Diversity Of Anammox Bacteria Research Articles

Metagenomic evidence of a novel anammox community in a cold aquifer with high nitrogen pollution

The process of anaerobic ammonium oxidation by nitrite (anammox) is a globally essential part of N cycle. To date, 8 Candidatus genera and more than 22 species of anammox bacteria have been discovered in various anthropogenic and natural habitats, including nitrogen-polluted aquifers. In this work, anammox bacteria were detected for the first time in the groundwater ecosystem with high anthropogenic nitrogen pollution (up to 1760 mg NO3−-N/L and 280 mg NH4+-N/L) and low year-round temperature (7–8 °C) in the zone of a uranium sludge repository. Further metagenomic analysis resulted in retrieval of metagenome-assembled genomes of 4 distinct anammox bacteria: a new genus named Ca. Frigussubterria, new species in Ca. Kuenenia, and two strains of a new species in Ca. Scalindua. Analysis of the genomes revealed essential genes involved in anammox metabolism. Both strains of Ca. Scalindua chemeplantae had a high copy number of genes encoding the cold shock proteins CspA/B, which can also function as an antifreeze protein (CspB). Ca. Kuenenia glazoviensis and Ca. Frigussubterria udmurtiae were abundant in less N-polluted site, while Ca. Scalindua chemeplantae inhabited both sites. Genes for urea utilization, reduction of insoluble Fe2O3 or MnO2, assimilatory sulfate reduction, reactive oxygen detoxification, nitrate reduction to ammonium, and putatively arsenate respiration were found. These findings enrich knowledge of the functional and phylogenetic diversity of anammox bacteria and improve understanding of the nitrogen cycle in polluted aquifers.

Diversity of Anammox Bacteria from Landfill Treatment Plant Sludge in Tropical Area

The anaerobic ammonium oxidation (anammox) process is known as the warm process. Tropical areas have an advantage due to their consistent temperature throughout the year. This study analyzed the diversity of anammox bacteria in the tropical area using leachate sludge from a landfill as an inoculum in a filter bioreactor (FtBR) and observed nitrogen removal performance. Ammonium and nitrite concentrations of 70, 150, and 200 mg-N/L were delivered into the reactor continuously with hydraulic retention time (HRT) of 24 h and 12 h and run for 131 days at ambient tropical temperature (25–28 °C). High performance achieved with nitrogen removal rate (NRR), nitrogen removal efficiency (NRE), and ammonium conversion efficiency (ACE) were 0.866 kg-N/m3.d, 99.19%, and 98.90%, respectively. The cultivated leachate sludge could perform an anammox process with four anammox species, Candidatus Brocadia fulgida, Candidatus Brocadia sapporoensis, Candidatus Brocadia sp uncultured, Candidatus Jettenia sp with abundance 6.52%, 13.82%, 0.77%, and 0.69%, respectively. These findings contribute to the advancement of biotechnology in wastewater treatment, particularly in tropical countries, and highlight the potential for highly cost-effective technology.

Anammox bacterial abundance and diversity in different temperatures of purple paddy soils by 13C-DNA stable-isotope probing combined with high-throughput sequencing.

Anaerobic ammonium oxidation (anammox) plays a vital role in the global nitrogen cycle by oxidizing ammonium to nitrogen under anaerobic environments. However, the existence, abundance, and diversity of anammox bacteria between different temperatures are less studied, particularly in purple paddy soils. 13C-DNA stable-isotope probe combined with Illumina MiSeq high-throughput sequencing was employed to explore soil abundance and diversity of anammox bacteria. In doing so, 40-60 cm depth soils from typical purple paddy soils in Chongqing, southwest China, were cultured under 12CO2-labeled and 13CO2-labeled at 35°C, 25°C, 15°C, and 5°C for 56 days. Anammox bacteria were not labeled at all by 13CO2 at 5°C. The highest abundance of anammox bacteria was found at 25°C (3.52 × 106~3.66 × 106 copies·g-1 dry soil), followed by 35°C and 15°C (2.01 × 106~2.37 × 106 copies·g-1 dry soil) and almost no increase at 5°C. The relative abundance of Candidatus Jettenia sp. was higher at 25°C and 15°C, while Candidatus Brocadia sp. was higher at 35°C and 5°C. Our results revealed differences in anammox bacteria at different temperatures in purple paddy soils, which could provide a better understanding of soil N cycling regulated by anammox bacteria.

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

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

Recent advances in environmental DNA‐based biodiversity assessment and conservation

Recent advances in environmental DNA‐based biodiversity assessment and conservation

Anaerobic ammonium oxidation (anammox) is the main microbial N loss pathway in alpine wetland soils of the Qinghai-Tibet Plateau

Anaerobic ammonium oxidation (anammox) is an important process in the biogeochemical cycle of nitrogen (N). However, knowledge remains limited on the anammox bacterial community, controlling factors, anammox rates and contributions to N loss in alpine wetland ecosystems with low temperatures and deficient oxygen concentrations. This study focused on the distribution, abundance and biodiversity of anammox bacteria and their contribution to N2 production in the rhizosphere and bulk soils of alpine wetlands from the Qinghai-Tibet Plateau along an altitude gradient and discussed their potential relationship with environmental variables. A high diversity of anammox bacteria was found in alpine wetland soils, with most of the detected anammox bacteria classified as unknown species. The anammox bacterial abundance based on the 16S rRNA gene ranged from 1.35 × 103 to 2.52 × 104 copies·g−1 in all the samples, and the anammox process generally contributed 62.66%–88.77% of the N2 production in rhizosphere and bulk soils among the sites at different altitudes, except for the summer bulk soil in Jiuzhi (30.52%) and Maduo (28.84%). The anammox bacterial community was closely linked to the NO2− concentration and water content, while the abundance and activity of anammox bacteria showed a significantly positive correlation with the NO3− concentrations and denitrification rates in both bulk and rhizosphere soils (p < 0.05). These results emphasized the key role of anammox in N cycling in the high-altitude alpine wetlands of Qinghai-Tibet, and extended our understanding of the community dynamics of anammox bacteria and their environmental importance.

Diversity, abundance, and distribution of anammox bacteria in shipping channel sediment of Hong Kong by analysis of DNA and RNA.

Anammox bacteria have been detected in various ecosystems, but their occurrence and community composition along the shipping channels have not been reported. In this study, anammox bacteria were recovered by PCR-amplified biomarker hzsB gene from the genomic DNA of the sediment samples. Phylogenetic tree revealed that Candidatus Scalindua and Ca. Brocadia dominated the anammox community of the Hong Kong channels; Ca. Scalindua spp. was present abundantly at the sites farther from the shore, whereas Ca. Jettenia and Ca. Kuenenia were detected as the minor members in the estuarine sediments near the shipping terminals. The highest values of Shannon-Wiener index and Chao1 were identified in the sediments along the Urmston road (UR), suggesting the highest α-diversity and species richness of anammox bacteria. PCoA analysis indicated that anammox bacterial communities along UR and Tai Hong (TH) channel were site-specific because these samples were grouped and clearly separated from the other samples. The maximum diversity of anammox bacteria was detected in UR samples, ranging from 6.28 × 105 to 1.28 × 106 gene copies per gram of dry sediment. A similar pattern of their transcriptional activities was also observed among these channels. Pearson's moment correlation and redundancy analysis indicated that NH4+-N was a strong factor shaping the community structure, which showed significant positive correlation with the anammox bacterial abundance and anammox transcriptional activities (p < 0.01, r > 0.8). Also, NH4+-N, (NO3- + NO2-)-N, and NH4+/NOX were additional key environmental factors that influenced the anammox community diversity and distribution. This study yields a better understanding of the ecological distribution of anammox bacteria and the dominant genera in selective niche.

Distribution and Community Composition of Anammox Bacteria in Shallow Groundwater of the Kathmandu Valley, Nepal.

The abundance and diversity of anaerobic ammonium oxidation (anammox) bacteria were assessed in 152 groundwater samples in the Kathmandu Valley, Nepal. Anammox bacterial 16S rRNA genes were detected in 54% (37/68) of samples collected in the dry season at 1.6×105–8.8×106 copies L–1, and in 60% (50/84) of samples collected in the wet season at 4.3×104–1.2×107 copies L–1. The 16S rRNA genes of “Candidatus Brocadia”, “Candidatus Anammoxoglobus”, and five new deduced anammox bacterial phylotypes were detected in the shallow groundwater samples. Diverse anammox bacteria were broadly distributed in the shallow groundwater aquifer of the Kathmandu Valley.

Simultaneous occurrence and analysis of both anammox and n-damo bacteria in five full-scale wastewater treatment plants

Anaerobic ammonium oxidation (anammox) and nitrite-dependent anaerobic methane oxidation (n-damo) processes are two newly discovered biochemical pathways for removal of reactive nitrogen species and methane. An investigation was initiated to investigate the simultaneous removal of ammonium and methane and the corresponding microorganisms in a full-scale sewage treatment plant and four landfill leachate treatment plants. In this study, hzsB and pmoA genes were used to amplify the genomic DNA of these samples to reveal the diversity of anammox bacteria and n-damo bacteria in these WWTPs. Both anammox bacteria and n-damo bacteria were detected successfully in all samples. The hzsB gene-based PCR amplified sequences featured three genera of Candidatus (Ca.) Brocadia, Ca. Kuenenia and Ca. Jettenia in these WWTPs, while the pmoA gene amplification showed two species of Ca. Methylomirabilis oxyfera and Ca. Methylomirabilis sinica. It was observed that after inoculation of anammox sludge, Brocadia becomes more dominant from the initial co-existing consortium of Kuenenia and Brocadia, and the community diversity decreased accordingly. Based on quantitative 16S rRNA gene PCR, the abundance of anammox bacteria ranged from 2.64 × 106 to 1.73 × 1013 copies per gram dry sludge in the five plants, particularly high on the carriers of landfill leachate wastewaters and the abundance of n-damo bacteria ranged from 2.52 × 107 to 2.19 × 108 copies per gram dry sludge in the five plants. Results shows that abundances of anammox bacteria and AOB (ammonium oxidizing bacteria) were limited by the lower ammonium in the sewage treatment plant, but were higher corresponding to ammonium concentration. Successful inoculation of anammox bacteria was achieved in practical engineering systems and the co-occurrence of anammox bacteria and n-damo bacteria plays an important role in N and C removal in WWTPs.

Effects of illumination on nirS denitrifying and anammox bacteria in the rhizosphere of submerged macrophytes

Visibility in lakes can decrease due to increases in the amounts of suspended solids and algae, which inhibits the growth of submerged macrophytes. However, the understanding about whether illumination reduction affects the nitrogen-cycling microorganisms in the rhizosphere of submerged macrophytes, is limited. The abundance and biodiversity of nirS denitrifying and anammox bacteria in the rhizosphere of Potamogeton crispus were studied under 0% (natural light), 20%, 40%, and 60% shading treatments. The abundance of the nirS gene was highest under 60% shading treatment, while the anammox 16S rRNA gene was highest under 40% shading treatment. Moreover, the abundance of the two genes were lower under natural light than under shading conditions during most sampling periods. The quantitative ratio of the two gene (anammox 16S rRNA to nirS gene) abundance fluctuated wildly with the distance away from the roots, under natural light and 20% shading treatment. However, the ratio varied relatively little under 40% and 60% shading treatments. The diversity of nirS denitrifying bacteria was high in the rhizosphere, while the diversity of anammox bacteria was low, and Candidatus Brocadia fulgida was dominant. This study revealed that illumination reduction not only facilitated the growth of nirS denitrifying and anammox bacteria in the rhizosphere, but also weakened the competition between the two bacteria.

Wide distribution of anaerobic ammonium‐oxidizing bacteria in the water column of the South China Sea: Implications for their survival strategies

AbstractAimAnammox bacteria are widely distributed in various environments, but the community composition and survival strategies of anammox bacteria in oligotrophic, deep‐sea water rich in dissolved oxygen (DO) remain unknown. We aimed to understand the distribution of anammox bacteria in the water columns of the South China Sea (SCS).Time periodThree cruises were in October 2014, October 2015 and September 2016, respectively.LocationSix water columns were obtained in the SCS, China (E 111–120°, N 16–22°).MethodsThe diversity and community composition of anammox bacteria were investigated through a high‐throughput sequencing technique targeting the anammox 16S rRNA gene.ResultsUnexpectedly, phylogenetic analysis showed that Ca. Brocadia (78.35%) was the dominant genus while Ca. Scalindua and unclassified species accounted for 12.62% and 9.03%, respectively. The highest diversity of anammox bacteria and concentrations of particulate organic matter (POM) were simultaneously observed in the 50–200 m layer, suggesting that particles may be a favourable niche for anammox bacteria. The wide distribution of anammox bacteria in the DO‐rich sea waters suggests two possible survival strategies: one strategy is attaching to particles and using anaerobic anammox metabolism to produce energy, and the other strategy is free‐living and using aerobic metabolism to produce energy.Main conclusionsA high diversity of anammox bacteria was found in the aerobic water columns, and Ca. Brocadia was the clearly dominant genus. Furthermore, anammox microbes could improve their viability by switching their metabolic pathways between anaerobic and aerobic conditions. Overall, our study has improved the understanding of the distribution and survival strategies of anammox communities in an aerobic marine environment and could provide new ideas for engineering applications in wastewater treatment with anammox technology.

Optimization of a method for diversity analysis of anammox bacteria using high-throughput sequencing of 16S rRNA gene amplicon

High-throughput sequencing of 16S rRNA amplicons is an effective method for diversity analysis of anammox bacteria. However, the corresponding taxonomic database and suitable cut-off value are unavailable for processing high-throughput sequencing data. This study is the first to construct a taxonomic database, comprising 17 sequences of enriched anammox strains (regarded as seed sequences) and 2925 uncultured sequences from environmental samples. Moreover, a suitable cut-off value was determined based on pairwise evolutionary distances between the 16S rRNA gene sequences of the 17 identified species and diversity indexes of community in the taxonomic database. Furthermore, the proposed method was validated with multiple environmental samples. In summary, the taxonomic database and proposed cut-off value targeting the 16S rRNA gene presented in this study can be effectively employed to explore the diversity of anammox bacteria.

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

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

Removal Capacities and Environmental Constrains of Denitrification and Anammox Processes in Eutrophic Riverine Sediments

Excessive nitrogen (N) loading has had severe consequences in coastal zones around the world. Denitrification and anammox are major microbial pathways for removing N in aquatic environments before it is exported to the coast. To assess two processes in eutrophic riverine systems, the denitrification and anammox and their bacterial participants were investigated in sediments of the Xiaoqing (XQ) River and Jiaolai (JL) River in Northeast China. By combining the evidence from N15 isotope tracing experiment and functional gene-based analysis, it was found that denitrification and anammox are ubiquitous along the investigated riverine sediments. The denitrification varied from 39.38 to 1433.01 nmol N2 m−2 h−1. Moreover, the anammox rates were in the range of 15.91 to 1209.97 nmol N2 m−2 h−1. Quantitative PCR results revealed that the nirK and nirS genes were in the order of 104–106 copies g−1 and 103–105 copies g−1, respectively, in both river sediments, while the hzsA was in the order of 106–105 copies g−1 in XQ at approximately two orders of magnitude compared with JL. The phylogenetic analysis of functional genes revealed the high diversity of the denitrifier and low diversity of anammox bacteria. Variance partitioning analyses verified that the grain particle characteristics were the major factor group determined the N removal efficiency. The denitrification and anammox processes were estimated to have removed 16.1% of the inorganic nitrogen inputs before being exported to Laizhou Bay, which highlights that a more extensive understanding of the regularity of the N removal processes is important in the technical remediation of eutrophication problems.

Anammox bacterial abundance and biodiversity in greenhouse vegetable soil are influenced by high nitrate content

The anaerobic ammonium oxidizing (anammox) process has been found to play an important role in terrestrial ecosystems in recent years. However, the diversity and abundance of anammox bacteria in nitrogen (N)-rich agricultural soils under high fertilizer greenhouse conditions are still unclear. Two greenhouse fields with different N fertilizer input levels were chosen, and their soil profiles were studied with molecular technologies, including quantitative polymerase chain reaction assay, a clone library, and phylogenetic analysis based on hzsB (encoding anammox hydrazine synthase β-subunit) gene. Molecular analyses suggested that anammox bacteria were at their highest density at 10–20 cm soil depth, and that the anammox bacterial abundance was significantly lower at high N than at low N. Candidatus Brocadia was the sole anammox bacterial genus throughout the soil depth profiles. The highest diversity of anammox bacteria was found at 30–40 cm soil depth, and different phylotypic clusters of Candidatus Brocadia were associated with specific soil environmental factors, such as nitrates, soil depth, and total N. Correlation analyses and redundancy analyses confirmed that high nitrate content associated with high N fertilizer input had a significant negative influence on the abundance and biodiversity of anammox bacteria. These results imply that excessive use of N fertilizer would affect arid land soil N loss to the atmosphere by the anammox pathway.

Environmental factors determining distribution and activity of anammox bacteria in minerotrophic fen soils.

In contrast to the pervasive occurrence of denitrification in soils, anammox (anaerobic ammonium oxidation) is a spatially restricted process that depends on specific ecological conditions. To identify the factors that constrain the distribution and activity of anammox bacteria in terrestrial environments, we investigated four different soil types along a catena with opposing ecological gradients of nitrogen and water content, from an amended pasture to an ombrotrophic bog. Anammox was detected by polymerase chain reaction (PCR) and quantitative PCR (qPCR) only in the nitrophilic wet meadow and the minerotrophic fen, in soil sections remaining water-saturated for most of the year and whose interstitial water contained inorganic nitrogen. Contrastingly, aerobic ammonia oxidizing microorganisms were present in all examined samples and outnumbered anammox bacteria usually by at least one order of magnitude. 16S rRNA gene sequencing revealed a relatively high diversity of anammox bacteria with one Ca. Brocadia cluster. Three additional clusters could not be affiliated to known anammox genera, but have been previously detected in other soil systems. Soil incubations using 15N-labeled substrates revealed that anammox processes contributed about <2% to total N2 formation, leaving nitrification and denitrification as the dominant N-removal mechanism in these soils that represent important buffer zones between agricultural land and ombrotrophic peat bogs.

Diversity of anammox bacteria and contribution to the nitrogen loss in surface sediment

Anaerobic ammonium oxidizing bacteria are the key players of nitrogen cycling in different kinds of ecosystems. Here, the abundance, activity, and community composition of anammox bacteria in the surface sediments of Jiaozhou Bay (JZB) were investigated. Results indicated that dominant OTUs with 97% similarity were affiliated to Ca. Scalindua (75.37%), Ca. Brocadia (9.40%), Ca. Kuenenia (1.46%), Cluster 1 (5.41%), and Cluster 2 (8.36%) by high-throughput sequencing analysis. The abundance of anammox bacteria were quantified by anammox specific 16S rRNA gene, which ranged from (5.88 ± 1.20) × 104 to (1.41 ± 0.08) × 106 copies per gram. Anammox rates in JZB, measured by 15N tracing technique, ranged from 0.01 to 0.24 nmol N g−1 h−1, contributing 0.07%–18.55% to N2 production, and the sediment nitrogen loss caused by anammox was estimated at 1042.33 t N per year. NH4+ and NO2− contents were the limiting factors affecting the anammox bacterial community composition and abundance, respectively. Meanwhile, high NO3− favors the growth of diverse anammox bacteria in surface sediments of JZB. Overall, these results significantly enhance our understanding of the anammox activity, community composition, and nitrogen removal contribution in hypernutrified and semi-closed bay.

Diversity of anammox bacteria and abundance of functional genes for nitrogen cycling in the rhizosphere of submerged macrophytes in a freshwater lake in summer

PURPOSE: Submerged plants make an important contribution to nitrogen cycling in lakes including in the rhizosphere microenvironment through microbial activities. The main objective of this study was to investigate the abundance of functional genes for nitrogen cycling and the ecological relationship between these genes in the rhizosphere sediment of a freshwater lake in summer. MATERIALS AND METHODS: Sediment from the rhizosphere of four submerged macrophytes (Ceratophyllum demersum, Hydrilla verticillata, Potamogeton maackianus, and Vallisneria spiralis) was sampled in Lake Liangzi, China, in summer. The anammox bacteria community structure and abundance of five functional genes for nitrogen cycling, ammonia monooxygenase (amoA) of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA), anammox 16S rRNA, and nitrite reductase genes (nirK and nirS) in the sampled sediment, were determined. RESULTS AND DISCUSSION: A total of 100 anammox gene sequences were grouped into eight operational taxonomic units (OTUs) and genus Ca. Kuenenia was the dominant species in Lake Liangzi in summer. Quantitative polymerase chain reaction (qPCR) revealed that gene copies of AOA amoA (2.42 × 10⁶ copies g⁻¹) were more than one order of magnitude higher than those of AOB amoA (1.98 × 10⁵ copies g⁻¹). The nirS gene (4.13 × 10⁸ copies g⁻¹) was more abundant than the nirK gene (7.28 × 10⁷ copies g⁻¹). There was no significant difference in the abundance of the AOB amoA gene among the rhizosphere of the four macrophytes. Redundancy analysis (RDA) showed a positive correlation between the abundance of the anammox 16S rRNA gene, AOA amoA and AOB amoA, which suggested two of these microbes may have provided a substrate for anammox bacteria in summer. CONCLUSIONS: The diversity of anammox in the rhizosphere of submerged macrophytes of the freshwater lake in summer was very low, but the plant species could affect the abundance of most nitrogen circulating bacteria, especially for anammox bacteria. Anammox 16S rRNA gene was positively correlated with four other functional genes, indicating that all four genes had significant effects on anammox bacteria.

Unexpectedly high diversity of anammox bacteria detected in deep-sea surface sediments of the South China Sea.

Candidatus Scalindua is an exclusive genus of anammox bacteria known to exhibit low diversity found in deep-sea ecosystems. In this study, the community composition of anammox bacteria in surface sediments of the South China Sea was analyzed using high-throughput sequencing techniques. Results indicated that the dominant operational taxonomic units were related to three different genera of anammox bacteria, identified as Ca. Scalindua (87.29%), Ca. Brocadia (10.27%) and Ca. Kuenenia (2.44%), in order of decreasing abundance. Quantitative PCR analysis of anammox-specific 16S rRNA and hzsB genes confirmed that the abundance of anammox bacteria in deep-sea surface sediments ranged from 4.34 × 105 to 3.91 × 107 and 1.62 × 105 to 1.63 × 108 copies per gram, respectively. The ACE, Chao1 and Shannon estimators for anammox bacteria were significantly higher than those reported in previous studies. Pearson correlation and redundancy analyses indicated that depth and temperature were the key factors affecting the distribution, abundance and diversity of anammox bacteria in deep-sea sediments. We herein report the wide distribution of Ca. Kuenenia and Ca. Brocadia in deep-sea sediments and provide comprehensive information on the distribution and ecological significance of anammox bacteria in deep-sea environments.

Shifts in the anammox bacterial community structure and abundance in sediments from the Changjiang Estuary and its adjacent area

Anaerobic ammonium oxidation (anammox) is an important process in marine nitrogen cycle. In this study, diverse anammox bacteria were identified in the sediments of the Changjiang (Yangtze) Estuary and its adjacent area. Specifically, the community characters of anammox bacteria in the studied area were studied by quantitative polymerase chain reaction (qPCR), as well as 16S rRNA gene- and functional gene (hzo)-based Roche 454 sequencing. The abundance of denitrifying bacteria detected by the nirS gene was greater than that of anammox bacteria. 16S rRNA and hzo gene fragments affiliating with known anammox bacterial lineages were recovered, and the two major phylotypes belonged to the Candidatus Scalindua (Ca. Scalindua) genus, with >90% sequence similarity. A phylogenetic analysis detected the Scalindua and Brocadia genera together with some anammox-like bacterial clusters, which suggested a higher diversity in the studied ecosystem than in open ocean environment, where only Scalindua genus was detected. A redundancy analysis (RDA) showed that total organic carbon (TOC) and total nitrogen (TN) content in sediments significantly influenced anammox bacterial abundance of. Spearman correlation analyses confirmed that the spatial variation in anammox bacterial abundance was highly correlated with TOC (P<0.01) and TN (P<0.01) contents in sediments.