Microbial Nitrate Reduction Research Articles

Role of Oxides of Nitrogen in Tobacco-Specific Nitrosamine Formation in Flue-Cured Tobacco

Abstract Tobacco is known to contain a class of nitrosamines known as tobacco-specific nitrosamines or TSNA. Nitrosation of naturally occurring tobacco alkaloids is commonly accepted as the mechanism of TSNA formation in tobacco. Because green and freshly harvested tobaccos are virtually free of TSNA, formation and accumulation of TSNA are generally considered to occur during the curing process. Most recent hypotheses have focused on microbial reduction of nitrate to nitrite and other oxides of nitrogen (NOcompounds) that react with tobacco alkaloids to form TSNA during curing. This natural microbial process remains the prevalent hypothesis for TSNA formation in burley and other air-cured tobaccos. However, a different mechanism for the formation of TSNA in flue-cured tobacco, independent of microbial activity, is documented in this paper. It is common practice to flue-cure Virginia or blonde tobacco in bulk barns that incorporate forced air ventilation and temperature control. For the last thirty-five years, many modern bulk barns in North America generally have used liquid propane gas (LPG) with direct-fired burners that exhaust combustion gases directly into the barn where the tobacco is exposed to those gases. Our studies indicate that LPG combustion by-products in the exhaust stream, namely NO, react with naturally occurring tobacco alkaloids to form TSNA. Heat exchange curing methods preclude exposure of the tobacco to combustion gases and by-products, thereby eliminating this significant source of TSNA formation, without degrading leaf quality or smoking character. Research findings from 1998 and 1999 are presented to demonstrate the role of NOgases in TSNA formation and the significance of direct-fired curing as a primary source of TSNA formation in flue-cured tobacco. Also, data from an extensive barn conversion program in 2000, which resulted in a 94% average reduction in TSNA levels in cured flue-cured leaf, are presented.

Effect of emersion and immersion on the porewater nutrient dynamics of an intertidal sandflat in Tokyo Bay

Porewater nutrient dynamics during emersion and immersion were investigated during different seasons in a eutrophic intertidal sandflat of Tokyo Bay, Japan, to elucidate the role of emersion and immersion in solute transport and microbial processes. The water content in the surface sediment did not change significantly following emersion, suggesting that advective solute transport caused by water table fluctuation was negligible. The rate of change in nitrate concentration in the top 10 mm of sediments ranged from −6.6 to 4.8 μmol N l −1 bulk sed. h −1 during the whole period of emersion. Steep nutrient concentration gradients in the surface sediment generated diffusive flux of nutrients directed downwards into deeper sediments, which greatly contributed to the observed rates of change in porewater nutrient concentration for several cases. Microbial nitrate reduction within the subsurface sediment appeared to be strongly supported by the downward diffusive flux of nitrate from the surface sediment. The stimulation of estimated nitrate production rate in the subsurface layer in proportion to the emersion time indicates that oxygenation due to emersion caused changes in the sediment redox environment and affected the nitrification and/or nitrate reduction rates. The nitrate and soluble reactive phosphorus pools in the top 10 mm of sediment decreased markedly during immersion (up to 68% for nitrate and up to 44% for soluble reactive phosphorus), however, this result could not be solely explained by molecular diffusion.

Effects of mouth cleansing on the levels of exhaled nitrous oxide in young and older adults

Nitrous oxide (N 2O) is produced by denitrification, i.e. by microbial reduction of nitrate (NO 3 −). Our previous studies have established an analytical method for demonstrating the existence of N 2O in exhaled air, and we showed that levels of N 2O in exhaled air increase with age after puberty. However, the source of this change and its biological significance are still unclear. The purpose of this study was to examine whether the oral microorganisms are the main source of N 2O. We measured exhaled N 2O in 35 young adults (aged 19–29 years) and 34 older adults (aged 61–79 years) before and after mouth cleansing. N 2O was measured using an infrared-photoacoustic analyzer equipped with an optical filter (UA0985, 2215 cm −1). Participants were classified as producers and non-producers according to the levels of exhaled N 2O relative to the level in the atmosphere. N 2O production differed significantly between the young adult producers and the older adult producers. Mouth cleansing resulted in an immediate reduction in exhaled N 2O in both groups. We only found seven (20.0%) producers in the young, and 32 (94.1%) producers in the older after mouth washing. The differences before and after mouth cleansing were significant in both groups ( P<0.01 in the young and P<0.05 in the older). The oral cavity is a major source of N 2O. However, since approximately half-levels of N 2O were still observed in exhaled air after mouth cleansing, there may exist another N 2O source in the human body.

Microbiologically influenced stress corrosion cracking failure of admiralty brass condenser tubes in a nuclear power plant cooled by freshwater

The failure of admiralty brass condenser tubes in a nuclear power plant was investigated. Metallurgical analyses had indicated that stress corrosion cracking (SCC) could have caused the failure. Studies were carried out to see if bacteria could have played a role in bringing about the conditions which resulted in SCC of the tubes. Cooling water (Ranapratap Sagar lake, Kota, Rajasthan) quality and biofilm formation were monitored by analysing various physical, chemical, biochemical and biological parameters. Metal coupons were exposed online in the cooling water system to assess the microbial growth on the coupon surface by SEM. Corrosion rates were assayed by weight loss and corrosion products were analysed by XRD and ESCA. The study revealed the microbial reduction of nitrate to ammonia (estimated to be of the order of 5.8 mg l −1 at the substratum–biofilm interface) which resulted in SCC of the admiralty brass tubes.

Nitrogen isotope indicators of seasonal source variability to groundwater

A nitrogen isotope study of soil water and groundwater in southern Indiana, USA, in 1991–1992 demonstrated considerable variations in nitrate degradation processes compared to an earlier investigation in 1986–1987. Although N-fertilizers were applied in May 1991, the δ15N values in soil water decreased in February 1992, indicating its delayed release into the system after substantial rainfall. The δ15N values of groundwater decreased from +12.3‰ in November 1991 to +11.3‰ in February 1992, and to +7.5‰ in March 1992. The increased residence time of nitrate in the soil resulted in increased denitrification, ammonia volatilization and plant uptake, and reduced threat to the groundwater quality. The 1986–1987 study in the area reported that excessive rainfall during the summer rapidly transported the nitrate to deeper horizons and drastically reduced volatilization and microbial reduction of nitrate, thus increasing the immediate threat to the groundwater quality in the area. The present study demonstrated that nitrogen isotopic signatures can be used to determine the effects of local soil type, rainfall, and land-use practices on the fate of nitrate in the subsurface.

Measuring Nitrous Oxide in Exhaled Air by Gas Chromatography and Infrared Photoacoustic Spectrometry

Nitrous oxide (N2O) is a relatively stable compound, present at ∼310 nL/L in the atmosphere. It is produced predominantly by microbial reduction of nitrate (NO3−). This process, called denitrification, is the conversion of nitrate to gaseous nitrogen compounds, resulting in a product of nitrogen (N2) or nitrous oxide under most conditions. Many kinds of denitrifying bacteria have been isolated from the human oral cavity, upper respiratory tract, and alimentary tract (e.g.) (1)(2)(3)(4), including pathogens of Pseudomonas , Neisseria , and Campylobacter. Taking these studies into consideration, it is proper to assume that the concentrations of N2O in exhaled air exceed those in the atmosphere, although no studies have been published related to N2O in exhaled air. The purpose of this study is to establish an analytical method for detection of N2O in exhaled air by using gas chromatography (GC) and infrared-photoacoustic spectrometry …

Degradation of ethylenethiourea (ETU) in oxic and anoxic sandy aquifers.

Ethylenethiourea is an important degradation product of ethylenebisdithiocarbamate fungicides, which are widely used in different kinds of crops. The ethylenebisdithiocarbamate group includes maneb, zineb and mancozeb. The ethylenebisdithiocarbamates are not highly toxic and degrade rapidly in the presence of moisture and oxygen, forming different compounds. One of these is the polar ethylenethiourea, which is relatively stable. Thus, this compound appears to be a potential contaminant for groundwater. Batch experiments were carried out under biotic as well as abiotic conditions to study the degradation dependence of concentration, temperature and organic matter. The decomposition of ethylenethiourea under abiotic conditions was found to be less than 5% of the degradation under biotic conditions. Further, ethylenethiourea showed to be stable over a period of 150 days at 20 degrees C in tap water as well as in batch with soil sterilized with NaN3. The degradation of ethylenethiourea depends on the concentration in the water implying first order reaction kinetics. The microbial degradation of ethylenethiourea is highly temperature dependent with aerobic Q10 between 2.9 and 4.2, and an anaerobic between 2.1 and 2.5. A minor increase in degradation rates was observed by application of nitrate and manure to the batches. The experiments show extremely complete degradation of ethylenethiourea in the presence of microbial nitrate reduction with pyrite which occurs in deeper parts of the aquifers.

Abiotic Nitrate Reduction to Ammonium: Key Role of Green Rust

Leaching of nitrate from soils and sediments can be reduced in anoxic environments due to denitrification to N2O/N2 or reduction of nitrate to ammonium. While microbial dissimilatory reduction of nitrate to ammonia is well known, it is shown here that this conversion can also proceed at appreciable rates in abiotic systems in the presence of green rust compounds [FeII4FeIII2(OH)12SO4·yH2O]. In the reaction nitrate is stoichiometrically reduced to ammonium, and magnetite (Fe3O4) is the sole Fe-containing product. At a constant pH of approximately 8.25 and 25 °C, the rate expression is given as: d[NH4+]/dt = k[Fe(II)]GR[NO3-],where k = 4.93 × 10-5 ± 0.39 × 10-5 L mol-1 s-1. In anoxic soils and sediments, this reaction may also lead to a nitrate to ammonium reduction, at rates of similar magnitude or even higher than microbial reduction rates. Hence green rust should be considered a possible important reductant for nitrate reduction to ammonium in subsoils, sediments, or aquifers where microbially mediated reduction rates are small.

CAMBRIDGE PRIZE LECTURE NITRATE REDUCTION AND N-NITROSATION IN BREWING*

Microbial nitrate reduction is the principal route of N-nitrosamine formation in brewing. The role of different groups of brewery microorganisms possessing different mechanisms of nitrate reduction is discussed together with the influence these have on N-nitrosamine levels. The relative importance of microbial and chemical catalysis of N-nitrosamine formation in beer production is also considered and reviewed in the light of recent data from other food processing industries.

Inhibitory effects of sulphur compounds, copper and tungsten on nitrate reduction by mixed rumen micro-organisms.

1. The inhibitory effects of inorganic and organic sulphur-containing compounds, copper and tungsten on nitrate reduction by mixed rumen micro-organisms were investigated in two in vitro studies. 2. Coarsely strained rumen fluid from nitrate-adapted (Expt 1) or non-adapted (Expt 2) Suffolk Down wethers maintained on lucerne (Medicago sativa) cubes was used as an inoculum. In Expt 1, anaerobic incubation was carried out for 24 h for each medium supplemented with 10 mM-sodium nitrate and the following chemicals: 0, 1, 2, 3, 5, 8 and 10 mM-sodium sulphide, 1 and 10 mM-sodium sulphite, 1 and 10 mM-sodium sulphate, 1 and 10 mM-L-cysteine, 1 and 10 mM-DL-methionine, 1 mM-sodium tungstate and 1 mM-copper sulphate. In Expt 2, 1 and 10 mM-Na2S, 1 and 10 mM-L-cysteine, 1 mM-Na2WO4, and 1 mM-CuSO4 were added to incubation media to test for chemical inhibition of microbial reduction of nitrate. 3. In Expt 1, the amount of nitrite formed decreased with increasing concentration of sulphide-S added. The additions of L-cysteine, W and Cu suppressed nitrite formation in media from both nitrate-adapted and non-adapted sheep. 4. In contrast to the effects of sulphide, L-cysteine and W counteracted, to some degree, nitrate-induced reduction of volatile fatty acid (VFA) production. Addition of Cu to the media resulted in a further depression of VFA production.

FK409, a novel vasodilator isolated from the acid-treated fermentation broth of Streptomyces griseosporeus. III. Reaction mechanism and synthesis.

FK409 (1), a novel vasodilator, is a semi-artificial fermentation product of Streptomyces griseosporeus No. 16917, which was cultured in a medium containing nitrate. And the acid-treatment of the broth is essential for the generation of FK409. FK409 was considered to be formed via a novel synchronous nitrosation-nitration reaction of FR-900411 (2) which was produced by the strain as a precursor of FK409. The conversion of FK-900411 to FK409 proceeded under acidic conditions with nitrite formed by microbial reduction of nitrate. Total synthesis of FK409 was achieved starting from (E)-2-ethyl-2-butenal (3) via a nitrosation reaction of FR-900411 (2) as a key step.

Coidingham Loch, S.E. Scotland

SUMMARY. 1. Coidingham Loch (Berwickshire. Scotland) (area. 8.4 ha, mean depth 2.9 m, max. depth 12.3 m) belongs to Hakansson's convex shape category. It lies in a basin of Silurian Greywackes rock within 0.25 km of coastal sea cliffs (c. 133 m a.s.l.). The theoretical hydraulic replacement time is 3.17 years.2. The loch stratifies intermittently in summer. Fluctuations in oxygen concentration generally correspond to spells of mixing and stratification; low values of 10% saturation occur at the bottom.3. The sum of the concentrations of major cations (Na+, K+, Ca2+, Mg2+) is in accordance with measured conductivities ranging between 380 μS cm−1 and 420 μS cm−1 (k.25). The ratios (by equivalents) of Na+/Cl− (0.04) are similar to those in sea‐water, whilst values for Ca+2+/Cl− (0.85–1.01) and Mg2+/Cl− (0.79–0.88) reflect the bedrock.4. Nitrate concentrations were lowest (&lt;0.05 mg N1−1) in summer following losses from the column of 107 mg N m−2 1−1, a rate corresponding well with published figures on microbial nitrate reduction. Nitrate increased at a rate of 8μg N I−1 d−1 to a winter maximum of 1.55 mg N I−1. Mass balance calculations show that if this rise is attributed to run‐off from surrounding land, a loss rate of 11.1 kg N ha−1 yr−1 would be required; this value is also commensurate with published figures.5. Changes in phosphorus and factors controlling them contrast markedly with those of nitrate. The minimum concentration of 55 μg total P l−1 (mainly in soluble reactive form) occurs in spring. An increase to the maximum ofc. 300 μg l−1 in summer is sustained mainly by release from the sediments at a regular rate of 3 μg P l−1 d−1 (8.7 mg m−2 d−1). Adsorption by the sediments is considered to be the major process accounting for autumnal losses of phosphorus of 2.6 mg P M−2d−1.6. Silica showed a less regular seasonal pattern, but varied some 45‐fold with a maximum of 2.25 mg SiO2, l−1 in August.

Interaction between pectin and rat hindgut microflora.

The contents of the lower alimentary tract from rats fed a semisynthetic, pectin-supplemented diet showed increased nitrate reductase activity and an increase in the amount of luminal contents in the intestine and cecum. Nitrate reductase activity was associated with the insoluble fraction of the gut contents which was sedimented by centrifugation (5,100 X g,20 min) and was abolished after treating the animals with streptomycin, neomycin, and bacitracin for 7 days. The pectin-dependent increase in cecal size and microbial nitrate reduction were reversed when animals were transferred from a pectin-supplemented onto a control semisynthetic diet. Polygalacturonic acid (pectic acid) was without effect on either cecal size or cecal microbial nitrate reductase activity. The studies demonstrate that pectin influences microbial metabolism in the alimentary tract.

Nitrate reductase activity and nitrite levels in the saliva of habitual users of various tobacco products

Nitrite found in human saliva is the product of the microbial reduction of nitrate circulating through the salivary glands. Saliva samples were collected under controlled conditions from volunteers who were habitual users of different types of tobacco products (tobacco chewers, cigarette smokers, bidi smokers and masheri users) and from controls. The saliva samples were analysed for nitrite levels and for nitrate reductase activity spectrophotometrically. Samples were collected from two different areas, Bombay (urban) and Ghodegaon (rural). Salivary nitrite levels in the control groups ranged from 1·6 ppm in Ghodegaon to 11 ppm in Bombay. The nitrite levels of the masheri-using groups from both locations and of the tobacco-chewing group from Bombay were significantly higher than those of the controls. A number of volunteers showed undetectable levels of salivary nitrate reductase. Volunteers who chewed tobacco or used masheri had higher levels of nitrate reductase activity than the controls. However, there did not seem to be any clear correlation between nitrite levels and nitrate reductase activity in the saliva.

Immobilized cells in microbial nitrate reduction

The microorganismPseudomonas denitrificans was immobilized in alginate. These immobilized cells were capable of reducing 0.8 mg NO 3 (-) /min/g wet weight of cells.

Nitrate reductase activity and nitrite levels in the saliva of habitual users of various tobacco products

Nitrite found in human saliva is the product of the microbial reduction of nitrate circulating through the salivary glands. Saliva samples were collected under controlled conditions from volunteers who were habitual users of different types of tobacco products (tobacco chewers, cigarette smokers, bidi smokers and masheri users) and from controls. The saliva samples were analysed for nitrite levels and for nitrate reductase activity spectrophotometrically. Samples were collected from two different areas, Bombay (urban) and Ghodegaon (rural). Salivary nitrite levels in the control groups ranged from 1·6 ppm in Ghodegaon to 11 ppm in Bombay. The nitrite levels of the masheri-using groups from both locations and of the tobacco-chewing group from Bombay were significantly higher than those of the controls. A number of volunteers showed undetectable levels of salivary nitrate reductase. Volunteers who chewed tobacco or used masheri had higher levels of nitrate reductase activity than the controls. However, there did not seem to be any clear correlation between nitrite levels and nitrate reductase activity in the saliva.

Comparison of Effects of Nitrate, Nitrite, and Nitric Oxide on Reduction of Nitrous Oxide to Dinitrogen by Soil Microorganisms

AbstractRecent work has shown that nitrate inhibits reduction of nitrous oxide (N2O) to dinitrogen (N2) by soil microorganisms under anaerobic conditions. Studies to investigate the possibility that this inhibition is caused by nitrite or nitric oxide (NO) formed through microbial reduction of nitrate showed that both NO and nitrite inhibit reduction of N2O to N2 by soil microorganisms under anaerobic conditions (helium atmosphere) but that the inhibitory effect of NO on N2O reduction is much smaller than the effects of nitrate or nitrite. Comparison of the effects of nitrate, nitrite, and mixtures of nitrate and nitrite on reduction of N2O to N2 by soils incubated under He showed that nitrate per se inhibits N2O reduction and did not confirm a recent suggestion that the inhibitory effect of nitrate on N2O reduction is due to nitrite formed through microbial reduction of nitrate.

Microbial Nitrate Reduction in Freshwater Sediments

Nitrate reductase activity was three to four orders of magnitude greater in freshwater sediments than in the overlying water. Viable (most probable number) counts of denitrifiers provided sufficient resolution to distinguish between anoxic and surface waters, and between these and sediments, but did not correlate with differences between or within sediment cores. Activity within the sediment depended on the electrode potential (E h) profile, which in turn was related to the degree of turbulence and oxygen concentration in the overlying water. Sediments from the littoral zone or those in contact with oxygenated water were oxidizing to a depth of 5 to 10 mm and the E h then decreased rapidly. In these sediments nitrate reductase activity was often at its maximum at a depth of 10 to 15 mm, on the E h gradient, and coincided with a mean E h value of 210 mV. Under reducing conditions theE h gradient moved upwards and nitrate reductase activity was greatest at thesediment-water interface. These observations were supported by analyses of the nitrogen gas content of the sediments. Inhibition of the enzymes with chlorate indicated that approximately 60 % ofthe activity was dissimilatory in sediments where the E h was greater than+100 mV, and that this proportion increased to more than 90 % when the E h fell below + 50 mV. Although the evidence was not conclusive, there was also some indication that nitrate reductase activity in aerobic surface sediments was greater in the larger (&gt; 250 μm) particle size fraction, which suggested that these particles might act as microsites for nitrate respiration.

Naturally occuring nitrate/nitrite in foods

AbstractA review of the occurrence of nitrate in unprocessed foods showed that high concentrations are frequently found in vegetables. Spinach and lettuce commonly exceed 1000 parts/106 nitrate while, of the root vegetables, beets, turnips and radishes are similarly rich in nitrate. In general, the pulses contain less nitrate than leaf and root vegetables, and most fruits contain little nitrate. Fresh dairy produce is usually low in nitrate. Well waters in some agricultural areas may contain nitrate concentrations so high as to represent a hazard if used as the sole water source for infants, but municipal supplies in the UK rarely exceed 45 parts/106 although they frequently approach this. It is concluded that vegetables and water supplies make a greater contribution to the mean weekly nitrate intake than do cured meats. Nitrite concentrations are usually very low in fresh, undamaged fruits, vegetables and drinking water but adverse storage conditions can lead to (mainly microbial) reduction of nitrate. In these circumstances vegetables naturally rich in nitrate may accumulate nitrite at concentrations which can be toxic to infants.

Measurement of gaseous losses of nitrogen from soils

The measurement of gaseous losses of nitrogen from a red-brown earth has been investigated by direct determination of the evolved gaseous products. The results of field investigations, enclosed growth chamber experiments, and incubation experiments have indicated that the majority of the losses as N 2O are due to the microbial reduction of soil nitrate at anaerobic microsites within the generally aerobic soil. The detection and measurement of N 2O in the soil atmosphere by analyses for N 2O in samples obtained from equilibrium diffusion reservoirs provided a satisfactory and convenient means of detecting losses of nitrogen and of observing the seasonal distributions of nitrous oxide in the soil profile. Aspects of this problem requiring further investigation before the magnitude of the total gaseous losses can be accurately assessed are indicated.