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Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O

The importance of understanding the fate of nitrate (NO3&#8722;), which is the dominant N species transferred from terrestrial to aquatic ecosystems, has ...

Chuo University

The goal of this study was to elucidate the mechanisms of nitrous oxide (NO) production from a bioreactor for partial nitrification (PN). Ammonia-oxidizing bacteria (AOB) enriched from a sequencing batch reactor (SBR) were subjected to NO production pathway tests. The NO pathway test was initiated by supplying an inorganic medium to ensure an initial NH-N concentration of 160 mg-N/L, followed by NO (20 mg-N/L) and dual NHOH (each 17 mg-N/L) spikings to quantify isotopologs of gaseous NO (NO, NO, and NO). NO production was boosted by NHOH spiking, causing exponential increases in mRNA transcription levels of AOB functional genes encoding hydroxylamine oxidoreductase (haoA), nitrite reductase (nirK), and nitric oxide reductase (norB) genes. Predominant production of NO among NO isotopologs (46% of total produced NO) indicated that coupling of NHOH with NO produced NO via N-nitrosation hybrid reaction as a predominant pathway. Abiotic hybrid NO production was also observed in the absence of the AOB-enriched biomass, indicating multiple pathways for NO production in a PN bioreactor. The additional NO pathway test, where NH was spiked into 400 mg-N/L of NO concentration, confirmed that the hybrid NO production was a dominant pathway, accounting for approximately 51% of the total NO production.

Hybrid Nitrous Oxide Production from a Partial Nitrifying Bioreactor: Hydroxylamine Interactions with Nitrite.

The inhibitory effect of 20 substances of various chemical species on the anaerobic ammonia oxidation (anammox) activity of an enrichment culture, predominated by Candidatus Brocadia, was determined systematically by using a N tracer technique. The initial anammox rate was determined during first 25 min with a small-scale anaerobic batch incubation supplemented with possible inhibitors. Although Cu and Mn did not inhibit anammox, the remaining 18 substances [Ni, Zn, Co, [Formula: see text] , Fe, 4 amines, ethylenediaminetetraacetic acid (EDTA), ethylenediamine-N,N'-bis (2-hydroxyphenylacetic acid) (EDDHA), citric acid, nitrilotriacetic acid (NTA), N,N-dimethylacetamide (DMA), 1,4-dioxane, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF) and tetrahydrofuran (THF)] were inhibitory. Inhibitory effect of NTA, EDDHA, THF, DMF, DMA and amines on anammox was first determined in this study. Inhibitory effects of metals were re-evaluated because chelators, which may interfere inhibitory effect, have been used to dissolve metal salts into assay solution. The relative anammox activities as a function of concentration of each substance were described successfully (R > 0.91) either with a linear inhibition model or with a Michaelis-Menten-based inhibition model. IC values were estimated based on either model, and were compared. The IC values of the 4 chelators (0.06-2.7 mM) and 5 metal ions (0.02-1.09 mM) were significantly lower than those of the 4 amines (10.6-29.1 mM) and 5 organic solvents (3.5-82 mM). Although it did not show any inhibition within 25 min, 0.1 mM Cu completely inhibited anammox activity in 240 min, suggesting that the inhibitory effect caused by Cu is time-dependent.

Yuichi Suwa

Department of Biological Sciences,
Faculty of Science and Engineering,
Department of Biological Sciences, Faculty of Science and Engineering

Chuo University

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on ¹⁴NH₄⁺/¹⁵NH₄⁺ Analyses via Sequential Conversion to N₂O

Yuichi Suwa

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Biological Sciences,Faculty of Science and Engineering,Department of Biological Sciences, Faculty of Science and Engineering

Chuo University

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O

Department of Biological Sciences,
Faculty of Science and Engineering,
Department of Biological Sciences, Faculty of Science and Engineering

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on ¹⁴NH₄⁺/¹⁵NH₄⁺ Analyses via Sequential Conversion to N₂O