Anaerobic Nitrate Research Articles

Bacterial drug tolerance under clinical conditions is governed by anaerobic adaptation but not anaerobic respiration.

Noninherited antibiotic resistance is a phenomenon whereby a subpopulation of genetically identical bacteria displays phenotypic tolerance to antibiotics. We show here that compared to Escherichia coli, the clinically relevant genus Burkholderia displays much higher levels of cells that tolerate ceftazidime. By measuring the dynamics of the formation of drug-tolerant cells under conditions that mimic in vivo infections, we show that in Burkholderia bacteria, oxygen levels affect the formation of these cells. The drug-tolerant cells are characterized by an anaerobic metabolic signature and can be eliminated by oxygenating the system or adding nitrate. The transcriptome profile suggests that these cells are not dormant persister cells and are likely to be drug tolerant as a consequence of the upregulation of anaerobic nitrate respiration, efflux pumps, β-lactamases, and stress response proteins. These findings have important implications for the treatment of chronic bacterial infections and the methodologies and conditions that are used to study drug-tolerant and persister cells in vitro.

RNA-seq analysis of the influence of anaerobiosis and FNR on Shigella flexneri.

BackgroundShigella flexneri is an important human pathogen that has to adapt to the anaerobic environment in the gastrointestinal tract to cause dysentery. To define the influence of anaerobiosis on the virulence of Shigella, we performed deep RNA sequencing to identify transcriptomic differences that are induced by anaerobiosis and modulated by the anaerobic Fumarate and Nitrate Reduction regulator, FNR.ResultsWe found that 528 chromosomal genes were differentially expressed in response to anaerobic conditions; of these, 228 genes were also influenced by FNR. Genes that were up-regulated in anaerobic conditions are involved in carbon transport and metabolism (e.g. ptsG, manX, murQ, cysP, cra), DNA topology and regulation (e.g. ygiP, stpA, hns), host interactions (e.g. yciD, nmpC, slyB, gapA, shf, msbB) and survival within the gastrointestinal tract (e.g. shiA, ospI, adiY, cysP). Interestingly, there was a marked effect of available oxygen on genes involved in Type III secretion system (T3SS), which is required for host cell invasion and pathogenesis. These genes, located on the large Shigella virulence plasmid, were down regulated in anaerobiosis in an FNR-dependent manner. We also confirmed anaerobic induction of csrB and csrC small RNAs in an FNR-independent manner.ConclusionsAnaerobiosis promotes survival and adaption strategies of Shigella, while modulating virulence plasmid genes involved in T3SS-mediated host cell invasion. The influence of FNR on this process is more extensive than previously appreciated, although aside from the virulence plasmid, this transcriptional regulator does not govern expression of genes on other horizontally acquired sequences on the chromosome such as pathogenicity islands.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-438) contains supplementary material, which is available to authorized users.

Effect of operating modes on simultaneous anaerobic sulfide and nitrate removal in microbial fuel cell

The effect of operating modes on the simultaneous sulfide and nitrate removal were studied in two-chamber microbial fuel cells (MFCs). The batch and continuous operating modes were compared and evaluated in terms of substrate removal and electricity generation. Upon gradual increase in the influent sulfide concentration from 60 to 1,020 S mg L(-1), and the hydraulic retention time decrease from 17.2 to 6 h, the MFC accomplished a good substrate removal efficiency whereby nitrogen and sulfate were the main end products. The removal efficiency of the MFC in the continuous mode was much higher than that in the batch mode, and its current densities in the continuous mode were more stable and higher than in the batch mode, which could be explained by the linear relationship between electrons released by the substrates and accepted on the electrodes. The electricity output in the continuous mode of the MFC was higher than that in the batch mode. MFC's operation in the continuous mode was a better strategy for the simultaneous treatment of sulfide and nitrate.

Production and consumption of nitrous oxide in nitrate-ammonifying Wolinella succinogenes cells.

Global warming is moving more and more into the public consciousness. Besides the commonly mentioned carbon dioxide and methane, nitrous oxide (N2O) is a powerful greenhouse gas in addition to its contribution to depletion of stratospheric ozone. The increasing concern about N2O emission has focused interest on underlying microbial energy-converting processes and organisms harbouring N2O reductase (NosZ), such as denitrifiers and ammonifiers of nitrate and nitrite. Here, the epsilonproteobacterial model organism Wolinella succinogenes is investigated with regard to its capacity to produce and consume N2O during growth by anaerobic nitrate ammonification. This organism synthesizes an unconventional cytochrome c nitrous oxide reductase (cNosZ), which is encoded by the first gene of an atypical nos gene cluster. However, W. succinogenes lacks a nitric oxide (NO)-producing nitrite reductase of the NirS- or NirK-type as well as an NO reductase of the Nor-type. Using a robotized incubation system, the wild-type strain and suitable mutants of W. succinogenes that either produced or lacked cNosZ were analysed as to their production of NO, N2O and N2 in both nitrate-sufficient and nitrate-limited growth medium using formate as electron donor. It was found that cells growing in nitrate-sufficient medium produced small amounts of N2O, which derived from nitrite and, most likely, from the presence of NO. Furthermore, cells employing cNosZ were able to reduce N2O to N2. This reaction, which was fully inhibited by acetylene, was also observed after adding N2O to the culture headspace. The results indicate that W. succinogenes cells are competent in N2O and N2 production despite being correctly grouped as respiratory nitrate ammonifiers. N2O production is assumed to result from NO detoxification and nitrosative stress defence, while N2O serves as a terminal electron acceptor in anaerobic respiration. The ecological implications of these findings are discussed.

Genomic features of a bumble bee symbiont reflect its host environment.

Here, we report the genome of one gammaproteobacterial member of the gut microbiota, for which we propose the name "Candidatus Schmidhempelia bombi," that was inadvertently sequenced alongside the genome of its host, the bumble bee, Bombus impatiens. This symbiont is a member of the recently described bacterial order Orbales, which has been collected from the guts of diverse insect species; however, "Ca. Schmidhempelia" has been identified exclusively with bumble bees. Metabolic reconstruction reveals that "Ca. Schmidhempelia" lacks many genes for a functioning NADH dehydrogenase I, all genes for the high-oxygen cytochrome o, and most genes in the tricarboxylic acid (TCA) cycle. "Ca. Schmidhempelia" has retained NADH dehydrogenase II, the low-oxygen specific cytochrome bd, anaerobic nitrate respiration, mixed-acid fermentation pathways, and citrate fermentation, which may be important for survival in low-oxygen or anaerobic environments found in the bee hindgut. Additionally, a type 6 secretion system, a Flp pilus, and many antibiotic/multidrug transporters suggest complex interactions with its host and other gut commensals or pathogens. This genome has signatures of reduction (2.0 megabase pairs) and rearrangement, as previously observed for genomes of host-associated bacteria. A survey of wild and laboratory B. impatiens revealed that "Ca. Schmidhempelia" is present in 90% of individuals and, therefore, may provide benefits to its host.

Dissimilatory nitrate reduction by Aspergillus terreus isolated from the seasonal oxygen minimum zone in the Arabian Sea.

BackgroundA wealth of microbial eukaryotes is adapted to life in oxygen-deficient marine environments. Evidence is accumulating that some of these eukaryotes survive anoxia by employing dissimilatory nitrate reduction, a strategy that otherwise is widespread in prokaryotes. Here, we report on the anaerobic nitrate metabolism of the fungus Aspergillus terreus (isolate An-4) that was obtained from sediment in the seasonal oxygen minimum zone in the Arabian Sea, a globally important site of oceanic nitrogen loss and nitrous oxide emission.ResultsAxenic incubations of An-4 in the presence and absence of oxygen and nitrate revealed that this fungal isolate is capable of dissimilatory nitrate reduction to ammonium under anoxic conditions. A 15N-labeling experiment proved that An-4 produced and excreted ammonium through nitrate reduction at a rate of up to 175 nmol 15NH4+ g-1 protein h-1. The products of dissimilatory nitrate reduction were ammonium (83%), nitrous oxide (15.5%), and nitrite (1.5%), while dinitrogen production was not observed. The process led to substantial cellular ATP production and biomass growth and also occurred when ammonium was added to suppress nitrate assimilation, stressing the dissimilatory nature of nitrate reduction. Interestingly, An-4 used intracellular nitrate stores (up to 6–8 μmol NO3- g-1 protein) for dissimilatory nitrate reduction.ConclusionsOur findings expand the short list of microbial eukaryotes that store nitrate intracellularly and carry out dissimilatory nitrate reduction when oxygen is absent. In the currently spreading oxygen-deficient zones in the ocean, an as yet unexplored diversity of fungi may recycle nitrate to ammonium and nitrite, the substrates of the major nitrogen loss process anaerobic ammonium oxidation, and the potent greenhouse gas nitrous oxide.

Influence of the molybdenum cofactor biosynthesis on anaerobic respiration, biofilm formation and motility in Burkholderia thailandensis

Burkholderia thailandensis is closely related to Burkholderia pseudomallei, a bacterial pathogen and the causative agent of melioidosis. B. pseudomallei can survive and persist within a hypoxic environment for up to one year and has been shown to grow anaerobically in the presence of nitrate. Currently, little is known about the role of anaerobic respiration in pathogenesis of melioidosis. Using B. thailandensis as a model, a library of 1344 transposon mutants was created to identify genes required for anaerobic nitrate respiration. One transposon mutant (CA01) was identified with an insertion in BTH_I1704 (moeA), a gene required for the molybdopterin biosynthetic pathway. This pathway is involved in the synthesis of a molybdopterin cofactor required for a variety of molybdoenzymes, including nitrate reductase. Disruption of molybdopterin biosynthesis prevented growth under anaerobic conditions, when using nitrate as the sole terminal electron acceptor. Defects in anaerobic respiration, nitrate reduction, motility and biofilm formation were observed for CA01. Mutant complementation with pDA-17:BTH_I1704 was able to restore anaerobic growth on nitrate, nitrate reductase activity and biofilm formation, but did not restore motility. This study highlights the potential importance of molybdoenzyme-dependent anaerobic respiration in the survival and virulence of B. thailandensis.

Microbial community structure and functioning in marine sediments associated with diffuse hydrothermal venting assessed by integrated meta‐omics

Deep-sea hydrothermal vents are unique environments on Earth, as they host chemosynthetic ecosystems fuelled by geochemical energy with chemolithoautotrophic microorganisms at the basis of the food webs. Whereas discrete high-temperature venting systems have been studied extensively, the microbiotas associated with low-temperature diffuse venting are not well understood. We analysed the structure and functioning of microbial communities in two diffuse venting sediments from the Jan Mayen vent fields in the Norwegian-Greenland Sea, applying an integrated 'omics' approach combining metatranscriptomics, metaproteomics and metagenomics. Polymerase chain reaction-independent three-domain community profiling showed that the two sediments hosted highly similar communities dominated by Epsilonproteobacteria, Deltaproteobacteria and Gammaproteobacteria, besides ciliates, nematodes and various archaeal taxa. Active metabolic pathways were identified through transcripts and peptides, with genes of sulphur and methane oxidation, and carbon fixation pathways highly expressed, in addition to genes of aerobic and anaerobic (nitrate and sulphate) respiratory chains. High expression of chemotaxis and flagella genes reflected a lifestyle in a dynamic habitat rich in physico-chemical gradients. The major metabolic pathways could be assigned to distinct taxonomic groups, thus enabling hypotheses about the function of the different prokaryotic and eukaryotic taxa. This study advances our understanding of the functioning of microbial communities in diffuse hydrothermal venting sediments.

Corynebacterium glutamicum ArnR Controls Expression of Nitrate Reductase Operon narKGHJI and Nitric Oxide (NO)-Detoxifying Enzyme Gene hmp in an NO-Responsive Manner

Corynebacterium glutamicum ArnR is a novel transcriptional regulator that represses expression of the nitrate reductase operon narKGHJI and the nitric oxide (NO)-detoxifying flavohemoglobin gene hmp under aerobic conditions. In a previous study, we showed that ArnR-mediated repression is relieved during anaerobic nitrate respiration, but we could not pinpoint the specific signal that ArnR senses. In this study, we show that in the absence of nitrate, ArnR-mediated repression is maintained under anaerobic conditions. The derepression in response to nitrate is eliminated by disruption of narG, suggesting that ArnR senses nitrate derivatives generated during nitrate respiration. Specifically, the hmp gene is upregulated in the presence of nitrite or nitric oxide (NO) in an ArnR-dependent manner, although the response of narK appears to be greatly affected by ArnR-independent regulation. In vitro binding of ArnR to the narK and hmp promoter regions is more strongly inhibited by NO than by nitrite. We previously showed that the UV-visible spectrum of ArnR is typical of a Fe-S cluster-containing protein. Site-directed mutagenesis of each of three cysteine residues, which are possibly involved in coordination of the cofactor in the ArnR protein, results in loss of the binding of this protein to its target promoters in vitro and eliminates the repression of the target genes in vivo under aerobic conditions. These observations suggest that the cofactor coordinated by these three cysteine residues in the ArnR protein plays a critical role in the NO-responsive expression of the narKGHJI operon and the hmp gene.

Nitrate enhances N2O emission more than ammonium in a highly acidic soil

Nitrous oxide (N2O) is produced naturally in soils through microbial processes of nitrification and denitrification. In recent years, the long-term application of nitrogen-heavy fertilizers has led to the acidification of tea orchard soils with high N2O emission. The present research aimed at finding out which process (nitrification or denitrification) dominates in N2O production, whether certain fertilizer managements could reduce N2O emission, and the effects of fertilizer management on the abundance of functional genes. Two nitrification inhibitors, 3, 4-dimethylpyrazole phosphate (DMPP) and dicyandiamide (DCD), combined with different N fertilizers (ammonium sulfate and potassium nitrate) were applied to highly acidic tea orchard soil in an aerobic incubation experiment. Both amoA and nosZ gene abundances from different treatments were determined by quantitative PCR. An anaerobic nitrate effect test was carried out using C2H2 inhibition method. The application of nitrate fertilizers significantly (P < 0.05) enhanced total N2O emission. A linear regression analysis between total N2O emission and average nitrate contents indicated that denitrification is the dominant source of N2O in this tea orchard soil. In the anaerobic incubation, no significant difference of N2O emission was observed between KNO3 and no KNO3 treatments before 96 h. Quantitative PCR revealed lower copy numbers of nosZ in nitrate-associated fertilizer-treated soils than the soils from other treatments. Compared with the control, ammonium fertilizers with DCD or DMPP significantly (P < 0.05) inhibited nitrate production as well as N2O. These results showed that denitrification is the dominant source of N2O in this highly acidic soil. Nitrate addition could significantly inhibit the abundance of nitrous oxide reductase, therefore causing high N2O emission. The application of ammonium fertilizers with DCD or DMPP could significantly reduce N2O emission, possibly due to the effective inhibition of nitrate production.

Metabolic versatility of toluene‐degrading, iron‐reducing bacteria in tidal flat sediment, characterized by stable isotope probing‐based metagenomic analysis

DNA stable isotope probing and metagenomic sequencing were used to assess the metabolic potential of iron-reducing bacteria involved in anaerobic aromatic hydrocarbon degradation in oil spill-affected tidal flats. In a microcosm experiment, (13) C-toluene was degraded with the simultaneous reduction of Fe(III)-NTA, which was also verified by quasi-stoichiometric (13) C-CO2 release. The metabolic potential of the dominant member affiliated with the genus Desulfuromonas in the heavy DNA fraction was inferred using assembled scaffolds (designated TF genome, 4.40 Mbp with 58.8 GC mol%), which were obtained by Illumina sequencing. The gene clusters with peripheral pathways for toluene and benzoate conversion possessed the features of strict and facultative anaerobes. In addition to the class II-type benzoyl-CoA reductase (Bam) of strict anaerobes, the class I-type (Bcr) of facultative anaerobes was encoded. Genes related to the utilization of various anaerobic electron acceptors, including iron, nitrate (to ammonia), sulfur and fumarate, were identified. Furthermore, genes encoding terminal oxidases (caa3 , cbb3 and bd) and a diverse array of genes for oxidative stress responses were detected in the TF genome. This metabolic versatility may be an adaptation to the fluctuating availability of electron acceptors and donors in tidal flats.

Role of Diatoms in the Spatial-Temporal Distribution of Intracellular Nitrate in Intertidal Sediment

Intracellular nitrate storage allows microorganisms to survive fluctuating nutrient availability and anoxic conditions in aquatic ecosystems. Here we show that diatoms, ubiquitous and highly abundant microalgae, represent major cellular reservoirs of nitrate in an intertidal flat of the German Wadden Sea and are potentially involved in anaerobic nitrate respiration. Intracellular nitrate (ICNO3) was present year-round in the sediment and was spatially and temporally correlated with fucoxanthin, the marker photopigment of diatoms. Pyrosequencing of SSU rRNA genes of all domains of life confirmed that ICNO3 storage was most likely due to diatoms rather than other known nitrate-storing microorganisms (i.e., large sulfur bacteria and the eukaryotic foraminifers and gromiids). Sedimentary ICNO3 concentrations reached up to 22.3 µmol dm-3 at the sediment surface and decreased with sediment depth to negligible concentrations below 5 cm. Similarly, the ICNO3/fucoxanthin ratio and porewater nitrate (PWNO3) concentrations decreased with sediment depth, suggesting that ICNO3 of diatoms is in equilibrium with PWNO3, but is enriched relative to PWNO3 by 2-3 orders of magnitude. Cell-volume-specific ICNO3 concentrations in a diatom mat covering the sediment surface during spring were estimated at 9.3-46.7 mmol L-1. Retrieval of 18S rRNA gene sequences related to known nitrate-storing and nitrate-ammonifying diatom species suggested that diatoms in dark and anoxic sediment layers might be involved in anaerobic nitrate respiration. Due to the widespread dominance of diatoms in microphytobenthos, the total nitrate pool in coastal marine sediments may generally be at least two times larger than derived from porewater measurements and partially be recycled to ammonium.

Crystal structures of nitric oxide reductases provide key insights into functional conversion of respiratory enzymes

Respiration is an essential biological process to get bioenergy, ATP, for all kingdoms of life. Cytochrome c oxidase (COX) plays central role in aerobic respiration, catalyzing the reduction of O(2) coupled with pumping proton across the biological membrane. Nitric oxide reductase (NOR) involved in anaerobic nitrate respiration is suggested to be evolutionary related to COX and share the same progenitor with COX, on the basis of the amino acid sequence homology. Contrary to COX, NOR catalyzes the reduction of nitric oxide and shows no proton pumping ability. Thus, the respiratory enzyme acquires (or loses) proton pumping ability in addition to the conversion of the catalytic property along with the environmental change on earth. Recently, we solved the structures of two types of NORs, which provides novel insights into the functional conversion of the respiratory enzymes. In this review, we focus on the structural similarities and differences between COXs and NORs and discuss possible mechanism for the functional conversion of these enzymes during molecular evolution.

Simultaneous anaerobic sulfide and nitrate removal coupled with electricity generation in Microbial Fuel Cell

Two-chamber Microbial Fuel Cells (MFC) using graphite rods as electrodes were operated for simultaneous anaerobic sulfide and nitrate removal coupled with electricity generation. The MFC showed good ability to remove substrates. When the influent sulfide and nitrate concentrations were 780mg/L and 135.49mg/L, respectively, the removal percentages of sulfide and nitrate were higher than 90% and the main end products were nitrogen and sulfate. The MFC also showed good ability to generate electricity, and the voltage went up with the rise of influent substrate concentrations. When the external resistance was 1000Ω, its highest steady voltage was 71mV. Based on the linear relationship between the electrons released by substrates and accepted by electrode, it was concluded that the electricity generation was coupled with the substrate conversion in the MFC.

Construction and characterization of nitrate and nitrite respiring Pseudomonas putida KT2440 strains for anoxic biotechnical applications

Pseudomonas putida KT2440 is frequently used in biotechnical research and applications due to its metabolic versatility and organic solvent resistance. A major drawback for a broad application is the inability of the bacterium to survive and grow under anoxic conditions, which prohibits the production of oxygen-sensitive proteins and metabolites. To develop a P. putida strain, which is able to survive under anoxic conditions, the enzymatic systems of anaerobic nitrate and nitrite respiration were introduced into KT2440. For this purpose, two cosmids encoding all structural, maturation and regulatory genes for P. aeruginosa nitrate reductase (pNAR) and nitrite- and nitric oxide reductase (pNIR-NOR) were stably maintained in P. putida KT2440. Transcriptome analyses revealed expression of the encoded nar, nir and nor operons and accessory genes under anoxic conditions. The produced enzyme systems efficiently reduced nitrate or nitrite, respectively, sustaining anaerobic life of recombinant KT2440. Interestingly, anaerobic life of P. putida induced genes involved in arginine-fermentation and genes encoding a putative copper stress resistance operon.

Simultaneous anaerobic sulfide and nitrate removal in microbial fuel cell

Two-chamber microbial fuel cells (MFCs) were operated to remove sulfide and nitrate simultaneously using activated sludge in this study. Compared with control experiment, the MFC showed its ability to remove nitrate and sulfide simultaneously and generate electricity. When the external resistance was 1000Ω, the initial concentrations of sulfide and nitrate were about 60 and 10.5mgL−1, respectively, maximum current density of the MFC was 138.31mAm−2. In the end of a typical cycle, it decreased to 12.20mAm−2. The main end products were nitrogen and sulfate. The microorganisms attached to the anode electrode had electrochemical activity, and the transfer mechanism of electron in MFC was different from that in control MFC.

Simultaneous ANAMMOX and denitrification (SAD) process in batch tests

The occurrence of simultaneous anaerobic ammonia oxidation and nitrate reduction (SAD) processes by enrichment culture in the presence of glucose were clarified in batch tests. Nitrate conversion and the formation of interim by-products were investigated under autotrophic and mixotrophic conditions. Eventually, the nitrite was fully consumed and co-occurred with ammonia oxidation. The effect of penicillin G and methanol on the SAD process was also investigated. Methanol addition led to complete loss of ANAMMOX activity at concentrations as low as 1 mM. Penicillin G has little effect on the SAD process. Scanning electron microscopy (SEM) observation and denaturing gradient gel electrophoresis (DGGE) analysis revealed that ANAMMOX bacteria and co-existing bacteria are responsible for the SAD process. In conclusion, this study indicates that the ratio of nitrogen to organic carbon, and the cooperation and competition between microbes can affect the dynamics of this process. It has a potential application to remove ammonia and nitrate in the presence of organic matter by the SAD process.

Arhodomonas recens sp. nov., a halophilic alkane-utilizing hydrogen-oxidizing bacterium from the brines of flotation enrichment of potassium minerals

A halophilic nonpigmented rod-shaped (0.8–1.0 × 2.0–2.5 μm), gram-negative bacterium with a single polar flagellum (strain RS91) was isolated from acidic brines of flotation enrichment of potassium minerals (Silvinit Co., Solikamsk, Russia). The strain grew in the media with 2 to 25% NaCl (optimum at 10–12%), 20–45°C (optimum at 37°C), and pH 5.5–8.5 (optimum 6.5–7.5). It was an aerobe or facultative anaerobe incapable of fermentation. The strain was characterized by the absence of growth on glucose, fructose, and citrate, extensive aerobic growth on n-hexadecane and in the mineral medium with H2 + O2 + CO2 in the gas phase, anaerobic nitrate reduction with acetate or hydrogen (under H2 + CO2 + N2), and variable fatty acid composition. The DNA G+C content was 68.2 mol %. Phylogenetic analysis based on 16S rRNA gene sequencing revealed that while strain RS91 was most closely related to Arhodomonas aquaeolei HA-1T (98.3%) and Nitrococcus mobilis (98.1%), it was only remotely related to the halophilic phototroph Halorhodospira halophila (90.6%). Based on the combination of its phenotypic and genotypic characteristics, the organism was classified as a new species of the genus Arhodomonas, family Ectothiorhodospiraceae with the proposed name Arhodomonas recens sp. nov. The type strain is RS91T (= IEGM 796T = VKPM B-11280T).

Anammox Bacterial Abundance, Activity, and Contribution in Riparian Sediments of the Pearl River Estuary

The hypothesis of an anammox hotspot in river riparian zones was put forward based on our investigation on freshwater ecotones for over 25 years and previous anammox research. Here we used a complementary array of methods including isotope-pairing technique, quantitative PCR assays, and 16S rRNA and hydrazine synthase gene (hzsB) clone libraries to document the spatiotemporal evidence for a high abundance zone of anammox bacteria in river riparian sediment with observed abundance of 1.3-12 × 10(6) (summer) and 1.4-20 × 10(8) (winter) hydrazine synthase gene copies g(-1), which is the highest abundance in natural environments recorded so far. Meanwhile high anammox bacterial biodiversity were detected with 'Brocadia' and 'Kuenenia' dominating. However, the high anammox bacterial abundances were not related with high activities and contributions for nitrogen gas generation. The anammox activities ranged from 0.07 to 0.15 nmol N cm(-3) h(-1) (summer) to 1.0-2.6 nmol N cm(-3) h(-1) (winter) with high temporal heterogeneity. The retrieval of archaeal and bacterial amoA sequences indicated that nitrifying microbes might be the major source of nitrite for anammox bacteria in winter, while in summer the anaerobic nitrate reduction is more likely the main source. On the basis of (15)N tracing technology, it was estimated that a total loss of 0.67-9.62 g N m(-2) yr(-1) is linked to anammox in the riparian zone while denitrification contributed 96.2-170.3 g N m(-2) yr(-1) in Pearl River riparian sediments.

Phage-Mediated Acquisition of a Type III Secreted Effector Protein Boosts Growth of Salmonella by Nitrate Respiration

ABSTRACTInformation on how emerging pathogens can invade and persist and spread within host populations remains sparse. In the 1980s, a multidrug-resistant Salmonella enterica serotype Typhimurium clone lysogenized by a bacteriophage carrying the sopE virulence gene caused an epidemic among cattle and humans in Europe. Here we show that phage-mediated horizontal transfer of the sopE gene enhances the production of host-derived nitrate, an energetically highly valuable electron acceptor, in a mouse colitis model. In turn, nitrate fuels a bloom of S. Typhimurium in the gut lumen through anaerobic nitrate respiration while suppressing genes for the utilization of energetically inferior electron acceptors such as tetrathionate. Through this mechanism, horizontal transfer of sopE can enhance the fitness of S. Typhimurium, resulting in its significantly increased abundance in the feces.