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Anaerobic ammonium oxidation (anammox) is a promising and efficient biological nitrogen removal process, which can economically treat wastewater without organic supplement and aeration. However, to date, the insufficient nitrite in wastewater is the foremost problem encountered in anammox process. This restriction hinders full-scale application of anammox worldwide. Nitrite can be provided by innovative processes such as autotrophic denitrification and denitrifying anaerobic methane oxidation (DAMO). Therefore, the synergy between them and anammox is feasible means to solve the bottleneck. This review unravels the advantages and operating strategies of autotrophic denitrification, DAMO and their coupled processes with anammox. Besides, different electron donors such as reductive sulfur, iron, hydrogen, manganese and methane are analyzed in the two processes. The characteristics of microbial populations and their synergies in microbial communities are deciphered, and nitrogen removal contributions through different microbes are also highlighted. Still, nitrogen conversion pathways are clarified in the processes with different electron donors, and metabolic mechanisms of both autotrophic denitrifiers and DAMO microbes are revealed. Finally, the challenges to be focused in autotrophic denitrification and DAMO processes are proposed, and future perspectives on their coupled process with anammox are also put forward. [ABSTRACT FROM AUTHOR]

Water reservoir sediments represent a distinct habitat that harbors diverse microbial resources crucial for nitrogen cycling processes. The discovery of resuscitation promoting factor (Rpf) has been recognized as a crucial development in understanding the potential of microbial populations. However, our understanding of the relationship between microorganisms containing rpf-like genes and nitrogen-cycling functional populations remains limited. The present study explored the distribution patterns of rpf-like genes and nitrogen-cycling genes in various water reservoir sediments, along with their correlation with environmental factors. Additionally, the co-occurrence of rpf-like genes with genes associated with the nitrogen cycle and viable but non-culturable (VBNC) formation was investigated. The findings indicated the ubiquitous occurrence of Rpf-like domains and their related genes in the examined reservoir sediments. Notably, rpf-like genes were predominantly associated with Bradyrhizobium, Nitrospira, and Anaeromyxobacter, with pH emerging as the primary influencing factor for their distribution. Genera such as Nitrospira, Bradyrhizobium, Anaeromyxobacter, and Dechloromonas harbor the majority of nitrogen-cycling functional genes, particularly denitrification genes. The distribution of nitrogen-cycling microbial communities in the reservoir sediments was mainly influenced by pH and NH4 +. Notably, correlation network analysis revealed close connections between microorganisms containing rpflike genes and nitrogen-cycling functional populations, as well as VBNC bacteria. These findings offer new insights into the prevalence of rpf-like genes in the water reservoir sediments and their correlation with nitrogen-cycling microbial communities, enhancing our understanding of the significant potential of microbial nitrogen cycling. [ABSTRACT FROM AUTHOR]

Nitrate poses a potential threat to aquatic ecosystems. This study focuses on the sulfur autotrophic denitrification mechanism in the process of water culture wastewater treatment, which has been successfully applied to the degradation of nitrogen in water culture farm effluents. However, the coexistence of organic acids in the treatment process is a common environmental challenge, significantly affecting the activity of denitrifying bacteria. This paper aims to explore the effects of adding benzoic acid and lactic acid on denitrification performance, organic acid removal rate, and microbial population abundance in sulfur autotrophic denitrification systems under optimal operating conditions, sulfur deficiency, and high hydraulic load. In experiments with 50 mg·L−1 of benzoic acid or lactic acid alone, the results show that benzoic acid and lactic acid have a stimulating effect on denitrification activity, with the stimulating effect significantly greater than the inhibitory effect. Under optimal operating conditions, the average denitrification rate of the system remained above 99%; under S/N = 1.5 conditions, the average denitrification rate increased from 88.34% to 91.93% and 85.91%; under HRT = 6 h conditions, the average denitrification rate increased from 75.25% to 97.79% and 96.58%. In addition, the addition of organic acids led to a decrease in microbial population abundance. At the phylum level, Proteobacteria has always been the dominant bacterial genus, and its relative abundance significantly increased after the addition of benzoic acid, from 40.2% to 61.5% and 62.4%. At the genus level, Thiobacillus, Sulfurimonas, Chryseobacterium, and Thermomonas maintained high population abundances under different conditions. Practitioner Points: Employing autotrophic denitrification process for treating high‐nitrate wastewater.Utilizing organic acids as external carbon sources.Denitrifying bacteria demonstrate high utilization efficiency towards organic acids.Organic acids promote denitrification more than they inhibit it.The promotion is manifested in the enhancement of activity and microbial abundance. [ABSTRACT FROM AUTHOR]

Subsurface wastewater infiltration system (SWIS) is an ecological wastewater treatment technology that has the advantages such as low operating costs, satisfactory pollutant removal effects and ecological service functions. However, emerging compounds in wastewater has increased uncertainties in its treatment performance. In this study, antibiotics were added to the raw water with stepwise increasing concentrations, and the content of pollutants and structure of microbial populations were analyzed, aiming to qualitatively and quantitatively reveal the effect of sulfamethoxazole (SMX), oxytetracycline (OTC) and levofloxacin hydrochloride (HCl-Lev) antibiotics on denitrification rate of SWIS and explore the responses of microbial community. The results showed that the SMX, OTC and HCl-Lev removal rates ranged 34.4–48.7%, negatively correlating with the influent loads in SWIS. Under the stress of compound antibiotic (30.90 ± 0.39–32.49 ± 0.37 mg L−1), N removal rate decreased from 89.8 ± 1.4 (control) to 43.6 ± 2.0% and 38.9 ± 5.0% with increasing the concentrations of antibiotics. As a result, the effluent NH4+-N, NO3−-N, NO2−–N and TN hardly meet the discharge standards in China. Proteobacteria, Acidobacteria, Bacillus, Firmicutes and Bacteroidetes dominated in SWIS, accounting for about 70–90% of all microorganisms, independent of the antibiotics additions. RDA analysis showed that the activities of urease and catalase were negatively correlated with the concentrations of COD, NH4+–N, NO3−–N, TN, SMX, OTC, and HCl-Lev, further indicating that in SWIS, nitrogen and organic compounds are mainly removed by microbial degradation. [ABSTRACT FROM AUTHOR]

Sulphur‐driven denitrification is a low‐cost process for the treatment of nitrate‐contaminated water. However, a comprehensive understanding of core populations and microbial interactions of a sulphur‐based denitrifying system is lacking. This study presents results from three replicated denitrifying systems amended with thiosulphate and operated under a low C/N ratio. Amplicon sequencing revealed gradual enrichments of a few abundant denitrifiers. Based on genome‐centred metagenomics and metatranscriptomics, a core set of microbes was identified in the systems, with Pseudomonas 1 and Thauera 2 being the most abundant ones. Although the replicates showed different enrichments, generalized observations were summarized. Most core populations conserved energy from denitrification coupled with sulphur. Pseudomonas 1 and Thauera 2 were able to finish complete denitrification. Surprisingly, they were also able to synthesize almost all amino acids and vitamins. In contrast, less abundant members, including Pseudomonas 2, were relatively auxotrophic and required an exogenous supply of amino acids and vitamins. The high expression of enzymes involved in biosynthesis and transport systems indicated their syntrophic relationships. The genomic findings suggested life strategies and interactions of the core thiosulphate‐based denitrifying microbiome, with implications for nitrate‐polluted water remediation. [ABSTRACT FROM AUTHOR]

Microbial fuel cell (MFC) technology with decarbonization and denitrification is considered to be advantageous in treating wastewater with a low carbon-to-nitrogen ratio. In this study, MFC was treated with different concentrations of nitrate-nitrogen. The MFC technology revealed significant treatment advantages when compared to both abiotic electrode treatment and microbial treatment only. The best treatment effect was recorded when the MFC's nitrate-nitrogen ( N O 3 − − N ) concentration was 414 mg/L. The running of the MFC system showed that it produced a stable output voltage of up to 0.17 V within 160 h. It showed a power density of up to 40.18 mW/m2, 1.58 times M1 (138 mg/L, 25.49 mW/m2), and 4.48 times non-biological electrode. The removal rate of N O 3 − − N was 97.48%, but the lack of anode electron supply resulted in the incomplete reduction of nitrate-nitrogen and accumulation of nitritenitrogen. Nitrate-nitrogen concentration in the study had no significant impact on microbial population diversity. However, the relative abundance of Proteobacteria increased from 47.3% to 65.4% when N O 3 − − N concentration increased from 138 to 414 mg/L. Burkholderiales, Hydrogenophilales, and Rhodocyclales were the main denitrifying bacteria. These results demonstrate promise in supporting the development of microbial cathode denitrification. [ABSTRACT FROM AUTHOR]

Long-term anthropogenic nitrate (NO3−) enrichment is a serious threat to many coastal systems. Nitrate reduction coupled with the oxidation of reduced forms of sulfur is conducted by chemolithoautotrophic microbial populations in a process that decreases nitrogen (N) pollution. However, little is known about the diversity and distribution of microbes capable of carbon fixation within salt marsh sediment and how they respond to long-term NO3− loading. We used genome-resolved metagenomics to characterize the distribution, phylogenetic relationships, and adaptations important to microbial communities within NO3−-enriched sediment. We found NO3− reducing sulfur oxidizers became dominant members of the microbial community throughout the top 25 cm of the sediment following long-term NO3− enrichment. We also found that most of the chemolithoautotrophic genomes recovered contained striking metabolic versatility, including the potential for complete denitrification and evidence of mixotrophy. Phylogenetic reconstruction indicated that similar carbon fixation strategies and metabolic versatility can be found in several phylogenetic groups, but the genomes recovered here represent novel organisms. Our results suggest that the role of chemolithoautotrophy within NO3−-enriched salt marsh sediments may be quantitatively more important for retaining carbon and filtering NO3− than previously indicated and further inquiry is needed to explicitly measure their contribution to carbon turnover and removal of N pollution. [ABSTRACT FROM AUTHOR]

Shrimp is closely associated with different microbial populations of the gut and the environment, particularly of the water. Despite significant microbiome research in shrimp, a direct relationship between the shrimp's gut microbiota and the habitat environment remains unclear. The bacterial profiles of the shrimp intestine and its aqueous environment were compared by compiling data from earlier research to characterize the dynamic interaction between shrimp and habitat. According to the integrated analysis, shrimp, water, and sediment all had significant operational taxonomic units (OTUs), with shrimp intestine having less OTUs and sediment having more. Furthermore, 66 biological activities were shown to be common in shrimp and water bacteria, including nitrate reduction, methylotrophy, methanol oxidation, intracellular parasites, human infectious diarrhoea, fermentation, and others. These mechanisms might represent the primary bacterial processes related with intestine function, revealing new information on shrimp and water ecology. Although the relative abundances in the bacterial composition were different in shrimp intestine, water and sediment, the bacterial communities were almost similar, indicating the close interaction between host and the environment in microbiome. Notably, the significant distribution of disease-related pathogens including Vibrio and Flavobacterium in shrimp intestine and habitat water provided valuable information for disease prediction and shrimp health management in the aquaculture industry. In summary, many common microbes and bacterial processes that occur in the shrimp intestine and surrounding environment were revealed, and further functional analysis might help to modulate these processes to promote shrimp development and health. [ABSTRACT FROM AUTHOR]

The presence of dissolved organic nitrogen (DON) in stormwater treatment processes is a continuous challenge because of the intertwined nature of its decomposition, bioavailability, and biodegradability and its unclear molecular characteristics. In this paper, 21 T Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in combination with quantitative polymerase chain reaction was applied to elucidate the molecular change of DON and microbial population dynamics in a field-scale water filtration system filled with two specialty adsorbents for comparison in South Florida where the dry and wet seasons are distinctive annually. The adsorbents included CPS (clay-perlite and sand sorption media) and ZIPGEM (zero-valent iron and perlite-based green environmental media). Our study revealed that seasonal effects can significantly influence the dynamic characteristics and biodegradability of DON. The microbial population density in the filter beds indicated that three microbial species in the nitrogen cycle were particularly thrived for denitrification, dissimilatory nitrate reduction to ammonium, and anaerobic ammonium oxidation via competition and commensalism relationships during the wet season. Also, there was a decrease in the compositional complexity and molecular weight of the DON groups (C n H m O p N 1 , C n H m O p N 2 , C n H m O p N 3 , and C n H m O p N 4), revealed by the 21 T FT-ICR MS bioassay, driven by a microbial population quantified by polymerase chain reaction from the dry to the wet season. These findings indirectly corroborate the assumption that the metabolism of microorganisms is much more vigorous in the wet season. The results affirm that the sustainable materials (CPS and ZIPGEM) can sustain nitrogen removal intermittently by providing a suitable living environment in which the metabolism of microbial species can be cultivated and enhanced to facilitate physico-chemical nitrogen removal across the two types of green sorption media. [Display omitted] • ZIPGEM media mix performs better than CPS media mix for nitrogen removal. • DON decomposition deeply affects the removal rate of nitrogen in the surface water filtration system. • Photoammonification and mineralization are the key steps of the DON partial fraction decomposition. [ABSTRACT FROM AUTHOR]

Free cyanide (CN-) is a threat to metabolic functions of the microbial population used for the treatment of wastewater, particularly, total nitrogen removal (TN) consortia which gets inhibited by CN- in wastewater treatment plants (WWTPs). Many other methods are used to treat CN- prior to the TN removal stages; however, these methods increase the operational cost of the WWTPs. The capability of a microbial population to use multiple substrates is critical in WWTP and in eliminating inhibition associated with CN-. Previously, cyanide resistant bacteria were used to eliminate the inhibitory effect of CN- towards simultaneous nitrification and aerobic denitrification (SNaD). However, a study to predict the degradation efficiency of the microorganism was required. In this study, response surface methodology (RSM) and cybernetic models were used to predict and optimize SNaD performance for TN removal under CN- conditions. Physiological parameters influencing the SNaD were pH 6.5 and 36.5oC, with TN and CN- degradation efficiency of 78.6 and 80.2%, respectively. These results show a complete elimination of the CNinhibitory effect towards SNaD and show the prediction ability of both RSM and the cybernetic models used. These results exhibited a promising solution in the control, management, and optimization of SNaD. [ABSTRACT FROM AUTHOR]

[Display omitted] • High CO 2 /H 2 ratio increased the hydrogen utilization and the denitrification rate. • High CO 2 /H 2 ratio improved the electron transfer activity of sludge. • High CO 2 /H 2 ratio promoted the denitrification and homoacetogenic activity. • Homoacetogenesis – heterotrophic denitrification pathway was established. • Homoacetogens and heterotrophic denitrifying microorganisms were enriched. Hydrogenotrophic denitrification, an environment-friendly process for organic-free influents, is limited due to poor hydrogen mass transfer efficiency and significant pH fluctuations. In this study, we manipulated the carbon dioxide-to-hydrogen ratio to improve hydrogenotrophic denitrification. When carbon dioxide-to-hydrogen ratio was 1:1 (carbon dioxide, 200 ml: hydrogen, 200 ml), the hydrogen utilization and denitrification rates were 2.4 times and 3.0 times that when carbon dioxide-to-hydrogen ratio was 0:1 (carbon dioxide, 0 ml: hydrogen, 200 ml), respectively. The pH fluctuation decreased from 3.1±0.3 to 0.2±0.1. Furthermore, the hydrogenotrophic denitrification, acetoclastic denitrification, homoacetogenic, and electron transfer activities of the sludge were improved. A high carbon dioxide-to-hydrogen ratio augmented the acid-producing and heterotrophic denitrifying microorganism populations. By maintaining a high carbon dioxide-to-hydrogen ratio, the dominant hydrogenotrophic autotrophic denitrification pathway was transformed into a homoacetogenesis-heterotrophic denitrification pathway, thereby achieving higher hydrogen utilization and denitrification rates. [ABSTRACT FROM AUTHOR]

Haloferax mediterranei (R4) belongs to the group of halophilic archaea, one of the predominant microbial populations in hypersaline environments. In these ecosystems, the low availability of oxygen pushes the microbial inhabitants toward anaerobic pathways and the presence of N-oxyanions favor denitrification. In a recent study comparing three Haloferax species carrying dissimilatory N-oxide reductases, H. mediterranei showed promise as a future model for archaeal denitrification. This work further explores the respiratory physiology of this haloarchaeon when challenged with ranges of nitrite and nitrate concentrations and at neutral or sub-neutral pH during the transition to anoxia. Moreover, to begin to understand the transcriptional regulation of N-oxide reductases, detailed gas kinetics was combined with gene expression analyses at high resolution. The results show that H. mediterranei has an expression pattern similar to that observed in the bacterial Domain, well-coordinated at low concentrations of N-oxyanions. However, it could only sustain a few generations of exponential anaerobic growth, apparently requiring micro-oxic conditions for de novo synthesis of denitrification enzymes. This is the first integrated study within this field of knowledge in haloarchaea and Archaea in general, and it sheds lights on denitrification in salty environments. [ABSTRACT FROM AUTHOR]

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The single-well push-pull test (SWPPT) was adapted to quantify in denitrification rates and to assess microbial population dynamics in a highly nitrate-contaminated aquifer (105-311 NO3 mg L-1). In SWPPT through addition of fumarate as carbon source into test wells, significant NO3-consumtion was monitored in the well. The average zero- and first order rate coefficients were 7.85 and 0.82 mmol L-1 day-1, respectively. Degradation rate of injected fumarate is 15.22 (zero-order) and 0.51 (first-order) mmol L-1 day-1, respectively. Significant fumarate (electron donor, ED) and NO3(electron acceptor, EA) consumption, the production of dissolved CO2 during denitrification tests, and N2O production strongly indicate that the EAs consumption was mainly due to microbial activity. Therefore, SWPPT may be useful for quantifying in situ denitrification rates and for assessing microbial population dynamics in nitrate-contaminated aquifers in Silty Clay layer. [ABSTRACT FROM AUTHOR]

Hydroponic agriculture is one of the sectors that generate the highest amounts of nitrogen-containing wastewater. Sulfur-autotrophic denitrification is considered a promising technology due to its stable and excellent denitrification performance, cost-effectiveness, and operational advantages. In order to investigate the denitrification performance and the contribution of the filter layer under high NO 3 --N concentration (600 mg·L−1), this experiment designed a denitrification system using Na 2 S 2 O 3 as an electron donor. The results showed that the reactor achieved the highest denitrification efficiency with a hydraulic retention time of 12 h, pH of 7, and sulfur to nitrogen ratio of 2, maintaining a stable NO 3 --N removal efficiency of 99%. The majority of NO 3 --N was removed by the bottom filter layer (0–300 mm), accounting for 86% of the total denitrification. The microbial community in the lower part of the filter column was dominated by Proteobacteria , with relatively high abundances of the genera Chryseobacterium , Thiobacillus , and Sulfurimonas. Similarly, the microbial community structure in the upper filter layer was dominated by Proteobacteria , with an increased abundance of the genus Chryseobacterium and a significant reduction in the abundance of Sulfurimonas. The study indicates that SAD can achieve stable and efficient denitrification of wastewater from hydroponic reverse osmosis concentrate. Moreover, higher NO 3 --N concentrations can influence the bacterial community structure within the reactor. • Sodium thiosulfate as a sulfur source donor for sulfur-driven denitrification. • Treatment of High Nitrogen Wastewater Using Autotrophic Denitrification Process. • Studied the Variation in Nitrogen Element Content Along the Filter Column • Analyzed the Dominant Microbial Population Along the Filter Column. [ABSTRACT FROM AUTHOR]

Globally, agriculture is the largest source of nitrous oxide (N 2 O), a potent greenhouse gas (GHG). A recognised tool to prevent its loss from agricultural soils is the presence of a shallow water table. A four-year lysimeter experiment (2011–2014) was conducted in northeast Italy to investigate how water table levels affect N 2 O emissions after different N fertilisation techniques. Soil surface flux and groundwater-dissolved N 2 O were studied under free drainage and at two shallow water table levels (60 cm and 120 cm) and at two levels of N input (250 and 368 kg N ha −1  y −1 ), using dry manure in 2011 and 2012 and fresh manure in 2013 and 2014. DNA was extracted from soils and quantitative PCR (qPCR) was used to assess the size of nitrifying, denitrifying and N 2 -fixing bacterial communities. at three soil depths. The day after pre-seeding fertiliser incorporation, N 2 O emission started to be detected and continued for two-three weeks; brief measurable emissions also followed top–dressing fertilisation events. Cumulative N 2 O emission measured between 0.97 and 2.33 kg N 2 O-N ha −1  y −1 , corresponding to emission factors from 0.4% to 1.1%. Manure fertilisation significantly affected the N dose only when applied as fresh manure. Water-filled pore space (WFPS) affected daily N 2 O emissions with a significant interaction with fertilisation level. The two N input levels showed differences only when WFPS was >40%, which revealed N availability as key to increased N 2 O emissions at high water content, supposedly by fostering anaerobic denitrification. No significant relationships were observed between peak N 2 O emissions and the values of the temperature or irrigation variables recorded during the experimental observation period. Groundwater dissolved N 2 O-N concentrations measured about 1.7 μg L −1 with some peak variability from nitrate leaching. Quantitative PCR assays demonstrated that shifts in microbial population that can be involved in oxidation processes and heterotrophic denitrification occurred in the soil, even though the contributions of the different N pathways on N 2 O emissions were indistinguishable. Indeed, both nitrifying and denitrifying genes were simultaneously promoted by the high fertilisation input and hindered by the high water table level. Shallow groundwater conditions appeared to reduce N 2 O emissions probably by favouring complete denitrification. These results suggest that in the Po Plain, regulated by the Nitrate Directive, shallow groundwater conditions, with a balanced N input, may mitigate air and water pollution. [ABSTRACT FROM AUTHOR]

Background: The production of toxic metabolites has shaped the spatial and temporal arrangement of metabolic processes within microbial cells. While diverse solutions to mitigate metabolite toxicity have evolved, less is known about how evolution itself is affected by metabolite toxicity. We hypothesized that the pace of molecular evolution should increase as metabolite toxicity increases. At least two mechanisms could cause this. First, metabolite toxicity could increase the mutation rate. Second, metabolite toxicity could increase the number of available mutations with large beneficial effects that selection could act upon (e.g., mutations that provide tolerance to toxicity), which consequently would increase the rate at which those mutations increase in frequency. Results: We tested this hypothesis by experimentally evolving the bacterium Pseudomonas stutzeri under denitrifying conditions. The metabolite nitrite accumulates during denitrification and has pH-dependent toxic effects, which allowed us to evolve P. stutzeri at different magnitudes of nitrite toxicity. We demonstrate that increased nitrite toxicity results in an increased pace of molecular evolution. We further demonstrate that this increase is generally due to an increased number of available mutations with large beneficial effects and not to an increased mutation rate. Conclusions: Our results demonstrate that the production of toxic metabolites can have important impacts on the evolutionary processes of microbial cells. Given the ubiquity of toxic metabolites, they could also have implications for understanding the evolutionary histories of biological organisms. [ABSTRACT FROM AUTHOR]

River tributaries are ecologically important environments that function as sinks of inorganic nitrogen. To gain greater insight into the nitrogen cycle (N-cycle) in these environments, the distributions and activities of microbial populations involved in the N-cycle were studied in riparian and stream sediments of the Santa Fe River (SFR) tributaries located in northern Florida, USA. Riparian sediments were characterized by much higher organic matter content, and extracellular enzyme activities, including cellobiohydrolase, β- d -glucosidase, and phenol oxidase than stream sediments. Compared with stream sediments, riparian sediments exhibited significantly higher activities of nitrification, denitrification, dissimilatory nitrate reduction to ammonia (DNRA) and anaerobic ammonia oxidation; correspondingly, with higher copies of amoA (a biomarker for enumerating nitrifiers), nirS and nirK (for denitrifiers), and nrfA (for DNRA bacteria). Among N-cycle processes, denitrification showed the highest activities and the highest concentrations of the corresponding gene ( nirK and nirS ) copy numbers. In riparian sediments, substantial nitrification activities (6.3 mg-N kg soil −1 d −1 average) and numbers of amoA copies (7.3 × 10 7 copies g soil −1 average) were observed, and nitrification rates correlate with denitrification rates. The guild structures of denitrifiers and nitrifiers in riparian sediments differed significantly from those found in stream sediments, as revealed by analysis of nirS and archaeal amoA sequences. This study shows that riparian sediments serve as sinks for inorganic nitrogen loads from non-point sources of agricultural runoff, with nitrification and denitrification associated with elevated levels of carbon and nitrogen contents and extracellular enzyme activities. [ABSTRACT FROM AUTHOR]

Slow-releasing precipitating tablets (SRPTs) and slow-releasing floating tablets (SRFTs) were formulated to release fumarate as a carbon source (CS) and/or electron donor (ED) in an in situ biological heterotrophic denitrification system. These tablets were prepared using pharmaceutical manufacturing. Soil column tests were conducted to evaluate nitrate denitrification efficacy, microbial population changes, and mass balance of fumarate and potential electron acceptors. Significant and simultaneous consumption of both fumarate and nitrate, and the production and consumption of nitrite were observed in both SRPT-treated and SRFT-treated soil columns. These results suggest that SRPT and SRFT releasing fumarate, induce heterotrophic biological denitrification. In the SRPT- and SRFT-treated columns, 65% and 73% of fumarate were associated with heterotrophic denitrification, respectively. Particularly, surplus citric acid, originally designed to serve as a floating agent, was utilized for 36% and 28% for SRFT flotation and denitrification, respectively. The results of 16s RNA analyses revealed that a bacterium that shared 99% 16s rRNA sequence similarity with those of Azoarcus sp. AN9, and Pseudogulbenkiania sp. NH8B, a facultative heterotrophic denitrifier, was detected in the column effluent. This study confirms that SRPT and SRFT can effectively operate long-term in situ biological denitrification processes, because it is possible to supply detailed CS and/or ED uniformly by applying both SRPT and SRFT in the well. [Display omitted] • SRPT and SRFT could supply CS and/or ED uniformly in groundwater. • 65% and 73% of fumarate contained in SRPT and SRFT were used for denitrification. • Floating agents of citric acid in SRFT used floatation, and CS and/or ED. • Heterotrophic denitrification was dominant in the genomes studied. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metagenomic analysis revealed microbial nitrogen metabolism of two-stage A/O-MBBR. • Genes for nitrification and denitrification were enriched in oxic and anoxic MBBRs. • Microbial populations were different in pre-anoxic, oxic and post-anoxic MBBRs. • Nitrospira and Nitrosomonas were predominant in oxic MBBRs. • Dominant denitrifying genera were different in pre- and post-anoxic MBBRs. To explore the microbial nitrogen metabolism of a two-stage anoxic/oxic (A/O)-moving bed biofilm reactor (MBBR), biofilms of the system's chambers were analyzed using metagenomic sequencing. Significant differences in microbial populations were found among the pre-anoxic, oxic and post-anoxic MBBRs (P < 0.01). Nitrospira and Nitrosomonas had positive correlations with ammonia nitrogen (NH 4 +-N) removal, and were also predominant in oxic MBBRs. These organisms were the hosts of functional genes for nitrification. The denitrifying genera were predominant in anoxic MBBRs, including Thiobacillus and Sulfurisoma in pre-anoxic MBBRs and Dechloromonas and Thauera in post-anoxic MBBRs. The four genera had positive correlations with total nitrate and nitrite nitrogen (NO X −-N) removal and were the hosts of functional genes for denitrification. Specific functional biofilms with different microbial nitrogen metabolisms were formed in each chamber of this system. This work provides a microbial theoretical support for the two-stage A/O-MBBR system. [ABSTRACT FROM AUTHOR]

Aerobic denitrification bacteria are currently being explored as promising microorganisms with which to treat wastewater containing concentrated ammonium and organic carbon at psychrophilic temperatures. However, little is know regarding the mixed culture of these microbes under low-temperature shocks. In this study, a lab-scale aerobic denitrifying process was established in a sequencing bioreactor at 25 °C, and successfully performed in a short-term temperature downshift period that ranged from 25 °C to 5 °C. The specific aerobic denitrification rate was maximized at 15 °C [15.33 mg N/(g SS h)], and this process effectively removed chemical oxygen demand (COD) and nitrate (above 90%) even at 5 °C. The results of Illumina MiSeq 16S rRNA amplicon analysis revealed a relatively stable microbial community across the transitional periods of temperature. Pseudomonas was the most abuntant genus below 15 °C, and the amount of species Pseudomonas alcaligenes significantly increased at 5 °C with potassium nitrate as the primary nitrogen source. The communities of aerobic denitrifying bacteria in the temperature downshift period were all highly organized functionally, and they were relatively stably across the temperature gradient. These results will enhance understanding regarding the microbial ecology of aerobic denitrifiers in mixed cultures, leading to a more effective controlling of aerobic denitrification process during temperature transition states. [ABSTRACT FROM AUTHOR]

Denitrification was measured in three structurally different coastal microbial mats by using the stable isotope technique. The composition of the denitrifying community was determined by analyzing the nitrite reductase (nirS and nirK) genes using clone libraries and the GeoChip. The highest potential rate of denitrification (7.0 ± 1.0 mmol N m-2 d-1) was observed during summer at station 1 (supra-littoral). The rates of denitrification were much lower in the stations 2 (marine) and 3 (intermediate) (respectively 0.1 ± 0.05 and 0.7 ± 0.2 mmol N m-2 d-1) and showed less seasonality when compared to station 1. The denitrifying community at station 1 was also more diverse than that at station 2 and 3, which were more similar to each other than either of these stations to station 1. In all three stations, the diversity of both nirS and nirK denitrifiers was higher in summer when compared to winter. The location along the tidal gradient seems to determine the composition, diversity and activity of the denitrifier community, which may be driven by salinity, nitrate/nitrite and organic carbon. Both nirS and nirK denitrifiers are equally present and therefore they are likely to play a role in the denitrification of the microbial mats studied. [ABSTRACT FROM AUTHOR]

Denitrifying MFC was successfully coupled with anaerobic ammonium oxidation process in this study. With the help of cathode electrons, the stoichiometry relationship Δ − NH 3 -N:Δ − NO 2 − -N:Δ + NO 3 − -N was approximate 1:1.37:0.03 during the stable operation, which demonstrated its further nitrite and nitrate reduction. According to microbial community analysis, Candidatus Brocadia sinica was the main anammox community, and Rhodopseudomonas palustris with electrochemical driven denitrifying ability, especially enriched in biofilm. Higher abundance of nirK genes in biofilm (compare to the control) and invariable amx genes in suspended sludge were responsible for its better nitrogen removal. The sludge and biofilm performed their own duties on anammox and denitrification, respectively, according to genes quantification. Under the totally autotrophic system, electron donors were “concentrated supplied” and easy to control, which avoided the suppression of anammox growth, making this autotrophic coupling process appears to be more promising. [ABSTRACT FROM AUTHOR]

The competition for electrons has been recently demonstrated to affect the reduction rates of the nitrogen oxides in a methanol enriched denitrifying community. The aim of this study was to test if electron competition also occurred when other substrates were used for denitrification and if that could have an effect on the potential nitrous oxide (N 2 O) production and subsequent consumption. A denitrifying culture was developed in a sequencing batch reactor using nitrate as electron acceptor and a combination of acetate, ethanol and methanol as carbon sources. Four sets of batch tests were conducted using acetate, ethanol, methanol and a combination of the three carbon sources respectively. For each set the effect of nitrate, nitrite and nitrous oxide on each other reduction rates when present individually or in combination was assessed. Results show that reduction rates are affected by the type of substrate added, probably due to different microbial populations specialized with consuming a particular substrate. Also, N 2 O reduction rate is the most reduced under the different electron competition scenarios tested, which results in N 2 O accumulation in some cases. The effect of substrate limitation on N 2 O reduction was also assessed. [ABSTRACT FROM AUTHOR]

The microbial community and the nirS - and nirK -encoding denitrifiers in the intertidal sediments along Laizhou Bay in China were studied using pyrosequencing and real-time quantitative PCR (qPCR), respectively. There were three primary intertidal zones: Laizhou (La), Weifang Harbor (We), and Dongying (Do). Significant differences in composition and abundances at the different taxonomic levels were observed among the three bacterial communities. The qPCR results indicated that the nirS gene abundance varied from 8.67 × 10 5 to 5.68 × 10 6 copies/g wet weight (ww), whereas the nirK gene abundance varied from 1.26 × 10 5 to 1.89 × 10 6 copies/g ww. The canonical correlation analysis (CCA) indicated that the sand percentage was the most important factor in shaping the bacterial community followed by silt percentage, NO 2 − , TOC, DO, pH, and clay percentage, whereas the clay percentage, pH, NO 3 − , DO, NO 2 − , TOC, silt percentage, and sand percentage were the most important factors associated with regulating the abundance of nirS - and nirK -encoding denitrifiers. [ABSTRACT FROM AUTHOR]

Factors affecting community structure and connectivity within systems are crucial for provision of microbial ecosystem-services (e.g., soil nitrogen cycling), but what these factors are and how they are affected by land-use and management is poorly understood. Biogeochemical cycles are disrupted in agricultural-systems, providing an excellent opportunity to investigate the roles of management and land-use in shaping microbial communities and ecosystem function. We investigated soil ammonia oxidisers under different cropping practices and within a nearby grassy woodland; representing a gradient of physical/chemical disturbance. Land-use and management practices resulted in significant differences in community structure. Major differences in system connectivity were observed between land-uses, but not within management practices, indicating that land-use change is the major driver of ecosystem change, rather than management within land-uses. Agricultural ammonia oxidiser communities appeared to be less well connected and rely less on biotic interactions than those in natural systems, perhaps a reflection of the extent to which natural feedback loops are disturbed in managed systems. Smaller, but significant, differences were also evident between management treatments. Despite differences in community structure and connectivity there was, however, no significant effect on potential N-cycle rates, indicating that although land-use and management impacts may drive community changes, these do not necessarily translate into changes in functional capacity. [ABSTRACT FROM AUTHOR]

The identification of the key nitrous oxide ( N2O) production pathways is important to establish a strategy to mitigate N2O emission. In this study, we combined real-time gas-monitoring analysis, 15 N stable isotope analysis, denitrification functional gene transcriptome analysis and microscale N2O concentration measurements to identify the main N2O producers in a partial nitrification ( PN) aerobic granule reactor, which was fed with ammonium and acetate. Our results suggest that heterotrophic denitrification was the main contributor to N2O production in our PN aerobic granule reactor. The heterotrophic denitrifiers were probably related to R hodocyclales bacteria, although different types of bacteria were active in the initial and latter stages of the PN reaction cycles, most likely in response to the presence of acetate. Hydroxylamine oxidation and nitrifier denitrification occurred, but their contribution to N2O emission was relatively small (20-30%) compared with heterotrophic denitrification. Our approach can be useful to quantitatively examine the relative contributions of the three pathways (hydroxylamine oxidation, nitrifier denitrification and heterotrophic denitrification) to N2O emission in mixed microbial populations. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fullerene, routinely considered as bacteriostat, was found having stimulatory effect. [•] Fullerene enriched several bacteria in a denitrifying microbial community. [•] Growth and metabolic activities of a Bacillus isolate were promoted by fullerene. [Copyright &y& Elsevier]

The elemental sulfur (S 0 ) recovery was evaluated in the presence of nitrate in two development models of simultaneous desulfurization and denitrification (SDD) process. At the loading rates of 0.9 kg S/(m 3 ·day) for sulfide and 0.4 kg N/(m 3 ·day) for nitrate, S 0 conversion rate was 91.1% in denitrifying sulfide removal (DSR) model which was higher than in integrated simultaneous desulfurization and denitrification (ISDD) model (25.6%). A comprehensive analysis of functional diversity, structure and metabolic potential of microbial communities was examined in two models by using functional gene array (GeoChip 2.0). GeoChip data indicated that diversity indices, community structure, and abundance of functional genes were distinct between two models. Diversity indices (Simpson's diversity index (1/ D ) and Shannon–Weaver index ( H ′)) of all detected genes showed that with elevated influent loading rate, the functional diversity decreased in ISDD model but increased in DSR model. In contrast to ISDD model, the overall abundance of dsr genes was lower in DSR model, while some functional genes targeting from nitrate-reducing sulfide-oxidizing bacteria (NR-SOB), such as Thiobacillus denitrificans , Sulfurimonas denitrificans , and Paracoccus pantotrophus were more abundant in DSR model which were highly associated with the change of S 0 conversion rate obtained in two models. The results obtained in this study provide additional insights into the microbial metabolic mechanisms involved in ISDD and DSR models, which in turn will improve the overall performance of SDD process. [ABSTRACT FROM AUTHOR]

Highlights: [•] Biochar amendment did not affect the microbial community structure. [•] Biochar presence increased the relative abundance of 50% of the detected bacteria. [•] Biochar presence aided nitrogen cycling bacteria after urine addition. [•] Nitrogen cycling genes changed in a way consistent with microbe abundance changes. [•] Biochar amendment did not reduce N2O flux under the conditions tested. [Copyright &y& Elsevier]

The effects of anthraquinone-2,6-disulfonate (AQDS) on microbial populations and the biocatalysing characteristics of AQDS on denitrifying strain GW1 are discussed. The results showed that microbial population abundances were 30, 6, 12 and 18% during the different periods (1st, 5th, 10th and 20th days). Strain GW1 utilized AQDS as an electron acceptor in the respiration chain and reduced AQDS to hydroquinone (QH2). The nitrate removal efficiency of strain GW1 was increased 1.14–1.63 fold with 0.04–0.32 mmol/L AQDS. A linear correlation was found between the nitrate removal reaction constant(where VSS is volatile suspended solids) and AQDS concentration (CAQDS), which wask=19.332 CAQDS+11.115(R2=0.9749). The stabilized oxidation–reduction potential (ORP) values with AQDS were lower 22–92 mv than the control during the denitrification process. The concentration of nitrite sequentially accumulated up to around 250 mg/L when nitrate have removed completely. The results suggested that AQDS as redox mediator was capable of biocatalysing the nitrate and nitrite removal rate. [ABSTRACT FROM PUBLISHER]

A novel microbial consortium (BM-S-1) enriched from natural soils was successfully used to treat tannery wastewater from leather manufacturing industries in Korea on a pilot scale. The objective of this study was to determine whether augmentation with a novel microbial consortium BM-S-1could successfully treat the recalcitrant wastewater without chemical pre-treatment in a tannery wastewater treatment system. Chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) were monitored for water quality. The microbial population dynamics were analyzed using pyrosequencing, and denitrifying bacteria were quantified using real-time PCR (RT-PCR). The removal efficiencies for COD, TN and TP were greater than 91%, 79%, and 90%, respectively. The dominant phyla in the buffering tank (B), primary aeration (PA), secondary aeration (SA) and sludge digestion tank (SD) were Proteobacteria, Firmicutes, Bacteroidetes, Planctomycetes and Deinococcus-Thermus. Cluster analysis based on the UniFrac distance of the species in the different stages showed that the PA is similar to the SA, whereas the B is similar to the SD. qPCR of thenosZgenes showed the highest abundance of denitrifiers in B, which was increased 734-fold compared to the influent (I). It was hypothesized that anaerobic denitrifiers and the diverse microbial community may play important roles in the biological treatment of tannery wastewater. This technology may also contribute to the full-scale treatment of industrial wastewater containing food processing wastewater and marine sediment with high organic content. [ABSTRACT FROM AUTHOR]

Highlights: [•] A 3-D biofilm-electrode reactor was used for wastewater denitrification. [•] A nitrate removal of 98.3% was obtained with C/N ratio of 3.0 and HRT of 7h. [•] Both heterotrophic and autotrophic bacteria were responsible for nitrate removal. [•] A phylogenetic tree of gene sequences in biofilm was established. [•] The biofilm was abundant with Thauera-like and Enterobacter-like bacteria. [Copyright &y& Elsevier]

Abstract: Denitrification of high concentration of nitrate wastewater was investigated in expanded granular sludge bed (EGSB) reactor with sodium acetate as the carbon source. The optimal parameters were achieved with C/N mole ratio of 2.0, liquid up-flow velocity (V up) of 3.0m/h and pH of 6.2–8.2. Complete denitrification can be achieved even with nitrate nitrogen concentration as high as 14000mg/L. Furthermore, 454-pyrosequencing technology was used to analyze bacterial diversity. Results showed that a total of 5573 sequences were obtained which could be affiliated to 6 phylogenetic groups, including Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes, Chloroflexi and unclassified phylum. Proteobacteria (84.53%) was the dominant microbial population, followed by Firmicutes (13.24%) and Actinobacteria (0.38%). The dominate phylum was different from that in other anaerobic system. [Copyright &y& Elsevier]

Abstract: This study aimed to investigate nitrogen mass removal rates and microorganisms in planted columns that simulate vertical flow constructed wetlands. Two synthetic wastewaters, with mean NH4–N concentrations of 471±19 and 475±17mg/L, were treated in six individual columns. Under steady hydraulic and pollutant loading, average NH4–N removal rate was in the range of 21–47g/m2d, and average TN removal was 0–27g/m2d. Higher redox potential values benefitted ammonia removal but limited TN removal. The supply of organic carbon, by adding glucose into the synthetic wastewater, slightly reduced ammonia removal rate, but significantly enhanced TN removal. The variation of temperature between 14°C and 20°C had no effect on nitrogen removal. The seeding of microorganisms using diluted activated sludge, and submerging the columns with treated effluent for three days per week, appeared to intensify aerobic microbial degradation activities; oxygen consumption reached 53–363g O2/m2d, which was equivalent to upward air flux of 0.18–1.21m3/m2d in individual columns. Fluorescence in situ hybridization analysis of bacterial mass revealed the population densities of nitrifying bacteria, and specific denitrifying bacteria (Azoarcus-Thauera-cluster, genus Hyphomicrobium, genus Paracoccus, and family Saprospiraceae). Denitrifier Azoarcus-Thauera-cluster was the dominant bacterial group (58% of all cells) when organic carbon is available. Without organic carbon, ammonium oxidizing bacteria (AOB) dominate microbial populations in the columns. [Copyright &y& Elsevier]

Abstract: Nitrogen removal in wastewater treatment systems such as constructed wetlands mainly relies on autotrophic nitrification followed by heterotrophic denitrification. Two major microbial groups are now believed to be involved in ammonia oxidation during the first step of nitrification: ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA). Here we determined the abundance and composition of ammonia-oxidizing organisms and their seasonal population changes in a constructed wetland to determine the potential links between the constructed wetland water quality and nitrifying microbial population. By using specific primers targeting the amoA genes of AOA and AOB and real-time quantitative polymerase chain reaction (q-PCR), AOA were found to be generally higher than AOB in wetland soils and water in both summer and winter over a 2-year period of sampling. The AOB were not detected at the outlet of the first wetland treatment unit in the winter seasons indicating their more sensitivity to low temperature than AOA. Terminal restriction fragment length polymerization (T-RFLP) analysis confirmed low peak intensities for the AOB species in the winter. The removal efficiencies of NH4 +-N in wetland water in the summer and winter were 96% and 93%, respectively, while the wetland effluent NO3 −-N concentrations increased from 4mg/L in the winter to 11mg/L in the summer. The more complete nitrification was correlated with higher abundance of ammonia-oxidizing organisms in summer than in winter. Furthermore, nitrification was correlated with a substantial increase of AOB population while the number of AOA in soils remained unchanged. These results suggest that nitrification is mainly driven by AOB in the constructed wetlands treating ammonia-laden wastewater. [Copyright &y& Elsevier]

Abstract: The effect of solids retention time on reactor performance and microbial community composition in anoxic/aerobic membrane bioreactors (A/O-MBR) were investigated in this study. Experimental results showed high removal efficiencies of conventional pollutants. Antibiotics removal efficiencies were obviously affected by SRT changes. Longer SRT (above 30days) was proved to be suitable operational condition for antibiotics removal. Denaturing gradient gel electrophoresis (DGGE) and clone library analysis revealed that bacteria belong to Betaproteobacteria and Gammaproteobacteria were the dominant species during wastewater treatment and antibiotics removal. SRT significantly influenced the relative numbers of nitrifying bacteria. Removal efficiency of total nitrogen (TN) decreased when SRT was 3days, because nitrogen loading exceeded the denitrification ability of the reactors. Unlike tet C and tet E genes, sulfa antibiotics resistance gene presented a decreasing tendency with the decrease of SRT, and finally affected sulfa antibiotics removal efficiencies. [Copyright &y& Elsevier]

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). [ABSTRACT FROM AUTHOR]

Abstract: Copper is an essential element, however, this heavy metal is an inhibitor of microbial activity at relatively low concentrations. The objective of this study was to evaluate the inhibitory effect of copper(II) towards various microbial trophic groups responsible for the removal of organic constituents and nutrients in wastewater treatment processes. The results of the batch bioassays indicated that copper(II) caused severe inhibition of key microbial populations in wastewater treatment systems. Denitrifying bacteria were found to be very sensitive to the presence of copper(II). The concentrations of copper(II) causing 50% inhibition (IC50) on the metabolic activity of denitrifiers was 0.95mgL−1. Copper was also inhibitory to fermentative bacteria, aerobic glucose-degrading heterotrophs, and nitrifying bacteria (IC50 values=3.5, 4.6 and 26.5mgL−1, respectively). Nonetheless, denitrifying and nitrifying bacteria showed considerable recovery of their metabolic activity after only several days of exposure to high copper levels (up to 25 and 100mg Cu(II) L−1 for denitrification and nitrification, respectively). The recovery could be due to attenuation of soluble copper or to microbial adaptation. [Copyright &y& Elsevier]

Abstract: Sludge characteristics and nitrogen removal are investigated in this study for a conventional, aerated membrane bioreactor (C-MBR) and low oxygen, simultaneous nitrification–denitrification (SND) membrane bioreactor (SND-MBR). The SND-MBR is characterized as having a higher transmembrane pressure (TMP) and larger flocs within the activated sludge (AS). Greater and more varied concentrations of soluble chemical oxygen demand (sCOD) and transparent exopolymer substances (TEPS) were also realized. The C-MBR had a positive correlation between TMP and TEPS and between sCOD and TEPS with correlation coefficients of 0.8292 and 0.8299 respectively; no correlation was detected for the SND-MBR. The SND-MBR was able to remove 80% of the total nitrogen (TN) with 48% of influent TN being removed by SND; 31% of TN was removed by the C-MBR. Characterization of microbial populations within each MBR revealed that the C-MBR favored the development of Nitrospira and Nitrobacter while the SND-MBR favored Paracoccus and Nitrosospira species. [Copyright &y& Elsevier]

Abstract: The microbial community (bacterial, archaeal, and fungi) and eight genes involved in the nitrogen biogeochemical cycle (nifH, nitrogen fixation; bacterial and archaeal amoA, ammonia oxidation; narG, nitrate reduction; nirS, nirK, nitrite reduction; norB, nitric oxide reduction; and nosZ, nitrous oxide reduction) were quantitatively assessed in this study, via real-time PCR with DNA extracted from three Antarctic soils. Interestingly, AOB amoA was found to be more abundant than AOA amoA in Antarctic soils. The results of microcosm studies revealed that the fungal and archaeal communities were diminished in response to warming temperatures (10 °C) and that the archaeal community was less sensitive to nitrogen addition, which suggests that those two communities are well-adapted to colder temperatures. AOA amoA and norB genes were reduced with warming temperatures. The abundance of only the nifH and nirK genes increased with both warming and the addition of nitrogen. NirS-type denitrifying bacteria outnumbered NirK-type denitrifiers regardless of the treatment used. Interestingly, dramatic increases in both NirS and NirK-types denitrifiers were observed with nitrogen addition. NirK types increase with warming, but NirS-type denitrifiers tend to be less sensitive to warming. Our findings indicated that the Antarctic microbial nitrogen cycle could be dramatically altered by temperature and nitrogen, and that warming may be detrimental to the ammonia-oxidizing archaeal community. To the best of our knowledge, this is the first report to investigate genes associated with each process of the nitrogen biogeochemical cycle in an Antarctic terrestrial soil environment. [Copyright &y& Elsevier]

In many areas of China, tidal wetlands have been converted into agricultural land for rice cultivation. However, the consequences of land use changes for soil microbial communities are poorly understood. Therefore, we investigated bacterial and archaeal communities involved in inorganic nitrogen turnover (nitrogen fixation, nitrification, and denitrification) based on abundances and relative species richness of the corresponding functional genes along a soil chronosequence ranging between 50 and 2,000 years of paddy soil management compared to findings for a tidal wetland. Changes in abundance and diversity of the functional groups could be observed, reflecting the different chemical and physical properties of the soils, which changed in terms of soil development. The tidal wetland was characterized by a low microbial biomass and relatively high abundances of ammonia-oxidizing microbes. Conversion of the tidal wetlands into paddy soils was followed by a significant increase in microbial biomass. Fifty years of paddy management resulted in a higher abundance of nitrogen-fixing microbes than was found in the tidal wetland, whereas dominant genes of nitrification and denitrification in the paddy soils showed no differences. With ongoing rice cultivation, copy numbers of archaeal ammonia oxidizers did not change, while that of their bacterial counterparts declined. The nirK gene, coding for nitrite reductase, increased with rice cultivation time and dominated its functionally redundant counterpart, nirS, at all sites under investigation. Relative species richness showed significant differences between all soils with the exception of the archaeal ammonia oxidizers in the paddy soils cultivated for 100 and 300 years. In general, changes in diversity patterns were more pronounced than those in functional gene abundances. [ABSTRACT FROM AUTHOR]

Abstract: The effect of ammonium concentration on the microbial population and performance of a biofilter operated at methane concentrations of 0.3% (v/v) was studied. In a range of ammonium concentration from 0.05 to 0.5gN-NH4 +/L, the removal efficiency, carbon dioxide production rate, biomass production, ammonium conversion and nitrate production rate were determined. The middle biofilter section microbial population was analyzed using denaturing gradient gel electrophoresis (DGGE). DNA sequence analysis revealed that the bacteria colonizing the middle biofilter section belonged essentially to 4 physiological groups: methanotrophs, methylotrophs, nitrifying and denitrifying bacteria. Ammonium concentration affected the presence of bacteria from each group and the interactions among them defined the biofilter performance. In the range of ammonium concentrations tested, the methane removal efficiency decreased from 70 to 13%, the carbon dioxide production rate from 25 to 7.5g/(m3 h), and the mean of dry biomass content in the packed bed from 12.8 to 6.7gbiomass/kg filter bed. The nitrate production rate increased with ammonium concentration; however, it presented negative values at nitrate concentrations around 0.5gN/L. This suggests that denitrification occurred due to favourable conditions for the growth of denitrifiers. An analysis of methane biodegradation at different layers of the biofilter shows that the methanotrophic and nitrifying activities were more important in the upper section of the biofilter. [Copyright &y& Elsevier]

Abstract: CO2 capture and geological storage offers an option for reducing man-made greenhouse gas emissions. But one major concern related to geological CO2 storage is the possibility of leakage from the reservoir and subsequent effects on the environment, which cannot completely be excluded. This study aims at investigating the environmental impact of CO2 release from reservoirs into near surface terrestrial environments. To understand the effect of CO2 leakage on such an ecosystem, detailed knowledge on the abundance and diversity of plants and microorganisms is essential. Therefore, an ecosystem study has been conducted within the Network of Excellence “CO2GeoNet” on a natural CO2 vent at the Laacher See, Germany. Near surface CO2 conditions and CO2 fluxes of the venting area were described by means of conventional soil gas measurement equipment, and brought up the difference between the CO2 anomalies and their surroundings. A comparison of the soil columns between control sites and the centre of the venting area showed a small but significant change in the soil pH below 10cm. The botanical survey revealed vegetation changes which, like the investigation of important soil microbial communities, showed significant differences between the CO2-rich sites (up to 90% and more of soil gas), medium CO2 sites (∼20%), and control locations with background CO2 concentrations. The ecosystem appears to be adapted to the different conditions through species substitution or adaptation, showing a shift towards anaerobic and acidotolerant to acidophilic species under elevated CO2 concentrations. It is hoped that the final outcome of this ongoing study will be the identification of possible botanical and microbial indicators, whose presence or absence provides easily detectable evidence for leakage of CO2 from deep reservoirs into near surface terrestrial ecosystems. [Copyright &y& Elsevier]

Abstract: SBR (Sequencing Batch Reactor) treatment systems are made up of an artificial ecosystem where they develop the microorganisms under controlled and limited conditions, in which the pH, organic load and oxygen within the reactor vary spatially and in time. This causes the microbial population to be neither uniform nor constant and therefore reflects the conditions to which they have been exposed during the treatment system. Nitrifying and denitrifying bacteria in a SBR pilot system were monitored over 252days, using two types of wastewater in the treatment; one with a high amount of organic matter and the other with a high amount of ammonium, both originating from a meat product processing plant. The two types of wastewater were mixed in different proportions with the aim of varying the organic and ammoniacal loading in the influent, thus allowing the most suitable conditions for obtaining high removal efficiencies in the combined treatment of organic matter and ammonia to be determined. The results showed efficiencies of 99%, 98% and 71% in CODF, BOD5 and NH4 +–N, respectively, and a microbial density of about 2.35×107 MPN/100mL for nitrifying bacteria and 2.25×107 MPN/100mL for denitrifying bacteria. [Copyright &y& Elsevier]

A pilot-scale system was established to examine the feasibility of in situ U(VI) immobilization at a highly contaminated aquifer (U.S. DOE Integrated Field Research Challenge site, Oak Ridge, TN). Ethanol was injected intermittently as an electron donor to stimulate microbial U(VI) reduction, and U(VI) concentrations fell to below the Environmental Protection Agency drinking water standard (0.03 mg liter -1). Microbial communities from three monitoring wells were examined during active U(VI) reduction and maintenance phases with GeoChip, a high-density, comprehensive functional gene array. The overall microbial community structure exhibited a considerable shift over the remediation phases examined. GeoChip-based analysis revealed that Fe(III)-reducing bacterial (FeRB), nitrate-reducing bacterial (NRB), and sulfate-reducing bacterial (SRB) functional populations reached their highest levels during the active U(VI) reduction phase (days 137 to 370), in which denitrification and Fe(III) and sulfate reduction occurred sequentially. A gradual decrease in these functional populations occurred when reduction reactions stabilized, suggesting that these functional populations could play an important role in both active U(VI) reduction and maintenance of the stability of reduced U(IV). These results suggest that addition of electron donors stimulated the microbial community to create biogeochemical conditions favorable to U(VI) reduction and prevent the reduced U(IV) from reoxidation and that functional FeRB, SRB, and NRB populations within this system played key roles in this process. [ABSTRACT FROM AUTHOR]

Rice paddy soil has been shown to have strong denitrifying activity. However, the microbial populations responsible for the denitrification in various rice paddy soils are not well known. In the present study, key denitrifiers were identified in six rice paddy soils by comparing the bacterial community structures in soils with strong denitrifying activity with those in soils without the activity. The effect of crop rotation on the denitrifier populations was also examined. Our study revealed three notable findings: (1) community structures of total bacteria were similar among the six rice paddy soils with different soil characteristics, (2) the populations that responded to denitrification-inducing conditions differed with soil type (Andosol, Gley soil or Gray lowland soil), (3) the populations that responded to denitrification-inducing conditions were similar within each type of soil, regardless of the cropping system (e.g. continuous or rotation). [ABSTRACT FROM AUTHOR]

Two different types of biomass, capable for Enhanced Biological Phosphorus Removal (EBPR), a UCT (University of Cape Town) type and a sludge enriched with DPAOs (Denitrifying Phosphorus Accumulating Organisms) were tested in batch reactors under specific operational and environmental conditions, in order to achieve a direct comparison of their phosphorus removal capability. Three types of batch reactors were operated, Anaerobic/Oxic (AO), Anaerobic/Anoxic (A2) and Anaerobic/Anoxic/Oxic (A2O), under controlled temperature and pH conditions. Maximum anaerobic specific phosphate release, substrate utilization, as well as denitrification and phosphate uptake rates under aerobic and anoxic conditions were determined and compared for the two different microbial populations. Experimental results indicated no significant difference between the anoxic and the aerobic phosphorus (P) uptake rates, respectively for DPAO and UCT sludge. The UCT sludge was also found to achieve anoxic P uptake, however to much less extend compared to the DPAO sludge. It has also been proved that anoxic P uptake seems to negatively affect the total P removal efficiency of this type of sludge, even under following aerobic conditions. Based on these findings, denitrifying phosphorus removal systems are proved comparable to conventional EBPR configurations (UCT), concerning phosphorus removal efficiency, while their operation is accompanied by potential advantages. [ABSTRACT FROM AUTHOR]

Rice paddy soil has been shown to have strong denitrifying activity. However, the microbial populations responsible for nitrate respiration and denitrification have not been well characterized. In this study, we performed a clone library analysis of >1,000 clones of the nearly full-length 16S rRNA gene to characterize bacterial community structure in rice paddy soil. We also identified potential key players in nitrate respiration and denitrification by comparing the community structures of soils with strong denitrifying activity to those of soils without denitrifying activity. Clone library analysis showed that bacteria belonging to the phylum Firmicutes, including a unique Symbiobacterium clade, dominated the clones obtained in this study. Using the template match method, several operational taxonomic units (OTUs), most belonging to the orders Burkholderiales and Rhodocyclales, were identified as OTUs that were specifically enriched in the sample with strong denitrifying activity. Almost one-half of these OTUs were classified in the genus Herbaspirillum and appeared >10-fold more frequently in the soils with strong denitrifying activity than in the soils without denitrifying activity. Therefore, OTUs related to Herbaspirillum are potential key players in nitrate respiration and denitrification under the conditions used. [ABSTRACT FROM AUTHOR]

In this work, competition for two nitrogen resources (nitrate-, nitrite-nitrogen) between three hydrogen oxidizing denitrifying populations (Acidovorax sp. strain Ic3 (X 1), Paracoccus sp. strain Ic1 (X 2), and Acinetobacter sp. strain Ic2 (X 3)) was examined. The dynamics of three systems of microbial populations (system I: X 1 − X 3, system II: X 2 − X 3, and system III: X 1 − X 2 − X 3), grown in a chemostat, was studied using bifurcation analysis. The chemostat is the most common type of biological reactor used for the study of microbial growth under controlled conditions. The effect of the operating parameters (i.e., dilution rate and feed nitrate nitrogen concentration) on the long-term behavior of the systems showed that X 3 was the predominant population for a wide range of combinations of dilution rate and feed nitrate nitrogen concentration. Also, coexistence of two populations (X 2 X 3, X 1 X 3) was observed. The results of the bifurcation analysis were also used to determine the denitrification rate and the nitrite nitrogen accumulation for each of the three systems as a function of the dilution rate (up to 0.17h−1) and the feed nitrate nitrogen concentration (up to 300mg/L). The highest denitrification rate was achieved by system I (28mg/Lh). A comparison between the three systems showed that the nitrite nitrogen concentration in system I was less than the one in system III, while the two systems gave similar denitrification rates. The second system had the greatest accumulation of nitrites with the lowest denitrification rate. [Copyright &y& Elsevier]