In the global nitrogen cycle, bacterial denitrification is recognized as the only quantitatively important process that converts fixed nitrogen to atmospheric nitrogen gas, N 2 , thereby influencing many aspects of ecosystem function and global biogeochemistry. However, we have found that a process novel to the marine nitrogen cycle, anaerobic oxidation of ammonium coupled to nitrate reduction, contributes substantially to N 2 production in marine sediments. Incubations with 15 N-labeled nitrate or ammonium demonstrated that during this process, N 2 is formed through one-to-one pairing of nitrogen from nitrate and ammonium, which clearly separates the process from denitrification. Nitrite, which accumulated transiently, was likely the oxidant for ammonium, and the process is thus similar to the anammox process known from wastewater bioreactors. Anaerobic ammonium oxidation accounted for 24 and 67% of the total N 2 production at two typical continental shelf sites, whereas it was detectable but insignificant relative to denitrification in a eutrophic coastal bay. However, rates of anaerobic ammonium oxidation were higher in the coastal sediment than at the deepest site and the variability in the relative contribution to N 2 production between sites was related to large differences in rates of denitrification. Thus, the relative importance of anaerobic ammonium oxidation and denitrification in N 2 production appears to be regulated by the availability of their reduced substrates. By shunting nitrogen directly from ammonium to N 2 , anaerobic ammonium oxidation promotes the removal of fixed nitrogen in the oceans. The process can explain ammonium deficiencies in anoxic waters and sediments, and it may contribute significantly to oceanic nitrogen budgets.

Cryptic Sulfur Cycling Aerobic bacteria and ocean circulation patterns control the formation and distribution of oxygen-minimum zones at moderate depth in the oceans. These habitats host microorganisms that thrive on other metabolic substrates in the absence of oxygen—most commonly, metabolizing thermodynamically favorable nitrogen compounds like nitrate. Off the coast of Chile, however, Canfield et al. (p. 1375 , published online 11 November; see the Perspective by Teske ) suggest that bacteria may often reduce sulfate as well. Metagenomic sequencing revealed the presence of both sulfate-reducing and sulfide-oxidizing bacteria. With the coincidence of sulfate and nitrate reduction, the sulfur and nitrogen cycles may be intimately linked; for example, sulfate reduction could provide nitrogen-rich ammonium for bacteria that ultimately transform it into nitrogen gas.

In oxygen-depleted zones of the open ocean, and in anoxic basins and fjords, denitrification (the bacterial reduction of nitrate to give N2) is recognized as the only significant process converting fixed nitrogen to gaseous N2. Primary production in the oceans is often limited by the availability of fixed nitrogen such as ammonium or nitrate, and nitrogen-removal processes consequently affect both ecosystem function and global biogeochemical cycles. It was recently discovered that the anaerobic oxidation of ammonium with nitrite--the 'anammox' reaction, performed by bacteria--was responsible for a significant fraction of N2 production in some marine sediments. Here we show that this reaction is also important in the anoxic waters of Golfo Dulce, a 200-m-deep coastal bay in Costa Rica, where it accounts for 19-35% of the total N2 formation in the water column. The water-column chemistry in Golfo Dulce is very similar to that in oxygen-depleted zones of the oceans--in which one-half to one-third of the global nitrogen removal is believed to occur. We therefore expect the anammox reaction to be a globally significant sink for oceanic nitrogen.

ABSTRACT-During experimental light-dark cycles, O9 in the tissue of the colonial scleractinian corals Favia sp. and Acropora sp reached >250 % of air saturation after a few minutes in light. Immediately after darkenmg, 0; was depleted rapidly, and within 5 mm the 0; concentration at the tissue surface reached < 2 % of air saturation. The pH of the tissue changed within 10 min from about 8.5 in the light to 7.3 m the dark. Oxygen and pH profiles revealed a diffusive boundary layer of flow-dependent thickness, which limited coral respiration in the dark. The light field at the tissue surface (measured as scalar irradiance, Eo) differed strongly with respect to light intensity and spectral composition from the incident collimated light (measured as downwelling irradiance, Ed) Scalar irradiance reached up to 180 % of Ed at the coral tissue surface for wavelengths subject to less absorption by the coral tissue (600 to 650 run and >680 nm). The scalar irradiance spectra exhibited bands of chlorophyll a (chl a ) (675 run), chl c (630 to 640 nm) and pendinin (540 nm) absorption and a broad absorption band due to chlorop h y l l~ and carotenoids between 400 and 550 nm. The shape of both action spectra and photosynthesis vs irradiance (Pvs I) curves depended on the choice of the light intensity parameter. Calculations of miha1 slopes and onset of light saturation, Ik, showed that P vs Eo curves exhibit a lower initial slope and a higher 4 than corresponding Pvs Ed curves. Coral respiration in light was calculated as the difference between the measured gross and net photosynthesis, and was found to be >6 times higher at a saturating irradiance of 350 pEm m 2 s 1 than the dark respiration measured under identical hydrodynamic conditions (flow rate of 5 to 6 cm ssl).

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Objective To assess the effect of virtual reality training on an actual laparoscopic operation.Design Prospective randomised controlled and blinded trial.Setting Seven gynaecological departments in the Zeeland region of Denmark.Participants 24 first and second year registrars specialising in gynaecology and obstetrics.Interventions Proficiency based virtual reality simulator training in laparoscopic salpingectomy and standard clinical education (controls).Main outcome measure The main outcome measure was technical performance assessed by two independent observers blinded to trainee and training status using a previously validated general and task specific rating scale. The secondary outcome measure was operation time in minutes.Results The simulator trained group (n=11) reached a median total score of 33 points (interquartile range 32-36 points), equivalent to the experience gained after 20-50 laparoscopic procedures, whereas the control group (n=10) reached a median total score of 23 (22-27) points, equivalent to the experience gained from fewer than five procedures (P<0.001). The median total operation time in the simulator trained group was 12 minutes (interquartile range 10-14 minutes) and in the control group was 24 (20-29) minutes (P<0.001). The observers’ inter-rater agreement was 0.79.Conclusion Skills in laparoscopic surgery can be increased in a clinically relevant manner using proficiency based virtual reality simulator training. The performance level of novices was increased to that of intermediately experienced laparoscopists and operation time was halved. Simulator training should be considered before trainees carry out laparoscopic procedures.Trial registration ClinicalTrials.gov NCT00311792.

We quantified the removal of fixed nitrogen as N 2 production by anammox and N 2 and N 2 O production by denitrification over a distance of 1900 km along the coasts of Chile and Peru, using short-term incubations with 15 N-labeled substrates. The eastern South Pacific contains an oxygen minimum zone (OMZ) characterized by an anoxic, nitrate-and nitrite-rich layer of , 200-m thickness below 30-90 m of oxic water. Anammox and denitrification were almost exclusively recorded when the in situ O 2 concentration was below detection, indicating that the induction of these processes is highly oxygen sensitive. Anammox was detected in 70% of the samples from anoxic depths. Denitrification was detected in fewer samples, but maximum rates were an order of magnitude higher than those of anammox. In our incubations denitrification was responsible for 72% of the total N 2 production and 77% of the total removal of fixed nitrogen including N 2 O production. However, at the individual depths it could be one or the other process that was responsible for all of the nitrogen removal. Anammox activity was highest just below the oxic-anoxic interface and declined exponentially with depth, whereas no depth dependence was discerned for denitrification. Denitrification resulted in net production of N 2 O in some of the samples and consumption of added 15 N 2 O in others. Together with the accumulation of NO

A major percentage (20 to 40%) of global marine fixed-nitrogen loss occurs in oxygen minimum zones (OMZs). Concentrations of O2 and the sensitivity of the anaerobic N2-producing processes of anammox and denitrification determine where this loss occurs. We studied experimentally how O2 at nanomolar levels affects anammox and denitrification rates and the transcription of nitrogen cycle genes in the anoxic OMZ off Chile. Rates of anammox and denitrification were reversibly suppressed, most likely at the enzyme level. Fifty percent inhibition of N2 and N2O production by denitrification was achieved at 205 and 297 nM O2, respectively, whereas anammox was 50% inhibited at 886 nM O2. Coupled metatranscriptomic analysis revealed that transcripts encoding nitrous oxide reductase (nosZ), nitrite reductase (nirS), and nitric oxide reductase (norB) decreased in relative abundance above 200 nM O2. This O2 concentration did not suppress the transcription of other dissimilatory nitrogen cycle genes, including nitrate reductase (narG), hydrazine oxidoreductase (hzo), and nitrite reductase (nirK). However, taxonomic characterization of transcripts suggested inhibition of narG transcription in gammaproteobacteria, whereas the transcription of anammox narG, whose gene product is likely used to oxidatively replenish electrons for carbon fixation, was not inhibited. The taxonomic composition of transcripts differed among denitrification enzymes, suggesting that distinct groups of microorganisms mediate different steps of denitrification. Sulfide addition (1 µM) did not affect anammox or O2 inhibition kinetics but strongly stimulated N2O production by denitrification. These results identify new O2 thresholds for delimiting marine nitrogen loss and highlight the utility of integrating biogeochemical and metatranscriptomic analyses.