A microdiversity study of anammox bacteria reveals a novel Candidatus Scalindua phylotype in marine oxygen minimum zones

The anaerobic oxidation of ammonium (anammox) contributes significantly to the global loss of fixed nitrogen and is carried out by a deep branching monophyletic group of bacteria within the phylum Planctomycetes. Various studies have implicated anammox to be the most important process responsible for the nitrogen loss in the marine oxygen minimum zones (OMZs) with a low diversity of marine anammox bacteria. This comprehensive study investigated the anammox bacteria in the suboxic zone of the Black Sea and in three major OMZs (off Namibia, Peru and in the Arabian Sea). The diversity and population composition of anammox bacteria were investigated by both, the 16S rRNA gene sequences and the 16S-23S rRNA internal transcribed spacer (ITS). Our results showed that the anammox bacterial sequences of the investigated samples were all closely related to the Candidatus Scalindua genus. However, a greater microdiversity of marine anammox bacteria than previously assumed was observed. Both phylogenetic markers supported the classification of all sequences in two distinct anammox bacterial phylotypes: Candidatus Scalindua clades 1 and 2. Scalindua 1 could be further divided into four distinct clusters, all comprised of sequences from either the Namibian or the Peruvian OMZ. Scalindua 2 consisted of sequences from the Arabian Sea and the Peruvian OMZ and included one previously published 16S rRNA gene sequence from Lake Tanganyika and one from South China Sea sediment (97.9-99.4% sequence identity). This cluster showed only 相似文献   

Depth trends of soil organic matter C:N and 15N natural abundance controlled by association with minerals

Anaerobic ammonium oxidation (anammox) is believed to be an important sink for fixed inorganic nitrogen in terrestrial and aquatic ecosystems, and many studies have reported that macroscale oxic–anoxic interfaces, such as riparian zones, were hotspots of anammox reaction. However, no research has linked microscale interfaces with the anammox process in natural environments. This study provides evidence for the presence of anammox bacteria and potential anammox activity on the suspended sediment (SPS) in the oxic water of the Yellow River. The anammox bacteria in the overlying water were mainly attached to SPS. The abundance of anammox bacteria in the overlying water was positively correlated with SPS concentration (R ² = 0.97, P < 0.01), with abundance ranging from 9.5 × 10² to 1.5 × 10⁴ hydrazine synthase gene copies per g of SPS. Phylogenic analysis of anammox bacteria revealed that the SPS phase was dominated by Candidatus Brocadia. Candidatus Scalindua genera was detected in this study with a conductivity of 1100 μS cm^?1. Moreover, \(^{15} {\text{NH}}_{4}^{ + }\)-amended anaerobic incubation of the overlying water showed that the average potential anammox activity was 0.076 nmol-N L^?1 day^?1. The ¹⁵N labeling simulation experiments demonstrated the occurrence of anammox in the oxic water of the Yellow River. This study suggests that the anammox process at the SPS–water interface might be a non-negligible pathway for the loss of fixed nitrogen in natural freshwaters, but this remains to be determined in further studies.     

Stable carbon isotopic fractionations associated with inorganic carbon fixation by anaerobic ammonium-oxidizing bacteria

Isotopic analyses of Candidatus "Brocadia anammoxidans," a chemolithoautotrophic bacterium that anaerobically oxidizes ammonium (anammox), show that it strongly fractionates against (13)C; i.e., lipids are depleted by up to 47 per thousand versus CO(2). Similar results were obtained for the anammox bacterium Candidatus "Scalindua sorokinii," which thrives in the anoxic water column of the Black Sea, suggesting that different anammox bacteria use identical carbon fixation pathways, which may be either the Calvin cycle or the acetyl coenzyme A pathway.     

Anaerobic ammonium-oxidizing bacteria in marine environments: widespread occurrence but low diversity

Laboratory and field studies have indicated that anaerobic ammonium oxidation (anammox) is an important process in the marine nitrogen cycle. In this study 11 additional anoxic marine sediment and water column samples were studied to substantiate this claim. In a combined approach using the molecular methods, polymerase chain reaction (PCR), qualitative and quantitative fluorescence in situ hybridization (FISH), as well as (15)N stable isotope activity measurements, it was shown that anammox bacteria were present and active in all samples investigated. The anammox activity measured in the sediment samples ranged from 0.08 fmol cell(-1) day(-1) N(2) in the Golfo Dulce (Pacific Ocean, Costa Rica) sediment to 0.98 fmol cell(-1) day(-1) N(2) in the Gullmarsfjorden (North Sea, Sweden) sediment. The percentage of anammox cell of the total population (stained with DAPI) as assessed by quantitative FISH was highest in the Barents Sea (9% +/- 4%) and in most of the samples well over 2%. Fluorescence in situ hybridization and phylogenetic analysis of the PCR products derived from the marine samples indicated the exclusive presence of members of the Candidatus'Scalindua' genus. This study showed the ubiquitous presence of anammox bacteria in anoxic marine ecosystems, supporting previous observations on the importance of anammox for N cycling in marine environments.     

New anaerobic, ammonium-oxidizing community enriched from peat soil

Anaerobic ammonium-oxidizing (anammox) bacteria have been recognized as an important sink for fixed nitrogen and are detected in many natural environments. However, their presence in terrestrial ecosystems has long been overlooked, and their contribution to the nitrogen cycling in natural and agricultural soils is currently unknown. Here we describe the enrichment and characterization of anammox bacteria from a nitrogen-loaded peat soil. After 8 months of incubation with the natural surface water of the sampling site and increasing ammonium and nitrite concentrations, anammox cells constituted 40 to 50% of the enrichment culture. The two dominant anammox phylotypes were affiliated with "Candidatus Jettenia asiatica" and "Candidatus Brocadia fulgida." The enrichment culture converted NH(4)(+) and NO(2)(-) to N(2) with the previously reported stoichiometry (1:1.27) and had a maximum specific anaerobic ammonium oxidation rate of 0.94 mmol NH(4)(+)·g (dry weight)(-1)·h(-1) at pH 7.1 and 32°C. The diagnostic anammox-specific lipids were detected at a concentration of 650 ng·g (dry weight)(-1), and pentyl-[3]-ladderane was the most abundant ladderane lipid.     

Research of Iron Reduction and the Iron Reductase Localization of Anammox Bacteria

The iron-reducing capability of anammox bacteria was examined in this study using Percoll purified anammox bacteria. Anammox bacteria could reduce Fe(III) to Fe(II) with organic matters as the electron donor. The activity of anammox iron-reducing process was dependent on different electron donor, acceptor and pH. The highest iron-reducing activity of anammox bacteria was achieved with Fe(III)-NTA (nitrilotriacetic acid) as electron acceptor and formate as the electron donor at pH7. Similar to other iron reducers, 80 % of the iron reductase in anammox bacteria was located in the membrane fraction. Due to the chemical oxidant of NO₂ ^? and the NO₃ ^? dependent ferrous iron oxidation by anammox bacteria, the iron-reducing activity of anammox bacteria could be severely inhibited when iron-reducing pathway and the anammox process were coupled. However, the total nitrogen removal efficiency was not significantly affected in the presence of Fe(III). The iron-reducing capability of anammox bacteria could influence both N and Fe cycle on earth, and it is a potential way for wastewater treatment.     

Anammox bacteria disguised as denitrifiers: nitrate reduction to dinitrogen gas via nitrite and ammonium

Anaerobic ammonium-oxidizing (anammox) bacteria oxidize ammonium with nitrite and produce N(2). They reside in many natural ecosystems and contribute significantly to the cycling of marine nitrogen. Anammox bacteria generally live under ammonium limitation, and it was assumed that in nature anammox bacteria depend on other biochemical processes for ammonium. In this study we investigated the possibility of dissimilatory nitrate reduction to ammonium by anammox bacteria. Physically purified Kuenenia stuttgartiensis cells reduced (15)NO(3) (-) to (15)NH(4) (+) via (15)NO(2) (-) as the intermediate. This was followed by the anaerobic oxidation of the produced ammonium and nitrite. The overall end-product of this metabolism of anammox bacteria was (15)N(15)N dinitrogen gas. The nitrate reduction to nitrite proceeds at a rate of 0.3 +/- 0.02 fmol cell(-1) day(-1) (10% of the 'normal' anammox rate). A calcium-dependent cytochrome c protein with a high (305 mumol min(-1) mg protein(-1)) rate of nitrite reduction to ammonium was partially purified. We present evidence that dissimilatory nitrate reduction to ammonium occurs in Benguela upwelling system at the same site where anammox bacteria were previously detected. This indicates that anammox bacteria could be mediating dissimilatory nitrate reduction to ammonium in natural ecosystems.     

The depth-specific significance and relative abundance of anaerobic ammonium-oxidizing bacteria in estuarine sediments (Medway Estuary, UK)

Variations in the overall and depth-specific significance of anammox were measured using (15) N isotope experiments in both bioirrigated and undisturbed sediments of the Medway Estuary, UK. This was performed over two surveys, alongside FISH experiments, to identify and track shifts in the relative abundance of anammox organisms with depth. In Survey 1 (initially screening for the presence of anammox), the potential for anammox (ra) decreased from 32% upstream to 6% downstream. In Survey 2, depth-specific values of ra varied between a maximum of 37% upstream and a minimum of 4% downstream. This was linked to a small population of anammox organisms accounting for 相似文献   

Potential Contribution of Anammox to Nitrogen Loss from Paddy Soils in Southern China

The anaerobic oxidation of ammonium (anammox) process has been observed in diverse terrestrial ecosystems, while the contribution of anammox to N₂ production in paddy soils is not well documented. In this study, the anammox activity and the abundance and diversity of anammox bacteria were investigated to assess the anammox potential of 12 typical paddy soils collected in southern China. Anammox bacteria related to “Candidatus Brocadia” and “Candidatus Kuenenia” and two novel unidentified clusters were detected, with “Candidatus Brocadia” comprising 50% of the anammox population. The prevalence of the anammox was confirmed by the quantitative PCR results based on hydrazine synthase (hzsB) genes, which showed that the abundance ranged from 1.16 × 10⁴ to 9.65 × 10⁴ copies per gram of dry weight. The anammox rates measured by the isotope-pairing technique ranged from 0.27 to 5.25 nmol N per gram of soil per hour in these paddy soils, which contributed 0.6 to 15% to soil N₂ production. It is estimated that a total loss of 2.50 × 10⁶ Mg N per year is linked to anammox in the paddy fields in southern China, which implied that ca. 10% of the applied ammonia fertilizers is lost via the anammox process. Anammox activity was significantly correlated with the abundance of hzsB genes, soil nitrate concentration, and C/N ratio. Additionally, ammonia concentration and pH were found to be significantly correlated with the anammox bacterial structure.     

Candidatus "Scalindua brodae", sp. nov., Candidatus "Scalindua wagneri", sp. nov., two new species of anaerobic ammonium oxidizing bacteria

Anaerobic ammonium oxidation (anammox) is both a promising process in wastewater treatment and a long overlooked microbial physiology that can contribute significantly to biological nitrogen cycling in the world's oceans. Anammox is mediated by a monophyletic group of bacteria that branches deeply in the Planctomycetales. Here we describe a new genus and species of anaerobic ammonium oxidizing planctomycetes, discovered in a wastewater treatment plant (wwtp) treating landfill leachate in Pitsea, UK. The biomass from this wwtp showed high anammox activity (5.0 +/- 0.5 nmol/mg protein/min) and produced hydrazine from hydroxylamine, one of the unique features of anammox bacteria. Eight new planctomycete 16S rRNA gene sequences were present in the 16S rRNA gene clone library generated from the biomass. Four of these were affiliated to known anammox 16S rRNA gene sequences, but branched much closer to the root of the planctomycete line of descent. Fluorescence in situ hybridization (FISH) with oligonucleotide probes specific for these new sequences showed that two species (belonging to the same genus) together made up > 99% of the planctomycete population which constituted 20% of the total microbial community. The identification of these organisms as typical anammox bacteria was confirmed with electron microscopy and lipid analysis. The new species, provisionally named Candidatus "Scalindua brodae" and "Scalindua wagneri" considerably extend the biodiversity of the anammox lineage on the 16S rRNA gene level, but otherwise resemble known anammox bacteria. Simultaneously, another new species of the same genus, Candidatus "Scalindua sorokinii", was detected in the water column of the Black Sea, making this genus the most widespread of all anammox bacteria described so far.     

Stark Contrast in Denitrification and Anammox across the Deep Norwegian Trench in the Skagerrak

Environmental anaerobic ammonium oxidation (anammox) was demonstrated for the first time in 2002, using ¹⁵N labeling, in homogenized sediment from the Skagerrak, where it accounted for up to 67% of N₂ production. We returned to some of these original sites in 2010 to make measurements of nitrogen and carbon cycling under conditions more representative of those in situ, quantifying anammox and denitrification, together with oxygen penetration and consumption, in intact sediment cores. Overall, oxygen consumption and N₂ production decayed with water depth, as expected, but the drop in N₂ production was relatively more pronounced. Whereas we confirmed the dominance of N₂ production by anammox (72% and 77%) at the two deepest sites (∼700 m of water), anammox was conspicuously absent from two shallower sites (∼200 m and 400 m). At the shallower sites, we could measure no anammox activity with either intact or homogeneous sediment, and quantitative PCR (16S rRNA) gave a negligible abundance of anammox bacteria in the anoxic layers. Such an absence of anammox, especially at one locale where it was originally demonstrated, is hard to reconcile. Despite the dominance of anammox at the deepest sites, anammox activity could not make up for the drop in denitrification, and assuming Redfield ratios for the organic matter being mineralized, the estimated retention of fixed N actually increased to 90% to 97% of that mineralized, whereas it was 80% to 86% at the shallower sites.     

Enrichment and characterization of an anammox bacterium from a rotating biological contactor treating ammonium-rich leachate

Anaerobic ammonium oxidation with nitrite to N2 (anammox) is a recently discovered microbial reaction with interesting potential for nitrogen removal from wastewater. We enriched an anammox culture from a rotating disk contactor (near K?lliken, Switzerland) that was used to treat ammonium-rich leachate with low organic carbon content. This enrichment led to a relative population size of 88% anammox bacteria. The microorganism carrying out the anammox reaction was identified by analysis of the 16S rDNA sequence and by fluorescence in situ hybridization (FISH) with 16S-rRNA-targeting probes. The percentage sequence identity between the 16S rDNA sequences of the K?lliken anammox organism and the archetype anammox strain Candidatus Brocadia anammoxidans was 90.9%, but between 98.5 and 98.9% with Candidatus Kuenenia stuttgartiensis, an organism identified in biofilms by molecular methods. The K?lliken culture catalyzed the anaerobic oxidation of ammonium with nitrite in a manner seemingly identical to that of Candidatus B. anammoxidans, but exhibited higher tolerance to phosphate (up to 20 mM) and to nitrite (up to 13 mM) and was active at lower cell densities. Anammox activity was observed only between pH 6.5 and 9, with an optimum at pH 8 and a temperature optimum at 37 degrees C. Hydroxylamine and hydrazine, which are intermediates of the anammox reaction of Candidatus B. anammoxidans, were utilized by the K?lliken organisms, and approximately 15% of the nitrite utilized during autotrophic growth was converted to nitrate. Electron microscopy showed a protein-rich region in the center of the cells surrounded by a doughnut-shaped region containing ribosomes and DNA. This doughnut-shape region was observed with FISH as having a higher fluorescence intensity. Similar to Candidatus B. anammoxidans, the K?lliken anammox organism typically formed homogenous clusters containing up to several hundred cells within an extracellular matrix.     

The membrane bioreactor: a novel tool to grow anammox bacteria as free cells

In a membrane bioreactor (MBR), fast growth of anammox bacteria was achieved with a sludge residence time (SRT) of 12 days. This relatively short SRT resulted in a--for anammox bacteria--unprecedented purity of the enrichment of 97.6%. The absence of a selective pressure for settling, and dedicated cultivation conditions led to growth in suspension as free cells and the complete absence of flocs or granules. Fast growth, low levels of calcium and magnesium, and possibly the presence of yeast extract and a low shear stress are critical for the obtainment of a completely suspended culture consisting of free anammox cells. During cultivation, a population shift was observed from Candidatus "Brocadia" to Candidatus "Kuenenia stuttgartiensis." It is hypothesized that the reason for this shift is the higher affinity for nitrite of "Kuenenia." The production of anammox bacteria in suspension with high purity and productivity makes the MBR a promising tool for the cultivation and study of anammox bacteria.     

Anaerobic ammonium oxidation (Anammox) in immobilized activated sludge biofilms during the treatment of weak wastewater

This work studied the formation of molecular nitrogen by the microbial population of immobilized activated sludge of the domestic wastewater treatment plants (WWTP) that employ the technology developed by ZAO ECOS Company. The technology includes physicochemical water pretreatment and treated water recycling. A hard flexible fibrous brush carrier is used for the immobilization of microorganisms. The presence of both aerobic and anaerobic microorganisms and functioning of the methanogenic microbial community was shown in the biofilms developing on the carrier fibers and in suspended sludge. The high efficiency of nitrogen removal at a low C/N ratio was established to be due to the conjugated nitrification, denitrification, and anammox processes, whose functioning was demonstrated by laboratory cultivation methods and by studying the processes in batch and continuous reactors. Fluorescence in situ hybridization with 16S rRNA-targeted oligonucleotide probes (FISH) revealed bacteria belonging to the order Planctomycetales, particularly their anammox group. This work is the first evidence of the important role of the anammox process in the combined system of physicochemical and biological treatment of weak wastewater (BCDEAMOX).     

Candidatus "Anammoxoglobus propionicus" a new propionate oxidizing species of anaerobic ammonium oxidizing bacteria

The bacteria that mediate the anaerobic oxidation of ammonium (anammox) are detected worldwide in natural and man-made ecosystems, and contribute up to 50% to the loss of inorganic nitrogen in the oceans. Two different anammox species rarely live in a single habitat, suggesting that each species has a defined but yet unknown niche. Here we describe a new anaerobic ammonium oxidizing bacterium with a defined niche: the co-oxidation of propionate and ammonium. The new anammox species was enriched in a laboratory scale bioreactor in the presence of ammonium and propionate. Interestingly, this particular anammox species could out-compete other anammox bacteria and heterotrophic denitrifiers for the oxidation of propionate in the presence of ammonium, nitrite and nitrate. We provisionally named the new species Candidatus "Anammoxoglobus propionicus".     

Application of anaerobic ammonium-oxidizing consortium to achieve completely autotrophic ammonium and sulfate removal

The simultaneous ammonium and sulfate removal was detected in an anammox reactor, consisted of ammonium oxidization with sulfate deoxidization, and subsequently traditional anammox process, in via of middle medium nitrite with solid sulfur and N2 as the terminal products. The pure anammox bacteria offered a great biotechnological potential for the completely autotrophic reaction indicated by batch tests. Denaturing gradient gel electrophoresis (DGGE) analysis further revealed that a new organism belonging to Planctomycetales was strongly enriched in the defined niche: the redox of ammonium and sulfate. The new species "Anammoxoglobussulfate" was so considered as holding a critical role in the ammonium oxidization with sulfate deoxidization to nitrite. Afterwards, the Planctomyces existing in the bacteria community performed the anammox process together to achieve the complete nitrogen and sulfate removal. The potential use of sulfate as electron acceptor for ammonium oxidizing widens the usage of anammox bacteria.     

Potential interactions of particle-associated anammox bacteria with bacterial and archaeal partners in the Namibian upwelling system

Recent studies have shown that the anaerobic oxidation of ammonium by anammox bacteria plays an important role in catalyzing the loss of nitrogen from marine oxygen minimum zones (OMZ). However, in situ oxygen concentrations of up to 25 microM and ammonium concentrations close to or below the detection limit in the layer of anammox activity are hard to reconcile with the current knowledge of the physiology of anammox bacteria. We therefore investigated samples from the Namibian OMZ by comparative 16S rRNA gene analysis and fluorescence in situ hybridization. Our results showed that "Candidatus Scalindua" spp., the typical marine anammox bacteria, colonized microscopic particles that were likely the remains of either macroscopic marine snow particles or resuspended particles. These particles were slightly but significantly (P < 0.01) enriched in Gammaproteobacteria (11.8% +/- 5.0%) compared to the free-water phase (8.1% +/- 1.8%). No preference for the attachment to particles could be observed for members of the Alphaproteobacteria and Bacteroidetes, which were abundant (12 to 17%) in both habitats. The alphaproteobacterial SAR11 clade, the Euryarchaeota, and group I Crenarchaeota, were all significantly depleted in particles compared to their presence in the free-water phase (16.5% +/- 3.5% versus 2.6% +/- 1.7%, 2.7% +/- 1.9% versus <1%, and 14.9% +/- 4.6% versus 2.2% +/- 1.8%, respectively, all P < 0.001). Sequence analysis of the crenarchaeotal 16S rRNA genes showed a 99% sequence identity to the nitrifying "Nitrosopumilus maritimus." Even though we could not observe conspicuous consortium-like structures of anammox bacteria with particle-enriched bacterioplankton groups, we hypothesize that members of Gammaproteobacteria, Alphaproteobacteria, and Bacteroidetes play a critical role in extending the anammox reaction to nutrient-depleted suboxic water layers in the Namibian upwelling system by creating anoxic, nutrient-enriched microniches.     

In situ activity and spatial organization of anaerobic ammonium-oxidizing (anammox) bacteria in biofilms

We investigated autotrophic anaerobic ammonium-oxidizing (anammox) biofilms for their spatial organization, community composition, and in situ activities by using molecular biological techniques combined with microelectrodes. Results of phylogenetic analysis and fluorescence in situ hybridization (FISH) revealed that "Brocadia"-like anammox bacteria that hybridized with the Amx820 probe dominated, with 60 to 92% of total bacteria in the upper part (<1,000 microm) of the biofilm, where high anammox activity was mainly detected with microelectrodes. The relative abundance of anammox bacteria decreased along the flow direction of the reactor. FISH results also indicated that Nitrosomonas-, Nitrosospira-, and Nitrosococcus-like aerobic ammonia-oxidizing bacteria (AOB) and Nitrospira-like nitrite-oxidizing bacteria (NOB) coexisted with anammox bacteria and accounted for 13 to 21% of total bacteria in the biofilms. Microelectrode measurements at three points along the anammox reactor revealed that the NH(4)(+) and NO(2)(-) consumption rates decreased from 0.68 and 0.64 micromol cm(-2) h(-1) at P2 (the second port, 170 mm from the inlet port) to 0.30 and 0.35 micromol cm(-2) h(-1) at P3 (the third port, 205 mm from the inlet port), respectively. No anammox activity was detected at P4 (the fourth port, 240 mm from the inlet port), even though sufficient amounts of NH(4)(+) and NO(2)(-) and a high abundance of anammox bacteria were still present. This result could be explained by the inhibitory effect of organic compounds derived from biomass decay and/or produced by anammox and coexisting bacteria in the upper parts of the biofilm and in the upstream part of the reactor. The anammox activities in the biofilm determined by microelectrodes reflected the overall reactor performance. The several groups of aerobic AOB lineages, Nitrospira-like NOB, and Betaproteobacteria coexisting in the anammox biofilm might consume a trace amount of O(2) or organic compounds, which consequently established suitable microenvironments for anammox bacteria.     

Ammonium removal performance of anaerobic ammonium-oxidizing bacteria immobilized in polyethylene glycol gel carrier

Anaerobic ammonium-oxidizing (anammox) bacteria were immobilized in polyethylene glycol gel carriers. A small amount of seed sludge [0.24% (w/v)] was entrapped in the carriers, and continuous feeding tests were performed. Nitrogen removal activity increased gradually, reaching 3.7 kg N/m(3) reactor per day on day 67. The average of nitrogen conversion rate was calculated as 3.4 kg N/m(3) reactor per day. Microscopic examination clearly showed that small red clusters formed in the gel carrier. Moreover, fluorescence in situ hybridization analysis revealed that these clusters consisted of anammox bacteria. From real-time polymerase chain reaction analysis, the growth of anammox bacteria in the gel carriers was clearly shown by increased concentration of 16S rRNA gene of planctomycete from 4.3 x 10(8) to 4.2 x 10(9) copies/ml between days 41 and 55. To determine the effects of inoculation on the start-up of the reactor, the amount of seed sludge in the gel carrier was varied and it was found that the start-up period could be reduced to as little as 25 days when a sludge concentration of 1.4% (w/v) was used. This is the first report of successful immobilization and cultivation of anammox bacteria in a gel carrier.     

Anaerobic ammonium oxidation (anammox) in different natural ecosystems

Anammox (anaerobic ammonium oxidation), which is a reaction that oxidizes ammonium to dinitrogen gas using nitrite as the electron acceptor under anoxic conditions, was an important discovery in the nitrogen cycle. The reaction is mediated by a specialized group of planctomycete-like bacteria that were first discovered in man-made ecosystems. Subsequently, many studies have reported on the ubiquitous distribution of anammox bacteria in various natural habitats, including anoxic marine sediments and water columns, freshwater sediments and water columns, terrestrial ecosystems and some special ecosystems, such as petroleum reservoirs. Previous studies have estimated that the anammox process is responsible for 50% of the marine nitrogen loss. Recently, the anammox process was reported to account for 9-40% and 4-37% of the nitrogen loss in inland lakes and agricultural soils respectively. These findings indicate the great potential for the anammox process to occur in freshwater and terrestrial ecosystems. The distribution of different anammox bacteria and their contribution to nitrogen loss have been described in different natural habitats, demonstrating that the anammox process is strongly influenced by the local environmental conditions. The present mini-review summarizes the current knowledge of the ecological distribution of anammox bacteria, their contribution to nitrogen loss in various natural ecosystems and the effects of major influential factors on the anammox process.