Dissimilatory nitrate reduction by Propionibacterium acnes.

Propionibacterium acnes P13 was isolated from human feces. The bacterium produced a particulate nitrate reductase and a soluble nitrite reductase when grown with nitrate or nitrite. Reduced viologen dyes were the preferred electron donors for both enzymes. Nitrous oxide reductase was never detected. Specific growth rates were increased by nitrate during growth in batch culture. Culture pH strongly influenced the products of dissimilatory nitrate reduction. Nitrate was principally converted to nitrite at alkaline pH, whereas nitrous oxide was the major product of nitrate reduction when the bacteria were grown at pH 6.0. Growth yields were increased by nitrate in electron acceptor-limited chemostats, where nitrate was reduced to nitrite, showing that dissimilatory nitrate reduction was an energetically favorable process in P. acnes. Nitrate had little effect on the amounts of fermentation products formed, but molar ratios of acetate to propionate were higher in the nitrate chemostats. Low concentrations of nitrite (ca. 0.2 mM) inhibited growth of P. acnes in batch culture. The nitrite was slowly reduced to nitrous oxide, enabling growth to occur, suggesting that denitrification functions as a detoxification mechanism.     

Dissimilatory nitrate reduction by Propionibacterium acnes

Propionibacterium acnes P13 was isolated from human feces. The bacterium produced a particulate nitrate reductase and a soluble nitrite reductase when grown with nitrate or nitrite. Reduced viologen dyes were the preferred electron donors for both enzymes. Nitrous oxide reductase was never detected. Specific growth rates were increased by nitrate during growth in batch culture. Culture pH strongly influenced the products of dissimilatory nitrate reduction. Nitrate was principally converted to nitrite at alkaline pH, whereas nitrous oxide was the major product of nitrate reduction when the bacteria were grown at pH 6.0. Growth yields were increased by nitrate in electron acceptor-limited chemostats, where nitrate was reduced to nitrite, showing that dissimilatory nitrate reduction was an energetically favorable process in P. acnes. Nitrate had little effect on the amounts of fermentation products formed, but molar ratios of acetate to propionate were higher in the nitrate chemostats. Low concentrations of nitrite (ca. 0.2 mM) inhibited growth of P. acnes in batch culture. The nitrite was slowly reduced to nitrous oxide, enabling growth to occur, suggesting that denitrification functions as a detoxification mechanism.     

Dissimilatory nitrate and dimethylsulphoxide reduction in Rhodopseudomonas capsulata

Abstract The electron flow to the dissimilatory nitrate reductase (NRII), and dimethylsulphoxide (DMSO) oxidoreductase in Rhodopseudomonas capsulata strains was studied. Our results support the view that DMSO reduction, like dissimilatory nitrate reduction was linked to the electron transfer chain and probably coupled to energy conservation.     

Dissimilatory nitrate reduction to nitrate, nitrous oxide, and ammonium by Pseudomonas putrefaciens.

The influence of redox potential on dissimilatory nitrate reduction to ammonium was investigated on a marine bacterium, Pseudomonas putrefaciens. Nitrate was consumed (3.1 mmol liter-1), and ammonium was produced in cultures with glucose and without sodium thioglycolate. When sodium thioglycolate was added, nitrate was consumed at a lower rate (1.1 mmol liter-1), and no significant amounts of nitrite or ammonium were produced. No growth was detected in glucose media either with or without sodium thioglycolate. When grown on tryptic soy broth, the production of nitrous oxide paralleled growth. In the same medium, but with sodium thioglycolate, nitrous oxide was first produced during growth and then consumed. Acetylene caused the nitrous oxide to accumulate. These results and the mass balance calculations for different nitrogen components indicate that P. putrefaciens has the capacity to dissimilate nitrate to ammonium as well as to dinitrogen gas and nitrous oxide (denitrification). The dissimilatory pathway to ammonium dominates except when sodium thioglycolate is added to the medium.     

Growth of Clostridium tertium and Clostridium septicum in chemically defined media.

Defined media for the growth of Clostridium tertium and Clostridium septicum are described. The requirements for growth of these two species are compared with each other and with those of Clostridium perfringens.     

Dissimilatory nitrate reduction to nitrate, nitrous oxide, and ammonium by Pseudomonas putrefaciens

The influence of redox potential on dissimilatory nitrate reduction to ammonium was investigated on a marine bacterium, Pseudomonas putrefaciens. Nitrate was consumed (3.1 mmol liter-1), and ammonium was produced in cultures with glucose and without sodium thioglycolate. When sodium thioglycolate was added, nitrate was consumed at a lower rate (1.1 mmol liter-1), and no significant amounts of nitrite or ammonium were produced. No growth was detected in glucose media either with or without sodium thioglycolate. When grown on tryptic soy broth, the production of nitrous oxide paralleled growth. In the same medium, but with sodium thioglycolate, nitrous oxide was first produced during growth and then consumed. Acetylene caused the nitrous oxide to accumulate. These results and the mass balance calculations for different nitrogen components indicate that P. putrefaciens has the capacity to dissimilate nitrate to ammonium as well as to dinitrogen gas and nitrous oxide (denitrification). The dissimilatory pathway to ammonium dominates except when sodium thioglycolate is added to the medium.     

The physiological function of nitrate reduction in Clostridium perfringens.

Fermentation-balance studies have been carried out on Clostridium perfringens grown in the presence and absence of nitrate in the medium. Nitrate is able to serve as an electron acceptor for these bacteria, permitting increased growth yields over those obtained in its absence. This increase is due to an increase in the proportion of metabolite molecules which can participate in substrate-level phosphorylation reactions when an inorganic acceptor is available. The nitrate reduction can be regarded as a primitive form of anaerobic respiration in these bacteria, since it is clearly coupled to their energy metabolism and is not assimilative in function. We believe that the existence of this kind of energy metabolism in these bacteria has significant evolutionary implications.     

细菌硝酸盐异化还原成铵过程及其在河口生态系统中的潜在地位与影响

细菌硝酸盐异化还原成铵(DNRA)过程能够将河口沉积物中的硝氮转化为氨氮,是河口生态系统中潜在的重要氮循环过程之一。本文介绍DNRA机理与分类,综述河口生态系统中DNRA的地位与影响,并总结河口生态系统中几种重要生态因子对DNRA过程的调控与影响。目前DNRA的机理还有待完善。深入研究各类河口生态系统中环境因子对DNRA的调控与影响机制,并研发新的研究方法,将为我国河口地区的水资源保护和生态治理提供科学依据。     

Dissimilatory nitrate reduction by a strain ofClostridium butyricum isolated from estuarine sediments

Nitrate dissimilation in chemostat grown cultures ofClostridium butyricum SS6 has been investigated. Sucrose limited cultures grown on nitrate produced nitrite as the principal end-product of nitrate reduction whilst under nitrate-limiting conditions ammonia accumulated in the spent media. Nitrate reduction was accompanied by the synthesis of a soluble nitrate reductase (123 nmol·NADH oxidised · min^-1 · mg protein^-1) and in addition, under N-limiting conditions, a soluble nitrite reductase (56 nmol NADH oxidised min^-1 · mg protein^-1). Corresponding ammonia grown cultures synthesised neither enzyme. Concurrent with the dissimilation of nitrate to nitrite and ammonia cell population densities increased by 18% (C-limitation) and 32% (N-limitation). Spent media analyses of the fermentation products from ammonia and nitrate grown cells showed the accumulation of acetate in nitrate dissimilating cultures. Molar ratios of acetate/butyrate increased by a factor of 5 (C-limitation) to 12 (N-limitation) upon adding nitrate to the growth medium. In C-limited cultures, grown on nitrate, hydrogenase activity was 340 nmol · min^-1 · mg protein^-1 and under N-limitation this increased to 906 nmol · min^-1 · mg protein^-1. Since N-limited cultures are electron acceptor limited, the increase in hydrogenase activity enables excess electrons to be spilled by this route.     

Growth of Clostridium tertium and Clostridium septicum in Chemically Defined Media

Defined media for the growth of Clostridium tertium and Clostridium septicum are described. The requirements for growth of these two species are compared with each other and with those of Clostridium perfringens.     

Dissimilatory nitrate reduction in fungi under conditions of hypoxia and anoxia: A review

Recent progress in studies of anaerobic nitrate reduction and nitrous oxide formation in fungi has been reviewed. Current understanding of the biochemistry of nitrate and nitrite reduction to nitrous oxide and ammonium under oxygen limitation is presented, with emphasis on patterns of fungal co-denitrification, properties of the enzymes involved, and prevalence of nitrate respiration among fungal species.     

Dissimilatory nitrate reduction in fungi under conditions of hypoxia and anoxia: a review

Recent progress in studies of anaerobic nitrate reduction and nitrous oxide formation in fungi has been reviewed. Current understanding of the biochemistry of nitrate and nitrite reduction to nitrous oxide and ammonium under oxygen limitation is presented, with emphasis on patterns of fungal co-denitrification, properties of the enzymes involved, and prevalence of nitrate respiration among fungal species.     

Dissimilatory nitrate reduction by Pseudomonas alcaliphila with an electrode as the sole electron donor

Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were considered two alternative pathways of dissimilatory nitrate reduction. In this study, we firstly reported that both denitrification and DNRA occurred in Pseudomonas alcaliphila strain MBR with an electrode as the sole electron donor in a double chamber bio‐electrochemical system (BES). The initial concentration of nitrate appeared as a factor determining the type of nitrate reduction with electrode as the sole electron donor at the same potential (?500 mV). As the initial concentration of nitrate increased, the fraction of nitrate reduced through denitrification also increased. While nitrite (1.38 ± 0.04 mM) was used as electron acceptor instead of nitrate, the electrons recovery via DNRA and denitrification were 43.06 ± 1.02% and 50.51 ± 1.37%, respectively. The electrochemical activities and surface topography of the working electrode catalyzed by strain MBR were evaluated by cyclic voltammetry and scanning electron microscopy. The results suggested that cells of strain MBR were adhered to the electrode, playing the role of electron transfer media for nitrate and nitrite reduction. Thus, for the first time, the results that DNRA and denitrification occurred simultaneously were confirmed by powering the strain with electricity. The study further expanded the range of metabolic reactions and had potential value for the recognization of dissimilatory nitrate reduction in various ecosystems. Biotechnol. Bioeng. 2012; 109: 2904–2910. © 2012 Wiley Periodicals, Inc.     

Dissimilatory reduction of bisulfite by Desulfovibrio vulgaris.

The reduction of bisulfite by Desulfovibrio vulgaris was investigated. Crude extracts reduced bisulfite to sulfide without the formation (detection) of any intermediates such as trithionate or thiosulfate. When the particulate fractions was removed from crude extracts by high-speed centrifugation, the soluble supernatant fraction reduced bisulfite sequentially to trithionate, thiosulfate, and sulfide. Addition of particles or purified membranes to the soluble fraction restored the original activity demonstrated by crude extracts, i.e., reduction of bisulfite to sulfide without the formation of trithionate and/or thiosulfate. By using antiserum directed against bisulfite reductase, the reduction of bisulfite by crude extracts was inhibited. This finding, in addition to several recycling studies of thiosulfate reduction, provided evidence that bisulfite reduction by D. vulgaris operated through the pathway involving trithionate and thiosulfate as intermediates. The role of membranes in this process is discussed.     

Dissimilatory reduction of nitrate and nitrite in the bovine rumen: nitrous oxide production and effect of acetylene.

15N tracer methods and gas chromatography coupled to an electron capture detector were used to investigate dissimilatory reduction of nitrate and nitrite by the rumen microbiota of a fistulated cow. Ammonium was the only 15N-labeled end product of quantitative significance. Only traces of nitrous oxide were detected as a product of nitrate reduction; but in experiments with nitrite, up to 0.3% of the added nitrogen accumulated as nitrous oxide, but it was not further reduced. Furthermore, when 13NO3- was incubated with rumen microbiota virtually no [13N]N2 was produced. Acetylene partially inhibited the reduction of nitrite to ammonium as well as the formation of nitrous oxide. It is suggested that in the rumen ecosystem nitrous oxide is a byproduct of dissimilatory nitrite reduction to ammonium rather than a product of denitrification and that the latter process is absent from the rumen habitat.     

Dissimilatory perchlorate reduction: a review

In the United States anthropogenic activities are mainly responsible for the wide spread perchlorate contamination of drinking water, surface water, groundwater, and soil. Even at microgram levels, perchlorate causes toxicity to flora and fauna and affects growth, metabolism and reproduction in humans and animals. Reports of antithyroid effects of perchlorate and its detection in common food items have raised serious public health concerns, leading to extensive decontamination efforts in recent years. Several physico-chemical removal and biological decontamination processes are being developed. Although promising, ion exchange is a non-selective and incomplete process as it merely transfers perchlorate from water to the resin. The perchlorate-laden spent resins (perchlorate 200-500 mg L⁻¹) require regeneration resulting in production of concentrated brine (6-12% NaCl) or caustic waste streams. On the contrary, biological reduction completely degrades perchlorate into O₂ and innocuous Cl⁻. High reduction potential of ClO₄⁻/Cl⁻ (E° = ∼1.28 V) and ClO₃⁻/Cl⁻ pairs (E° = 1.03 V) makes these contaminants thermodynamically ideal e⁻ acceptors for microbial reduction. In recent years unique dissimilatory perchlorate reducing bacteria have been isolated and detailed studies pertaining to their microbiological, biochemical, genetics and phylogenetic aspects have been undertaken which is the subject of this review article while the various physico-chemical removal and biological reduction processes have been reviewed by others.     

The reduction of nitrate to ammonium by a Clostridium sp. isolated from soil

Cultures of Clostridium KDHS2 reduced 15NO3- to 15NH4+ with a concurrent increase in molar growth yield of 15.7% compared with fermentatively grown bacteria. The bacteria exhibited a Ks (NO3-) of 0.5 mM and reduced NO3- maximally at a rate of 0.1 mumol h(-1) mg dry wt)-1. A partially purified nitrate reductase was obtained which had a Km (NO3-) of 0.15 mM. The reduction of 13NO3- to 13NH4+ by resting bacteria was not inhibited by NH4+, glutamate, glutamine, methionine sulphoximine or azaserine. Glutamine synthetase affected neither the synthesis nor the activity of the NO3(-)-reducing enzymes. The results are consistent with the hypothesis that NO3- reduction to NH4+ in this Clostridium sp. is dissimilative. SO32-, but not SO42-, inhibited the reaction, apparently at the level of NO2- reduction.