Impacts of reduced sulfur components on active and resting ammonia oxidizers

Sulfide inhibition on polyphosphate accumulating organisms and glycogen accumulating organisms: Cumulative inhibitory effect and recoverability

Sulfate in wastewater can be reduced to sulfide and its impact on the stability of enhanced biological phosphorus removal (EBPR) is still unclear. In this study, the metabolic changes and subsequent recovery of polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs) were investigated at different sulfide concentrations. The results showed that the metabolic activity of PAOs and GAOs was mainly related to H2S concentration. Under anaerobic conditions, the catabolism of PAOs and GAOs was promoted at H2S concentrations below 79 mg/L S and 271 mg/L S, respectively, and inhibited above these concentrations; whereas anabolism was consistently inhibited in the presence of H2S. The phosphorus (P) release was also pH-dependent due to the intracellular free Mg2+ efflux from PAOs. H2S was more destructive to the esterase activity and membrane permeability of PAOs than those of GAOs and prompted intracellular free Mg2+ efflux of PAOs, resulting in worse aerobic metabolism and subsequent recovery of PAOs than GAOs. Additionally, sulfides facilitated the production of extracellular polymeric substances (EPS), especially tightly bound EPS. The amount of EPS in GAOs was significantly higher than that in PAOs. The above results indicated that sulfide had a stronger inhibition to PAOs than GAOs, and when sulfide was present, GAOs had a competitive advantage over PAOs in EBPR.

Dissimilatory nitrate reduction and functional genes in two subtropical rivers, China

Dissimilatory nitrate reduction processes, including denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA), are important pathways of nitrate transformation in the aquatic environments. In this study, we investigated potential rates of denitrification, anammox, and DNRA in the sediments of two subtropical rivers, Jinshui River and Qi River, with different intensities of human activities in their respective catchment, China. Our objectives were to assess the seasonality of dissimilatory nitrate reduction rates, quantify their respective contributions to nitrate reduction, and reveal the relationship between dissimilatory nitrate reduction rates, functional gene abundances, and physicochemicals in the river ecosystems. Our results showed higher rates of denitrification and anammox in the intensively disturbed areas in autumn and spring, and higher potential DNRA in the slightly disturbed areas in summer. Generally, denitrification, anammox, and DNRA were higher in summer, autumn, and spring, respectively. Relative contributions of nitrate reduction from denitrification, anammox, and DNRA were quite different in different seasons. Dissimilatory nitrate reduction rates and gene abundances correlated significantly with water temperature, dissolved organic carbon (DOC), sediment total organic carbon (SOC), NO₃^-, NH₄⁺, DOC/NO₃^-, iron ions, and sulfide. Understanding dissimilatory nitrate reduction is essential for restoring nitrate reduction capacity and improving and sustaining ecohealth of the river ecosystems.

Shifts in the relative abundance and potential rates of sediment ammonia-oxidizing archaea and bacteria along environmental gradients of an urban river-estuary-adjacent sea continuum

Ammonia-oxidizing archaea (AOA) and bacteria (AOB) play important roles in N cycling in sediments globally. However, little is known about their ammonia oxidation rates along a river-estuary-sea continuum. In this study, we investigated how the potential ammonia oxidation rates (PARs) of AOA and AOB changed spatially along a continuum comprising three habitats: the Shanghai urban river network, the Yangtze Estuary, and the adjacent East China Sea, in summer and winter. The AOA and AOB PARs (0.53 ± 0.49 and 0.72 ± 0.69 μg N g^-1 d^-1, mean ± SD, respectively) and their amoA gene abundance (0.47 ± 0.85 × 10⁶ and 2.4 ± 3.54 × 10⁶ copies g^-1, respectively) decreased along the continuum, particularly from the urban river to the estuary, driven by decreasing sediment total organic C and N and other correlated inorganic nutrients (e.g., NH₄⁺) along the gradient of anthropogenic influences. These spatial patterns were consistent between the seasons. The urban river network, where the anthropogenic influences were strongest, saw the largest seasonal differences, as both AOA and AOB had higher PARs and abundance in summer than in winter. The ratios between AOA and AOB PARs (~0.87 ± 0.51) and gene abundances (~0.25 ± 0.24), however, were predominantly <1, indicating an AOB-dominated community. Comparing the different NH₄⁺ consumption pathways, total aerobic oxidation accounted for 12-26% of the total consumption, with the largest proportion in the estuary, where the system was well oxygenated, and the lowest in the adjacent sea, where inorganic N was highly depleted. This study revealed the spatiotemporal patterns of AOA and AOB potential rates and gene abundance along gradients of human influences and identified organic matter and nutrients as key environmental factors that shaped the variation of AOA and AOB along the continuum.

Estuarine microbial diversity and nitrogen cycling increase along sand-mud gradients independent of salinity and distance

Estuaries are depositional environments prone to terrigenous mud sedimentation. While macrofaunal diversity and nitrogen retention are greatly affected by changes in sedimentary mud content, its impact on prokaryotic diversity and nitrogen cycling activity remains understudied. We characterized the composition of estuarine tidal flat prokaryotic communities spanning a habitat range from sandy to muddy sediments, while controlling for salinity and distance. We also determined the diversity, abundance and expression of ammonia oxidizers and N₂ O-reducers within these communities by amoA and clade I nosZ gene and transcript analysis. Results show that prokaryotic communities and nitrogen cycling fractions were sensitive to changes in sedimentary mud content, and that changes in the overall community were driven by a small number of phyla. Significant changes occurred in prokaryotic communities and N₂ O-reducing fractions with only a 3% increase in mud, while thresholds for ammonia oxidizers were less distinct, suggesting other factors are also important for structuring these guilds. Expression of nitrogen cycling genes was substantially higher in muddier sediments, and results indicate that the potential for coupled nitrification-denitrification became increasingly prevalent as mud content increased. Altogether, results demonstrate that mud content is a strong environmental driver of diversity and N-cycling dynamics in estuarine microbial communities.

Genomic and Metabolic Insights into Two Novel Thiothrix Species from Enhanced Biological Phosphorus Removal Systems

Two metagenome-assembled genomes (MAGs), obtained from laboratory-scale enhanced biological phosphorus removal bioreactors, were analyzed. The values of 16S rRNA gene sequence identity, average nucleotide identity, and average amino acid identity indicated that these genomes, designated as RT and SSD2, represented two novel species within the genus Thiothrix, 'Candidatus Thiothrix moscowensis' and 'Candidatus Thiothrix singaporensis'. A complete set of genes for the tricarboxylic acid cycle and electron transport chain indicates a respiratory type of metabolism. A notable feature of RT and SSD2, as well as other Thiothrix species, is the presence of a flavin adenine dinucleotide (FAD)-dependent malate:quinone oxidoreductase instead of nicotinamide adenine dinucleotide (NAD)-dependent malate dehydrogenase. Both MAGs contained genes for CO₂ assimilation through the Calvin-Benson-Bassam cycle; sulfide oxidation (sqr, fccAB), sulfur oxidation (rDsr complex), direct (soeABC) and indirect (aprBA, sat) sulfite oxidation, and the branched Sox pathway (SoxAXBYZ) of thiosulfate oxidation to sulfur and sulfate. All these features indicate a chemoorganoheterotrophic, chemolithoautotrophic, and chemolithoheterotrophic lifestyle. Both MAGs comprise genes for nitrate reductase and NO-reductase, while SSD2 also contains genes for nitrite reductase. The presence of polyphosphate kinase and exopolyphosphatase suggests that RT and SSD2 could accumulate and degrade polyhosphates during the oxic-anoxic growth cycle in the bioreactors, such as typical phosphate-accumulating microorganisms.

Low-dose Ultraviolet-A irradiation selectively eliminates nitrite oxidizing bacteria for mainstream nitritation

Nitritation is currently known as a bottleneck for mainstream nitrite shunt or partial nitritation/anammox (PN/A). Here we propose a new approach to selectively eliminate nitrite oxidizing bacteria (NOB) for mainstream nitritation by low-dose ultraviolet-A (UVA) irradiation. The results showed that mainstream nitritation was rapidly achieved within 10 days with UVA irradiation at the dose of 0.87 μE L^-1 s^-1, and nitrite accumulation ratio (NO₂^--N/(NO₂^--N + NO₃^--N) ×100%) stabilized over 80%. Microbial community analysis revealed that two typical NOB populations (Nitrospira and Ca. Nitrotoga) detected in the control reactor were suppressed efficiently in UVA irradiation reactor, whereas the Nitrosomonas genus of ammonium oxidizing bacteria (AOB) remained at similar level. Intracellular reactive oxygen species (ROS) analysis indicated that NOB-dominant sludge tends to generate more intracellular ROS compared with AOB-dominant sludge in the presence of UVA, leading to the inactivation and elimination of NOB. Additionally, amounts of microalgae found in UVA irradiation reactor could help to suppress NOB by generating ROS during photosynthesis. Briefly, the UVA irradiation approach proposed in this study was shown to be promising in NOB suppression for reliable mainstream nitritation.

Experimental sulphide inhibition calibration method in nitrification processes: A case-study

Sulphide is one of the inhibitors in the nitrification process in WWTP in regions with sulphate rich soils. As little information is currently available on sulphide nitrification inhibition, the aim of this study was to develop a method based on a modification of the Successive Additions Method to calibrate the effect of sulphide on the activity of ammonia-oxidising bacteria (AOB) and nitrite-oxidising bacteria (NOB). The developed method was then applied to activated sludge samples from two WWTPs with different influent sulphide concentrations. In both cases, sulphide had a greater inhibitory effect on NOB than AOB activity. The sulphide inhibition was found to be lower in the activated sludge fed with sulphide-rich wastewater. The AOB and NOB activity measured at different sulphide concentrations could be accurately modelled with the Hill inhibition equation.

Biological ammonium and sulfide oxidation in a nitrifying sequencing batch reactor: Kinetic and microbial population dynamics assessments

A kinetic study was carried out in a sequencing batch reactor (SBR) (125 mg NH₄⁺-N/L) inoculated with a physiologically stable nitrifying sludge not previously acclimated to sulfur compounds and fed at different initial sulfide concentrations (2.5-20.0 mg HS^--S/L). Up to 10.0 mg HS^--S/L, the nitrifying process kept stable and complete, reaching an ammonium consumption efficiency (E_NH4+) of 100% and a nitrate yield (Y_NO3-) of 0.95 ± 0.03 mg NO₃^--N/mg NH₄⁺-N consumed. At 15.0 and 20.0 mg HS^--S/L, after an initial alteration in the nitrite oxidizing process, the Y_NO2- was decreasing throughout the cycles and the Y_NO3- increasing, obtaining in the last cycle at 20.0 mg HS^--S/L, an E_NH4+ of 100%, a Y_NO2- of zero, and a Y_NO3- of 0.80 mg NO₃^--N/mg NH₄⁺-N consumed. At the end of the period at 20.0 mg HS^--S/L, the specific rates of ammonium consumption and nitrate formation were 15 and 55% lower than their respective values in the control period without sulfide addition, showing that the sludge had a better metabolic adaptation for ammonium oxidizing activity than for nitrite oxidizing activity. The sludge acquired a higher sulfide oxidation capacity along the cycles. Bacterial population dynamics assessment indicated that the ammonium oxidizing bacteria (AOB) community was more diverse and stable than the nitrite oxidizing bacteria (NOB) community. The use of consortia with a previously stabilized nitrifying activity in SBR may constitute an alternative for eliminating simultaneously ammonium by nitrification and sulfide by sulfide oxidation and be implemented for the treatment of wastewater with ammonium and sulfide.

Stable granulation of seawater-adapted aerobic granular sludge with filamentous Thiothrix bacteria

Many sources of wastewater contain sulfides, which can cause excessive growth of filamentous bacteria such as Thiothrix sp. resulting in bulking sludge in conventional activated sludge systems. Granular sludge systems could potentially also suffer from the growth of filamentous bacteria. Uptake of easily degradable COD by the relatively slow growing Ca. Accumulibacter phosphatis bacteria and the absence of strong diffusion gradients due to plug flow feeding through the settled granular sludge bed are assumed to be the dominant factors for successful granulation. Sulfides will remain after this anaerobic phase and cause growth of sulfide-consuming bacteria such as Thiothrix sp. Here we observed the impact of growth of Thiothrix sp bacteria in a laboratory aerobic granular sludge reactor by feeding a mixture of acetate and thiosulfate in the influent. Thiothrix sp, proliferated when 18% of the influent COD was due to thiosulfate, forming 51.4 ± 8.3% of the total granular biomass. Despite the strong presence of these filamentous bacteria a well settling sludge was maintained (SVI₁₀ equal to 13.3 mL/g). These results confirm that sludge morphology is not necessarily a reflection of the cell morphology of the bacteria, but is highly influence by reactor operation. It also reiterates the fact that compact biofilms are formed when the substrate consumption rate is lower than the substrate transport rate.

Bacterial Community Shifts Driven by Nitrogen Pollution in River Sediments of a Highly Urbanized City

Effects of nitrogen pollution on bacterial community shifts in river sediments remain barely understood. Here, we investigated the bacterial communities in sediments of urban and suburban rivers in a highly urbanized city, Shanghai. Sediment nitrate (NO₃⁻) and ammonia (NH₄⁺) were highly accumulated in urban river. Operation Taxonomic Units (OTUs), Abundance-based Coverage Estimators (ACEs) and Chao 1 estimator in urban rivers were slightly lower than those in suburban rivers, while Shannon and Simpson indices were higher in urban rivers than those in suburban rivers. Proteobacteria, Firmicutes, and Bacteroidetes were the dominant bacterial phylum communities, accounting for 68.5–84.9% of all communities. In particular, the relative abundances of Firmicutes and Nitrospirae were significantly higher in suburban rivers than in urban rivers, while relative abundances of Bacteroidetes, Verrucomicrobia, and Spirochaetes were significantly lower in suburban rivers than in urban rivers. NH₄⁺ was significantly and negatively correlated with abundances of Firmicutes, Nitrospirae, and Actinobacteria. Importantly, the significant and negative effects of sediment NH₄⁺ on bacterial richness and diversity suggested that nitrogen pollution likely contribute to the decrease in the bacterial richness and diversity. The results highlight that nitrogen enrichment could drive the shifts of bacterial abundance and diversity in the urban river sediments where are strongly influenced by human activities under the rapid urbanization stress.

Synergistic Exposure of Return-Sludge to Anaerobic Starvation, Sulfide, and Free Ammonia to Suppress Nitrite Oxidizing Bacteria

A key step toward energy-positive sewage treatment is the development of mainstream partial nitritation/anammox, a nitrogen removal technology where aerobic ammonium-oxidizing bacteria (AerAOB) are desired, while nitrite-oxidizing bacteria (NOB) are not. To suppress NOB, a novel return-sludge treatment was investigated. Single and combined effects of sulfide (0-600 mg S L^-1), anaerobic starvation (0-8 days), and a free ammonia (FA) shock (30 mg FA-N L^-1 for 1 h) were tested for immediate effects and long-term recovery. AerAOB and NOB were inhibited immediately and proportionally by sulfide, with AerAOB better coping with the inhibition, while the short FA shock and anaerobic starvation had minor effects. Combinatory effects inhibited AerAOB and NOB more strongly. A combined treatment of sulfide (150 mg S L^-1), 2 days of anaerobic starvation, and FA shock (30 mg FA-N L^-1) inhibited AerAOB 14% more strongly compared to sulfide addition alone, while the AerAOB/NOB activity ratio remained constant. Despite no positive change being observed in the immediate-stress response, AerAOB recovered much faster than NOB, with a nitrite accumulation ratio (effluent nitrite on nitrite + nitrate) peak of 50% after 12 days. Studying long-term recovery is therefore crucial for design of an optimal NOB-suppression treatment, while applying combined stressors regularly may lead toward practical implementation.

Wastewater post-treatment for simultaneous ammonium removal and elemental sulfur recovery using a novel horizontal mixed aerobic-anoxic fixed-bed reactor configuration

A novel horizontal mixed anoxic-aerobic fixed-bed reactor configuration based on nitrification coupled with autotrophic denitrification using hydrogen sulfide as an electron donor was developed. The nitrification removal efficiency (RE) reached values greater than 99% but was slightly affected by the accumulation of dissolved sulfur species in the liquid phase. The denitrification RE reached 99% with a H₂S inlet load of 28.6 g S m^-3 h^-1, although the use of aluminum polychloride (PAC) as a sulfur coagulant in the anoxic zone affected the buffering capacity of the system and resulted in a decrease in the RE. The performance of the reactor was primarily affected by the buffering capacity of the system, and this effect could be controlled with an increase in the NaHCO₃ concentration. The recovery of biogenic elemental sulfur was possible using PAC as a coagulant, although the solid collected at the bottom of the settling tank contained only 1.5% S⁰.

Long-term effects of sulphide on the enhanced biological removal of phosphorus: The symbiotic role of Thiothrix caldifontis

Thiothrix caldifontis was the dominant microorganism (with an estimated bio-volume of 65 ± 3%) in a lab-scale enhanced biological phosphorus removal (EBPR) system containing 100 mg of sulphide per litre in the influent. After a gradual exposure to the presence of sulphide, the EBPR system initially dominated by Candidatus Accumulibacter phosphatis Clade I (98 ± 3% bio-volume) (a known polyphosphate accumulating organism, PAO) became enriched with T. caldifontis. Throughout the different operating conditions studied, practically 100% phosphate removal was always achieved. The gradual increase of the sulphide content in the medium (added to the anaerobic stage of the alternating anaerobic-aerobic sequencing batch reactor) and the adjustment of the aerobic hydraulic retention time played a major role in the enrichment of T. caldifontis. T. caldifontis exhibited a mixotrophic metabolism by storing carbon anaerobically as poly-β-hydroxy-alkanoates (PHA) and generating the required energy through the hydrolysis of polyphosphate. PHA was used in the aerobic period as carbon and energy source for growth, polyphosphate, and glycogen formation. Apparently, extra energy was obtained by the initial accumulation of sulphide as an intracellular sulphur, followed by its gradual oxidation to sulphate. The culture enriched with T. caldifontis was able to store approximately 100 mg P/g VSS. This research suggests that T. caldifontis could behave like PAO with a mixotrophic metabolism for phosphorus removal using an intracellular sulphur pool as energy source. These findings can be of major interest for the biological removal of phosphorus from wastewaters with low organic carbon concentrations containing reduced S-compounds like those (pre-)treated in anaerobic systems or from anaerobic sewers.

Effects of electron acceptors on sulphate reduction activity in activated sludge processes

The concentration of sulphate present in wastewater can vary from 10 to 500 mg SO₄²⁻/L. During anaerobic conditions, sulphate is reduced to sulphide by sulphate-reducing bacteria (SRB). Sulphide generation is undesired in wastewater treatment plants (WWTPs). Previous research indicated that SRB are inhibited by the presence of electron acceptors (such as O₂, NO₃ and NO₂). However, the contact times and concentrations used in those studies are by far higher than occur in WWTPs. Since sulphide can influence the biological nitrogen and phosphorus removal processes, this research aimed to understand how the different electron acceptors commonly present in biological nutrient removal (BNR) systems can affect the proliferation of SRB. For this purpose, a culture of SRB was enriched in a sequencing batch reactor (approx. 88% of the total bacteria population). Once enriched, the SRB were exposed for 2 h to typical concentrations of electron acceptors like those observed in BNR systems. Their activity was assessed using three different types of electron donors (acetate, propionate and lactate). Oxygen was the most inhibiting electron acceptor regardless the carbon source used. After exposure to oxygen and when feeding acetate, an inactivation time in the sulphate reduction activity was observed for 1.75 h. Once the sulphate reduction activity resumed, only 60% of the original activity was recovered. It is suggested that the proliferation of SRB is most likely to occur in BNR plants with an anaerobic fraction higher than 15% and operating at sludge retention times higher than 20 days (at a temperature of 20 °C). These results can be used to implement strategies to control the growth of sulphate reducers that might compete for organic carbon with phosphate-accumulating organisms.

Treatment of a submerged anaerobic membrane bioreactor (SAnMBR) effluent by an activated sludge system: the role of sulphide and thiosulphate in the process

This work studies the use of a well-known and spread activated sludge system (UCT configuration) to treat the effluent of a submerged anaerobic membrane bioreactor (SAnMBR) treating domestic wastewater. Ammonia, phosphate, dissolved methane and sulphide concentrations in the SAnMBR effluent were around 55 mg NH4-N L(-1), 7 mg PO4-P L(-1), 30 mg non-methane biodegradable COD L(-1), and 105 mg S(2-) L(-1) respectively. The results showed a nitrification inhibition caused by the presence of sulphur compounds at any of the solids retention time (SRT) studied (15, 20 and 25 days). This inhibition could be overcome increasing the hydraulic retention time (HRT) from 13 to 26 h. Among the sulphur compounds, sulphide was identified as the substance which caused the nitrification inhibition. When the nitrification was well established, removal rates of nitrogen and phosphorus of 56% and 45% were reached respectively. The sulphide present in the influent was completely oxidised to sulphate, contributing this oxidation to the denitrification process. Moreover, the presence of methanotrophic bacteria, detected by FISH technique, could also contribute to the denitrification.

Significance of archaeal nitrification in hypoxic waters of the Baltic Sea

Ammonia-oxidizing archaea (AOA) of the phylum Thaumarchaeota are widespread, and their abundance in many terrestrial and aquatic ecosystems suggests a prominent role in nitrification. AOA also occur in high numbers in oxygen-deficient marine environments, such as the pelagic redox gradients of the central Baltic Sea; however, data on archaeal nitrification rates are scarce and little is known about the factors, for example sulfide, that regulate nitrification in this system. In the present work, we assessed the contribution of AOA to ammonia oxidation rates in Baltic deep basins and elucidated the impact of sulfide on this process. Rate measurements with (15)N-labeled ammonium, CO(2) dark fixation measurements and quantification of AOA by catalyzed reporter deposition-fluorescence in situ hybridization revealed that among the three investigated sites the highest potential nitrification rates (122-884 nmol l(-1)per day) were measured within gradients of decreasing oxygen, where thaumarchaeotal abundance was maximal (2.5-6.9 × 10(5) cells per ml) and CO(2) fixation elevated. In the presence of the archaeal-specific inhibitor GC(7), nitrification was reduced by 86-100%, confirming the assumed dominance of AOA in this process. In samples spiked with sulfide at concentrations similar to those of in situ conditions, nitrification activity was inhibited but persisted at reduced rates. This result together with the substantial nitrification potential detected in sulfidic waters suggests the tolerance of AOA to periodic mixing of anoxic and sulfidic waters. It begs the question of whether the globally distributed Thaumarchaeota respond similarly in other stratified water columns or whether the observed robustness against sulfide is a specific feature of the thaumarchaeotal subcluster present in the Baltic Deeps.

The effects of aerobic/anoxic period sequence on aerobic granulation and COD/N treatment efficiency

The effects of period sequence (anoxic-aerobic and aerobic-anoxic) on aerobic granulation from suspended seed sludge, and COD, N removal efficiencies were investigated in two sequencing batch reactors. More stable granules with greater sizes (1.8-3.5mm) were developed in R1 (anoxic-aerobic sequence). Yet, no significant difference was observed between the reactors in terms of removal efficiencies. Under optimum operational conditions, 92-95% COD, 89-90% TAN and 38-46% total nitrogen removal efficiencies were achieved. The anoxic-aerobic period sequence (R1) resulted in almost complete denitrification during anoxic periods while aerobic-anoxic sequence (R2) led to nitrate accumulation due to limited-carbon source and further granule disintegration. NH3-N concentration of 15-28 mg/L was found to inhibit COD removal up to 30%. This study also revealed the inhibitory sulfide production during anoxic periods. Sulfate concentration of 52.6-70.2mg/L was found to promote sulfate reduction and sulfide generation (0.24-0.62 mg/L) which, together with free-ammonia, inhibited TAN oxidation by 10-50%.

Potential for Nitrogen Fixation and Nitrification in the Granite-Hosted Subsurface at Henderson Mine, CO

The existence of life in the deep terrestrial subsurface is established, yet few studies have investigated the origin of nitrogen that supports deep life. Previously, 16S rRNA gene surveys cataloged a diverse microbial community in subsurface fluids draining from boreholes 3000 feet deep at Henderson Mine, CO, USA (Sahl et al., 2008). The prior characterization of the fluid chemistry and microbial community forms the basis for the further investigation here of the source of NH(4) (+). The reported fluid chemistry included N(2), NH(4) (+) (5-112 μM), NO(2) (-) (27-48 μM), and NO(3) (-) (17-72 μM). In this study, the correlation between low NH(4) (+) concentrations in dominantly meteoric fluids and higher NH(4) (+) in rock-reacted fluids is used to hypothesize that NH(4) (+) is sourced from NH(4) (+)-bearing biotite. However, biotite samples from the host rocks and ore-body minerals were analyzed by Fourier transform infrared (FTIR) microscopy and none-contained NH(4) (+). However, the nitrogenase-encoding gene nifH was successfully amplified from DNA of the fluid sample with high NH(4) (+), suggesting that subsurface microbes have the capability to fix N(2). If so, unregulated nitrogen fixation may account for the relatively high NH(4) (+) concentrations in the fluids. Additionally, the amoA and nxrB genes for archaeal ammonium monooxygenase and nitrite oxidoreductase, respectively, were amplified from the high NH(4) (+) fluid DNA, while bacterial amoA genes were not. Putative nitrifying organisms are closely related to ammonium-oxidizing Crenarchaeota and nitrite-oxidizing Nitrospira detected in other subsurface sites based upon 16S rRNA sequence analysis. Thermodynamic calculations underscore the importance of NH(4) (+) as an energy source in a subsurface nitrification pathway. These results suggest that the subsurface microbial community at Henderson is adapted to the low nutrient and energy environment by their capability of fixing nitrogen, and that fixed nitrogen may support subsurface biomass via nitrification.

Simultaneous oxidation of ammonium, p-cresol and sulfide using a nitrifying sludge in a multipurpose bioreactor: a novel alternative

A nitrifying continuous stirred tank reactor was used as multipurpose bioreactor and it was operated for 325 days at 220 mg NH(4)(+)-N/Ld, 89 mg p-cresol-C /Ld and 36-76 mg S(2-)/Ld. The bioreactor was fed in sequential way, firstly with ammonium, achieving a consumption efficiency of 89%, with a nitrate yield of 0.99. Afterward, p-cresol was fed, achieving ammonium and p-cresol consumption efficiencies of 95% and 100%, respectively. The nitrate yield was higher and no aromatic intermediaries from p-cresol were detected. Finally sulfide was fed and the consumption efficiencies for all substrates were of 100%, being nitrate, HCO(3)(-) and sulfate the end products. The kinetic results showed that biological sulfide consumption was 13-fold faster than the chemical oxidation. This is the first time that a nitrifying reactor can be used for multiple purposes and also for the simultaneous removal of ammonium, sulfide and p-cresol in one step.

The behavior of nitrifying sludge in presence of sulfur compounds using a floating biofilm reactor

The tolerance, kinetic and oxidizing capability of a nitrifying sludge exposed to different initial concentrations of sulfide (1.7 to 18mg/L) was evaluated in batch experiments. A nitrifying sludge fed with ammonium and thiosulfate and produced in steady state conditions was used as inoculum. Sulfide induced a significant effect either on ammonium consumption rates or nitrite accumulation. In spite of the nitrifying kinetic was affected, the ammonium consumption efficiencies were close to 100%, with nitrate production yields around 1.0. The IC(50) value for ammonium oxidizing-process was 13mg/L of sulfide. Sulfide was oxidized in two steps: first sulfide was oxidized to elemental sulfur and afterward into sulfate. FISH oligonucleotide probes for Thiobacillusdenitrificans, Nitrosomonas spp., and Nitrobacter spp. were used in order to know if these bacteria were part of the microbial ecology. The obtained results showed that under nitrifying conditions are possible to carry out simultaneously two biological processes, nitrification and sulfur oxidation.

Environmental factors shaping the ecological niches of ammonia-oxidizing archaea

For more than 100 years it was believed that bacteria were the only group responsible for the oxidation of ammonia. However, recently, a new strain of archaea bearing a putative ammonia monooxygenase subunit A (amoA) gene and able to oxidize ammonia was isolated from a marine aquarium tank. Ammonia-oxidizing archaea (AOA) were subsequently discovered in many ecosystems of varied characteristics and even found as the predominant causal organisms in some environments. Here, we summarize the current knowledge on the environmental conditions related to the presence of AOA and discuss the possible site-related properties. Considering these data, we deduct the possible niches of AOA based on pH, sulfide and phosphate levels. It is proposed that the AOA might be important actors within the nitrogen cycle in low-nutrient, low-pH, and sulfide-containing environments.

Partial nitrification achieved by pulse sulfide doses in a sequential batch reactor

A nitrifying sequential batch reactor operated under 2-day cyclic aerobic and anoxic conditions was pulse dosed with incremental sulfide concentrations during anoxic conditions. The nitrite-oxidizing bacteria were found to be more sensitive to sulfide than the ammonia oxidizers. A maximum of nitrite-N to (nitrite-N + nitrate-N) accumulation ratio of 0.75 was obtained at an initial pulse sulfide-S concentration of 45 mg/L under pH control at 7.5 +/- 0.2 and fully mixing conditions. Total ammonium nitrogen was removed almost 100% at a removal rate of 0.73 +/- 0.05 g/L x day, achieved during the aerobic days of the cycles. Denaturing gradientgel electrophoresis (DGGE) and fluorescence in situ hybridization (FISH) analyses indicated the shift in the ammonia- and nitrite-oxidizing populations triggered by sulfide addition, partial nitrification, and subsequent recovery to complete nitrification. Interestingly, archaeal amoA genes were retrieved under the conditions of sulfide addition. These results indicate that the pulse sulfide application can be used as a tool to accumulate nitrite, which is of importance for the subsequent anaerobic ammonium oxidation (anammox) process in the achievement of complete nitrogen removal.

Putative ammonia-oxidizing Crenarchaeota in suboxic waters of the Black Sea: a basin-wide ecological study using 16S ribosomal and functional genes and membrane lipids

Within the upper 400 m at western, central and eastern stations in the world's largest stratified basin, the Black Sea, we studied the qualitative and quantitative distribution of putative nitrifying Archaea based on their genetic markers (16S rDNA, amoA encoding for the alpha-subunit of archaeal ammonia monooxygenase), and crenarchaeol, the specific glycerol diphytanyl glycerol tetraether of pelagic Crenarchaeota within the Group I.1a. Marine Crenarchaeota were the most abundant Archaea (up to 98% of the total archaeal 16S rDNA copies) in the suboxic layers with oxygen levels as low as 1 microM including layers where previously anammox bacteria were described. Different marine crenarchaeotal phylotypes (both 16S rDNA and amoA) were found at the upper part of the suboxic zone as compared with the base of the suboxic zone and the upper 15-30 m of the anoxic waters with prevailing sulfide concentrations of up to 30 microM. Crenarchaeol concentrations were higher in the sulfidic chemocline as compared with the suboxic zone. These results indicate an abundance of putative nitrifying Archaea at very low oxygen levels within the Black Sea and might form an important source of nitrite for the anammox reaction.

Vertical migration of aggregated aerobic and anaerobic ammonium oxidizers enhances oxygen uptake in a stagnant water layer

Ammonium can be removed as dinitrogen gas by cooperating aerobic and anaerobic ammonium-oxidizing bacteria (AerAOB and AnAOB). The goal of this study was to verify putative mutual benefits for aggregated AerAOB and AnAOB in a stagnant freshwater environment. In an ammonium fed water column, the biological oxygen consumption rate was, on average, 76 kg O(2) ha(-1) day(-1). As the oxygen transfer rate of an abiotic control column was only 17 kg O(2) ha(-1) day(-1), biomass activity enhanced the oxygen transfer. Increasing the AnAOB gas production increased the oxygen consumption rate with more than 50% as a result of enhanced vertical movement of the biomass. The coupled decrease in dissolved oxygen concentration increased the diffusional oxygen transfer from the atmosphere in the water. Physically preventing the biomass from rising to the upper water layer instantaneously decreased oxygen and ammonium consumption and even led to the occurrence of some sulfate reduction. Floating of the biomass was further confirmed to be beneficial, as this allowed for the development of a higher AerAOB and AnAOB activity, compared to settled biomass. Overall, the results support mutual benefits for aggregated AerAOB and AnAOB, derived from the biomass uplifting effect of AnAOB gas production.