Some properties of a Klebsiella pneumoniae ammonium transport negative mutant (Amt−)

The main property of an Amt^- (ammonium transport negative) mutant of Klebsiella pneumoniae is its inability to accumulate NH ₄ ⁺ intracellularly. When growing on nitrogen sources other than NH ₄ ⁺ , the mutant constantly looses NH₃ by diffusion. This loss results in poor growth. The NH₃ excretion suggests the existence of a futile cycle (NH₃ loss/NH ₄ ⁺ reabsorption) in the wild type and possibly other bacterial strains, which do not constantly excrete NH₃.Dedicated to Prof. R. H. Burris     

Effect of nickel on certain physiological and biochemical behaviors of an acid tolerantChlorella vulgaris

This study concerns the inhibitory effects of acid pH and nickel on growth, nutrient (NO₃ ^- and NH₄ ⁺) uptake, carbon fixation, O₂ evolution, electron transport chain and enzyme (nitrate reductase and ATPase) activities of acid tolerant and wild-type strains of Chlorella vulgaris. Though a general reduction in all these variables was noticed with decreasing pH, the tolerant strain was found to be metabolically more active than the wild-type. A reduced cation (NH₄ ⁺, Na⁺, K⁺ and Ca²⁺) uptake, coupled with a facilitated influx of anions (NH₄ ⁺, PO₄ ^3- and HCO₃ ^-), suggested the development of a positive membrane potential in acid tolerant Chlorella. Nevertheless, a tremendous increase in ATPase activity at decreasing pH revealed the involvement of superactive ATPase in exporting H⁺ ions and keeping the internal pH neutral. A difference in Na⁺ and K⁺ efflux of the two strains at decreasing pH suggests there is a difference in membrane permeability. The low toxicity of Ni in the acid tolerant strain may be due to the low Ni uptake brought about by a change in membrane potential as well as in permeability. Hence, the development of superactive ATPase and a change in both membrane potential and permeability not only offers protection against acidity, but also co-tolerance to metals.     

Anaerobic ammonia-oxidation coupled with Fe3+ reduction by an anaerobic culture from a piggery wastewater acclimated to NH4 +/Fe3+ medium

The oxidation of ammonia coupled with the reduction of iron is a unique pathway mostly reported in soils and sediments. An anaerobic sludge from a piggery wastewater treatment plant had been acclimated to an NH⁺/Fe³⁺-rich environment to secure an enrichment culture and investigate an anaerobic ammonia oxidation coupled with an iron reduction. The enrichment culture showed an average pH of 6.8 and the concentration of mixed liquor volatile suspended solid was measured as 1,120 mg/L. The mol ratio of oxidized NH₄ ⁺ and reduced Fe³⁺ was 0.33 mol NH₄ ⁺/mol Fe³⁺. It was suggested that the culture acclimated to NH₄ ⁺/Fe³⁺ contained the anaerobic ammonia oxidizing bacteria as well and thus NH₄ ⁺ was fully oxidized to NO₃ ⁻ by the bacterial consortia. In a batch experiment using the culture, the oxidation of NH₄ ⁺ was increased as the initial concentration increased. However, it was suspected from the experimental results that other iron reducing bacteria had grown under the environment applied for the enrichment culture. As a result, it was observed that heterotrophic and autotrophic iron reducers were competing for Fe³⁺.     

Ammonia production from yeast extract and its effect on growth of the hyperthermophilic archaeonSulfolobus solfataricus

Utilization of yeast extract and formation of byproduct metabolite were investigated for hyperthermophilic archaeonSulfolobus solfataricus (DSM 1617). In both batch and fed-batch cultivations ofS. solfataricus, maximal cell density, NH₄ ⁺ ion production and pH change were highly dependent on the ratio of yeast extract to glucose in the medium. Variation of NH₄ ⁺ ion level was identified as a major cause of pH change during cultivation, and acidification of culture broth was attributed to consumption of NH₄ ⁺ ions rather than formation of acid byproducts. It was also observed that increase of NH₄ ⁺ ion concentrations in the medium resulted in greater degree of growth inhibition.     

Utilization of Ammonium as a Nitrogen Source : Effects of Ambient Acidity on Growth and Nitrogen Accumulation by Soybean

Dry matter accumulation of plants utilizing NH₄⁺ as the sole nitrogen source generally is less than that of plants receiving NO₃⁻ unless acidity of the root-zone is controlled at a pH of about 6.0. To test the hypothesis that the reduction in growth is a consequence of nitrogen stress within the plant in response to effects of increased acidity during uptake of NH₄⁺ by roots, nonnodulated soybean plants (Glycine max [L.] Merr. cv Ransom) were grown for 24 days in flowing nutrient culture containing 1.0 millimolar NH₄⁺ as the nitrogen source. Acidities of the culture solutions were controlled at pH 6.1, 5.1, and 4.1 ± 0.1 by automatic additions of 0.01 n H₂SO₄ or Ca(OH)₂. Plants were sampled at intervals of 3 to 4 days for determination of dry matter and nitrogen accumulation. Rates of NH₄⁺ uptake per gram root dry weight were calculated from these data. Net CO₂ exchange rates per unit leaf area were measured on attached leaves by infrared gas analysis. When acidity of the culture solution was increased from pH 6.1 to 5.1, dry matter and nitrogen accumulation were reduced by about 40% within 14 days. Net CO₂ exchange rates per unit leaf area, however, were not affected, and the decreased growth was associated with a reduction in rates of appearance and expansion of new leaves. The uptake rates of NH₄⁺ per gram root were about 25% lower throughout the 24 days at pH 5.1 than at 6.1. A further increase in solution acidity from pH 5.1 to 4.1 resulted in cessation of net dry matter production and appearance of new leaves within 10 days. Net CO₂ exchange rates per unit leaf area declined rapidly until all viable leaves had abscised by 18 days. Uptake rates of NH₄⁺, which were initially about 50% lower at pH 4.1 than at 6.1, continued to decline with time of exposure until net uptake ceased at 10 days. Since these responses also are characteristic of the sequence of responses that occur during onset and progression of a nitrogen stress, they corroborate our hypothesis.     

Plasma-membrane H+-ATPases are expressed in pitchers of the carnivorous plant Nepenthes alata Blanco

Nepenthes is a unique genus of carnivorous plants that can capture insects in trapping organs called pitchers and digest them in pitcher fluid. The pitcher fluid includes digestive enzymes and is strongly acidic. We found that the fluid pH decreased when prey accumulates in the pitcher fluid of Nepenthes alata. The pH decrease may be important for prey digestion and the absorption of prey-derived nutrients. To identify the proton pump involved in the acidification of pitcher fluid, plant proton-pump homologs were cloned and their expressions were examined. In the lower part of pitchers with natural prey, expression of one putative plasma-membrane (PM) H⁺-ATPase gene, NaPHA3, was considerably higher than that of the putative vacuolar H⁺-ATPase (subunit A) gene, NaVHA1, or the putative vacuolar H⁺-pyrophosphatase gene, NaVHP1. Expression of one PM H⁺-ATPase gene, NaPHA1, was detected in the head cells of digestive glands in the lower part of pitchers, where proton extrusion may occur. Involvement of the PM H⁺-ATPase in the acidification of pitcher fluid was also supported by experiments with proton-pump modulators; vanadate inhibited proton extrusion from the inner surface of pitchers, whereas bafilomycin A₁ did not, and fusicoccin induced proton extrusion. These results strongly suggest that the PM H⁺-ATPase is responsible for acidification of the pitcher fluid of Nepenthes. Received: 8 June 2000 / Accepted: 8 August 2000     

Thermophilic amylase-producing bacteria from Vietnamese soils

Of 25 bacterial isolates from Vietnamese soils, two were identified asBacillus stearothermophilus and one asThermoactinomyces thalpophilus, both thermophilic, amylase-producing bacteria. Amylase activity was highest in the presence of cassava starch as carbon source and (NH₄)₂HPO₄ as nitrogen source. The strains exhibit a high amylase productivity within the first 5 to 7 h of cultivation at 55°C. The crude enzyme had optima of pH 6.5 and 70°C.     

The Influence of Ammonium Nitrate,pH and Indole Butyric Acid on Root Induction and Survival in Soil of Micropropagated <Emphasis Type="Italic">Eucalyptus globulus</Emphasis>

Rooting of Eucalyptus globulus shoots was influenced by the concentration of the indole butyric acid (IBA) and NH₄ ⁺ in the root-induction medium. Optimum plantlet vigor and survival were achieved using low concentrations (1 – 2.5 μM) of IBA and when NH₄NO₃ was removed. Removal of NH₄ ⁺ also had a significant effect on medium pH, its presence caused a decrease in pH as the culture period proceeded. When different nitrate compounds (excluding NH₄NO₃) were used as the nitrogen source, the medium pH was more stable and this was associated with higher root production. The higher root production, in association with appropriate IBA concentrations, produced plantlets with higher survival and better growth on transfer to soil. This revised version was published online in July 2006 with corrections to the Cover Date.     

Replacement of potassium ions by ammonium ions in different micro-organisms grown in potassium-limited chemostat culture

The biomass concentration extant in potassiumlimited cultures of either Klebsiella pneumoniae or Bacillus stearothermophilus (when growing at a fixed temperature and dilution rate in a glucose/ammonium salts medium) increased progressively as the medium pH value was raised step-wise from 7.0 to 8.5. Because the macromolecular composition of the organisms did not vary significantly, this increase in biomass could not be attributed to an accumulation of storage-type polymers but appeared to reflect a pH-dependent decrease in the cells' minimum K⁺ requirement. Significantly, this effect of pH was not eviden with cultures in which no ammonium salts were present and in which either glutamate or nitrate was added as the sole nitrogen source; however, it was again manifest when various concentrations of NH₄Cl were added to the glutamate-containing medium. This suggested a functional replacement of K⁺ by NH ₄ ⁺ , a proposition consistent with the close similarity of the ionic radii of the potassium ion (1.33 Å) and the ammonium ion (1.43 Å). At pH 8.0, and with a medium containing both glutamate (30 mM) and NH₄Cl (100 mM), cultures of B. stearothermophilus would grow without added potassium at a maximum rate of 0.7 h^-1. Under these conditions the cells contained maximally 0.1% (w/w) potassium (derived from contaminating amounts of this element in the medium constituents), a value which should be compared with one of 1.4% (w/w) for cells growing in a potassiumlimited medium containing initially 0.5 mM K⁺. Qualitatively similar findings were made with cultures of K. pneumoniae; and whereas one may not conclude that NH ₄ ⁺ can totally replace K⁺ in the growth of these bacteria, it can clearly do so very extensively.     

Seasonal variability of apoplastic NH4 + and pH in an intensively managed grassland

The stomatal compensation point of ammonia (_s) is a major factor controlling the exchange of atmospheric ammonia (NH₃) with vegetation. It is known to depend on the supply of nitrogen and to vary among plant species, but its seasonal variation has not yet been reported for grassland. In this study, we present the temporal variation of apoplastic NH₄ ⁺ concentration ([NH₄ ⁺]_apo) and pH (pH_apo) measured in leaves of Lolium perenne L. in a grassland, through two periods of cutting / fertilisation, followed by a livestock grazing period. The total free NH₄ ⁺ concentration measured in foliage ([NH₄ ⁺]_fol), and soil mineral NH₄ ⁺ and NO₃ ^– concentration are also presented. The value of [NH₄ ⁺]_apo varied from less than 0.01 mM to a maximum of 0.5 mM occurring just after fertilisation, whereas the apoplastic pH ranged from pH 6 to 6.5 for most of the time and increased up to pH 7.8, 9 days after the second fertilisation, when grazing started. [NH₄ ⁺]_fol varied between 20 and 50 g N-NH₄ ⁺ g^–1 f.w. The compensation point at 20°C, ranged from 0.02 g NH₃ m^–3 between the fertilisations to 10 g NH₃ m^–3 just after the second fertilisation. The reasons for these seasonal changes are discussed, with respect to plant metabolism and the concentration of ammonium and nitrate in the soil.     

Nitrogen metabolism by heterotrophic bacterial assemblages in Antarctic coastal waters

Field studies to examine the in situ assimilation and production of ammonium (NH₄ ⁺) by bacterial assemblages were conducted in the northern Gerlache Strait region of the Antarctic Peninsula. Short term incubations of surface waters containing ¹⁵N-NH₄ ⁺ as a tracer showed the bacterial population taking up 0.041–0.128 g-atoms Nl^–1d^–1, which was 8–25% of total NH₄ ⁺ uptake rates. The large bacterial uptake of NH₄ ⁺ occurred even at low bacterial abundance during a rich phytoplankton bloom. Estimates of bacterial production using ³H-leucine and -adenine were l.0gCl^–1 d^–1 before the bloom and 16.2 g Cl^–1 d^–1 at the bloom peak. After converting bacterial carbon production to an estimate of nitrogen demand, NH₄ ⁺ was found to supply 35–60% of bacterial nitrogen requirements. Bacterial nitrogen demand was also supported by dissolved organic nitrogen, generally in the form of amino acids. It was estimated, however, that 20–50% of the total amino acids taken up were mineralized to NH₄ ⁺. Bacterial production of NH₄ ⁺ was occurring simultaneously to its uptake and contributed 27–55% of total regenerated NH₄ ⁺ in surface waters. Using a variety of ¹⁵N-labelled amino acids it was found that the bacteria metabolized each amino acid differently. With their large mineralization of amino acids and their relatively low sinking rates, bacteria appear to be responsible for a large portion of organic matter recycling in the upper surface waters of the coastal Antarctic ecosystem.     

Optimization and elucidation of interactions between ammonium, nitrate and phosphate inCentella asiatica cell culture using response surface methodology

The effects of macronutrients (NO₃ ⁻, NH₄ ⁺ and PO₄ ³⁻) on cell growth and triterpenoids production inCentella asiatica cell suspension cultures were analyzed using the Box-Behnken response surface model experimental design. In screening and optimization experiments, PO₄ ³⁻ as a single factor significantly influenced cell growth where increasing the phosphate level from 0.1 to 2.4 or 2.6 mM, elevated cell growth from 3.9 to 14–16 g/L. The optimum values predicted from the response surface model are 5.05 mM NH₄ ⁺, 15.0 mM NO₃ ⁻ and 2.6 mM PO₄ ³⁻, yielding 16.0 g/L cell dry weight with 99% fitness to the experimental data. While the NH₄ ⁺-NO₃ ⁻ interaction influenced cell growth positively in the optimization experiment, NH₄ ⁺ and NO₃ ⁻ as single factors; and interactions of NO₃ ⁻-PO₄ ³⁻, NH₄ ⁺-PO₄ ³⁻ and NH₄ ⁺-NO₃ ⁻ were all negative in the screening experiment. Cell growth and the final pH level were positively affected by PO₄ ³⁻, but negatively affected by NH₄ ⁺ and NH₄ ⁺-PO₄ ³⁻ interactions. The different effects of factors and their interactions on cell growth and final pH are influenced by a broad or narrow range of macronutrient concentrations. The productions of triterpenoids however were lower than 4 mg/g cell dry weight.     

Influence of Protein Synthesis on NO(3) Reduction, NH(4) Accumulation, and Amide Synthesis in Suspension Cultures of Paul's Scarlet Rose

Changes in the concentrations of NH₄⁺ and amides during the growth of suspension cultures of rose (Rosa cv. Paul's Scarlet) cells were examined. When cells were grown in medium possessing only NO₃⁻ as a nitrogen source, the concentrations of NH₄⁺ and amides increased to 4.0 × 10⁻¹ and 5.9 micromoles per gram fresh weight, respectively. The amounts of both constituents declined during the later stages of growth. When a trace amount of NH₄⁺ was added to the NO₃⁻ base starting medium, the concentration of NH₄⁺ in the cells was increased to 7.0 × 10⁻¹ micromoles per gram fresh weight.     

Effects of Environmental Factors on Anammox Bacterial Community Structure in Sediments of a Freshwater Aquaculture Farm,Yangcheng Lake

Previous studies have reported wide distribution of anaerobic ammonia oxidation (anammox) bacteria in various ecosystems. However, little is known about the distribution of anammox bacteria under varying environmental conditions in intensive aquaculture systems. In Yangcheng Lake, a famous crab farm situated in the Yangtze River Delta, sediment samples were collected in October (feeding period) and January (nonfeeding period) to analyze the distribution and diversity of anammox bacteria and their relationships with environmental factors. Based on the functional biomarker of Anammox bacteria, hzo gene, anammox bacterial clone libraries were constructed and their abundances were determined by quantitative PCR (qPCR). The Anammox bacteria were detected in the lake with the abundances ranging from 0.70 × 10⁵ to 6.05 × 10⁵ copies per gram of sediment. Sequences from eight clone libraries yielded seven unique operational taxonomic units (OTUs), distantly related to the Candidatus Jettenia genera with a similarity of about 91%. The Anammox bacterial community structures, diversities and abundances varied spatiotemporally with environmental conditions. In October, the level of the nitrogen compounds, the diversity, evenness and abundance of Anammox bacteria were higher than in January. The predominant OTU of samples changed from HZO-OTU-1 (34.25%) in January to HZO-OTU-2 (28.90%) in October. Moreover, the site (SW) nearing to sewage inlet was lack of HZO-OTU-7 in January. Canonical correspondence analysis (CCA) showed that the pore water NO₂^? concentration, ammonium to nitrogen oxides ratio (NH₄⁺/NO_x^?) and total organic carbon to total nitrogen ratio (TOC/TN) contributed most to Anammox bacterial community structures variances. Pearson correlations analysis revealed that the Anammox bacteria abundance had positive co-relationships with TN, NH₄⁺, NO₃^? concentrations, and negative correlation with TOC/TN in porewater.     

Ammonia inhibition in anaerobic digestion: A review

Even though ammonia is an essential nutrient for bacterial growth, it may inhibit methanogenesis during anaerobic digestion process if it is available at high concentrations. Therefore, ammonia is regarded as a potential inhibitor during anaerobic digestion, particularly when dealing with complex type of substrates such as manure or the organic fraction of municipal solid waste (OFMSW). Ammonia is produced through biological degradation of nitrogenous matter. Ammonium ion (NH₄⁺) and free ammonia (NH₃) are the two principal forms of inorganic ammonia nitrogen. Both forms can directly and indirectly cause inhibition in an anaerobic digestion system. Particularly, free ammonia (FAN) is a powerful inhibitor in an anaerobic digester above threshold concentrations. Process inhibition is related to the particular characteristics of the substrate to be anaerobically digested, pH, process temperature (mesophilic or thermophilic), type of the seed sludge (inoculum), the reactor configuration and to the concentrations of ammonium and ammonia. In this paper, ammonia inhibition in anaerobic digestion systems and the recovery efforts after inhibition are discussed. Furthermore, the impacts of ammonia inhibition on the microbial population available in anaerobic digesters, namely bacteria and Archaea, are also evaluated in detail.     

Benthic decomposition of Zostera marina roots: a controlled laboratory experiment

The initial benthic decomposition of Zostera marina roots was studied in a controlled flow-through chamber experiment for 23 days. Sediment chambers without added roots served as controls. The inflowing and outflowing artificial seawater (ASW) was analyzed for O₂, ΣCO₂, urea-N, NH₄⁺ and NO₂⁻+NO₃⁻. Sediment profiles of Eh, particulate organic carbon (POC) and nitrogen, dissolved organic nitrogen (DON), dissolved free amino acids (DFAA), urea-N, NH₄⁺, DFAA and urea turnover rates, sulfate reduction and counts of total anaerobic heterotrophic bacteria and different functional groups were determined. Fluxes of O₂, ΣCO₂, urea-N and NH₄⁺ were stimulated during root decomposition compared to the unamended control. There were indications of stimulated bacterial growth based on counts of total anaerobic heterotrophic bacteria, anaerobic phosphatase utilizers, ammonifyers and sulfate reducers. Independent estimates of nitrogen and carbon incorporation into bacterial biomass during root decomposition indicate that a major fraction of the nitrogen for microbial growth was mobilized from the indigenous particulate organic nitrogen (PON) pool, whereas the energy source for bacterial growth was mainly obtained from the added eelgrass roots. Most of the nitrogen mineralized during root decomposition was incorporated into the bacterial biomass resulting in a low efflux of urea-N and inorganic nitrogen from the sediment to the water column.     

Effects of pH on ammonium uptake by Typha latifolia L.

The effects of solution pH on NH₄⁺ uptake kinetics and net H⁺ extrusion by Typha latifolia L. were studied during short-term (days) and long-term (weeks) exposure to pH in the range of pH 3.5–8.0. The NH₄⁺ uptake kinetics were estimated from depletion curves using a modified Michaelis-Menten model. T. latifolia was able to grow in solution culture with NH₄⁺ as the sole N source and to withstand a low medium pH for short periods (days). With prolonged exposure (weeks) to pH 3.5, however, the plants showed severe symptoms of stress and stopped growing. The solution pH affected NH₄⁺ uptake kinetics. The affinity for NH₄⁺, as quantified by the half saturation constant (K_1/2) and C_min (the NH₄⁺ concentration at which uptake ceases), decreased with pH. K_1/2 was increased from 7.1 to 19.2 mmol m^?3 and C_min from 2.0 to 5.7 mmol m^?3 by lowering the pH in steps from 8.0 to 3.5. V_max was, however, largely unaffected by pH (～22 μmol h^?1 g^?1 root dry weight). Under prolonged exposure to constant pH, growth rates were highest at PH 5.0 and 6.5. At pH 8.0 growth was slightly depressed and at pH 3.5 growth completely stopped. NH₄⁺ uptake kinetics were similar at pH 5.0, 6.5 and 8.0 whereas at pH 3.5 NH₄⁺ uptake almost completely stopped. The ratio between net H⁺ extrusion and NH₄⁺ uptake decreased significantly at low pH. The adverse effects of low pH on NH₄⁺ uptake kinetics are probably a consequence of a reduced H⁺-ATPase activity and/or an increased re-entry of H⁺ at low pH, and the associated decrease in the electrochemical gradient across the plasma membranes of the root cells.     

Spatial Distribution and Factors Shaping the Niche Segregation of Ammonia-Oxidizing Microorganisms in the Qiantang River,China

Ammonia oxidation is performed by both ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). However, the current knowledge of the distribution, diversity, and relative abundance of these two microbial groups in freshwater sediments is insufficient. We examined the spatial distribution and analyzed the possible factors leading to the niche segregation of AOA and AOB in the sediments of the Qiantang River, using clone library construction and quantitative PCR for both archaeal and bacterial amoA genes. pH and NH₄⁺-N content had a significant effect on AOA abundance and AOA operational taxonomy unit (OTU) numbers. pH and organic carbon content influenced the ratio of AOA/AOB OTU numbers significantly. The influence of these factors showed an obvious spatial trend along the Qiantang River. This result suggested that AOA may contribute more than AOB to the upstream reaches of the Qiantang River, where the pH is lower and the organic carbon and NH₄⁺-N contents are higher, but AOB were the principal driver of nitrification downstream, where the opposite environmental conditions were present.     

Epidemiology of wheat take-all as influenced by soil pH and temporal changes in inorganic soil N

Summary Soil pH, NH ₄ ⁺ and NO ₃ ⁻ concentrations in soil, and take-all root rot of winter wheat grown in the field were measured concurrently from sowing to anthesis in order to relate disease development to liming and N fertilization practices. Experimental variables included soil pH (5.5 and 6.0) and three N sources (NH₄NO₃, (NH₄)₂SO₄, NH₄Cl) banded with the seed at sowing in factorial combination with the same three N sources topdressed in the spring. Take-all severity was increased by increasing soil pH and by fertilization with NO ₃ ⁻ . Disease severity on crown roots increased exponentially following spring N fertilization and was affected more by soil pH and N-form than was severity on seminal roots. Grain yield ranged from 4.70 Mgha⁻¹ with spring NH₄NO₃ at soil pH 6.0 to 7.65 Mgha⁻¹ with spring NH₄Cl at soil pH 5.5. Sixty-six percent of the variability in grain yield was explained by the number of take-all infected crown roots per tiller at anthesis. Oregon Agric. Exp. Stn. technical paper no. 7707.     

Shewanella putrefaciens CN32对粘土附着态铵氮释放的影响

【目的】研究产胞外分泌物微生物Shewanella putrefaciens CN32对土壤中常见粘土矿物附着态NH_4~+的释放效果及影响机制。【方法】以吸附NH_4~+的蒙脱石、蛭石、伊蒙混层矿物和黑云母为对象,通过监测S. putrefaciens CN32作用下不同粘土释放的NH_4~+含量及过程,以及监测微生物量及释放的胞外聚合物(Extracellular Polymeric Substances,EPS)的含量变化,研究S. putrefaciens CN32作用下不同粘土矿物类型附着态NH_4~+释放的差异性。【结果】粘土矿物附着态NH_4~+含量从高到低依次为蒙脱石蛭石伊蒙混层矿物黑云母(黑云母NH_4~+吸附量极低,会在非生物作用下几乎完全释放),CN32作用下粘土附着态NH_4~+相对释放量依次为蒙脱石伊蒙混层矿物蛭石;然而,尽管CN32有效促进了粘土附着态NH_4~+释放,但释放的NH_4~+并未在溶液中大量累积,而是多被微生物同化吸收转化为生物有机氮(EPS为主)并吸附在粘土表面,且粘土对EPS的吸附能力表现为蒙脱石伊蒙混层矿物蛭石黑云母;由于粘土吸附NH_4~+及EPS都与矿物中的羟基(结构水或层间水)关系密切,推测EPS对矿物羟基的竞争吸附可能是CN32促进NH_4~+释放的重要原因之一。【结论】以上结果表明,产EPS微生物S. putrefaciens CN32能够促进各类粘土矿物的附着态NH_4~+释放,但释放的NH_4~+可以通过微生物作用转化为有机氮,从而在减少NH_4~+流失的同时增加土壤氮肥的生物可利用性,因此微生物在降低土壤氮肥流失、转化土壤氮肥污染过程中可能起到了重要作用,也揭示了深入系统地分析不同类型土壤(粘土类型不同)中粘土附着态NH_4~+在不同功能微生物作用下的迁移转化过程,是精准评估土壤氮肥施用效率及流失风险的前提之一。