crystallization not only achieves simultaneous nitrogen removal and phosphorus recovery, but also cultivates excellent anammox granules. However, a floatation and wash-out of anammox-HAP granules was occurred at low phosphate concentrations. In this study, a reactor inoculated with mature anammox-HAP granules and fed with low phosphate (5 mg P/L) was added with granular activated carbon (GAC) to maintain sludge granulation and nitrogen-removing stability. At influent total nitrogen >800 mg/L and nitrogen loading rate ~ 9.8 kg/m³/d, a satisfactory nitrogen removal of around 88% was maintained during 140 days of operation. Insufficient phosphate supplement resulted in a sludge bulking, with suspended solid and sludge density decreased whereas sludge water content and expansion ratio increased due to HAP loss. Nevertheless, the sludge re-granulation was found at the later stage as the proportion of granules in 2.8- 3.35 mm went up to 37.4% after large granules disintegrated into small pieces at the initial stage. The settling velocity was finally ranging from 129.8 to 182.2 m/h. In addition, Candidatus Brocadia was increased from 2.1% to 20.1% and dominated in the microbial community. These findings suggest GAC was able to promote re-granulation of anammox-HAP granules at low phosphate concentration, which avoids sludge flotation and widens their application as an inoculum.

Mucisphaera calidilacus gen. nov., sp. nov., a novel planctomycete of the class Phycisphaerae isolated in the shallow sea hydrothermal system of the Lipari Islands

For extending the current collection of axenic cultures of planctomycetes, we describe in this study the isolation and characterisation of strain Pan265^T obtained from a red biofilm in the hydrothermal vent system close to the Lipari Islands in the Tyrrhenian Sea, north of Sicily, Italy. The strain forms light pink colonies on solid medium and grows as a viscous colloid in liquid culture, likely as the result of formation of a dense extracellular matrix observed during electron microscopy. Cells of the novel isolate are spherical, motile and divide by binary fission. Strain Pan265^T is mesophilic (temperature optimum 30-33 °C), neutrophilic (pH optimum 7.0-8.0), aerobic and heterotrophic. The strain has a genome size of 3.49 Mb and a DNA G + C content of 63.9%. Phylogenetically, the strain belongs to the family Phycisphaeraceae, order Phycisphaerales, class Phycisphaerae. Our polyphasic analysis supports the delineation of strain Pan265^T from the known genera in this family. Therefore, we conclude to assign strain Pan265^T to a novel species within a novel genus, for which we propose the name Mucisphaera calidilacus gen. nov., sp. nov. The novel species is the type species of the novel genus and is represented by strain Pan265^T (= DSM 100697^T = CECT 30425^T) as type strain.

Effects of pharmaceuticals on the nitrogen cycle in water and soil: a review

The effects of pharmaceuticals on the nitrogen cycle in water and soil have recently become an increasingly important issue for environmental research. However, a few studies have investigated the direct effects of pharmaceuticals on the nitrogen cycle in water and soil. Pharmaceuticals can contribute to inhibition and stimulation of nitrogen cycle processes in the environment. Some pharmaceuticals have no observable effect on the nitrogen cycle in water and soil while others appeared to inhibit or stimulate for it. This review reports on the most recent evidence of effects of pharmaceuticals on the nitrogen cycle processes by examination of the potential impact of pharmaceuticals on nitrogen fixation, nitrification, ammonification, denitrification, and anammox. Research studies have identified pharmaceuticals that can either inhibit or stimulate nitrification, ammonification, denitrification, and anammox. Among these, amoxicillin, chlortetracycline, ciprofloxacin, clarithromycin, enrofloxacin, erythromycin, narasin, norfloxacin, and sulfamethazine had the most significant effects on nitrogen cycle processes. This review also clearly demonstrates that some nitrogen transformation processes such as nitrification show much higher sensitivity to the presence of pharmaceuticals than other nitrogen transformations or flows such as mineralization or ammonia volatilization. We conclude by suggesting that future studies take a more comprehensive approach to report on pharmaceuticals' impact on the nitrogen cycle process.

The Planctomycetia: an overview of the currently largest class within the phylum Planctomycetes

The phylum Planctomycetes comprises bacteria with uncommon features among prokaryotes, such as cell division by budding, absence of the bacterial tubulin-homolog cell division protein FtsZ and complex cell plans with invaginations of the cytoplasmic membrane. Although planctomycetes are ubiquitous, the number of described species and isolated strains available as axenic cultures is still low compared to the diversity observed in metagenomes or environmental studies. An increasing interest in planctomycetes is reflected by the recent description of a large number of new species and their increasing accessibility in terms of pure cultures. In this review, data from all taxonomically described species belonging to Planctomycetia, the class with the currently highest number of characterized members within the phylum Planctomycetes, is summarized. Phylogeny, morphology, physiology, ecology and genomic traits of its members are discussed. This comprehensive overview will help to acknowledge several aspects of the biology of these fascinating bacteria.

Metagenomic Analysis of Five Phylogenetically Distant Anammox Bacterial Enrichment Cultures

Anaerobic ammonium-oxidizing (anammox) bacteria are slow-growing and fastidious bacteria, and limited numbers of enrichment cultures have been established. A metagenomic ana-lysis of our 5 established anammox bacterial enrichment cultures was performed in the present study. Fourteen high-quality metagenome-assembled genomes (MAGs) were obtained, including those of 5 anammox Planctomycetota (Candidatus Brocadia, Ca. Kuenenia, Ca. Jettenia, and Ca. Scalindua), 4 Bacteroidota, and 3 Chloroflexota. Based on the gene sets of metabolic pathways involved in the degradation of polymeric substances found in Chloroflexota and Bacteroidota MAGs, they are expected to be scavengers of extracellular polymeric substances and cell debris.

Variations of N concentrations and microbial community in the start-up of anammox using anaerobic heterotrophic sludge: Influence of a long reaction-phase time and comparison of the efficiencies of attached-versus suspended-growth cultures

Anaerobic sludge was capable of producing anaerobic ammonium oxidation (anammox) cultures. However, the low activity of anammox bacteria in the seed sludge often led to a long time for stable anammox to initiate. The objective of this study was to investigate the influence of an extended reaction-phase time in the sequencing batch reactor (SBR) on the rapid startup of anaerobic ammonium oxidation (anammox) using anaerobic heterotrophic bacteria as the seed sludge. After the startup, suspended and attached bacteria in anammox were separately analyzed for comparison. The variations of nitrogen concentrations and shifts of the microbial community structures were studied. The results showed that anammox occurred after a long reaction-phase time in the SBR with the efficient removals of NH₄⁺ (96.4%) and NO₂^- (99.8%). The effective NO₂^- treatment before anammox startup was attributable to inevitable denitrification or dissimilatory nitrate reduction (e.g., Denitratisoma). The occurrence of anammox was supported by the anammox stoichiometry, bacteria diversity variation, and principal component analysis. The overall nitrogen removal rate (NRR) and nitrogen removal efficiency (NRE) was 0.07 kg/m³-d and 92.8%, respectively. The relative molar quantities of NH₄⁺ and NO₂^- removed as well as N₂ and NO₃^- formed were 1(1):1.29(1.32):1.45(1.02):0.15(0.26), as the numbers in the parentheses represent the theoretical values. Denitratisoma and Desulfatiglans dominated in the seed sludge, whereas Candidatus_Jettenia abundances were significantly higher in anammox attached- (26.0%) and suspended-growth cultures (14.5%). Fifty-three genera were simultaneously identified in all samples, suggesting their importance in the startup of anammox from anaerobic sludge. Candidatus_Jettenia was observed to be more associated with the growth of anammox biofilm (the abundances were 26.0% and 14.5% in attached- and suspended-growth cultures, respectively) and supported the fine nitrogen removal performance in the attached-growth cultures.

Insights into complete nitrate removal in one-stage nitritation-anammox by coupling heterotrophic denitrification

Nitritation-anammox has been considered to be the most promising process for nitrogen (N) removal from wastewater. However, the anammox reaction still produces an amount of nitrate, which cannot be removed further. This study hypothesizes that heterotrophic denitrification can be an appealing option to remove the residual nitrate in the one-stage nitritation-anammox process. Through monitoring N-removal performance and microbial community succession of a laboratory microaerobic reactor, the effect of four different levels of oxygen supply on nitrate removal was investigated. The reactor was continuously fed with real manure-free piggery wastewater containing ~240 mg NH₄⁺-N/L and chemical oxygen demand (COD)/total nitrogen (TN) ratio of less than 1 for 180 days. With a high influent loading rate of 0.7 kg N/(m³·d), efficient total nitrogen removal (>80 %) was achieved during stable operation of dissolved oxygen (DO) concentrations between 0.3 and 0.6 mg O₂/L, indicating N-removal via the nitritation-anammox pathway in the low-carbon wastewater treatment. At the same time, the effluent nitrate reduced with decreased oxygen supply and completely depleted at DO of 0.3 ± 0.1 mg O₂/L. In addition to oxygen, preventing ammonia nitrogen from falling to very low levels (<10 mg/L) could be also useful for the complete nitrate removal and stable nitritation-anammox. 16S rRNA gene-based analyses confirmed a complex microbial community including nitrifiers, denitrifiers and anammox bacteria in the biomass of the reactor. Collectively, this study provides new insights into high-level N-removal of a nitritation-anammox process by complete nitrate depletion.

Optimization nutrient removal at different volume ratio of anoxic-to-aerobic zone in integrated fixed-film activated sludge (IFAS) system

This study evaluated the influence of different volume ratios of the anoxic-to-aerobic zone (V_ano/V_aer) on the enhancement of nitrogen and phosphorus removal in an integrated fixed-film activated sludge (IFAS) system. As the V_ano/V_aer increased from 1:2 to 2:1, the removal of organic carbon, nitrogen and phosphorus nutrients of the IFAS system was improved. At V_ano/V_aer = 1:1, the removal effect of nitrogen and phosphorus nutrients was optimal, and the average removal rates of COD, NH₄⁺-N, TN, and TP of the system reached 90 ± 3.2%, 98.2 ± 1.4%, 88.9 ± 2.2%, and 89.1 ± 2.7%, respectively. As the volume of the anoxic zone continued to increase, the denitrifying phosphate-accumulating capacity of the system was enhanced, and the highest ratio of specific anoxic and aerobic phosphorus uptake rate could reach 65.3%. Analysis of the molecular evaluation showed that, the proportion of nitrifying bacteria in the biofilm gradually increased as V_ano increased. Moreover, denitrifying phosphate-accumulating organisms (DNPAOs), ammonia-oxidizing archaea (AOA), and anaerobic ammonium oxidizing (Anammox) bacteria were all enriched all showed enrichment in the biofilm of fiber carriers, which further strengthened the system's synergistic removal of nitrogen and phosphorus.

Achieving stable mainstream nitrogen and phosphorus removal assisted by hydroxylamine addition in a continuous partial nitritation/anammox process from real sewage

Hydroxylamine (NH₂OH) as the putative intermediate for anammox ensures the robustness of partial nitritation/anammox (PN/A) process; however, the feasible for NH₂OH addition to improve the stability of PN/A process under low-strength ammonia (NH₄⁺-N) condition need to be further investigated. In this study, the restoration and steady operation of mainstream PN/A process were investigated to treat real sewage with in situ NH₂OH added in a continuous alternating anoxic/aerobic with integrated fixed-film activated sludge (A³-IFAS) reactor. Results showed that the deteriorated PN/A process caused by nitrate (NO₃^--N) built-up was rapidly restored with a distinct decrease of the NO₃^--N_produced/NH₄⁺-N_consumed ratio from 28.7% to <10.0% within 20 days, after 5 mg N/L of NH₂OH was added daily into the aerobic zone of A³-IFAS reactor. After 230 days of operation, the average total nitrogen (TN) and phosphate (PO₄^3--P) removal efficiencies of 80.8% and 91.5%, respectively were stably achieved, with average effluent sCOD, NH₄⁺-N, TN and PO₄^3--P concentrations reaching 23.1, 2.3, 7.7 and 0.4 mg/L, respectively. Microbial community characterization revealed Candidatus Brocadia (3.60% and 2.92%) and Ignavibacteriae (1.56% and 2.66%) as the dominant anammox bacteria and denitrifying bacteria, respectively, jointly attached in the biofilm_1 and biofilm_2, while Candidatus Microthrix (5.17%) dominant in floc sludge was main responsible for phosphorus removal. This study confirmed that NH₂OH addition is an effective strategy for nitrite-oxidizing bacteria suppression, contributing to the in situ restoration of PN/A process and high stable mainstream nitrogen and phosphorus removal in a continuous PN/A process from real sewage.

Classification of uncultivated anammox bacteria and Candidatus Uabimicrobium into new classes and provisional nomenclature as Candidatus Brocadiia classis nov. and Candidatus Uabimicrobiia classis nov. of the phylum Planctomycetes and novel family Candidatus Scalinduaceae fam. nov to accommodate the genus Candidatus Scalindua

The phylum Planctomycetes is metabolically unique group of bacteria divided in two classes Planctomycetia and Phycisphaerae. Anaerobic ammonia-oxidizing (anammox) bacteria are the uncultured representatives of the phylum Planctomycetes. Anammox bacterial genera are placed in the family Candidatus (Ca.) Brocadiaceae of the order Ca. Brocadiales, assigned to the class Planctomycetia. Phylogenetic analysis, showed that the anammox bacteria and Ca. Uabimicrobium form a divergent clade from the rest of the cultured representatives of the phylum Planctomycetes. The phylogenetic study, pairwise distance and Average Amino acid Identity (AAI) showed that anammox bacteria don't belong to the classes Planctomycetia and Phycisphaerae. Anammox bacteria and Ca. Uabimicrobium form a deep-branching third clade in the phylogenetic analysis indicating that it is the most ancient third class within the phylum Planctomycetes. Phenotypic characters also separate anammox bacteria from classes Planctomycetia and Phycisphaerae. Therefore, based on phenotypic, phylogenetic, pairwise distance, AAI and phylogenomic analysis we propose a novel class Ca. Brocadiia to accommodate the order Ca. Brocadiales of anammox bacteria except Ca. Anammoximicrobium. Genera Ca. Jettenia, Ca. Anammoxoglobus, Ca. Kuenenia and Ca. Brocadia show their phylogenetic affiliation to the family Ca. Brocadiaceae. However, Ca. Scalindua showed a distant relationship with the family Ca. Brocadiaceae. Therefore, we suggest the exclusion of the genus Ca. Scalindua from the family Ca. Brocadiaceae; and propose its inclusion under a novel family with a provisional name as Ca. Scalinduaceae fam. nov. Similarly, Ca. Uabimicrobium amporphum showed distinct phylogenetic affiliation, therefore we propose a novel class Ca. Uabimicrobiia classis nov. to accommodate the genus Ca. Uabimicrobium.

Efficient nitrogen removal from mainstream wastewater through coupling Partial Nitritation, Anammox and Methane-dependent nitrite/nitrate reduction (PNAM)

The application of partial nitritation and anammox to remove nitrogen from mainstream wastewater is of great interest because of the potential to reduce energy cost and carbon dosage. However, this process confronts a dilemma of relatively high effluent nitrogen concentration (>10 mg N/L), owning to the unwanted prevalence of nitrite-oxidizing bacteria (NOB) and the intrinsic nitrate production by anammox bacteria. Here, a novel technology, named the one-stage PNAM, that integrates Partial Nitritation, Anammox and Methane-dependent nitrite/nitrate reduction reactions, was developed in a single membrane biofilm reactor (MBfR). With feeding of synthetic mainstream wastewater containing ∼50 mg NH₄⁺-N/L at a hydraulic retention time of 12 h, more than 95% nitrogen was removed in the established one-stage PNAM process at a practically useful rate of 0.1 kg N/m³/d. Microbial community characterization and in-situ batch tests revealed a sophisticated microbial structure consisting of ammonia-oxidizing bacteria (AOB), anammox bacteria, nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) bacteria and archaea, and a small fraction of NOB and aerobic methanotrophs. The role of methane in removing nitrate was confirmed by switching on/off the methane supply, which relaxed the requirement for NOB suppression. In addition, the established system was relatively robust against temperature variations, evidenced by a total nitrogen removal efficiency above 80% at temperature as low as 14 ℃. The results provide a promising alternative for efficient nitrogen removal from domestic wastewater using methane as the sole carbon source.

Activities and metabolic versatility of distinct anammox bacteria in a full-scale wastewater treatment system

Anaerobic ammonium oxidation (anammox) is a key N₂-producing process in the global nitrogen cycle. Major progress in understanding the core mechanism of anammox bacteria has been made, but our knowledge of the survival strategies of anammox bacteria in complex ecosystems, such as full-scale wastewater treatment plants (WWTPs), remains limited. Here, by combining metagenomics with in situ metatranscriptomics, complex anammox-driven nitrogen cycles in an anoxic tank and a granular activated carbon (GAC) biofilm module of a full-scale WWTP treating landfill leachate were constructed. Four distinct anammox metagenome-assembled genomes (MAGs), representing a new genus named Ca. Loosdrechtii, a new species in Ca. Kuenenia, a new species in Ca. Brocadia, and a new strain in "Ca. Kuenenia stuttgartiensis", were simultaneously retrieved from the GAC biofilm. Metabolic reconstruction revealed that all anammox organisms highly expressed the core metabolic enzymes and showed a high metabolic versatility. Pathways for dissimilatory nitrate reduction to ammonium (DNRA) coupled to volatile fatty acids (VFAs) oxidation likely assist anammox bacteria to survive unfavorable conditions and facilitate switches between lifestyles in oxygen fluctuating environments. The new Ca. Kuenenia species dominated the anammox community of the GAC biofilm, specifically may be enhanced by the uniquely encoded flexible ammonium and iron acquisition strategies. The new Ca. Brocadia species likely has an extensive niche distribution that is simultaneously established in the anoxic tank and the GAC biofilm, the two distinct niches. The highly diverse and impressive metabolic versatility of anammox bacteria revealed in this study advance our understanding of the survival and application of anammox bacteria in the full-scale wastewater treatment system.

Effect of inorganic carbon limitation on the nitrogen removal performance of the single-stage reactor containing anammox and nitritation gel carriers

Herein, the effect of inorganic carbon (IC) limitation on the nitrogen removal performance of the single-stage reactor containing nitritation and anammox gel carriers was investigated. As a result of a continuous feeding test, the effluent ammonium concentration increased as the IC concentration decreased, indicating the deterioration of nitritation activity, not anammox. Furthermore, the sensitivity of IC to anammox and nitritation activity was investigated in anammox and nitritation reactors, respectively. Consequently, the relationship between the effluent IC concentration and nitritation rate was well described using the Michaelis-Menten equation. The apparent K_m value of nitritation was calculated as 4.4 mg-C L^-1. In anammox reactor, it was calculated as 1.7 mg-C L^-1. These results revealed that the affinity of nitritation gel carriers to IC was lower than that of anammox, supporting that nitritation activity was easily deactivated by decrease in the IC concentration rather than anammox. Microbial community analysis revealed that Nitrosomonas europaea and Candidatus Jettenia asiatica were the dominant species of ammonium-oxidizing and anammox bacteria.

Mechanistic understanding of the pollutant removal and transformation processes in the constructed wetland system

Constructed wetland systems (CWs) are biologically and physically engineered systems to mimic the natural wetlands which can potentially treat the wastewater from the various point and nonpoint sources of pollution. The present study aims to review the various mechanisms involved in the different types of CWs for wastewater treatment and to elucidate their role in the effective functioning of the CWs. Several physical, chemical, and biological processes substantially influence the pollutant removal efficiency of CWs. Plants species Phragmites australis, Typha latifolia, and Typha angustifolia are most widely used in CWs. The rate of nitrogen (N) removal is significantly affected by emergent vegetation cover and type of CWs. Hybrid CWs (HCWS) removal efficiency for nutrients, metals, pesticides, and other pollutants is higher than a single constructed wetland. The contaminant removal efficiency of the vertical subsurface flow constructed wetlands (VSSFCW) commonly used for the treatment of domestic and municipal wastewater ranges between 31% and 99%. Biochar/zeolite addition as substrate material further enhances the wastewater treatment of CWs. Innovative components (substrate materials, plant species) and factors (design parameters, climatic conditions) sustaining the long-term sink of the pollutants, such as nutrients and heavy metals in the CWs should be further investigated in the future. PRACTITIONER POINTS: Constructed wetland systems (CWs) are efficient natural treatment system for on-site contaminants removal from wastewater. Denitrification, nitrification, microbial and plant uptake, sedimentation and adsorption are crucial pollutant removal mechanisms. Phragmites australis, Typha latifolia, and Typha angustifolia are widely used emergent plants in constructed wetlands. Hydraulic retention time (HRT), water flow regimes, substrate, plant, and microbial biomass substantially affect CWs treatment performance.

Biologically Available Chemical Energy in the Temperate but Uninhabitable Venusian Cloud Layer: What Do We Want to Know?

The cloud layer has been hypothesized to be the most habitable region of Venus. In the lower clouds, both temperature and pressure fall within bounds that support reproduction of microbial life on Earth, although the water activity of the sulfuric acid cloud droplets makes the clouds uninhabitable to known life. In this study, we carried out an analysis of CHNOPS (carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur) elements and potential redox couples in the cloud layer, and we used a microbial energetic growth model to investigate quantitatively the chemical energy available for microbial growth from methanogenesis, sulfate reduction, and hydrogen oxidation at temperatures between 278 and 350 K. The purpose was to improve knowledge of how far the venusian cloud layer comes from being habitable. Hydrogen oxidation was favorable at all temperatures; however, negative Gibbs free energies for sulfate reduction and methanogenesis depended critically on the assumed concentrations of electron donors, acceptors, and products. Improved measurements and the investigation of new molecules will allow us to better assess quantitatively how far Venus comes from possessing a habitable cloud layer and what would need to be different to make it habitable. We identify specific required measurements. These data will advance our understanding of the habitability of planetary atmospheres on extrasolar greenhouse worlds and the habitability of Earth when the planet eventually enters a greenhouse state.

Spatial variability pattern of the anaerobic ammonia-oxidizing bacterial community across a salinity gradient from river to ocean

In natural habitats, the diversity of anaerobic ammonia-oxidizing (anammox) bacteria could be affected by multiple environmental variables. In this study, we investigated the distribution of the anammox bacterial community in surface sediment from the Dongjiang River (riverine sediment, DJ) to the Pearl River Estuary (estuarine sediment, PRE) and then to the South China Sea (coastal sediment, SCS). The results revealed evident differences in the structural diversity of anammox bacteria in three different habitats. Candidatus Brocadia accounted for approximately 90% of the total anammox bacteria in DJ, conversely, Ca. Scalindua dominated in the SCS. Nevertheless, Ca. Scalindua, Ca. Brocadia and Ca. Kuenenia coexisted in the PRE. The qPCR results indicated that anammox bacterial 16S rRNA gene abundance ranged from 2.23 × 10⁵ to 1.19 × 10⁷ copies g^-1 of wet weight, but no significant correlation was found between the abundances and environmental variables (p > 0.05). The relative abundances of Ca. Brocadia gradually decreased with increasing salinity, and Ca. Scalindua showed the opposite trend, suggesting that salinity was a crucial factor in sculpturing the community composition of anammox bacteria in natural environments. Ca. Brocadia should be able to live in freshwater ecosystems, but it can also tolerate a certain level of salinity. Ca. Scalindua was halophilic anammox bacterium and exists only in saline environments. Ca. Kuenenia could adapt to a wide range of salinity and preferred to live in high DIN level conditions according to our search. The distribution pattern of anammox bacteria may be the result of microbial migration and long-term adaptation to salinity.

Novel Alcaligenes ammonioxydans sp. nov. from wastewater treatment sludge oxidizes ammonia to N2 with a previously unknown pathway

Heterotrophic nitrifiers are able to oxidize and remove ammonia from nitrogen-rich wastewaters but the genetic elements of heterotrophic ammonia oxidation are poorly understood. Here, we isolated and identified a novel heterotrophic nitrifier, Alcaligenes ammonioxydans sp. nov. strain HO-1, oxidizing ammonia to hydroxylamine and ending in the production of N₂ gas. Genome analysis revealed that strain HO-1 encoded a complete denitrification pathway but lacks any genes coding for homologous to known ammonia monooxygenases or hydroxylamine oxidoreductases. Our results demonstrated strain HO-1 denitrified nitrite (not nitrate) to N₂ and N₂ O at anaerobic and aerobic conditions respectively. Further experiments demonstrated that inhibition of aerobic denitrification did not stop ammonia oxidation and N₂ production. A gene cluster (dnfT1RT2ABCD) was cloned from strain HO-1 and enabled E. coli accumulated hydroxylamine. Sub-cloning showed that genetic cluster dnfAB or dnfABC already enabled E. coli cells to produce hydroxylamine and further to ¹⁵ N₂ from (¹⁵ NH₄ )₂ SO₄ . Transcriptome analysis revealed these three genes dnfA, dnfB and dnfC were significantly upregulated in response to ammonia stimulation. Taken together, we concluded that strain HO-1 has a novel dnf genetic cluster for ammonia oxidation and this dnf genetic cluster encoded a previously unknown pathway of direct ammonia oxidation (Dirammox) to N₂ .

Anammox bacteria in treating ammonium rich wastewater: Recent perspective and appraisal

The discovery of anammox process has provided eco-friendly and low-cost means of treating ammonia rich wastewater with remarkable efficiency. Furthermore, recent studies have shown that the possibility of operating the anammox process under low temperatures and high organic matter contents broadening the application of the anammox process. However, short doubling time and extensive levels of sensitivity towards nutrients and environmental alterations such as salinity and temperature are the limitations in practical applications of the anammox process. This review article provides the recent yet comprehensive viewpoint on anammox bacteria and the key perspectives in applying them as an efficient strategy for wastewater treatment.