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Manure from poultry operations is typically applied to nearby cropland and may affect nutrient loading and the spread of antibiotic resistance (ABR). We analyzed the concentrations of nitrogen and phosphorus and the occurrence of ABR in Escherichia coli (E. coli) and extra-intestinal pathogenic E. coli isolates from streams draining 15 small (

Manure from poultry operations is typically applied to nearby cropland and may affect nutrient loading and the spread of antibiotic resistance (ABR). We analyzed the concentrations of nitrogen and phosphorus and the occurrence of ABR in Escherichia coli (E. coli) and extra-intestinal pathogenic E. coli isolates from streams draining 15 small (

Anaerobic ammonium oxidation (anammox) contributes substantially to ocean nitrogen loss, particularly in anoxic marine zones (AMZs). Ammonium is scarce in AMZs, raising the hypothesis that organic nitrogen compounds may be ammonium sources for anammox. Biochemical measurements suggest that the organic compounds urea and cyanate can support anammox in AMZs. However, it is unclear if anammox bacteria degrade these compounds to ammonium themselves, or rely on other organisms for this process. Genes for urea degradation have not been found in anammox bacteria, and genomic evidence for cyanate use for anammox is limited to a cyanase gene recovered from the sediment bacterium Candidatus Scalindua profunda. Here, analysis of Ca. Scalindua single amplified genomes from the Eastern Tropical North Pacific AMZ revealed genes for urea degradation and transport, as well as for cyanate degradation. Urease and cyanase genes were transcribed, along with anammox genes, in the AMZ core where anammox rates peaked. Homologs of these genes were also detected in meta-omic datasets from major AMZs in the Eastern Tropical South Pacific and Arabian Sea. These results suggest that anammox bacteria from different ocean regions can directly access organic nitrogen substrates. Future studies should assess if and under what environmental conditions these substrates contribute to the ammonium budget for anammox.

In the Eastern Tropical North Pacific Oxygen Minimum Zone (ETNP‐OMZ), fish larvae undergo development amidst highly variable dissolved oxygen environments. As OMZs expand, understanding the implications of low‐oxygen environments on fish development becomes increasingly relevant for fisheries management and ecosystem modeling. Using horizontal zooplankton tows to track five oxygen levels (oxic [200 μmol/kg], hypoxic [100 μmol/kg] suboxic [10 μmol/kg], anoxic [<1 μmol/kg], and deep [10 μmol/kg at ~ 1000 m depth]), this study analyzed the three‐dimensional distribution of fish larvae and adults across the ETNP‐OMZ. Results revealed a wide midwater anoxic core, extending from Costa Rica to Baja California, that was almost devoid of fish larvae (< 1 larvae/1000 m3). Early larval stages primarily inhabited the oxic and hypoxic levels above the core, while postflexion and transformation stages occurred across a wider oxygen gradient, including the deep level below the anoxic core. Epipelagic species (e.g., Auxis sp.) were predominantly found in the surface oxic level, whereas coastal‐demersal species (e.g., Bregmaceros bathymaster, Ophidion spp.) were prevalent in the hypoxic level above the core. Meso‐bathypelagic species (e.g., Diogenichthys laternatus, Cyclothone spp.) were present throughout the study area, including below the anoxic core as transformation larvae and juveniles. These findings indicate that a vertical expansion of anoxic waters in OMZs could further constrain the habitat of epipelagic species, while also affecting the ontogenic vertical movements of meso‐bathypelagic species. [ABSTRACT FROM AUTHOR]

In the seasonally stratified Gulf of Aqaba Red Sea, both NO2- release by phytoplankton and NH4+ oxidation by nitrifying microbes contributed to the formation of a primary nitrite maximum (PNM) over different seasons and depths in the water column. In the winter and during the days immediately following spring stratification, NO2- formation was strongly correlated (R2=0.99) with decreasing irradiance and chlorophyll, suggesting that incomplete NO3- reduction by light limited phytoplankton was a major source of NO2-. However, as stratification progressed, NO2- continued to be generated below the euphotic depth by microbial NH4+ oxidation, likely due to differential photoinhibition of NH4+ and NO2- oxidizing populations. Natural abundance stable nitrogen isotope analyses revealed a decoupling of the δ15N and δ18O in the combined NO3- and NO2- pool, suggesting that assimilation and nitrification were co-occurring in surface waters. As stratification progressed, the δ15N of particulate N below the euphotic depth increased from -5‰ to up to +20‰.N uptake rates were also influenced by light; based on 15N tracer experiments, assimilation of NO3-, NO2-, and urea was more rapid in the light (434±24, 94±17, and 1194±48nmolNL-1day-1 respectively) than in the dark (58±14, 29±14, and 476±31nmolNL-1day-1 respectively). Dark NH4+ assimilation was 314±31nmolNL-1day-1, while light NH4+ assimilation was much faster, resulting in complete consumption of the 15N spike in less than 7h from spike addition. The overall rate of coupled urea mineralization and NH4+ oxidation (14.1±7.6nmolNL-1day-1) was similar to that of NH4+ oxidation alone (16.4±8.1nmolNL-1day-1), suggesting that mineralization of labile dissolved organic N compounds like urea was not a rate limiting step for nitrification. Our results suggest that assimilation and nitrification compete for NH4+ and that N transformation rates throughout the water column are influenced by light over diel and seasonal cycles, allowing phytoplankton and nitrifying microbes to contribute jointly to PNM formation. We identify important factors that influence the N cycle throughout the year, including light intensity, substrate availability, and microbial community structure. These processes could be relevant to other regions worldwide where seasonal variability in mixing depth and stratification influence the contributions of phytoplankton and non-photosynthetic microbes to the N cycle. © 2011 Elsevier Ltd.

We report a new method for determining the [sup.15]N/[sup.14]N of N[H.sub.4.sup.+] at natural abundance level in both freshwater and seawater. N[H.sub.4.sup.+] is first quantitatively oxidized to N[O.sub.2.sup.-] by hypobromite (Br[O.sup.-]) at pH ~ 12. After the addition of sodium arsenite to consume excess Br[O.sup.-], yield is verified by colorimetric N[O.sub.2.sup.-] determination. N[O.sub.2.sup.-] is further reduced to [N.sub.2]O using a 1:1 sodium azide and acetic acid buffer solution using previously established procedures. The product [N.sub.2]O is then analyzed for isotopic composition using a continuous flow purge and cryogenic trap system coupled to an isotope ratio mass spectrometer. Reliable [[delta].sup.15]N values (standard deviation is 0.3[per thousand] or better) are obtained over an N[H.sub.4.sup.+] concentration range of 0.5-10 [micro]M using 20 mL volumes of either freshwater or seawater samples. Higher concentration samples are readily diluted to lower concentration. Preexisting N[O.sub.2.sup.-] is removed by treatment with sulfanilic acid. There is no interference from any of the nitrogen-containing compounds tested except short-chain aliphatic amino acids (i.e., glycine) which typically are present at very low environmental concentrations. As compared to published methods, our approach is more robust, readily applicable at low concentrations and small sample volumes, and requires less time for preparation and analysis.

We present a novel method for nitrogen and oxygen natural isotopic abundance analysis of nitrate and nitrite of seawater and freshwater at environmental concentrations. The method involves the reduction of nitrate to nitrite using spongy cadmium with further reduction to nitrous oxide using sodium azide in an acetic acid buffer. For separate nitrite analysis, the cadmium reduction step is simply bypassed. Nitrous oxide is purged from the water sample and trapped cryogenically using an automated system with subsequent release into a gas chromatography column. The isolated nitrous oxide is then analyzed on a continuous flow isotope ratio mass spectrometer via an open split. This paper describes the basic protocol and reaction conditions required to obtain reproducible natural abundance level nitrogen and oxygen isotopic ratios from nitrate, nitrite, or both, and the results obtained to support these conclusions. A standard deviation less than 0.2%0 for nitrogen and 0.5%0 for oxygen was found for nitrate samples ranging in concentration from 40 to 0.5 [micro]M (better for nitrite), with a blank of 2 nmol for 50-mL samples. Nitrogen and oxygen isotopic fractionation and oxygen atom exchange were consistent within each batch of analysis. There was no interference from any seawater matrixes. Only one other method published to date can measure the nitrate oxygen isotopic abundance in seawater and none that do so for nitrite alone in the presence of nitrate. This method may prove to be simpler, faster, and obtain isotopic information for lower concentrations of nitrate and nitrite than other methods.

Author(s): Mark A. Altabet (corresponding author) [1]; Matthew J. Higginson [1]; David W. Murray [2] Most global biogeochemical processes are known to respond to climate change, some of which have [...]