Abstract  It has been less than two decades since anammox (anaerobic ammonium oxidation) coupled to nitrite reduction has been discovered. Already, this process has been recognized as an important sink for fixed nitrogen in the natural environment and has been implemented as a cost-effective ammonium removal technology. Still, little is known about the molecular mechanism of this remarkable reaction. In this mini review, we present an insight into how ammonium and nitrite are combined to form dinitrogen gas.

Abstract  Several small-scale surface flow constructed wetlands unplanted and planted (monoculture) with various macrophytes (Phragmites australis, Typha orientalis, Pennisetum purpureum, Ipomoea aquatica, and Pistia stratiotes) were established to continuously receive nitrate-contaminated groundwater. Soil characteristics and their effects on nitrate removal and soil denitrification were investigated. The results showed that planted wetland cells exhibited significantly higher (P < 0.05) nitrate removal efficiencies (70-99%) and soil denitrification rates (3.78-15.02 mu g N2O-N/g dry soil/h) than an unplanted covered wetland cell (1%, 0.11 mu g N2O-N/g/h). However, the unplanted uncovered wetland cell showed a nitrate removal efficiency (55%) lower than but a soil denitrification rate (9.12 mu g N2O-N/g/h) comparable to the planted cells. The nitrate removal rate correlated closely and positively with the soil denitrification rate for the planted cells, indicating that soil denitrification is an important process for removing nitrate in constructed wetlands. The results of nitrogen budget revealed that around 68.9-90.7% of the overall nitrogen removal could be attributed to the total denitrification. The soil denitrification rate was found to correlate significantly (P < 0.01) with the extractable organic carbon, organic matter, and in situ-measured redox potential of wetland soil, which accordingly were concluded as suitable indicators of soil denitrification rate and nitrate removal rate in nitrate treatment wetlands.

Abstract  A hydroponic experiment was carried out to determine the influence of replacing 20% of nitrate-N in nutrient solutions with 20 individual amino acids on growth, nitrate accumulation, and concentrations of nitrogen (N), phosphorus (P), and potassium (K) in pak-choi (Brassica chinensis L.) shoots. When 20% of nitrate-N was replaced with arginine (Arg) compared to the full nitrate treatment, pak-choi shoot fresh and dry weights increased significantly (P <= 0.05), but when 20% of nitrate-N was replaced with alanine (Ala), valine (Val), leucine (Leu), isoleucine (Ile), proline (pro), phenylalanine (Phe), methionine (Met), aspartic acid (Asp), glutamic acid (Glu), lysine (Lys), glycine (Gly), serine (Ser), threonine (Thr), cysteine (Cys), and tyrosine (Tyr), shoot fresh and dry weights decreased significantly (P <= 0.05). After replacing 20% of nitrate-N with asparagine (Asn) and glutamine (Gln), shoot fresh and dry weights were unaffected. Compared to the full nitrate treatment, amino acid replacement treatments, except for Cys, Gly, histidine (His), and Arg, significantly reduced (P <= 0.05) nitrate concentrations in plant shoots. Except for Cys, Len, Pro, and Met, total N concentrations in plant tissues of the other amino acid treatments significantly increased (P <= 0.05). Amino acids also affected total P and K concentrations, but the effects differed depending on individual amino acids. To improve pak-choi shoot quality, Gln and Asn, due to their insignificant effects on pak-choi growth, their significant reduction in nitrate concentrations, and their increase in macroelement content in plants, may be used to partially replace nitrate-N.

Abstract  Retinoids have been extensively studied in birds, fish and mammals where their imbalances are associated with adverse effects on growth and reproduction along with decreased embryo survival and deformities. Organochlorine compounds may alter the retinoid system but little is known about the effects of agricultural contaminants on their metabolism. In the Yamaska River project, the retinoid system in bullfrogs is monitored to investigate the possible impact of agricultural contaminants on retinoid homeostasis. Retinoids were measured in liver and plasma of male bullfrogs collected from six locations subject to increasing agricultural activity in the Yamaska River watershed. Bullfrogs living in medium and high agricultural activity areas demonstrated lower hepatic retinyl palmitate and higher hepatic retinol levels when compared to frogs associated with low contaminated sites. Changes in the concentration of hepatic esters could be related to an altered activity of REH or LRAT, enzymes respectively linked to the hydrolysis of retinyl palmitate and the esterification of retinol. A partial characterization and the analysis of liver microsomial REH and LRAT showed significantly higher hydrolysis and lower esterification activities in highly contaminated sites. Enzymatic activities seemed to be influenced by plasma DROH but not by plasma retinol. Bullfrogs from the most contaminated sites showed altered retinoic metabolism that should increase concern for frogs living in intensive agricultural areas. (C) 2008 Elsevier B.V. All rights reserved.

Abstract  The influence of environmental factors on the nitrogen fixation activity of free-living, terrestrial cyanobacteria from a high arctic area were investigated using experimental manipulations with two different types of field samples, including macroscopic sheets of Nostoc commune and soil samples with a cyanobacterial crust from a Puccinellia salt marsh. In addition, a cultured Anabaena sp. previously isolated from the salt marsh was examined. Nitrogen fixation activity was measured using the acetylene reduction method. The nitrogen fixation mainly took place in the light, but even after 12 h incubation in darkness, low activities were maintained. Phosphorus fertilization stimulated the nitrogen fixation activity, and the highest activities were obtained with about 300 mu M phosphate, both in the field samples and the cultured Anabaena sp. Ammonium (28 mM) immediately inhibited the nitrogen fixation activity of the cultured Anabaena sp, whereas 14 mM urea and 540 mu M glutamate led to a weaker and slower inhibition of the nitrogen fixation activity, showing that the cultured Anabaena sp. was able to assimilate these combined nitrogen sources. Nitrate did not have any inhibitory effect on nitrogen fixation activity, either in the field samples or in the cultured Anabaena sp. Both the field samples and the cultured Anabaena sp. showed tolerance against sodium chloride concentrations corresponding to the concentration in seawater. The temperature optimum of the nitrogen fixation activity of the cultured Anabaena sp. was about 20 degrees C.

Abstract  Chemical profiles of the Black Sea suboxic zone show a distribution of nitrogen species which is traditionally associated with denitrification, i.e. a secondary nitrite maximum associated with nitrate depletion and a N(2) gas peak. To better understand the distribution and diversity of the denitrifier community in the Black Sea suboxic zone, we combined a cultivation approach with cloning and sequencing of PCR-amplified nitrite reductase (nirS and nirK) genes. The Black Sea suboxic zone appears to harbour a homogeneous community of denitrifiers. For nirK, over 94% of the sequences fell into only three distinct phylogenetic clusters, and for nirS, a single closely related sequence type accounted for 91% of the sequences retrieved. Both nirS and nirK genes showed a dramatic shift in community composition at the bottom of the suboxic zone, but overall, nirK-based community composition showed much greater variation across depths compared with the highly uniform distribution of nirS sequences throughout the suboxic zone. The dominant nirK and nirS sequences differed at the amino acid level by at least 17% and 8%, respectively, from their nearest database matches. Denitrifying isolates recovered from the suboxic zone shared 97% 16S rRNA gene sequence similarity with Marinobacter maritimus. Analysis of the recently discovered nirS gene from the anammox bacterium Candidatus 'Kuenenia stuttgartiensis' revealed that mismatches with commonly used primers may have prevented the previous detection of this divergent sequence.

Abstract  Our understanding of the N cycle is affected by how accurately we can measure NH4+ in natural waters. Measuring NH4+ concentrations requires accounting for matrix effects (ME) that are caused by substances in the sample that attenuate or intensify the signal of the samples relative to the standards. We show that the ME calculation in the recently published fluorometric NH4+ method is mathematically incorrect, producing results that consistently underestimate NH4+ concentration as a nonlinear function of the ME. We provide the correct equation and offer an alternative approach that accounts for ME by using sample water rather than deionized water to make the standards, thereby producing a standard curve that contains the same background chemical properties as the samples. In addition, we show that the previous method for measuring a sample's background fluorescence does not include the background signal of the reagent or its interaction with the matrix constituents of the sample. We provide a new method for measuring a sample's background fluorescence that includes the background fluorescence of the sample, reagent, and their interaction. The simple changes we suggest produce more accurate and precise NH4+ measurements.

Abstract  In order to define the spatial and seasonal patterns of water and nutrient fluxes in a coastal lagoon, water residence times were estimated from salinities by using a simple salt balance model. Nutrient flows between different zones of the lagoon were measured during daily cycles in different seasons (dry: March to May; rainy: June to September; ''nortes'': October to February). The shortest residence times (140-168 days) correspond to the rainy season. During this season, large inflows of nitrate-nitrogen (NO3-), soluble reactive phosphorus (SRP), and silicon (SRSi) take place associated with groundwater discharges. NO3- and SRSi are trapped in the lagoon and ammonium and suspended particulate matter are released to the water column as water circulates through different zones of the lagoon for most of the year. During the dry season, moderate water residence times were estimated (175-201 days). Nitrogen and SRP are trapped in the inner zone of the lagoon and released in the outer zone, during this season. During the ''nortes'' season (water residence times between 240-286 days), SRP is released in the inner zone of the lagoon and a low net import from the sea takes place in the outer zone of the lagoon. In the annual budget, a net export of all the nutrients takes place from the lagoon to the sea. Mean sea level and freshwater discharges are the major factors regulating water turnover in the lagoon during all the year. Tidal and wind forces are also important in the outer zone of the lagoon during dry and ''nortes'' seasons.

Abstract  1. The possible effects on the hydrological and biogeochemical processes in the River Brede valley were studied from August 1994 to August 1996 based on measurements in piezometers installed along four transects across the river valley and two river monitoring stations located immediately upstream and downstream of the restored reach.

2. Groundwater discharge to the river varied considerably both along the restored river reach and from bankside to bankside. Comparison of the water balance derived from two river monitoring stations and the groundwater balance for the restored part of the river valley, based on Darcy's equation, indicated that a deep-lying regional aquifer probably discharges to the river in the restored area.

3. The nitrate balance for the floodplain revealed that 92 kg NO3-N ha(-1) year(-1) was removed during passage through the river valley, probably as a result of pyrite oxidation. In contrast, iron leaked from the floodplain to the river at the rate of 400 kg Fe ha(-1) year(-1).

4. A prolonged dry period, starting four months after completion of the restoration work and lasting for the remainder of the study period, makes it difficult to conclude whether the results obtained are reflective of river and floodplain restoration. Nitrate concentration measurements at the two river monitoring stations revealed no overall significant changes when comparing a pre-restoration period with two similar post-restoration periods. However, comparison of nitrate losses from an upstream control catchment and the restored reach catchment indicated enhanced removal of nitrate along the restored river reach during a three month period of flooding immediately following completion of restoration work (January to March 1995). (C) 1998 John Wiley & Sons, Ltd.

Abstract  Although good progress has been made to dissect and better understand both the main steps and the regulation of inorganic nitrogen assimilation in higher plants, the role of alternative metabolic pathways which are potentially able to incorporate ammonium into organic molecules is still not fully understood. One of them is the reaction catalysed by the mitochondrial enzyme glutamate dehydrogenase (NAD(H)-GDH, EC 1.4.1.2) which is either able to incorporate ammonium into 2-oxoglutarate to form glutamate or to function in the opposite direction to oxidise glutamate. Although it has been clearly demonstrated by the means of N-15- or C-13-labelling experiments that the later reaction occurs in the cell, it has been argued that under certain physiological conditions, when the ammonium concentration reaches a certain threshold. the enzyme is able to function in the aminating direction. More recently, it has been found that in grapes, a high proportion of the protein is located in the mitochondria of the phloem companion cells and that a significant amount of enzyme is present in the cytosolic fraction of senescing flowers. Using cytoimmunochemistry, we confirmed in the present study that, in other higher plant species, GDH protein is localised in the mitochondria of the phloem companion cells and in the cytosol of senescing organs or tissues. These findings open, therefore, new perspectives toward a better understanding of the function of GDH, particularly in relation to stress and plant development. Both transgenic studies per-formed in the past and the quantitative genetic approach presented in this paper strongly suggest that the reaction catalysed by NAD(H)-GDH is of major importance in the control of plant growth and productivity. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Abstract  A series of nutrient enrichment grow-out experiments were conducted in Monterey Bay, California. to assess the relative importance of nutrient availability on growth rates and biomass accumulation of the natural phytoplankton assemblage, During a series of four cruises, enrichments with nitrogen (as nitrate and ammonium), silicate, and Guillard's "f" medium consistently demonstrated that the phytoplankton were nitrogen limited, and that the addition of nitrate provided the most potential for growth and biomass accumulation. Contrary to previous reports for Monterey Bay, silicate was not found to limit the accumulation of biomass in this diatom-dominated system, although there was evidence that silicate additions can modify the uptake rates of the biomass-limiting substrate (nitrogen). We conclude that silicate is a regulating, but not limiting, nutrient in this study site. Our results are consistent with both the "shift-up" and "detrital" explanations for changes in specific uptake rates, During upwelling periods (May, September) when the biomass was dominated by phytoplankton, a shift-up type physiological response was observed that was not dependent on the uptake normalization procedure (e,g. chlorophyll versus PN), During the winter months (March, November), characterized by deep mixing, low light, and higher detrital N levels, the apparent shift-up response could be attributed to a change in the PN:Chl ratios and alleviation of light limitation due to the stable light regime provided by the enclosures. (C) 2000 Elsevier Science Ltd. All rights reserved.

Abstract  Hyporheic exchange plays a key role in the biogeochemical evolution of water and in ecosystem functioning at the local, reach, and watershed scales. Residence time is a fundamental metric to describe the possible transformation taking place in this exchange zone. With this in mind, we use a simple conceptual model to explore the residence time distributions (RTDs) of sinuosity-driven hyporheic zones (HZs) and to discriminate the individual effect of sinuosity (sigma), valley slope (J(x)), hydraulic conductivity (K), aquifer dispersivity (alpha(L)), and the biogeochemical timescales ( BTSs) that characterize the degradation of dissolved organic carbon in these hydrologic systems. We find that RTDs are characterized by one early mode and a late time power law behavior. For a given aquifer dispersivity, the shape of these distributions is stretched or compressed by changes in J(x), K, and sigma, having a strong influence on the net biogeochemical transformations within the HZ. Using BTSs proposed in previous studies and sensitivity analyses, we show the potential of sigma, J(x), and K to classify meander HZs as net sinks of nitrates or only modulators of the residence times in the subsurface where nitrate reduction is negligible. These findings can be used as predictive tools to quantify the potential of meanders as biogeochemical reactors at the watershed scale with the aid of remote sensing data and GIS processing techniques. These tools can guide experimental design, suggesting important locations to visit, sample, and/or instrument. Also, hyporheic restoration projects can use them for initial site selection and design of channel modifications.

Abstract  In the next decades, many soils will be subjected to increased drying/wetting cycles or modified water availability considering predicted global changes in precipitation and evapotranspiration. These changes may affect the turnover of C and N in soils, but the direction of changes is still unclear. The aim of the review is the evaluation of involved mechanisms, the intensity, duration and frequency of drying and wetting for the mineralization and fluxes of C and N in terrestrial soils. Controversial study results require a reappraisal of the present understanding that wetting of dry soils induces significant losses of soil C and N. The generally observed pulse in net C and N mineralization following wetting of dry soil (hereafter wetting pulse) is short-lived and often exceeds the mineralization rate of a respective moist control. Accumulated microbial and plant necromass, lysis of live microbial cells, release of compatible solutes and exposure of previously protected organic matter may explain the additional mineralization during wetting of soils. Frequent drying and wetting diminishes the wetting pulse due to limitation of the accessible organic matter pool. Despite wetting pulses, cumulative C and N mineralization (defined here as total net mineralization during drying and wetting) are mostly smaller compared with soil with optimum moisture, indicating that wetting pulses cannot compensate for small mineralization rates during drought periods. Cumulative mineralization is linked to the intensity and duration of drying, the amount and distribution of precipitation, temperature, hydrophobicity and the accessible pool of organic substrates. Wetting pulses may have a significant impact on C and N mineralization or flux rates in arid and semiarid regions but have less impact in humid and subhumid regions on annual time scales. Organic matter stocks are progressively preserved with increasing duration and intensity of drought periods; however, fires enhance the risk of organic matter losses under dry conditions. Hydrophobicity of organic surfaces is an important mechanism that reduces C and N mineralization in topsoils after precipitation. Hence, mineralization in forest soils with hydrophobic organic horizons is presumably stronger limited than in grassland or farmland soils. Even in humid regions, suboptimal water potentials often restrict microbial activity in topsoils during growing seasons. Increasing summer droughts will likely reduce the mineralization and fluxes of C and N whereas increasing summer precipitation could enhance the losses of C and N from soils.

Abstract  Ultrafine spherical yttrium aluminum garnet (YAG) powders have been synthesized via homogeneous precipitation method using urea as the precipitant. The precursor powders were calcinated at 1000 degrees C or 1100 degrees C for 4 hrs and then were studied by means of FE-SEM, XRD, FT-IR and TG-DTA. The result shows that the amount of ammonium sulfate has a significant effect on morphology and particle size of powders. Pure phase and spherical YAG particles with 350 nm in diameter can be obtained when the molar ratio of ammonium sulfate to aluminum nitrate is about 0.75 and the concentration of the metallic ions is 0.008M.

Abstract  In this work, we have developed a new method to synthesize a Fe3O4@graphene (Fe3O4@GN) composite. First, the precursor was synthesized through the decomposition of ferric nitrate in the presence of graphene oxide in the mixed solvent of CO2-expanded ethanol. Then, the precursor was converted to the Fe3O4@GN composite via thermal treatment in N-2 atmosphere. With the help of the CO2-expanded ethanol, Fe3O4 nanoparticles were coated on the surface of GN completely and uniformly with high loading. However, it is difficult to load Fe3O4 particles onto the surface of GN and most of the Fe3O4 particles were deviated away from GN and aggregated to form larger units in pure ethanol. When used as anode for Li-ion batteries (LIBs), the Fe3O4@GN composite with a graphene content of 25 wt% synthesized in CO2-expanded ethanol manifested excellent charge-discharge cycling stability and rate performance compared with the sample synthesized in ethanol. Such improved electrochemical performances should be attributed to the intimate contact between the GN and Fe3O4 nanoparticles in the composite. Since the present method does not need tedious pre-treatment, surfactant, or precipitate, it is a green or sustainable technology and the solvents could be recycled easily after simple phase separation. This facile method can be extended to the synthesis of other metal oxide composites, which are expected to have good performance as anode materials for LIBs and other applications.

Abstract  Turfgrasses are a promising means of cultivation for covering roof tops of buildings. Their low and frequently prostrate growth, their ability to provide total surface coverage, the increased tolerance of specific species to several stress factors such as drought, heat, solar irradiance, and air pollution make them good candidates for green roof plant material. In intensive green roof systems the selection of the substrate is of major importance since it was found to affect Festuca arundinacea growth while at the same time contributes to the roof weight. The effort to minimize the load applied onto the building necessitates the use of substrate amendments that are lightweight and usually coarse textured. However special care should be given to the environmental fate of the agrochemicals applied on these coarse textured substrates since nitrates were found to leach in excess from a sandy loam soil amended with perlite (30:70% v/v mix). In addition metalaxyl-m leached from the substrates in a manner that was reversely proportional to the amount of organic matter in the substrate. In extensive green roofs trials that included four different substrates with variable depth (7.5 and 15 cm) and two irrigation regimes (high and low) establishment rate of Zoysia matrella 'Zeon' was generally improved by substituting peat with compost in the substrates but performed poorly under water stress conditions. The stress was alleviated by increasing substrate depth from 7.5 to 15 cm. Further research is necessary to establish rigid standards for the use of turfgrasses on green roofs.

Abstract  Effects of simultaneous treatment with NaNO2 and butylated hydroxyanisole, catechol, or 3-methoxycatechol were examined in a rat multiorgan carcinogenesis model. Groups of 15 animals were given a single i.p. injection of 100 mg/kg of body weight diethylnitrosamine, 4 i.p. injections of 20 mg/kg of body weight N-methylnitrosourea, 4 s.c. injections of 40 mg/kg of body weight dimethylhydrazine, p.o. treatment with 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine in the drinking water for the first 2 weeks and p.o. treatment with 0.1% 2,2'-dihydroxy-di-n-propylnitrosamine in the drinking water for the next 2 weeks of the initial 4-week initiation period. Starting 3 days after the completion of these carcinogen treatments, animals were given diets containing 2% butylated hydroxyanisole, 0.8% catechol, 2% 3-methoxycatechol, or basal diet either alone or in combination with 0.3% sodium nitrite until week 28, when complete autopsy was performed. Histological examination showed that NaNO2 strongly enhanced development of forestomach lesions but inhibited that of glandular stomach lesions in rats simultaneously given catechol or 3-methoxycatechol with or without prior carcinogen exposure. 3-Methoxycatechol promoted esophageal carcinogenesis either with or without NaNO2, but promoting effects of catechol were evident only in the presence of NaNO2. In addition, treatment with NaNO2 after carcinogen exposure enhanced forestomach carcinogenesis. These results indicate that NaNO2 can modify phenolic antioxidant-induced cell proliferation and/or carcinogenesis, particularly in the upper digestive tract.

Abstract  HEEP COPYRIGHT: BIOL ABS. CARCINOGEN

Abstract  The formation of several photoproducts was observed in the phototransformation of 2-phenylphenol (II) induced by excitation of nitrate ions: 2-hydroxy-3- nitrobiphenyl (IV), 2-hydroxy-5-nitrobiphenyl (VI), phenylhydroquinone (VII), phenylbenzoquinone (VIII) and 2-hydroxydibenzofuran (M). The photolysis of nitrate ions leads to the formation of hydroxyl radicals and nitrogen dioxide. W results from the oxidation of II by hydroxyl radicals. VII is oxidized into WI which is photocyclised into IX. The formations of IV and Vl are enhanced in acidic solution. They are attributed to a reaction of a nitrogen oxide, NO2 or N2O4. This reaction competes with the disproportionation into nitrite and nitrate ions. The accelerated formation of IV and VI can be attributed to the excitation of nitrite ions.

Abstract  BACKGROUND: Few recent studies examined acute effects on health of individual chemical species in the particulate matter (PM) mixture, and most of them have been conducted in North America. Studies in Southern Europe are scarce. The aim of this study is to examine the relationship between particulate matter constituents and daily hospital admissions and mortality in five cities in Southern Europe.

METHODS: The study included five cities in Southern Europe, three cities in Spain: Barcelona (2003-2010), Madrid (2007-2008) and Huelva (2003-2010); and two cities in Italy: Rome (2005-2007) and Bologna (2011-2013). A case-crossover design was used to link cardiovascular and respiratory hospital admissions and total, cardiovascular and respiratory mortality with a pre-defined list of 16 PM10 and PM2.5 constituents. Lags 0 to 2 were examined. City-specific results were combined by random-effects meta-analysis.

RESULTS: Most of the elements studied, namely EC, SO4(2-), SiO2, Ca, Fe, Zn, Cu, Ti, Mn, V and Ni, showed increased percent changes in cardiovascular and/or respiratory hospitalizations, mainly at lags 0 and 1. The percent increase by one interquartile range (IQR) change ranged from 0.69% to 3.29%. After adjustment for total PM levels, only associations for Mn, Zn and Ni remained significant. For mortality, although positive associations were identified (Fe and Ti for total mortality; EC and Mg for cardiovascular mortality; and NO3(-) for respiratory mortality) the patterns were less clear.

CONCLUSIONS: The associations found in this study reflect that several PM constituents, originating from different sources, may drive previously reported results between PM and hospital admissions in the Mediterranean area.

Abstract  The oxidation of elemental palladium at 100 °C in a mixture of fuming nitric acid and a pyridine-SO3 complex leads to the anhydrous nitrate Pd(NO3 )2 (monoclinic, P21 /n, Z=2, a=469.12(3) pm, b=593.89(3) pm, c=805.72(4) pm, β=105.989(3)°, V=215.79(2) Å(3) ). The Pd(2+) ions are in square-planar coordination with four monodentate nitrate groups which are connected to further palladium atoms, leading to a layer structure. The reaction of elemental palladium with a mixture of fuming nitric acid and methanesulfonic acid at 120 °C leads to single crystals of Pd(CH3 SO3 )2 (monoclinic, P21 /n, Z=2, a=480.44(1) pm, b=1085.53(3) pm, c=739.78(2) pm, β=102.785(1)°, V=376.254(17) Å(3) ). Also in this structure the Pd(2+) ions are in square-planar coordination with four monodentate anions; however, the connection to adjacent palladium atoms leads to a chain-type structure. The thermal decomposition of the compounds has been investigated by means of DSC/TG measurements. Furthermore, IR and Raman spectra have been recorded, and an assignment of the observed vibrational frequencies has been carried out based on theoretical investigations.

Abstract  HEEP COPYRIGHT: BIOL ABS. The activity of autotrophic nitrifying bacteria, responsible for transformation of ammonia to nitrites, was evaluated in samples of water from the Venice lagoon. Quantification of this activity would be useful in understanding the self-purifying capacity of these waters, in which ammonia concentrations are often quite high. The sampling stations are representative of 3 different hydrological and biological situations. Samples were collected at high and low tide over a period of 13 mo. Activity was assayed measuring the amount of nitrite produced in cultures at different time intervals. The data were subjected to principal components analysis and related to some hydrobiological parameters. Autotrophic bacterial activity is greater in inner water (high nutrient concentrations, low salinity); this process occurs only occasionally in waters with characteristics of a marine coastal zone (low nutrient concentration, high salinity). The results showed a non-linear relationship between bacterial activity and inorganic N concentration in the waters. Though nitrifying activity was usually present at significant levels, it was judged to be inadequate to rapidly oxidize the very high concentrations of ammonia sometimes encountered in these waters.

Abstract  The discovery of ammonia-oxidizing archaea (AOA) of the phylum Thaumarchaeota and the high abundance of archaeal ammonia monooxygenase subunit A encoding gene sequences in many environments have extended our perception of nitrifying microbial communities. Moreover, AOA are the only aerobic ammonia oxidizers known to be active in geothermal environments. Molecular data indicate that in many globally distributed terrestrial high-temperature habits a thaumarchaeotal lineage within the Nitrosopumilus cluster (also called "marine" group I.1a) thrives, but these microbes have neither been isolated from these systems nor functionally characterized in situ yet. In this study, we report on the enrichment and genomic characterization of a representative of this lineage from a thermal spring in Kamchatka. This thaumarchaeote, provisionally classified as "Candidatus Nitrosotenuis uzonensis", is a moderately thermophilic, non-halophilic, chemolithoautotrophic ammonia oxidizer. The nearly complete genome sequence (assembled into a single scaffold) of this AOA confirmed the presence of the typical thaumarchaeotal pathways for ammonia oxidation and carbon fixation, and indicated its ability to produce coenzyme F420 and to chemotactically react to its environment. Interestingly, like members of the genus Nitrosoarchaeum, "Candidatus N. uzonensis" also possesses a putative artubulin-encoding gene. Genome comparisons to related AOA with available genome sequences confirmed that the newly cultured AOA has an average nucleotide identity far below the species threshold and revealed a substantial degree of genomic plasticity with unique genomic regions in "Ca. N. uzonensis", which potentially include genetic determinants of ecological niche differentiation.