Characterization of microbial community and kinetics for spent sulfidic caustic applied autotrophic denitrification

Spent sulfidic caustic was applied to sulfur utilizing autotrophic denitrification as the simultaneous source of electron donor and alkalinity. The two experiment set-up of upflow anoxic hybrid growth reactor (UAHGR) and upflow anoxic suspended growth reactor (UASGR) was adopted and nitrate removals were similar in both reactors. Approximately 90% of the initial nitrate was denitrified at nitrate loading rate of 0.15∼0.40 kgNO₃ ⁻/m³·d. The experimental stoichiometric ratio of sulfate production to nitrate removal was ranged from 1.5 to 2.1 mgSO₄ ²⁻/mgNO₃ ⁻. During the operation period, denaturing gradient gel electrophoresis (DGGE) analysis of polymerase chain reaction (PCR)-amplified 16S rDNA fragments for the sludge sample of both reactors showed the change of microbial communities. Thiobacillus denitrificans-like microorganism occupied 28.5% (18 clones) of the 63 clones by cloning the PCR products from the sludge sample of UAHGR. Acidovorax avenae, which can reduce nitrate to nitrogen gas while oxidizing phenol (heterotrophic denitrifier), was also found in 7 clones (11.1%). Although an organic carbon source was not added to the medium, a microorganism (Kaistella koreensis) capable of oxidizing organic compounds was found in 7 clones (11.1%). Therefore, the microbial community of spent sulfidic caustic applied autotrophic denitrification process well corresponds to the substrate components of spent sulfidic caustic. Through the batch cultivation of microorganisms in UAHGR, the microbial kinetic coefficients of spent sulfidic caustic applied autotrophic denitrification were estimated to be μ _max = 0.097 h⁻¹, k _d = 0.0021 h⁻¹, K _s = 200 mgNO₃ ⁻/L, and Y = 0.31 mgMLVSS/mgNO₃ ⁻.     

Simultaneous biological removal of sulfur, nitrogen and carbon using EGSB reactor

High-rate biological conversion of sulfide and nitrate in synthetic wastewater to, respectively, elemental sulfur (S⁰) and nitrogen-containing gas (such as N₂) was achieved in an expanded granular sludge bed (EGSB) reactor. A novel strategy was adopted to first cultivate mature granules using anaerobic sludge as seed sludge in sulfate-laden medium. The cultivated granules were then incubated in sulfide-laden medium to acclimate autotrophic denitrifiers. The incubated granules converted sulfide, nitrate, and acetate simultaneously in the same EGSB reactor to S⁰, N-containing gases and CO₂ at loading rates of 3.0 kg S m⁻³ d⁻¹, 1.45 kg N m⁻³ d⁻¹, and 2.77 kg Ac m⁻¹ d⁻¹, respectively, and was not inhibited by sulfide concentrations up to 800 mg l⁻¹. Effects of the C/N ratio on granule performance were identified. The granules cultivated in the sulfide-laden medium have Pseudomonas spp. and Azoarcus sp. presenting the heterotrophs and autotrophs that co-work in the high-rate EGSB-SDD (simultaneous desulfurization and denitrification) reactor.     

Biological nitrate removal in industrial wastewater treatment: which electron donor we can choose

Biological denitrification was reviewed regarding its potential application to treating nitrate in industrial wastewater. Although heterotrophic denitrification is an efficient and well-developed process, some carbon content in wastewater is essential to maintain bacterial activity. Because of the high operating cost of heterotrophic denitrification caused by the required addition of a carbon source and potential “carbon breakthrough”, the study of autotrophic denitrification has attracted the interest of numerous researchers. Many advances in autotrophic processes have been made in the application of novel concepts and reaction schemes. While the main advantage of autotrophic bacteria rests on the reduction of operating costs by the replacement of an external carbon source with a cheaper electron donor, further decrease in cost requires additional refinement of these processes, including further improvement of reactor structure and optimization of reaction conditions. In the long term, new concepts are required for a compact wastewater treatment process. This review addresses the state of the art of each electron donor candidate for its potential application to the treatment of industrial wastewater containing nitrate.     

A new method of autotrophic denitrification with spent sulfidic caustic as substrate and alkalinity source

A new method based on sulfide utilizing autotrophic denitrification was adopted to remove nitrate from wastewater and to reuse spent sulfidic caustic containing high sulfide and alkalinity levels. The experiments were performed using a bench-scale upflow anoxic hybrid growth reactor (UAHGR) and an upflow anoxic suspended growth reactor (UASGR) to characterize the stoichiometric relationship between sulfur and nitrate in the process as well as the performance of the reactors. The level of nitrate removal from the UAHGR and UASGR were maintained at over 90% at a nitrate loading rate ranging from 0.15∼0.40 kgNO₃ ⁻/m³·d and no significant nitrite accumulation was observed in either reactor. Although the influent pH values were higher than the optimum range of autotrophic denitrification at 8.7∼10.1, the effluent pH was stable at 7.2∼7.9 due to the production of hydrogen ions during operation. The stoichiometric ratio of sulfate production to nitrate removal was 1.5∼2.1 mgSO₄ ²⁻/mgNO₃ ⁻ in both reactors. A comparison of the reactor performance revealed that the chemical parameters of the UAHGR operation corresponded to a plug flow like type reactor while the chemical parameters of the UASGR operation corresponded to a completely stirred tank reactor like type reactor. UAHGR did not require sludge recycling due to the packed media while UASGR required 300∼700% sludge recycling. Therefore, spent sulfidic caustic could be used in the sulfur utilizing autotrophic denitrification processes as substrate and alkalinity sources.     

Obligately and facultatively autotrophic,sulfur- and hydrogen-oxidizing thermophilic bacteria isolated from hot composts

A variety of autotrophic, sulfur- and hydrogen-oxidizing thermophilic bacteria were isolated from thermogenic composts at temperatures of 60–80° C. All were penicillin G sensitive, which proves that they belong to the Bacteria domain. The obligately autotrophic, non-spore-forming strains were gram-negative rods growing at 60–80°C, with an optimum at 70–75°C, but only under microaerophilic conditions (5 kPa oxygen). These strains had similar DNA G+C content (34.7–37.6 mol%) and showed a high DNA:DNA homology (70–87%) with Hydrogenobacter strains isolated from geothermal areas. The facultatively autotrophic strains isolated from hot composts were gram-variable rods that formed spherical and terminal endospores, except for one strain. The strains grew at 55–75° C, with an optimum at 65–70° C. These bacteria were able to grow heterotrophically, or autotrophically with hydrogen; however, they oxidized thiosulfate under mixotrophic growth conditions (e.g. pyruvate or hydrogen plus thiosulfate). These strains had similar DNA G+C content (60–64 mol%) to and high DNA:DNA homology (> 75%) with the reference strain of Bacillus schlegelii. This is the first report of thermogenic composts as habitats of thermophilic sulfur- and hydrogen-oxidizing bacteria, which to date have been known only from geothermal manifestations. This contrasts with the generally held belief that thermogenic composts at temperatures above 60° C support only a very low diversity of obligatory heterotrophic thermophiles related to Bacillus stearothermophilus. Received: 20 July 1995 / Accepted: 25 September 1995     

Using modern low-oxygen marine ecosystems to understand the nitrogen cycle of the Paleo- and Mesoproterozoic oceans

During the productive Paleoproterozoic (2.4–1.8 Ga) and less productive Mesoproterozoic (1.8–1.0 Ga), the ocean was suboxic to anoxic and multicellular organisms had not yet evolved. Here, we link geologic information about the Proterozoic ocean to microbial processes in modern low-oxygen systems. High iron concentrations and rates of Fe cycling in the Proterozoic are the largest differences from modern oxygen-deficient zones. In anoxic waters, which composed most of the Paleoproterozoic and ~40% of the Mesoproterozoic ocean, nitrogen cycling dominated. Rates of N₂ production by denitrification and anammox were likely linked to sinking organic matter fluxes and in situ primary productivity under anoxic conditions. Additionally autotrophic denitrifiers could have used reduced iron or methane. 50% of the Mesoproterozoic ocean may have been suboxic, promoting nitrification and metal oxidation in the suboxic water and N₂O and N₂ production by partial and complete denitrification in anoxic zones in organic aggregates. Sulfidic conditions may have composed ~10% of the Mesoproterozoic ocean focused along continental margins. Due to low nitrate concentrations in offshore regions, anammox bacteria likely dominated N₂ production immediately above sulfidic zones, but in coastal regions, higher nitrate concentrations probably promoted complete S-oxidizing autotrophic denitrification at the sulfide interface.     

Dinitrogen and nitrous oxide produced by denitrification and nitrification in soil with and without barley plants

Summary To examine the effect of barley roots on denitrification, a pot experiment was designed to compare N₂O production and denitrification in soils with and without barley plants. Denitrification, N₂O resulting from denitrification and nitrification, and respiration were estimated by incubating pots with soil with and without intact plants in plastic bags at high moisture levels. C₂H₂-inhibition of nitrous oxide reductase (partial pressure of 10 kPa C₂H₂) was used to determine total denitrification rates while incubations with ambient air and with C₂H₂ at partial pressures of 2.5–5 Pa were used to estimate the amounts of N₂O released from autotrophic nitrification and from denitrification processes. Other sources of N₂O were presumed to be negligible. Potential denitrification, nitrification and root biomass were measured in subsamples collected from four soil depths. A positive correlation was found between denitrification rates and root biomass. N₂ was the predominant denitrification product found close to roots; N₂O formed by non autotrophic nitrifiers, assumed to be denitrifiers originated in soil not affected by growing roots. Apparently, roots promote denitrification because they consumed oxygen, thereby increasing the anaerobic volume of the soil. The ratio of actual to potential denitrification rates increased over time, especially in the presence of roots.     

Denitrification activity of Bradyrhizobium sp. isolated from Argentine soybean cultivated soils

Two hundred and fifty strains, all of them representatives of native Bradyrhizobium sp., isolated from soils cultivated with soybean have been characterized by their denitrification activity. In addition, the denitrification potential of those soils was also measured by evaluating the most-probable-number (MPN) of denitrifying bacteria and the denitrification enzyme assay (DEA). Of the 250 isolates tested, 73 were scored as probable denitrifiers by a preliminary screening method. Only 41 were considered denitrifiers because they produced gas bubbles in Durham tubes, cultures reached an absorbance of more than 0.1 and NO³⁻ and NO²⁻ were not present. Ten of these 41 were selected to confirm denitrification and to study denitrification genes. According to N₂O production and cell protein concentration with NO³⁻, the isolates could be differentiated in three categories of denitrifiers. The presence of the napA, nirK, norC and nosZ genes was detected by production of a diagnostic PCR product using specific primers. RFLP from the 16S-23S rDNA spacer region (IGS) revealed that denitrifiers strains could be characterized as Bradyrhizobium japonicum and strains which were non-respiratory denitrifiers as B. elkanii.     

Long-chain acylhomoserine lactones increase the anoxic ammonium oxidation rate in an OLAND biofilm

The oxygen-limited autotrophic nitrification/denitrification (OLAND) process comprises one-stage partial nitritation and anammox, catalyzed by aerobic and anoxic ammonium-oxidizing bacteria (AerAOB and AnAOB), respectively. The goal of this study was to investigate whether quorum sensing influences anoxic ammonium oxidation in an OLAND biofilm, with AnAOB colonizing 13% of the biofilm, as determined with fluorescent in situ hybridization (FISH). At high biomass concentrations, the specific anoxic ammonium oxidation rate of the OLAND biofilm significantly increased with a factor of 1.5 ± 0.2 compared to low biomass concentrations. Supernatant obtained from the biofilm showed no ammonium-oxidizing activity on itself, but its addition to low OLAND biomass concentrations resulted in a significant activity increase of the biomass. In the biofilm supernatant, the presence of long-chain acylhomoserine lactones (AHLs) was shown using the reporter strain Chromobacterium violaceum CV026, and one specific AHL, N-dodecanoyl homoserine lactone (C₁₂-HSL), was identified via LC-MS/MS. Furthermore, C₁₂-HSL was detected in an AnAOB-enriched community, but not in an AerAOB-enriched community. Addition of C₁₂-HSL to low OLAND biomass concentrations resulted in a significantly higher ammonium oxidation rate (p < 0.05). To our knowledge, this is the first report demonstrating that AHLs enhance the anoxic ammonium oxidation process. Future work should confirm which species are responsible for the in situ production of C₁₂-HSL in AnAOB-based applications.     

Characteristics of Autotrophic and Heterotrophic Denitrification by the Strain Pseudomonas sp. H117

Strain H117 was isolated from the Tang Yu reservoir. Based on the phylogenetic characteristics, strain H117, which was identified as Pseudomonas sp. strain H117, had the capability to utilize bicarbonate and sodium acetate as a carbon source under anaerobic conditions. Furthermore, the strain could grow on both autotrophic and heterotrophic media, and could perform both autotrophic and heterotrophic denitrification in the medium. Response surface methodology analysis demonstrated that the maximum degradation ratio of nitrate-occurred under the following conditions in the autotrophic medium: initial pH of 6.00, C/N ratio of 4.68 and temperature of 31.33°C. The maximum degradation ratio of nitrate occurred under the following conditions in the heterotrophic medium: initial pH of 6.16, C/N ratio of 8.23 and temperature of 28.48°C. Finally, the denitrification performance of strain H117 was evaluated under the optimum conditions. These results suggest that strain H117 has potential applications for the bioremediation of polluted groundwater.     

Nitrate reduction by Citrobacter diversus under aerobic environment

A new aerobic denitrifier, Citrobacter diversus, was isolated from both nitrification and denitrification sludge. To monitor the variation in the concentration of nitrogen oxides, aerobic denitrification by C. diversus was carried out in a batch reactor. When the nitrate concentration was greater than 180 mg N l⁻¹, the nitrate reduction rate became stable. The effect of the C/N ratio on the denitrification activity was also investigated. The results showed that the optimum denitrification activity was obtained when the C/N ratio was 4–5. The range of the C/N ratio was higher than that for traditional anoxic denitrification. The effect of the dissolved oxygen concentration was further studied; and it was found that the range of dissolved oxygen concentrations, both for specific growth rates and for specific denitrification rates, was 2–6 mg⁻¹. From these results, it can be concluded that both the concentration of dissolved oxygen and the C/N ratio are key factors in the aerobic denitrification by C. diversus. Received: 23 November 1999 / Received revision: 4 February 2000 / Accepted: 13 February 2000     

Heterotrophic nitrification–aerobic denitrification by novel isolated bacteria

Three novel strains capable of heterotrophic nitrification–aerobic denitrification were isolated from the landfill leachate treatment system. Based on their phenotypic and phylogenetic characteristics, the isolates were identified as Agrobacterium sp. LAD9, Achromobacter sp. GAD3 and Comamonas sp. GAD4, respectively. Batch tests were carried out to evaluate the growth and the ammonia removal patterns. The maximum growth rates as determined from the growth curve were 0.286, 0.228, and 0.433 h⁻¹ for LAD9, GAD3 and GAD4, respectively. The maximum aerobic nitrification–denitrification rate was achieved by the strain GAD4 of 0.381 mmol/l h, followed by LAD9 of 0.374 mmol/l h and GAD3 of 0.346 mmol/l h. Moreover, hydroxylamine oxidase and periplasmic nitrate reductase were successfully expressed in all the isolates. The relationship between the enzyme activities and the aerobic nitrification–denitrification rates revealed that hydroxylamine oxidation may be the rate-limiting step in the heterotrophic nitrification–aerobic denitrification process. The study results are of great significance to the wastewater treatment systems where simultaneous removal of carbon and nitrogen is desired.     

Nitrification, denitrification, and dechlorination in bleached kraft pulp mill wastewater

This study deals with combining the biologi cal removal of organic halogens with the removal of nitrogen from bleached kraft pulp mill wastewater in fluidized-bed reactors under nitrifying and denitrifying conditions. Untreated and biotreated bleached kraft pulp mill wastewaters had no detrimental effect on nitrification or denitrification. The nitrifying biofilm reactor, pregrown on synthetic inorganic feed with ammonia, removed without a lag phase adsorbable organic halogens [7.2 mg Cl (g biomass volatile solids)⁻¹day⁻¹] from bleached kraft pulp mill wastewater and selected chlorophenols from synthetic wastewater. Electron microscopical examination of the biofilm showed that bacteria, morphologically similar to the nitrifying species Nitrosomonas or Nitrobacter, and Nitrosospira were dominant. The denitrifying fluidized-bed reactor, pregrown on nitrate and methanol, denitrified without a lag phase bleached kraft pulp mill wastewater. Under denitrifying conditions, 35% of the total organic carbon content of untreated bleached kraft pulp mill waste water was removed. The reducing power delivered by untreated bleached kraft pulp mill wastewater for denitrification was 2 mmol electrons/mmol carbon mineralized. Dechlorination under denitrifying conditions was negligible. Received: 21 November 1996 / Received revision: 27 January 1997 / Accepted: 1 February 1997     

Denitrification and nitrous oxide emissions from riparian forests soils exposed to prolonged nitrogen runoff

Compared to upland forests, riparian forest soils have greater potential to remove nitrate (NO₃) from agricultural runoff through denitrification. It is unclear, however, whether prolonged exposure of riparian soils to nitrogen (N) loading will affect the rate of denitrification and its end products. This research assesses the rate of denitrification and nitrous oxide (N₂O) emissions from riparian forest soils exposed to prolonged nutrient runoff from plant nurseries and compares these to similar forest soils not exposed to nutrient runoff. Nursery runoff also contains high levels of phosphate (PO₄). Since there are conflicting reports on the impact of PO₄ on the activity of denitrifying microbes, the impact of PO₄ on such activity was also investigated. Bulk and intact soil cores were collected from N-exposed and non-exposed forests to determine denitrification and N₂O emission rates, whereas denitrification potential was determined using soil slurries. Compared to the non-amended treatment, denitrification rate increased 2.7- and 3.4-fold when soil cores collected from both N-exposed and non-exposed sites were amended with 30 and 60 μg NO₃-N g⁻¹ soil, respectively. Net N₂O emissions were 1.5 and 1.7 times higher from the N-exposed sites compared to the non-exposed sites at 30 and 60 μg NO₃-N g⁻¹ soil amendment rates, respectively. Similarly, denitrification potential increased 17 times in response to addition of 15 μg NO₃-N g⁻¹ in soil slurries. The addition of PO₄ (5 μg PO₄-P g⁻¹) to soil slurries and intact cores did not affect denitrification rates. These observations suggest that prolonged N loading did not affect the denitrification potential of the riparian forest soils; however, it did result in higher N₂O emissions compared to emission rates from non-exposed forest soils.     

Response of denitrification rate associated with wetting and drying cycles in a littoral wetland area of Lake Biwa,Japan

To clarify the relationship between denitrification activity and dry–wet levels in the littoral wetland sediments of Lake Biwa, Japan, denitrification rates and their regulating parameters (degree of dryness, redox potential, nitrate concentration) were measured on different moisture sediments. Redox potential in sediments was higher in the exposed region in contact with atmosphere than the flooded region covered with water. The nitrate concentration in interstitial waters was undetectable in the flooded region. On the other hand, concentration in the exposed region increased with increase in the degree of sediment dryness. The denitrification rate ranged from <0.001 to 0.88 μg N cm⁻³ h⁻¹ in the exposed region and increased with the increase in the degree of dryness. In the flooded region, on the other hand, no detectable rate (<0.001 μg N cm⁻³ h⁻¹) was observed. This indicates that the rates in the exposed region were mainly influenced by nitrate concentration in the interstitial waters accumulated by desiccation of sediments, whereas rates in the flooded region were strongly limited by no accumulation of nitrate in the anaerobic conditions. The potential denitrification rate, under the application condition of nitrate, ranged from 0.13 to 0.26 μg N cm⁻³ h⁻¹ in the flooded region and from 0.77 to 1.5 μg N cm⁻³ h⁻¹ in the exposed region. The potential rates in the flooded region had a tendency to be lower than those in the exposed region, implying that the number of denitrifying bacteria in the flooded region was low due to inactivation of aerobic respiration and denitrification in the denitrifying bacteria community. Kinetic parameters, maximum rate (V _max) and half-saturation constant (K _s) for denitrification were calculated on the experimental procedures of the wetting–drying cycles of sediments. Both parameters decreased by the wetting treatment and increased by the drying treatment. The fluctuation of V _max values with wetting–drying cycles indicated that the number of denitrifying bacteria was influenced by aerobic respiration and denitrification in the denitrifying bacteria community similar to the potential rates, and denitrifying enzyme was induced by the nitrate supplied by nitrification accelerated through the drying process. On the other hand, the fluctuation of K _s values implied that members of denitrifying bacteria were shifted to members of high nitrate affinity by wetting treatment and of low nitrate affinity by drying treatment.     

闽江河口短叶茳芏群落湿地沉积物反硝化强度对盐度的响应

为了探讨河口区湿地沉积物反硝化强度对盐度的响应,2015年7月选择闽江河口覆盖短叶茳芏的鳝鱼滩和道庆洲湿地沉积物为研究对象,采用密封厌氧培养,计算不同培养时期在不同盐度下的反硝化速率。结果表明,在反硝化培养的初期,鳝鱼滩的反硝化速率从低盐度到高盐度分别为(15.5±1.38)、(4.28±8.46)、(12.94±0.24)mg kg~(-1)d~(-1),道庆洲分别为(31.93±4.89)、(30.66±5.375)、(36.69±3.44)mg kg~(-1)d~(-1),鳝鱼滩的10天反硝化速率在0和10盐度下降幅度分别是5天的36.97%、53.01%,高于道庆洲22.64%、28.84%,后期随着时间的变化整体上呈现减小的趋势并趋于0。另外,鳝鱼滩和道庆洲反硝化活性随着时间呈现逐渐增加的趋势,其鳝鱼滩变化幅度在95.6%—99.8%,道庆洲为90.0%—96.7%,整个培养期间,鳝鱼滩的反硝化活性均高于道庆洲的反硝化活性。以上结果反映出盐度对闽江河口湿地沉积物的反硝化速率起到一定的抑制作用。     

Overwintering populations of Mesodinium rubrum (Ciliophora: Haptorida) in lakes of the Vestfold Hills, East Antarctica

 The autotrophic ciliate Mesodinium rubrum Lohmann was observed during winter and spring in saline lakes ranging in salinity from 2 to 78‰ in the Vestfold Hills, Antarctica. The ciliate remained active during winter, and contained chlorophyll even though the level of light available for photosynthesis was minimal. No evidence of encystment as a means of survival during winter was observed. A seasonal study in one of the lakes, Ace Lake, revealed that M. rubrum was present throughout the year at abundances ranging from 1×10⁴ to 3.5×10⁵ cells l^-1. During the winter period, when little light penetrated the lake’s ice cover, cells were most common immediately under the ice at 2 m, where cell numbers were typically 8×10⁴ cells l^-1. Received: 3 January 1996/Accepted: 21 April 1996     

Molecular diversity and temporal variation of picoeukaryotes in two Arctic fjords,Svalbard

Picoeukaryotes (protists <3 μm) form an important component of Arctic marine ecosystems, although knowledge of their diversity and ecosystem functioning is limited. In this study, the molecular diversity and autotrophic biomass contribution of picoeukaryotes from January to June 2009 in two Arctic fjords at Svalbard were examined using 18S environmental cloning and size-fractioned chlorophyll a measurements. A total of 62 putative picoeukaryotic phylotypes were recovered from 337 positive clones. Putative picoeukaryotic autotrophs were mostly limited to one species: Micromonas pusilla, while the putative heterotrophic picoeukaryote assemblage was more diverse and dominated by uncultured marine stramenopiles (MAST) and marine alveolate groups. One MAST-1A phylotype was the only phylotype to be found in all clone libraries. The diversity of picoeukaryotes in general showed an inverse relationship with total autotrophic biomass, suggesting that the conditions dominating during the peak of the spring bloom may have a negative impact on picoeukaryote diversity. Picoplankton could contribute more than half of total autotrophic biomass before and after the spring bloom and benefited from an early onset of the growth season, whereas larger cells dominated the bloom itself.     

Sulfur-driven autotrophic denitrification of nitric oxide for efficient nitrous oxide recovery

Nitrous oxide (N₂O) was previously deemed as a potent greenhouse gas but is actually an untapped energy source, which can accumulate during the microbial denitrification of nitric oxide (NO). Compared with the organic electron donor required in heterotrophic denitrification, elemental sulfur (S⁰) is a promising electron donor alternative due to its cheap cost and low biomass yield in sulfur-driven autotrophic denitrification. However, no effort has been made to test N₂O recovery from sulfur-driven denitrification of NO so far. Therefore, in this study, batch and continuous experiments were carried out to investigate the NO removal performance and N₂O recovery potential via sulfur-driven NO-based denitrification under various Fe(II)EDTA-NO concentrations. Efficient energy recovery was achieved, as up to 35.5%–40.9% of NO was converted to N₂O under various NO concentrations. N₂O recovery from Fe(II)EDTA-NO could be enhanced by the low bioavailability of sulfur and the acid environment caused by sulfur oxidation. The NO reductase (NOR) and N₂O reductase (N₂OR) were inhibited distinctively at relatively low NO levels, leading to efficient N₂O accumulation, but were suppressed irreversibly at NO level beyond 15 mM in continuous experiments. Such results indicated that the regulation of NO at a relatively low level would benefit the system stability and NO removal capacity during long-term system operation. The continuous operation of the sulfur-driven Fe(II)EDTA-NO-based denitrification reduced the overall microbial diversity but enriched several key microbial community. Thauera, Thermomonas, and Arenimonas that are able to carry out sulfur-driven autotrophic denitrification became the dominant organisms with their relative abundance increased from 25.8% to 68.3%, collectively.     

Isolation and physiological characterisation of Thiobacillus aquaesulis sp. nov., a novel facultatively autotrophic moderate thermophile

A moderately thermophilic, facultatively chemolithoautotrophic thiobacillus isolated from a thermal sulphur spring is described. It differs from all other species currently known to be in culture. It grows lithoautotrophically on thiosulphate, trithionate or tetrathionate, which are oxidized to sulphate. Batch cultures on thiosulphate do not produce tetrathionate, but do precipitate elemental sulphur during growth. In autotrophic chemostat cultures the organism produces yields on thiosulphate, trithionate and tetrathionate that are among the highest observed for a Thiobacillus. Autotrophic cultures contain ribulose bisphosphate carboxylase. Heterotrophic growth has been observed only on complex media such as yeast extract and nutrient broth. It is capable of autotrophic growth and denitrification under anaerobic conditions with thiosulphate and nitrate. It grows between 30 to 55° C, and pH 7 to 9, with best growth at about 43°C and pH 7.6. It contains ubiquinone Q-8, and its DNA contains 65.7 mol% G+C. The organism is formally described and named as Thiobacillus aquaesulis.Now the Department of Biological Sciences