Effects of Grazing by Flagellates on Competition for Ammonium between Nitrifying and Heterotrophic Bacteria in Chemostats

The enhanced mineralization of organic nitrogen by bacteriophagous protozoa is thought to favor the nitrification process in soils, in which nitrifying bacteria have to compete with heterotrophic bacteria for the available ammonium. To obtain more insight into this process, the influence of grazing by the bacteriovorous flagellate Adriamonas peritocrescens on the competition for limiting amounts of ammonium between the ammonium-oxidizing species Nitrosomonas europaea and the heterotrophic species Arthrobacter globiformis was studied in the presence of Nitrobacter winogradskyi in continuous cultures at dilution rates of 0.004 and 0.01 h^-1. The ammonium concentration in the reservoir was maintained at 2 mM, whereas the glucose concentration was increased stepwise from 0 to 7 mM. A. globiformis won the competition for limiting amounts of ammonium when the glucose concentration in the reservoirs increased, in agreement with previously described experiments in which the flagellates were not included. The numbers of nitrifying bacteria decreased as the numbers of heterotrophic bacteria rose with increasing glucose concentrations. Critical C/N ratios, i.e., ratios between glucose and ammonium in the reservoirs at which no nitrate was found in the culture vessels, of 12.5 and 10.5 were determined at dilution rates of 0.004 and 0.01 h^-1, respectively. Below these critical values, coexistence of the competing species was found. The numbers of nitrifying bacteria decreased more in the presence of flagellates than in their absence, presumably by selective predation on the nitrifying bacteria, either in the liquid culture or on the glass wall of the culture vessels. Despite this, the rate of nitrate production did not decrease more in the presence of flagellates than in their absence. This demonstrates that no correlation has to be expected between numbers of nitrifying bacteria and their activity and that a constant nitrification rate per cell cannot be assumed for nitrifying bacteria. Above the critical C/N ratios, low numbers of nitrifying bacteria were still found in the culture vessels, probably because of attachment of the nitrifying bacteria to the glass wall of the culture vessels. Like the numbers of heterotrophic bacteria, the numbers of flagellates increased when the glucose concentrations in the reservoirs increased. Numbers of 2 × 10⁵ and 12 × 10⁵ flagellates ml^-1 were found at 7 mM glucose at dilution rates of 0.004 and 0.01 h^-1, respectively. It was concluded that the critical C/N ratios were practically unaffected by the presence of protozoa. Although nitrate production rates were equal in the presence and absence of flagellates, the numbers of nitrifying bacteria decreased more strongly in their presence. This indicates a higher activity per nitrifying cell in the presence of flagellates.     

Immobilization of nitrifying bacteria in porous pellets of urethane gel for removal of ammonium nitrogen from waste-water

Summary The effects of immobilizing materials on the activity of nitrifying bacteria and removal of ammonium nitrogen (NH₄-N) from waste-water by immobilized nitrifying bacteria were investigated using six urethane prepolymers. With a urethane prepolymer containing 2.27% free isocyanate, a high activity yield of nitrifying bacteria was obtained. There was a drastic improvement over the conventional method of immobilization by acrylamide in the activity yield. Inorganic synthetic waste-water was treated at a high loading rate of 0.24 kg N·m^–3·day^–1. The NH₄-N concentration of the effluent could be reduced to 2 mg·1^–1 or less and the removal was 90%. The life of the pellets in terms of activity was at least 120 days. Offprint requests to: T. Sumino     

Activity of nitrifying populations in grassland soil polluted by polychlorinated biphenyls (PCBs)

The activity of nitrification was studied in the period of 1992 – 1994 in two grassland plots from the surroundings of a municipal waste incinerator. The soil parameters were fully comparable in both plots and the soils differed in the level of polychlorinated biphenyls (PCBs). The concentration of PCBs found in Klajdovka-control plot (KL): 4.4 ng g_{dry soil} ^–1 can be regarded as a background value, while the polluted plot, Bílá Hora (BH), contained increased amount of PCBs: 14.0 ng g_{dry soil} ^–1.The following parameters of nitrifying activity were determined: field concentrations of N_inorg species, mineralization potentials, nitrifying activity during long-term laboratory incubations, and the potential activity of both ammonium and nitrite oxidizers in short-term incubations in soil slurries. Simultaneous application of all these methods appeared to be very suitable for reliable assessment of nitrifying activity in the field.In the case of the polluted plot, the abnormal accumulation of nitrite was observed both in the field (e.g. in September 1992: BH-656.8 ng NO _inf2 ^– -N g_{dry soil} ^–1; KL-208.2 ng NO _inf2 ^– -N g_{dry soil} ^–1) and in the laboratory incubations. Furthermore, the capability of the polluted plot to nitrify higher amount of ammonium nitrogen appeared to be significantly reduced due to detrimental changes in the activity of nitrite-oxidizing community. In contrast to the nitrification, the mineralization potential did not differ between the plots throughout the sampling period.     

Immobilization of nitrifying bacteria by polyethylene glycol prepolymer

The effects of immobilizing materials on the activity of nitrifying bacteria were investigated by using 11 kinds of prepolymers of polyethylene glycol. Relative respiratory activity of immobilized nitrifying bacteria with polyethylene glycol metacrylate prepolymer was higher than that of polyethylene glycol acrylate prepolymer, and there was a tendency for relative respiratory activity to be higher with a prepolymer of greater molecular weight. With the polyethylene glycol prepolymer, there was a drastic improvement over the conventional method of immobilization by acrylamide in the relative respiratory activity of the pellet. Inorganic synthetic wastewater was treated under a high loading rate of 1.14 kg-N/m³·d. Influent NH₄-N could be removed to 2 mg/l or less and the nitrogen removal was 90%.     

Dynamics of viable nitrifier community and nutrient availability in dry tropical forest habitat as affected by cultivation and soil texture

Seasonal dynamics of N-mineralization and the size of the viable community of nitrifying bacteria were studied for a forest site and an adjoining cropland site. The forest site was dominated by Boswellia serrata and Acacia catechu in the tree layer, and by Nyctanthes arbortristis and Zizyphus glaberrima in the shrub layer. Crop sequence on the cropland site was Oryza sativa/Lens culinaris. The soil type in both the sites was ultisol (USDA). The cropland soil had significantly higher bulk density, and clay content but lower organic C, total N and total P than forest soil. The soil moisture content, numbers of ammonia-and nitrite oxidizing bacteria and N-mineralization rates were highest in the wet season and lowest in the dry season, while the size of mineral N and P pools showed a reverse trend in both sites. The numbers of free-living cells of ammonia-and nitrite oxidizing bacteria were significantly related with each other as well as with the soil moisture content and N-mineralization rates. In N-mineralization, NO ₃ ^– was the dominating form in the forest site during rainy season, while in other seasons in this site and in all the seasons in the cropland site, NH ₄ ⁺ -N was predominant. The N-mineralization rate and the number of viable nitrifying cells were consistently higher for the forest soil compared to the clay-rich cropland soil. The combination of low soil organic matter and high clay content suppressed the number of free-living cells of nitrifying bacteria and N-mineralization rates in the cropland site.     

Fate of 14C-Labeled Microbial Products Derived from Nitrifying Bacteria in Autotrophic Nitrifying Biofilms

The cross-feeding of microbial products derived from ¹⁴C-labeled nitrifying bacteria to heterotrophic bacteria coexisting in an autotrophic nitrifying biofilm was quantitatively analyzed by using microautoradiography combined with fluorescence in situ hybridization (MAR-FISH). After only nitrifying bacteria were labeled with [¹⁴C]bicarbonate, biofilm samples were incubated with and without NH₄⁺ as a sole energy source for 10 days. The transfer of ¹⁴C originally incorporated into nitrifying bacterial cells to heterotrophic bacteria was monitored with time by using MAR-FISH. The MAR-FISH analysis revealed that most phylogenetic groups of heterotrophic bacteria except the β-Proteobacteria showed significant uptake of ¹⁴C-labeled microbial products. In particular, the members of the Chloroflexi were strongly MAR positive in the culture without NH₄⁺ addition, in which nitrifying bacteria tended to decay. This indicated that the members of the Chloroflexi preferentially utilized microbial products derived from mainly biomass decay. On the other hand, the members of the Cytophaga-Flavobacterium cluster gradually utilized ¹⁴C-labeled products in the culture with NH₄⁺ addition in which nitrifying bacteria grew. This result suggested that these bacteria preferentially utilized substrate utilization-associated products of nitrifying bacteria and/or secondary metabolites of ¹⁴C-labeled structural cell components. Our results clearly demonstrated that the coexisting heterotrophic bacteria efficiently degraded and utilized dead biomass and metabolites of nitrifying bacteria, which consequently prevented accumulation of organic waste products in the biofilm.     

Nitrate production in the rhizosphere of Plantago species

Summary The production of nitrate in an old established dune grassland soil and its uptake by plants was studied by comparing amounts of mineral nitrogen and numbers of nitrifying bacteria in the rhizosphere on the one hand, and on the other accumulated nitrate and levels of nitrate reductase (NaR) of individual plants of three Plantago species,i. e., P. major, P. lanceolata andP. coronopus. For these three Plantago species andP. media basal levels of NaR in the absence of nitrate were determined in plants grown in culture solutions. The basal NaR levels ofP. major andP. media (species occurring on nutrient-rich soils) were significantly higher than those ofP. lanceolata andP. coronopus (species found on nutrient-poor soils). NaR activity increased in the presence of nitrate and was suppressed by ammonium.From the numbers of nitrifying bacteria in the rhizosphere and NaR activity in the leaves it was concluded that nitrate was produced in the root environments of the three Plantago species and that the compound was taken up by the plants. NaR activities and numbers of nitrifying bacteria were higher for individuals ofP. major than for those ofP. lanceolata andP. coronopus. No correlation was found between the ammonium levels and the numbers of nitrifying bacteria in the soil, and no indications of inhibition of nitrifying bacteria in the rhizosphere were obtained. For individuals ofP. lanceolata a correlation was found between the numbers of nitrifying bacteria in the soil and NaR activity in the leaves. The results are discussed in relation to the ecological habitats of the three species.Grassland Species Research Group Publication No.38.     

Measurement of potential activity of fixed nitrifying bacteria in biological filters used in drinking water production

Nitrification during biological filtration is being used more and more in drinking water production to remove ammonia, which can be the source of several water quality problems during distribution. In this process, ammonia is converted into nitrite and then into nitrate by fixed autotrophic nitrifying bacteria. The purpose of this work was to develop a technique to estimate fixed nitrifying biomass (sum of ammonia- and nitrite-oxidizing populations). The quantification of autotrophic nitrifying biomass was determined by potential nitrifying activity measurement. The production of oxidized forms of inorganic nitrogen (nitrates and nitrites) was measured after an incubation of 2 cm³ of colonized solid support in the presence of a 5-ml nitrifier medium containing 10 mg N-NH₄ L⁻¹ for 30 min at 32°C. The production rate of oxidized nitrogen in optimal conditions was measured and converted into nitrifying biomass by using the maximum specific oxidizing activity. This technique was shown to be appropriate for conditions encountered in the biological filters used in drinking water production and sufficiently simple to be used for routine measurements. Journal of Industrial Microbiology & Biotechnology (2000) 24, 161–166. Received 28 July 1999/ Accepted in revised form 11 November 1999     

Competition for Ammonium between Nitrifying and Heterotrophic Bacteria in Continuously Percolated Soil Columns

Although the absence of nitrate formation in grassland soils rich in organic matter has often been reported, low numbers of nitrifying bacteria are still found in these soils. To obtain more insight into these observations, we studied the competition for limiting amounts of ammonium between the chemolithotrophic ammonium-oxidizing species Nitrosomonas europaea and the heterotrophic species Arthrobacter globiformis in the presence of Nitrobacter winogradskyi with soil columns containing calcareous sandy soil. The soil columns were percolated continuously at a dilution rate of 0.007 h^-1, based on liquid volumes, with medium containing 5 mM ammonium and different amounts of glucose ranging from 0 to 12 mM.A. globiformis was the most competitive organism for limiting amounts of ammonium. The numbers of N. europaea and N. winogradskyi cells were lower at higher glucose concentrations, and the potential ammonium-oxidizing activities in the uppermost 3 cm of the soil columns were nonexistent when at least 10 mM glucose was present in the reservoir, although 10⁷ nitrifying cells per g of dry soil were still present. This result demonstrated that there was no correlation between the numbers of nitrifying bacteria and their activities. The numbers and activities of N. winogradskyi cells decreased less than those of N. europaea cells in all layers of the soil columns, probably because of heterotrophic growth of the nitrite-oxidizing bacteria on organic substrates excreted by the heterotrophic bacteria or because of nitrate reduction at reduced oxygen concentrations by the nitrite-oxidizing bacteria. Our conclusion was that the nitrifying bacteria were less competitive than the heterotrophic bacteria for ammonium in soil columns but that they survived as viable inactive cells. Inactive nitrifying bacteria may also be found in the rhizosphere of grassland plants, which is rich in organic carbon. They are possibly reactivated during periods of net mineralization.     

Nitrogen dynamics in seasonally flooded soils in the Amazon floodplain

Large areas of the Amazon are subject to seasonal flooding due to water level changes of the river. This flood pulse causes rapidly changing conditions for microorganisms living in the soils which affects the cycling of nitrogen in the ecosystem. An understanding of the nitrogen dynamics in the seasonally flooded soils is essential for the development of productive and sustainable management concepts. We measured nitrogen concentrations, denitrifier enzyme activity (DEA), cell numbers of nitrifying and denitrifying bacteria, respiration, pH and total carbon in the seasonally flooded soils over one entire annual hydrological cycle. By comparing three sites with different vegetation (forest, aquatic macrophyte stand and bare sediment with annual herbs) we assessed the effect of vegetation on soil nitrogen dynamics. Inorganic nitrogen was always dominated by ammonium indicating reduced conditions in the soil even during the terrestrial phase. Although conditions were generally poor for nitrification we observed high numbers of nitrifying bacteria between 10⁴ and 10⁷cells g^–1. Pulses of ammonium as well as high DEA were observed during the transition periods between aquatic and terrestrial phase. Thus the alternation between aquatic and terrestrial phase promotes nitrogen mineralization and denitrification in the soils. There were no plausible correlations between microbial activities and numbers with soil physical or chemical parameters except a relation between the numbers of nitrate reducing bacteria and soil moisture (R² = 0.81) and ammonium (R² = 0.92) at one site. This shows the complex regulation patterns in this habitat. Different vegetation did not alter the general patterns of nitrogen dynamics but the absolute extend of fluctuations. We conclude that both the soil physical and chemical changes directly caused by the flood pulse and the vegetation have a great impact on microbial nitrogen turnover in the soils. The effects of the flood pulse can be buffered by a fine soil texture or a litter layer which prevents desiccation of the soil during the terrestrial phase.     

Nitrogenase activity in the papyrus swamps of Lake Naivasha,Kenya

Nitrogenase activity (acetylene reduction activity) was found to occur universally in the Cyperus papyrus swamp in Lake Naivasha. Low rates of acetylene reduction activity (0.9–104.9 nmol C₂H₄ g d.wt. roots^-1 h^-1) were associated with excised roots of C. papyrus but higher rates of activity (89.0–280.4 nmol C₂H₄ g d.wt. roots^-1 h^-1) were associated with intact root systems of the plant. It was estimated that nitrogen fixation associated with young roots alone could supply about 26% of the nitrogen requirements of growing papyrus plants. Acetylene reduction activity in the lake bottom sediments was generally low and associated with adjacent papyrus stands. Plate counts of putative aerobic and facultatively anaerobic N₂-fixing bacteria associated with papyrus roots showed the presence of high numbers of diazotrophs (5.4 × 10⁶ CFU g d.wt. roots^-1). Fewer numbers of N₂-fixing bacteria were detected in the sediments (1.9 × 10³-3.2 × 10⁴ CFU g d.wt. sediment^-1).     

Length of Incubation for Enumerating Nitrifying Bacteria Present in Various Environments

The effect of incubation time on most-probable-number estimates of autotrophic nitrifying bacteria was investigated by using waters, rooted aquatic plants, sediments, and slimes as inoculum sources. Maximum most probable numbers of the NH₄⁺-oxidizing group were attained in 20 to 55 days (median, 25). Estimates of NO₂^- oxidizers were highest at termination (103 to 113) days.     

Activity of nitrifiers in relation to nitrogen nutrition of plants in natural ecosystems

Three aspects of the nitrate production in natural ecosystems are discussed,i.e. the population biology of nitrifying bacteria, the nitrate-producing activity of these organisms and the uptake of nitrate by higher plants. It is concluded that the three methods used in enumerating the nitrifying bacteria,i.e. the Most Probable Number method, the Fluorescent Antibody technique and the Potential Nitrification Rate, all have serious drawbacks and count different segments of the nitrifying populations.From the number of nitrifying bacteria no reliable estimate of the rate production can be obtained and also estimates that are made using field-incubation and¹⁵N–NH ₄ ⁺ techniques do not yield reliable data. Possibly the best results can be obtained using Schimel's method to estimate the actual nitrification rate using¹⁵N–NO ₃ ^– , but this method has still not been tested under different sets of soil conditions.From the nitrate reductase activity and the chemical composition of the plant a picture can be obtained of the quantities of nitrate and ammonium that have been taken up. However, it is shown that nitrate and ammonium are taken up in different proportions that they are produced. It is concluded that the various parameters have to be studied simultaneously, preferably in defined systems with plants, in which the participating organisms are known.     

Lithotrophic and Heterotrophic Bacteria in Deep Subsurface Sediments and Their Relation to Sediment Properties

Subsurface sediments obtained from three cores drilled to depths of 260 m below the surface in South Carolina were analyzed for heterotrophic bacteria; N₂‐fixing microaerophiles; and nitrifying, sulfur‐oxidizing, and H₂‐oxidizing lithotrophic bacteria. In addition, pore waters were extracted for chemical analysis of inorganic nitrogen species, sulfate, dissolved organic carbon, pH, and Eh. Autotroph populations were generally less than 10³ most probable number (MPN) g^‐1 dry sediment with sulfur‐oxidizing bacteria, detected in 60% of the sediment samples, being the most frequently encountered group. Nitrifying bacteria were detected mainly in sediments from one borehole (P28), and their populations in those sediments were correlated with pore‐water ammonium concentrations. Populations of heterotrophic bacteria in 60% of the sediments were greater than 10⁶ colony forming units (CFU) g^‐1 dry sediment and were typically lower in sediments of high clay content and low pH. Microaerophilic N₂‐fixing bacteria were cultured from >50% and bacteria capable of growth on H₂ were cultured from 35% of the subsurface sediments examined. Sediment texture, which controls porosity, water potential, and hydraulic conductivity, appears to be a major factor influencing microbial populations in coastal plain subsurface sediments.     

Population Ecology of Nitrifiers in a Stream Receiving Geothermal Inputs of Ammonium

The distribution, activity, and generic diversity of nitrifying bacteria in a stream receiving geothermal inputs of ammonium were studied. The high estimated rates of benthic nitrate flux (33 to 75 mg of N · m⁻² · h⁻¹) were a result of the activity of nitrifiers located in the sediment. Nitrifying potentials and ammonium oxidizer most probable numbers in the sediments were at least one order of magnitude higher than those in the waters. Nitrifiers in the oxygenated surface (0 to 2 cm) sediments were limited by suboptimal temperature, pH, and substrate level. Nitrifiers in deep (nonsurface) oxygenated sediments did not contribute significantly to the changes measured in the levels of inorganic nitrogen species in the overlying waters and presumably derived their ammonium supply from ammonification within the sediment. Ammonium-oxidizing isolates obtained by a most-probable number nonenrichment procedure were species of either Nitrosospira or Nitrosomonas, whereas all those obtained by an enrichment procedure (i.e., selective culture) were Nitrosomonas spp. The efficiency of the most-probable-number method for enumerating ammonium oxidizers was calculated to be between 0.05 and 2.0%, suggesting that measurements of nitrifying potentials provide a better estimate of nitrifying populations.     

黄土丘陵区不同植被土壤氮素转化微生物生理群特征及差异

采用最大或然计数法(most probable number, MPN)对黄土高原洞子沟流域不同植被恢复阶段土壤氮素微生物生理群(氨化细菌、亚硝化细菌、反硝化细菌)数量分布特征进行了测定,结果表明:1)土壤氨化细菌、亚硝化细菌和反硝化细菌数量随植被恢复而增加,三者最大值分别为最小值的74、4和31倍,其中氨化细菌和反硝化细菌的数量在铁杆蒿群落最低,辽东栎群落最高,亚硝化细菌数量在丁香群落最低,辽东栎群落最高;2)植被恢复对各氮素生理群影响不同,对氨化细菌影响最大,其次分别为反硝化细菌和亚硝化细菌;3)各氮素生理群数量差异较大,氨化细菌>反硝化细菌>亚硝化细菌。研究区氨化细菌占总数的75%-80%,反硝化细菌占20%-25%时,生态系统最为稳定;4)土壤理化性质与各功能菌关系紧密,其中,土壤容重和硝态氮含量与微生物数量相关性最大,全钾、矿化氮和微生物量氮也表现出很大的相关性。     

Seasonal distribution of nitrifying bacteria and rates of nitrification in coastal marine sediments

The distribution of nitrification potential (NP) with depth in sediment and season was investigated in a shallow sandy sediment (0.5 m water) and a deeper muddy sediment (17m water). In both sediments, nitrifying bacteria were present in the anoxic strata (oxygen penetration was 5 mm below the surface). The NP at 6–8 cm depth in the sediment was 50% and 10% of the surface NP at the sandy and muddy sediment, respectively. It is suggested that bioturbation and physical disturbance of the sediment were the most likely reasons for this distribution. The NP increased as sediment temperature decreased. This effect was less marked in the muddy sediment. It is concluded that during the summer, the numbers or specific activity of nitrifying bacteria diminished for the following reasons: There was decreased O₂ penetration into the sediment and increased competition for O₂ by heterotrophs; there was increased competition for NH₄ ⁺ and there was inhibition by H₂S. These effects counteracted the potentially higher growth rates and increased rates of NH₄ ⁺ production at the elevated summer temperatures. The potential nitrification rates in the upper 1 cm, which were measured at 22°C, were converted to calculated rates at the in situ temperature (Q₁₀=2.5) and in situ oxygen penetration. These calculated rates were shown to closely resemble the measured in situ rates of nitrification. The relationship between the in situ rates of nitrification and the nitrification potential is discussed.     

Screening and characterization of an aerobic nitrifying-denitrifying bacterium from activated sludge

Taking advantage of the good biocompatibility and high efficiency of nitrogen removal with microbes, nitrifying and denitrifying bacteria, are becoming increasingly more widely used for wastewater treatment and prevention of eutrophication. In this research, an aerobic nitrifying-denitrifying bacterium was successfully screened from activated sludge and identified as Pseudomonas sp. (CCTCC No M2010209) by the 16S rDNA sequence. The activity verification confirmed its nitrifying-denitrifying capability of removing ammonium, nitrate and nitrite nitrogen. The types of carbon sources and carbon-nitrogen ratio greatly influenced the removal efficiency of NH₄ ⁺-N and NO₃ ⁻-N. When the initial concentrations of NH₄ ⁺-N and NO₃ ⁻-N in synthetic wastewater were less than 70 and 50 mg/L, the nitrogen removal rates reached 94 and 90% in 9 h, respectively. Preliminary comparisons of nitrogen removal capacity between this isolate and other commercial preparations in the treatment of synthetic wastewater revealed its promising potential to be used in the actual wastewater treatment.     

Microscale Distribution of Populations and Activities of Nitrosospira and Nitrospira spp. along a Macroscale Gradient in a Nitrifying Bioreactor: Quantification by In Situ Hybridization and the Use of Microsensors

The change of activity and abundance of Nitrosospira and Nitrospira spp. along a bulk water gradient in a nitrifying fluidized bed reactor was analyzed by a combination of microsensor measurements and fluorescence in situ hybridization. Nitrifying bacteria were immobilized in bacterial aggregates that remained in fixed positions within the reactor column due to the flow regimen. Nitrification occurred in a narrow zone of 100 to 150 μm on the surface of these aggregates, the same layer that contained an extremely dense community of nitrifying bacteria. The central part of the aggregates was inactive, and significantly fewer nitrifiers were found there. Under conditions prevailing in the reactor, i.e., when ammonium was limiting, ammonium was completely oxidized to nitrate within the active layer of the aggregates, the rates decreasing with increasing reactor height. To analyze the nitrification potential, profiles were also recorded in aggregates subjected to a short-term incubation under elevated substrate concentrations. This led to a shift in activity from ammonium to nitrite oxidation along the reactor and correlated well with the distribution of the nitrifying population. Along the whole reactor, the numbers of ammonia-oxidizing bacteria decreased, while the numbers of nitrite-oxidizing bacteria increased. Finally, volumetric reaction rates were calculated from microprofiles and related to cell numbers of nitrifying bacteria in the active shell. Therefore, it was possible for the first time to estimate the cell-specific activity of Nitrosospira spp. and hitherto-uncultured Nitrospira-like bacteria in situ.     

硝化细菌群的富集及其去除城镇寡营养河道中氨氮污染的应用

[背景]随着工农业的发展,污水排放导致的氨氮超标逐渐成为水体污染的重要因素,脱氮已成为人们研究的重点.目前脱氮方法主要集中于硝化细菌的硝化作用,其将氨氮转化为硝酸盐氮,从而减少水体中氨氮的污染.由于工业废水和农业污水中的有机物含量较高,而且异养硝化细菌具有生长较快等优势,因此对异养菌的研究多于自养菌.然而现有的异养硝化...