Biogeography of anaerobic ammonia-oxidizing (anammox) bacteria

Cell Density-dependent Anammox Activity of Candidatus Brocadia sinica Regulated by N-acyl Homoserine Lactone-mediated Quorum Sensing

The activity of anaerobic ammonia-oxidizing (anammox) bacteria is considered to depend on cell density; however, this has not yet been confirmed due to the fastidious nature of anammox bacteria (e.g., slow growth, oxygen sensitivity, and rigid aggregate formation). In the present study, the cell density-dependent occurrence of anammox activity (14-15N2 gas production rate) was investigated using planktonic enrichment cultures of Candidatus Brocadia sinica. This activity was detectable when the density of cells was higher than 107‍ ‍cells‍ ‍mL-1 and became stronger with increases in cell density. At the cell densities, the transcription of the BROSI_A1042 and BROSI_A3652 genes, which are potentially involved in the biosynthesis and reception of N-acyl homoserine lactone (AHL), was detectable in Brocadia sinica cells. The presence of AHL molecules in the MBR culture of B. sinica was confirmed by an AHL reporter assay and gas chromatography mass spectrometry analysis. The exogenous addition of the MBR culture extract and AHL molecules (a cocktail of C6, C8, C10, and C12-homoserine lactones) increased the specific 14-15N2 production rate of B. sinica. These results suggest that the specific anammox activity of B. sinica is regulated by AHL-mediated quorum sensing.

Nitrite and nitrate as electron acceptors for bioelectrochemical ammonium oxidation under electrostatic field

Bioelectrochemical ammonium oxidation with nitrite and nitrate as electron acceptors was investigated in bulk solution exposed to electrostatic field. In a bioelectrochemical reactor, electroactive nitrogen removal bacteria including ammonium oxidizing exoelectrogens (AOE) and denitrifying electrotrophs (DNE) were enriched by electrostatic field of 0.2 V/cm in a bulk solution containing nitrite, nitrate, and ammonium. Ammonium was oxidized simultaneously with decreases in nitrite and nitrate as electron acceptors due to direct interspecies electron transfer between AOE and DNE. The specific ammonium oxidation rate was 48 mg NH₄-N/g VSS.d when nitrate fraction was 1/3 in the electron acceptor composed of nitrite and nitrate. The specific ammonium oxidation rate gradually decreased with increasing nitrate fraction. However, it was still 24 mg NH₄-N/g VSS.d when nitrate was the only electron acceptor. This indicates that nitrate can be used as an electron acceptor for bioelectrochemical ammonium oxidation, although it is a less effective than nitrite. This finding provides an advantage that strict nitritation which selectively produces nitrite from ammonium can be avoided when treating ammonia-rich wastewater in a bioelectrochemical reactor.

Global Distribution of Anaerobic Ammonia Oxidation (Anammox) Bacteria - Field Surveys in Wetland, Dryland, Groundwater Aquifer and Snow

The discovery of anaerobic ammonia oxidation (anammox) expanded our knowledge on the microbial nitrogen cycle. Previous studies report that anammox bacteria are distributed in a wide range of habitats and plays significant roles in the global nitrogen cycle. However, most studies focus only on individual ecosystems or datasets from public databases. To date, our understanding of how anammox bacteria respond to environmental properties and are distributed in different habitats on a global scale, remain unclear. To explore the global distribution of anammox bacteria, samples were collected from different habitats at different locations globally, including wetlands, drylands, groundwater aquifers and snow from 10 countries across six continents. We then used high-throughput amplicon sequencing targeting the functional gene hydrazine synthase (HZS) and generated community profiles. Results showed that Candidatus Brocadia is detected as the dominant genus on a global scale, accounting for 80.0% to 99.9% of the retrieved sequences in different habitats. The Jettenia-like sequences were the second most abundant group, accounting for no more than 19.9% of the retrieved sequences in all sites. The samples in drylands, wetlands and groundwater aquifers showed similar community composition and diversity, with the snow samples being the most different. Deterministic processes seem stronger in regulating the community composition of anammox bacteria, which is supported by the higher proportion explained by local-scale factors. Groundwater aquifers showed high gene abundance and the most complex co-occurrence network among the four habitat types, suggesting that it might be the preferred habitat of anammox bacteria. There is little competition between anammox bacterial species based on co-occurrence analysis. Hence, we could infer that environmental factors such as anaerobic and stable conditions, instead of substrate limitations, may be vital factors determining the anammox bacteria community. These results provide a better understanding of the global distribution of anammox bacteria and the ecological factors that affect their community structuring in diverse habitats.

Genome of a Novel Bacterium "Candidatus Jettenia ecosi" Reconstructed From the Metagenome of an Anammox Bioreactor

The microbial community of a laboratory-scale bioreactor based on the anammox process was investigated by using metagenomic approaches and fluorescent in situ hybridization (FISH). The bioreactor was initially inoculated with activated sludge from the denitrifying bioreactor of a municipal wastewater treatment station. By constantly increasing the ammonium and nitrite load, a microbial community containing the novel species of anammox bacteria "Candidatus Jettenia ecosi" developed in the bioreactor after 5 years when the maximal daily nitrogen removal rate reached 8.5 g/L. Sequencing of the metagenome of anammox granules and the binning of the contigs obtained, allowed a high quality draft genome of the dominant anammox bacterium, "Candidatus Jettenia ecosi" to be assembled. Annotation of the 3.9 Mbp long genome revealed 3970 putative protein-coding genes, 45 tRNA genes, and genes for 16S/23S rRNAs. Analysis of the genome of "Candidatus Jettenia ecosi" revealed genes involved in anammox metabolism, including nitrite and ammonium transporters, copper-containing nitrite reductase, a nitrate reductase complex, hydrazine synthase, and hydrazine dehydrogenase. Autotrophic carbon fixation could be accomplished through the Wood Ljungdahl pathway. The composition of the community was investigated through a search of 16S rRNA sequences in the metagenome and FISH analysis of the anammox granules. The presence of the members of Ignavibacteriae, Betaproteobacteria, Chloroflexi and other microbial lineages reflected the complexity of the microbial processes in the studied bioreactor performed by anammox Planctomycetes, fermentative bacteria, and denitrifiers.

Metagenomic insights into functional traits variation and coupling effects on the anammox community during reactor start-up

Anammox technology is an energy-efficient wastewater treatment process and anammox community structure has gained extensive attention. However, the dynamics of community functional traits are still elusive. Here, we combined the long-term reactor operation and metagenomic, multiple bioinformatic and network analyses to reveal the succession of anammox community and function traits during reactor start-up. We found the cooperation of denitrifiers that affiliated to the phylum Proteobacteria could reduce nitrite to dinitrogen gas. These organisms and genes had higher abundance after the inhibition phase, which could contribute to nitrite consuming and reactor performance recovery. Importantly, the Terrimonas and Anaerolinea organisms had ability of extracellular polymers secretion or aggregate formation. They had the highest abundance at the end of the lag phase, which could benefit for promoting the nitrogen removal rate (NRR). Meanwhile, Terrimonas and Anaerolinea bacteria could cooperate with methanogenic and nitrite-denitrifying methanotrophic organisms based on H₂ and CH₄, respectively. Since these organisms also had higher abundance after the inhibition phase, their cooperation could prevent anammox bacteria from nitrite inhibiting when the influent nitrite concentration was higher. The analysis of community and function shift is expected to emphasize the importance of functional bacteria in anammox process and provides a potential control strategy for nitrogen-containing wastewater treatment process.

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.

Sources of anammox granular sludge and their sustainability in treating low-strength wastewater

Anaerobic ammonium oxidation (anammox) has been widely applied in the treatment of high-strength nitrogen wastewaters. However, few engineering practices were reported to treat low-strength nitrogen wastewaters. In this study, three types of anammox granular sludge (GS) were separately collected from the expanded granular sludge bed (EGSB) reactors treating nitrogen wastewaters at high (H-), moderate (M-) and low (L-) nitrogen loading rates (NLRs), and employed for the treatment of low-strength nitrogen wastewater in sequencing batch advanced nitrogen removal (ANR) systems. The ANR system with M-GS (namely M-ANR system) was most useful. At the initial biomass concentration of 2.43 g-VSS·L^-1, cycle length of 8 h and influent total nitrogen (TN) concentration of less than 15 mg·L^-1, the performance data were as follows: effluent TN of less than 1 mg·L^-1, TN removal efficiency of more than 92.8%, the nitrogen removal rate (NRR) of 0.039 kg-N·m^-3·d^-1. The efficient performance lasted as long as 46 cycles, indicating the sustainability of the M-ANR system. The advanced microscopic analysis and metagenomic analysis were applied to reveal the successful but non-permanent treatment by the M-ANR system. The long-time lag between biomass decay and sludge activity decay provided a window period for the good performance of M-ANR system. However, the weak support of oligotrophic habitat for anaerobic ammonium oxidizing bacteria community was doomed to the degradation of anammox GS, resulting in gradual loss of their activities. A periodic addition of fresh M-GS or a periodic rejuvenation cultivation in the eutrophic habitat is necessary to achieve a permanent performance.

Effects of short- and long-term exposures of humic acid on the Anammox activity and microbial community

Humic acid has a controversial effect on the biological treatment processes. Here, we have investigated humic acid effects on the Anammox activity by studying the nitrogen removal efficiencies in batch and continuous conditions and analyzing the microbial community using Fluorescence in situ hybridization (FISH) technique. The results showed that the Anammox activity was affected by the presence of humic acid at a concentration higher than 70 mg/L. In fact, in the presence of humic acid concentration of 200 mg/L, the Anammox activity decreased to 57% in batch and under continuous condition, the ammonium removal efficiencies of the reactor decreased from 78 to 41%. This reduction of Anammox activity after humic acid addition was highlighted by FISH analysis which revealed a considerable reduction of the abundance of Anammox bacteria and the bacteria living in symbiosis with them. Furthermore, a total inhibition of Candidatus Brocadia fulgida was observed. However, humic acid has promoted heterotrophic denitrifying bacteria which became dominant in the reactor. In fact, the evolution of the organic matter in the reactor showed that the added humic acid was used as carbon source by heterotrophic bacteria which explained the shift of metabolism to the favor of heterotrophic denitrifying bacteria. Accordingly, humic acid should be controlled in the influent to avoid Anammox activity inhibition.

Anammox response to natural and anthropogenic impacts over the Yangtze River

Increasing attention has been paid to anaerobic ammonium oxidation (anammox) in river ecosystems due to their special role in the global nitrogen cycle from land to the ocean. This study have revealed the spatial patterns of anammox bacterial response to geographic characteristics and dam operation along the Yangtze River, using ¹⁵N tracers and molecular analyses of microbial communities in sediment samples over a 4300 km continuum. Here we found a significant temperature-related increase in anammox bacterial abundance and alpha diversity from mountainous area in the upper, fluvial plain area in the middle and lower reach, to the river mouth. In contrast, an opposite trend in anammox contribution to N₂ production (ra) was observed down the Yangtze River due to enhanced denitrification induced by spatial heterogeneity of total organic carbon. Interestingly, the Three Gorges Dam resulted in an intensive erosion and thus a change from muddy to sandy sediments within 400 km downstream the dam, which readjusted the anammox community characterized with a decreased bacterial diversity and enhanced anammox contribution to nitrogen loss. Our study highlights the importance of natural and anthropogenic impacts on anammox bacterial community and function in a complex large river ecosystem.

Electroactive microorganisms enriched from activated sludge remove nitrogen in bioelectrochemical reactor

The bioelectrochemical anaerobic nitrogen removal was demonstrated in an anaerobic batch reactor equipped with a pair of polarized bioelectrodes. The bioelectrochemical reactor was operated in sequential batch mode after inoculating activated sludge and polarizing the electrode to 0.6 V. The medium contains ammonium, nitrite, alkalinity and trace minerals, but no organic carbon source. By the repetitive sequential operation, simultaneous removals of ammonium, nitrite and alkalinity were improved, and the electrochemical activity of the bulk sludge was confirmed from the redox peaks of the cyclic voltammogram. This indicates that ammonia oxidizing exoelectrogens (AOE) and denitritating electrotrophs (DNE) were enriched more in the bulk solution. Biogas production that mainly consisted of nitrogen was observed from the bioelectrochemical reactor, and the minor components in the biogas were methane and carbon dioxide. This demonstrates that AOE use nitrite as an electron acceptor to oxidize ammonia. The requirements of nitrite and alkalinity for the removal of ammonia nitrogen are around 0.72 mg NO₂-N/mg NH₄-N and 1.73 mg as CaCO₃/mg NH₄-N, respectively, and nitrate was not produced as a by-product. The bacterial groups involved in the bioelectrochemical nitrogen removal are electroactive autotrophs and can be enriched from activated sludge by polarized electrode. This bioelectrochemical ammonia oxidation is a novel approach recommended for treatment of nitrogen-rich wastewater.

Efficient step-feed partial nitrification, simultaneous Anammox and denitrification (SPNAD) equipped with real-time control parameters treating raw mature landfill leachate

An innovative step-feed partial nitrification, simultaneous Anammox and denitrification (SPNAD), equipped with real-time control parameters, achieved efficient nitrogen removal from raw mature landfill leachate. The variables pH and ORP served as real time on-line parameters to flexibly control the durations of aerobic and anoxic. A nitrogen removal efficiency (NRE) of 98.7% and nitrogen removal rate (NRR) of 0.23 kg m^-3d^-1 were obtained at the influent NH₄⁺ -N, SCOD and total nitrogen (TN) of 1000 ± 250 mg L^-1, 1100 ± 200 mg L^-1, and 1300 ± 75 mg L^-1, respectively. Mass balance research demonstrated that Anammox contributed 69.3% to nitrogen removal and denitrification contributed 15.7%. A significant change in the Anammox community structure occurred (ca. Brocadia from 0.26% to 2.13%, ca. Kuenenia from 0.29% to 0.02%). This change is mainly attributed to different kinetic strategies (R-strategist of ca. Brocadia and K-strategist of ca. Kuenenia). Further study revealed the co-existence of functional microorganisms Nitrosomonas (3.0%), Cadidatus-Brocadia (2.13%), and Thauera (25.3%).

Soil Pollution Characteristics and Microbial Responses in a Vertical Profile with Long-Term Tannery Sludge Contamination in Hebei, China

An investigation was made into the effects of tannery sludge on soil chemical properties and microbial communities in a typical soil profile with long-term tannery sludge contamination, North China. The results showed that trivalent chromium (Cr(III)), ammonium, organic nitrogen, salinity and sulfide were the predominant contaminants in tannery sludge. Although the tannery sludge contained high chromium (Cr, 3,0970 mg/kg), the proportion of mobile Cr forms (exchangeable plus carbonate-bound fraction) only accounted for 1.32%. The X-ray diffraction and X-ray photoelectron spectroscopy results further demonstrated that the Cr existed in a stable state of oxides and iron oxides. The alkaline loam soil had a significant retardation effect on the migration of salinity, ammonium, Cr(III) and sulfide, and the accumulation of these contaminants occurred in soils (0⁻40 cm). A good correlation (R² = 0.959) was observed between total organic carbon (TOC) and Cr(III) in the soil profile, indicating that the dissolved organic matter from sludge leachate promoted the vertical mobility of Cr(III) via forming Cr(III)-organic complexes. The halotolerant bacteria (Halomonas and Tepidimicrobium) and organic degrading bacteria (Flavobacteriaceae, Tepidimicrobium and Balneola) became the dominant microflora in the soil profile. High contents of salinity, Cr and nitrogen were the main environmental factors affecting the abundance of indigenous microorganisms in soils.

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.

Negligible seeding source effect on the final ANAMMOX community under steady and high nitrogen loading rate after enrichment using poly(vinyl alcohol) gel carriers

This study investigated the effect of seeding source on the mature anaerobic ammonia oxidation (ANAMMOX) bacterial community niche in continuous poly(vinyl alcohol) (PVA) gel systems operated under high nitrogen loading rate (NLR) condition. Four identical column reactors packed with PVA gels were operated for 182 d using different seeding sources which had distinct community structures. The ANAMMOX reaction was achieved in all the bioreactors with comparable total and ANAMMOX bacterial 16S rRNA gene quantities. The bacterial community structure of the bioreactors became similar during operation; some major bacteria were commonly found. Interestingly, one ANAMMOX species, "Candidatus Brocadia sinica", was conclusively predominant in all the bioreactors, even though different seeding sludges were used as inoculum source, possibly due to the unique physiological characteristics of "Ca. Brocadia sinica" and the operating conditions (i.e., PVA gel-based continuous system and 1.0 kg-N/(m³·d) of NLR). The results clearly suggest that high NLR condition is a more significant factor determining the final ANAMMOX community niche than is the type of seeding source.

Study on the bacterial and archaeal community structure and diversity of activated sludge from three wastewater treatment plants

In this study, the bacterial and archaeal communities along with their functions of activated sludge from three wastewater treatment plants were investigated by Illumina MiSeq Platform. The treatment processes were modified A/A/O, DE oxidation ditch and pre-anaerobic carrousel oxidation ditch, respectively. The taxonomic analyses showed that Proteobacteria was the predominant bacterial phylum, and Nitrosospira was the dominant nitrification genus. Candidatus Accumulibacter was abundant in DE oxidation ditch process, and the main archaea communities were methanosaeta-like species which had the capability to anaerobic ammonia oxidation. The results illustrated that anaerobic ammonium oxidation played an important role in the nitrogen metabolism and there might be other unknown phosphate-accumulating organisms (PAOs) performing phosphorus removal in activated sludge. The predicted function analyses indicated that both bacteria and archaea were involved in nitrification, denitrification, ammonification and phosphorus removal processes, and their relative abundance varied metabolic modules differed from each other.

Single cell genomic and transcriptomic evidence for the use of alternative nitrogen substrates by anammox bacteria

Anaerobic ammonium oxidation (anammox) contributes substantially to ocean nitrogen loss, particularly in anoxic marine zones (AMZs). Ammonium is scarce in AMZs, raising the hypothesis that organic nitrogen compounds may be ammonium sources for anammox. Biochemical measurements suggest that the organic compounds urea and cyanate can support anammox in AMZs. However, it is unclear if anammox bacteria degrade these compounds to ammonium themselves, or rely on other organisms for this process. Genes for urea degradation have not been found in anammox bacteria, and genomic evidence for cyanate use for anammox is limited to a cyanase gene recovered from the sediment bacterium Candidatus Scalindua profunda. Here, analysis of Ca. Scalindua single amplified genomes from the Eastern Tropical North Pacific AMZ revealed genes for urea degradation and transport, as well as for cyanate degradation. Urease and cyanase genes were transcribed, along with anammox genes, in the AMZ core where anammox rates peaked. Homologs of these genes were also detected in meta-omic datasets from major AMZs in the Eastern Tropical South Pacific and Arabian Sea. These results suggest that anammox bacteria from different ocean regions can directly access organic nitrogen substrates. Future studies should assess if and under what environmental conditions these substrates contribute to the ammonium budget for anammox.

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.

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.

High-throughput analysis of anammox bacteria in wetland and dryland soils along the altitudinal gradient in Qinghai-Tibet Plateau

This study investigated the diversity, community composition, and abundance of anaerobic ammonium oxidation (anammox) bacteria along the altitudinal gradient in Qinghai–Tibet Plateau. Two types of soil samples (wetland and dryland soils, n = 123) were collected from 641 m to 5,033 m altitudes. Polymerase chain reaction (PCR) screening showed that anammox were not widespread, and were only detected in 9 sampling sites of the 50 sites tested by amplifying the 16S rRNA genes. Then, only samples collected from Linzhi (2,715 m), Rikaze (4,030 m), and Naqu (5,011 m), which were positive for the presence of anammox, were further processed to explore the biogeography of anammox bacteria in Qinghai–Tibet Plateau. Results of high‐throughput sequencing targeting the hydrazine synthesis β‐subunit (hzsB) gene revealed the presence of three known anammox genera (Candidatus Brocadia, Candidatus Jettenia, and Candidatus Kuenenia) in both soil types. Their diversity, community composition, and abundance did not show significant variation with altitude at large scale. However, it was the small‐scale environmental heterogeneities between wetland and dryland soils that determined their biogeographical distribution. Specifically, the dryland soils had higher diversity of anammox bacteria than the wetland soils, but their abundance patterns varied. The community composition of anammox bacteria were found to be influenced by soil nitrate content.

Alterations in anaerobic ammonium oxidation of paddy soil following organic carbon treatment estimated using 13C-DNA stable isotope probing

In this study, soil samples from the typical rice-wheat cropping system in Jiangsu Province, China, subjected to different fertilizer application treatments-no carbon (CK), urea (UR), straw (SR), pig manure (PM), starch (ST), and glucose (GL)-were used to determine potential anaerobic ammonium oxidation (anammox) rate and its association with bacterial abundance, diversity, and activity by using DNA stable isotope probing combined with ¹⁵N isotope tracing and molecular techniques. The effects of different organic carbon sources on anammox were significant, in the following order: GL > ST, SR > UR > PM; anammox activity differed significantly across treatments; however, the ¹³C active anammox bacteria were only closely related to Ca. Brocadia. The anammox hydrazine synthase β subunit functional gene sequences were highly associated with the Candidatus genus Brocadia in PM and CK treatments. The different organic carbon sources had different inhibitory effects with anammox rate, which dropped from 3.19 to 1.04 nmol dinitrogen gas g^-1 dry soil h^-1 among treatments. About 4.2-22.3% of dinitrogen gas emissions were attributed to anammox and indicated that a specific population of anammox bacteria was present and varied with the addition of exogenous organic compounds in paddy soils, although a small part of dinitrogen gas was emitted from the soil via anammox.

Effects of various fertilization regimes on abundance and activity of anaerobic ammonium oxidation bacteria in rice-wheat cropping systems in China

Anaerobic ammonium oxidation (anammox) is an important process in many marine and paddy ecosystems. However, few studies have reported on the contribution to the nitrogen cycle of anammox and its dynamics in rice-wheat cropping systems with different fertilization regimes. Here, isotope tracing and molecular techniques were used to determine the potential rates of anammox and their association with bacterial abundance, diversity, and activity. Rice-wheat cropping systems at two sites in Jiangsu Province, China were selected and the treatments at each site were: 1) no fertilization (CK), 2) 100% chemical fertilization (CF), 3) pig manure compost plus 50% chemical fertilization (PMCF), and 4) straw plus 100% chemical fertilization (SRCF). The results revealed that anammox bacteria with high abundance were detected in both the wheat and rice seasons. The abundance of anammox in PMCF treatment was higher than that in SRCF treatment in both Changshu and Jintan. Moreover, the abundance of anammox bacteria in CF treatment was significantly higher than that in CK in Changshu. Analysis of anammox hydrazine synthase β subunit (hzs-β) gene sequences showed that in the rice season, the anammox bacteria Ca. Brocadia, Ca. Scalindua, and Ca. Jettenia were present. In contrast, all of the anammox hydrazine oxidase (hzo) genes were affiliated with Ca. Brocadia, suggesting that hzs genes are more representative of anammox biological diversity compared to hzo. Sequences from the PMCF treatment where affiliated with both Ca. Jettenia and Ca. Brocadia, and showed the highest diversity. Anammox activity was detected in both the wheat and rice seasons, but there were significant differences between seasons. The anammox rates were in the range 0.34 to 1.04nmol dinitrogen gas∙g^-1 dry soil∙h^-1, and 3.15 to 9.62% of dinitrogen gas emissions were attributed to anammox. However, no significant difference among the fertilizer treatments for anammox activity was found in the study.

Microbial competition among anammox bacteria in nitrite-limited bioreactors

Phylogenetically diverse anammox bacteria have been detected in most of anoxic natural and engineered ecosystems and thus regarded as key players in the global nitrogen cycle. However, ecological niche differentiation of anammox bacteria remains unresolved despite its ecological and practical importance. In this study, the microbial competitions for a common substrate (nitrite) among three anammox species (i.e. "Candidatus Brocadia sinica", "Candidatus Jettenia caeni" and "Candidatus Kuenenia stuttgartiensis") were systematically investigated in nitrite-limited gel-immobilized column reactors (GICR) and membrane bioreactors (MBRs) under different nitrogen loading rates (NLRs). 16 S rRNA gene-based population dynamics revealed that "Ca. J. caeni" could proliferate only at low NLRs, whereas "Ca. B. sinica" outcompeted other two species at higher NLRs in both types of reactors. Furthermore, FISH analysis revealed that "Ca. J. caeni" was mainly present as spherical microclusters at the inner part (low NO₂^- environment), whereas "Ca. B. sinica" was present throughout the gel beads and granules. This spatial distribution supports the outcomes of the competition experiments. However, the successful competition of "Ca. J. caeni" at low NLR could not be explained with the Monod model probably due to inaccuracy of kinetic parameters such as half saturation constant (K_s) for nitrite and a difference in the maintenance rate (m). In addition, the growth of "Ca. K. stuttgartiensis" could not be observed in any experimental conditions, suggesting possible unknown factor(s) is missing. Taken together, NLR was one of factors determining ecological niche differentiation of "Ca. B. sinica" and "Ca. J. caeni".

Characterization of a Microbial Community in an Anammox Process Using Stored Anammox Sludge

This study investigated a rapid start-up anaerobic ammonium oxidation (Anammox) process by inoculation with stored Anammox sludge and characterized the associated microbial communities. The Anammox process took only 43 days to start. A high nitrogen removal rate of 1.13 kg N m−3 d−1 and a nitrogen loading rate of 1.28 kg N m−3 d−1 were achieved. The ratio of ammonium removal to nitrite removal to nitrate production (1:1:0.2) was slightly lower than the theoretical value, which indicated nitrogen removal by denitrification in the reactor. Illumina high-throughput sequencing of sludge samples confirmed the co-existence of Anammox bacteria and denitrifying bacteria in the reactor and demonstrated that denitrifying bacteria play a role in nitrogen removal during the Anammox process. The dominant microbes in the reactor were Proteobacteria, Chlorobi, Chloroflexi, and Planctomycetes. However, only one species of Anammox bacteria, Candidatus jettenia, was identified and had an abundance of 4.92%. Our results illustrate the relationship between Anammox reactor performance and microbial community succession.

Genetic diversity of marine anaerobic ammonium-oxidizing bacteria as revealed by genomic and proteomic analyses of 'Candidatus Scalindua japonica'

Anaerobic ammonium-oxidizing (anammox) bacteria affiliated with the genus 'Candidatus Scalindua' are responsible for significant nitrogen loss in oceans, and thus their ecophysiology is of great interest. Here, we enriched a marine anammox bacterium, 'Ca. S. japonica' from a Hiroshima bay sediment in Japan, and comparative genomic and proteomic analyses of 'Ca. S. japonica' were conducted. Sequence of the 4.81-Mb genome containing 4019 coding regions of genes (CDSs) composed of 47 contigs was determined. In the proteome, 1762 out of 4019 CDSs in the 'Ca. S. japonica' genome were detected. Based on the genomic and proteomic data, the core anammox process and carbon fixation of 'Ca. S. japonica' were further investigated. Additionally, the present study provides the first detailed insights into the genetic background responsible for iron acquisition and menaquinone biosynthesis in anammox bacterial cells. Comparative analysis of the 'Ca. Scalindua' genomes revealed that the 1502 genes found in the 'Ca. S. japonica' genome were not present in the 'Ca. S. profunda' and 'Ca. S. rubra' genomes, showing a high genomic diversity. This result may reflect a high phylogenetic diversity of the genus 'Ca. Scalindua'.

Comparison of inoculum sources for long-term process performance and fate of ANAMMOX bacteria niche in poly(vinyl alcohol)/sodium alginate gel beads

The process performance and microbial niche of anaerobic ammonia oxidation (ANAMMOX) bacteria were compared in two identical bioreactors inoculated with different inoculum sources (i.e., pre-cultured ANAMMOX bacteria: PAB and activated sludge: AS) entrapped in poly(vinyl alcohol)/sodium alginate (PVA/SA) gel beads for a long-term period (i.e., 1.5 years). The start-up period with AS was longer than that with PAB; however, both bioreactors were successfully operated over the long-term with stable ANAMMOX activity. After long-term operation, the 16S rRNA gene concentration of ANAMMOX bacteria in both bioreactors was significantly increased, and thereby became comparable. In addition, Candidatus Jettenia sp. became the dominant ANAMMOX species in both bioreactors. Our results suggested that the ANAMMOX performance and microbial niche of ANAMMOX bacteria became nearly identical during long-term operation despite the use of different inoculum sources. Therefore, the use of PVA/SA gel beads entrapping AS appears to be a relevant option for constructing an ANAMMOX process in places where a full-scale ANAMMOX process has never been done previously.

Enhanced nitrogen removal by membrane-aerated nitritation-anammox in a bioelectrochemical system

A bioelectrochemical system (BES) containing membrane-aerated nitritation-anammox in its cathode has been developed for enhancing nitrogen removal. Long-term performance and microbial community structure were investigated. The BES using loop operation and external voltage achieved the highest total nitrogen removal efficiency of 94.8±7.7%, and COD removal of 98.2±3.3% at hydraulic retention time of 60h and the lumen pressure of 10psi. The energy consumption of the system was 0.90kWhkgN^-1 or 0.38kWhkg COD^-1. Sequencing analyses revealed that ammonia oxidizing bacteria (0.2-7.4%), anammox bacteria (0.4-10.3%), denitrifying bacteria (5.8-13.1%), and electrogenic bacteria (4.6-12.8%) were in abundance of the microbial community in the cathode chamber, and their distributions were affected by the aeration and physical locations. These results encourage further investigation of membrane-aerated nitritation-anammox in BES for optimization and potential applications with actual wastewater.

Ecological Energetic Perspectives on Responses of Nitrogen-Transforming Chemolithoautotrophic Microbiota to Changes in the Marine Environment

Transformation and mobilization of bioessential elements in the biosphere, lithosphere, atmosphere, and hydrosphere constitute the Earth’s biogeochemical cycles, which are driven mainly by microorganisms through their energy and material metabolic processes. Without microbial energy harvesting from sources of light and inorganic chemical bonds for autotrophic fixation of inorganic carbon, there would not be sustainable ecosystems in the vast ocean. Although ecological energetics (eco-energetics) has been emphasized as a core aspect of ecosystem analyses and microorganisms largely control the flow of matter and energy in marine ecosystems, marine microbial communities are rarely studied from the eco-energetic perspective. The diverse bioenergetic pathways and eco-energetic strategies of the microorganisms are essentially the outcome of biosphere-geosphere interactions over evolutionary times. The biogeochemical cycles are intimately interconnected with energy fluxes across the biosphere and the capacity of the ocean to fix inorganic carbon is generally constrained by the availability of nutrients and energy. The understanding of how microbial eco-energetic processes influence the structure and function of marine ecosystems and how they interact with the changing environment is thus fundamental to a mechanistic and predictive understanding of the marine carbon and nitrogen cycles and the trends in global change. By using major groups of chemolithoautotrophic microorganisms that participate in the marine nitrogen cycle as examples, this article examines their eco-energetic strategies, contributions to carbon cycling, and putative responses to and impacts on the various global change processes associated with global warming, ocean acidification, eutrophication, deoxygenation, and pollution. We conclude that knowledge gaps remain despite decades of tremendous research efforts. The advent of new techniques may bring the dawn to scientific breakthroughs that necessitate the multidisciplinary combination of eco-energetic, biogeochemical and “omics” studies in this field.

Effect of freshwater mussels on the vertical distribution of anaerobic ammonia oxidizers and other nitrogen-transforming microorganisms in upper Mississippi river sediment

Targeted qPCR and non-targeted amplicon sequencing of 16S rRNA genes within sediment layers identified the anaerobic ammonium oxidation (anammox) niche and characterized microbial community changes attributable to freshwater mussels. Anammox bacteria were normally distributed (Shapiro-Wilk normality test, W-statistic =0.954, p = 0.773) between 1 and 15 cm depth and were increased by a factor of 2.2 (p < 0.001) at 3 cm below the water-sediment interface when mussels were present. Amplicon sequencing of sediment at depths relevant to mussel burrowing (3 and 5 cm) showed that mussel presence reduced observed species richness (p = 0.005), Chao1 diversity (p = 0.005), and Shannon diversity (p < 0.001), with more pronounced decreases at 5 cm depth. A non-metric, multidimensional scaling model showed that intersample microbial species diversity varied as a function of mussel presence, indicating that sediment below mussels harbored distinct microbial communities. Mussel presence corresponded with a 4-fold decrease in a majority of operational taxonomic units (OTUs) classified in the phyla Gemmatimonadetes, Actinobacteria, Acidobacteria, Plantomycetes, Chloroflexi, Firmicutes, Crenarcheota, and Verrucomicrobia. 38 OTUs in the phylum Nitrospirae were differentially abundant (p < 0.001) with mussels, resulting in an overall increase from 25% to 35%. Nitrogen (N)-cycle OTUs significantly impacted by mussels belonged to anammmox genus Candidatus Brocadia, ammonium oxidizing bacteria family Nitrosomonadaceae, ammonium oxidizing archaea genus Candidatus Nitrososphaera, nitrite oxidizing bacteria in genus Nitrospira, and nitrate- and nitrite-dependent anaerobic methane oxidizing organisms in the archaeal family “ANME-2d” and bacterial phylum “NC10”, respectively. Nitrosomonadaceae (0.9-fold (p < 0.001)) increased with mussels, while NC10 (2.1-fold (p < 0.001)), ANME-2d (1.8-fold (p < 0.001)), and Candidatus Nitrososphaera (1.5-fold (p < 0.001)) decreased with mussels. Co-occurrence of 2-fold increases in Candidatus Brocadia and Nitrospira in shallow sediments suggests that mussels may enhance microbial niches at the interface of oxic–anoxic conditions, presumably through biodeposition and burrowing. Furthermore, it is likely that the niches of Candidatus Nitrososphaera and nitrite- and nitrate-dependent anaerobic methane oxidizers were suppressed by mussel biodeposition and sediment aeration, as these phylotypes require low ammonium concentrations and anoxic conditions, respectively. As far as we know, this is the first study to characterize freshwater mussel impacts on microbial diversity and the vertical distribution of N-cycle microorganisms in upper Mississippi river sediment. These findings advance our understanding of ecosystem services provided by mussels and their impact on aquatic biogeochemical N-cycling.

Metagenomic Insights into Effects of Chemical Pollutants on Microbial Community Composition and Function in Estuarine Sediments Receiving Polluted River Water

Pyrosequencing and metagenomic profiling were used to assess the phylogenetic and functional characteristics of microbial communities residing in sediments collected from the estuaries of Rivers Oujiang (OS) and Jiaojiang (JS) in the western region of the East China Sea. Another sediment sample was obtained from near the shore far from estuaries, used for contrast (CS). Characterization of estuary sediment bacterial communities showed that toxic chemicals potentially reduced the natural variability in microbial communities, while they increased the microbial metabolic enzymes and pathways. Polycyclic aromatic hydrocarbons (PAHs) and nitrobenzene were negatively correlated with the bacterial community variation. The dominant class in the sediments was Gammaproteobacteria. According to Kyoto Encyclopedia of Genes and Genomes (KEGG) enzyme profiles, dominant enzymes were found in estuarine sediments, which increased greatly, such as 2-oxoglutarate synthase, acetolactate synthase, inorganic diphosphatase, and aconitate hydratase. In KEGG pathway profiles, most of the pathways were also dominated by specific metabolism in these sediments and showed a marked increase, for instance alanine, aspartate, and glutamate metabolism, carbon fixation pathways in prokaryotes, and aminoacyl-tRNA biosynthesis. The estuarine sediment bacterial diversity varied with the polluted river water inputs. In the estuary receiving river water from the more seriously polluted River Oujiang, the sediment bacterial community function was more severely affected.

Temporal and Spatial Dynamics of Sediment Anaerobic Ammonium Oxidation (Anammox) Bacteria in Freshwater Lakes

Anaerobic ammonium-oxidizing (anammox) process can play an important role in freshwater nitrogen cycle. However, the distribution of anammox bacteria in freshwater lake and the associated environmental factors remain essentially unclear. The present study investigated the temporal and spatial dynamics of sediment anammox bacterial populations in eutrotrophic Dianchi Lake and mesotrophic Erhai Lake on the Yunnan Plateau (southwestern China). The remarkable spatial change of anammox bacterial abundance was found in Dianchi Lake, while the relatively slight spatial shift occurred in Erhai Lake. Dianchi Lake had greater anammox bacterial abundance than Erhai Lake. In both Dianchi Lake and Erhai Lake, anammox bacteria were much more abundant in summer than in spring. Anammox bacterial community richness, diversity, and structure in these two freshwater lakes were subjected to temporal and spatial variations. Sediment anammox bacterial communities in Dianchi Lake and Erhai Lake were dominated by Candidatus Brocadia and a novel phylotype followed by Candidatus Kuenenia; however, these two lakes had distinct anammox bacterial community structure. In addition, trophic status determined sediment anammox bacterial community structure.

Potential role of anammox in nitrogen removal in a freshwater reservoir, Jiulonghu Reservoir (China)

Currently, the nitrogen removal potential of anaerobic ammonium oxidation (anammox) and its regulating factors in reservoir systems remain uncertain. Here, we provided the molecular and isotopic evidence for anammox in the freshwater sediment of Jiulonghu Reservoir that is located in Quzhou, Zhejiang Province, China. Diverse 16S rRNA gene sequences related to Candidatus Kuenenia and Candidatus Brocadia were detected by using high-throughput (Illumina MiSeq) sequencing of total bacterial 16S rRNA genes, and the Candidatus Brocadia was the most frequently detected anammox bacterial genus. The anammox bacterial abundance was determined based on quantitative PCR on hzsA (the alpha subunit of the hydrazine synthase) genes and varied from 3.1 × 10⁵ to 1.1 × 10⁶ copies g^-1 dry sediment. Homogenized sediments were further incubated with ¹⁵NO₃^- amendments to measure the potential anammox rates and determine the contribution of this process to dinitrogen gas (N₂) production. The potential rates of anammox ranged between 8.1 and 30.8 nmol N₂ g^-1 dry sediment day^-1, and anammox accounted for 7.7-20.5% of total N₂ production in sediment. Higher levels of anammox bacterial diversity, abundance, and activity were observed in the downstream with greater human disturbance than those in the upstream with less human disturbance. Correlation analyses suggested that the inorganic nitrogen level in sediment could be a key factor for the anammox bacterial abundance and activity. The results showed that the nitrogen removal via anammox may not be negligible in the examined reservoir and indicated that human activities could influence the anammox process in reservoir systems.

The S-Layer Protein of the Anammox Bacterium Kuenenia stuttgartiensis Is Heavily O-Glycosylated

Anaerobic ammonium oxidation (anammox) bacteria are a distinct group of Planctomycetes that are characterized by their unique ability to perform anammox with nitrite to dinitrogen gas in a specialized organelle. The cell of anammox bacteria comprises three membrane-bound compartments and is surrounded by a two-dimensional crystalline S-layer representing the direct interaction zone of anammox bacteria with the environment. Previous results from studies with the model anammox organism Kuenenia stuttgartiensis suggested that the protein monomers building the S-layer lattice are glycosylated. In the present study, we focussed on the characterization of the S-layer protein glycosylation in order to increase our knowledge on the cell surface characteristics of anammox bacteria. Mass spectrometry (MS) analysis showed an O-glycan attached to 13 sites distributed over the entire 1591-amino acid S-layer protein. This glycan is composed of six monosaccharide residues, of which five are N-acetylhexosamine (HexNAc) residues. Four of these HexNAc residues have been identified as GalNAc. The sixth monosaccharide in the glycan is a putative dimethylated deoxyhexose. Two of the HexNAc residues were also found to contain a methyl group, thereby leading to an extensive degree of methylation of the glycan. This study presents the first characterization of a glycoprotein in a planctomycete and shows that the S-layer protein Kustd1514 of K. stuttgartiensis is heavily glycosylated with an O-linked oligosaccharide which is additionally modified by methylation. S-layer glycosylation clearly contributes to the diversification of the K. stuttgartiensis cell surface and can be expected to influence the interaction of the bacterium with other cells or abiotic surfaces.

Contribution of Anammox to Nitrogen Removal in Two Temperate Forest Soils

Anaerobic ammonium oxidation with nitrite reduction to dinitrogen (termed anammox) has been reported to be an important process for removing fixed nitrogen (N) in marine ecosystems and in some agricultural and wetland soils. However, its importance in upland forest soils has never been quantified. In this study, we evaluated the occurrence of anammox activity in two temperate forest soils collected from northeastern China. With (15)N-labeled NO3 (-) incubation, we found that the combined potential of the N2 production rates of anammox and codenitrification ranged from 0.01 ± 0.01 to 1.2 ± 0.18 nmol N per gram of soil per hour, contributing 0.5% to 14.4% of the total N2 production along the soil profile. Denitrification was the main pathway of N2 production and accounted for 85.6% to 99.5% of the total N2 production. Further labeling experiments with (15)NH4 (+) and (15)NO2 (-) indicated that codenitrification was present in the mixed forest soil. Codenitrification and anammox accounted for 2% to 12% and 1% to 7% of the total N2 production, respectively. Two anammox species, "Candidatus Brocadia fulgida" and "Candidatus Jettenia asiatica," were detected in this study but in very low abundance (as indicated by the hzsB gene). Our results demonstrated that the anammox process occurs in forest soils, but the contribution to N2 loss might be low in these ecosystems. More research is necessary to determine the activities of different N2 releasing pathways in different forest soils.

IMPORTANCE

In this study, we examined the anammox activity in temperate upland forest soils using the (15)N isotope technique. We found that the anammox process contributed little to the N2 production rate in the studied forest soil. Two anammox organisms, "Candidatus Brocadia fulgida" and "Candidatus Jettenia asiatica," were detected. In addition, we found that codenitrification was another N2 production pathway in forest soils. Our results could contribute to the understanding of soil gaseous N losses and microbial controls in forest soils.

Ecology of Nitrogen Fixing, Nitrifying, and Denitrifying Microorganisms in Tropical Forest Soils

Soil microorganisms play important roles in nitrogen cycling within forest ecosystems. Current research has revealed that a wider variety of microorganisms, with unexpected diversity in their functions and phylogenies, are involved in the nitrogen cycle than previously thought, including nitrogen-fixing bacteria, ammonia-oxidizing bacteria and archaea, heterotrophic nitrifying microorganisms, and anammox bacteria, as well as denitrifying bacteria, archaea, and fungi. However, the vast majority of this research has been focused in temperate regions, and relatively little is known regarding the ecology of nitrogen-cycling microorganisms within tropical and subtropical ecosystems. Tropical forests are characterized by relatively high precipitation, low annual temperature fluctuation, high heterogeneity in plant diversity, large amounts of plant litter, and unique soil chemistry. For these reasons, regulation of the nitrogen cycle in tropical forests may be very different from that of temperate ecosystems. This is of great importance because of growing concerns regarding the effect of land use change and chronic-elevated nitrogen deposition on nitrogen-cycling processes in tropical forests. In the context of global change, it is crucial to understand how environmental factors and land use changes in tropical ecosystems influence the composition, abundance and activity of key players in the nitrogen cycle. In this review, we synthesize the limited currently available information regarding the microbial communities involved in nitrogen fixation, nitrification and denitrification, to provide deeper insight into the mechanisms regulating nitrogen cycling in tropical forest ecosystems. We also highlight the large gaps in our understanding of microbially mediated nitrogen processes in tropical forest soils and identify important areas for future research.

Multi-species measurements of nitrogen isotopic composition reveal the spatial constraints and biological drivers of ammonium attenuation across a highly contaminated groundwater system

Groundwater under industrial sites is characterised by heterogeneous chemical mixtures, making it difficult to assess the fate and transport of individual contaminants. Quantifying the in-situ biological removal (attenuation) of nitrogen (N) is particularly difficult due to its reactivity and ubiquity. Here a multi-isotope approach is developed to distinguish N sources and sinks within groundwater affected by complex industrial pollution. Samples were collected from 70 wells across the two aquifers underlying a historic industrial area in Belgium. Below the industrial site the groundwater contained up to 1000 mg N l(-1) ammonium (NH4(+)) and 300 mg N l(-1) nitrate (NO3(-)), while downgradient concentrations decreased to ∼1 mg l(-1) DIN ([DIN] = [NH4(+)N] + [NO3(-)N] + [NO2(-)N]). Mean δ(15)N-DIN increased from ∼2‰ to +20‰ over this flow path, broadly confirming that biological N attenuation drove the measured concentration decrease. Multi-variate analysis of water chemistry identified two distinct NH4(+) sources (δ(15)NNH4(+) from -14‰ and +5‰) within the contaminated zone of both aquifers. Nitrate dual isotopes co-varied (δ(15)N: -3‰ - +60‰; δ(18)O: 0‰ - +50‰) within the range expected for coupled nitrification and denitrification of the identified sources. The fact that δ(15)NNO2(-) values were 50‰-20‰ less than δ(15)NNH4(+) values in the majority of wells confirmed that nitrification controlled N turnover across the site. However, the fact that δ(15)NNO2(-) was greater than δ(15)NNH4(+) in wells with the highest [NH4(+)] shows that an autotrophic NO2(-) reduction pathway (anaerobic NH4(+) oxidation or nitrifier-denitrification) drove N attenuation closest to the contaminant plume. This direct empirical evidence that both autotrophic and heterotrophic biogeochemical processes drive N attenuation in contaminated aquifers demonstrates the power of multiple N isotopes to untangle N cycling in highly complex systems.

Long-term performance and microbial community characterization of an osmotic anammox system for removing reverse-fluxed ammonium

A novel osmotic anammox (OsAMX) system coupling nitritation-anammox with forward osmosis (FO) has been developed for removal of reverse-fluxed ammonium when using NH4HCO3 as a draw solute. In this study, long-term performance and microbial community structure were investigated. The nitritation-anammox reactor maintained an ammonium concentration of 7.0±5.0mgNL(-1) (DO=0.9±0.2mgO2L(-1)), while the FO achieved a water flux of 2.3±0.4LMH (0.5M NH4HCO3 draw). The low water flux was obtained likely due to concentration polarization, reverse salt flux (RSF) and membrane fouling. Sequencing analyses reveled that Candidatus Jettenia was the dominant anammox genus, while Candidatus Brocadia was most abundant in biofilm. The shift of anammox bacterial population indicated possible higher tolerance of Ca. Brocadia for DO or elevated RSF. These results encourage further investigation of OsAMX system optimization, membrane fouling migration strategies, and application with actual wastewater.

Diversity, Community Composition and Abundance of Anammox Bacteria in Sediments of the North Marginal Seas of China

Over the past few decades, anammox bacteria have been recognized as key players that contribute significantly to the release of large amounts of nitrogen in the global marine nitrogen cycle. In the present study, the diversity, community composition, and abundance of anammox bacteria from the sediments of four diverse regions in the north marginal seas in China were determined via clone library construction and a quantitative PCR analysis. The clone libraries retrieved by the 16S rRNA gene and Hzo gene markers indicated that “Candidatus Scalindua” was the predominant group throughout the sites examined. The 16S rRNA gene clone libraries revealed exceptional diversity by identifying two potential novel anammox clades, as evidenced by the high sequence similarities between these two clades and known anammox genera, and their unique phylogenetic positions with high bootstrap values. However, their potential roles in the anammox reaction need to be validated. Six novel members of Planctomycetes, divergent from the known genera of anammox bacteria, were also detected. A phylogenetic analysis by Hzo protein sequences revealed the existence of two known genera, i.e., “Candidatus Jettenia” and “Candidatus Anammoxoglobus”, which are rarely captured from marine sediments. Among all ecological parameters investigated, the distribution patterns and composition of anammox bacteria were found to be influenced by salinity, total organic matter, and temperature. The abundance of the anammox bacterial 16S rRNA gene from the sites examined ranged between 3.95×10⁵ and 9.21×10⁵ copies g⁻¹ wet sediment and positively correlated with the median size of the sediment sample.

Anammox-based technologies for nitrogen removal: Advances in process start-up and remaining issues

Nitrogen removal from wastewater via anaerobic ammonium oxidation (anammox)-based process has been recognized as efficient, cost-effective and low energy alternative to the conventional nitrification and denitrification processes. To date, more than one hundred full-scale anammox plants have been installed and operated for treatment of NH4(+)-rich wastewater streams around the world, and the number is increasing rapidly. Since the discovery of anammox process, extensive researches have been done to develop various anammox-based technologies. However, there are still some challenges in practical application of anammox-based treatment process at full-scale, e.g., longer start-up period, limited application to mainstream municipal wastewater and poor effluent water quality. This paper aimed to summarize recent status of application of anammox process and researches on technological development for solving these remaining problems. In addition, an integrated system of anammox-based process and microbial fuel cell is proposed for sustainable and energy-positive wastewater treatment.

Comparative analysis of two 16S rRNA gene-based PCR primer sets provides insight into the diversity distribution patterns of anammox bacteria in different environments

Due to the high divergence among 16S rRNA genes of anammox bacteria, different diversity pattern of the community could be resulted from using different primer set. In this study, the efficiencies and specificities of two commonly used sets, Amx368F/Amx820R and Brod541F/Amx820R, were evaluated by exploring the diversity characteristics of anammox bacteria in sediments from marine, estuary, and freshwater wetland. Statistical analysis indicated that the base mispairing rate between bases on 16S rRNA gene sequences retrieved by Amx368F/Amx820R and their corresponding ones on primer Brod541F was quite high, suggesting the different efficiency and specificity of Amx368F/Amx820R and Brod541F/Amx820R. Further experimental results demonstrated that multiple genera of anammox bacteria, including Ca. Scalindua, Ca. Brocadia, and Ca. Kuenenia, were able to be detected by Amx368F/Amx820R, but only Ca. Scalindua could be retrieved by Brod541F/Amx820R. Moreover, the phylogenetic clusters of Ca. Scalindua by Amx368F/Amx820R were different completely from those by Brod541F/Amx820R, presenting a significant complementary effect. By joint application of these two primer sets, the diversity distribution patterns of anammox bacteria in different environments were analyzed. Almost all retrieved sequences from marine sediments belonged to Ca. Scalindua. Sequences from freshwater wetland were affiliated to Ca. Brocadia and two new clusters, while high diversity of anammox bacteria was found in estuary, including Ca. Scalindua, Ca. Brocadia, and Ca. Kuenenia, corresponding to the river-sea intersection environmental feature. In total, these two prime sets have different characteristic for anammox bacteria detecting from environmental samples, and their combined application could achieve better diversity display of anammox community.