High Nitrite Concentrations Research Articles

Selective Aminothiazole‐Derivative Probe for Detection of Phosphate in Freshwater

AbstractPhosphate anions have been used in agriculture, the food industry, and cleaning products, and their excess causes eutrophication of drinking water and aquatic systems, affecting the entire aquatic ecosystem. This study developed an aminothiazole‐derivative selective probe to recognize phosphate, even in high levels of contaminants, through hydrogen donor groups using UV‐Vis and NMR spectroscopies to overcome the challenges. Chemosensors 1 depicted high sensibility and selectivity for PO43− anion demonstrated by the UV‐Vis; the limit of detection (LOD) for PO43− (2.4×10−7 mol dm−3) validated it as a chemosensor with low concentrations detection for anions, and 1 was utilized to detect and analyze real water samples with recoveries of 91 % and 109 %. NMR titrations confirmed that the binding mechanism of the chemosensors 1 occurred by hydrogen bonding of the NH amide group with that ion. Chemosensor 1 exhibited a low‐cost, easy‐to‐use, and selective phosphate detection in freshwater, even in high nitrite and nitrate anions concentrations in eutrophic environments.

Biomonitoring the status of aquatic bodies using zooplankton as surrogate species amidst urban landscape

The concept of surrogates in biodiversity assessments has been widely accepted in the recent years. Surrogates are taxonomic groups that indicate the overall biodiversity at a particular site. Zooplankton is an important component of the aquatic ecosystem, playing a major role in energy transfer between the phytoplankton or producers and the consumers at higher trophic levels. In this study zooplanktons were considered as surrogates for biomonitoring status of two aquatic bodies amidst urban landscape at the southern fringes of Kolkata, West Bengal, India through different seasons. Zooplankton diversity and abundance was found to vary with seasons in both the ponds in correlation with limnological parameters. Pond 1 was found to be larger in size, having partial macrophyte cover in comparison with Pond 2 which is smaller and devoid of any macrophyte cover over the study period. The Pond 1 elucidated higher diversity of zooplankton having higher water pH and phosphate concentration and less nitrite concentration. Pond 2 elaborated less zooplankton diversity with lower pH, less phosphate and higher nitrite concentration. Diversity and abundance of zooplankton surrogates provided valuable information about the status of water bodies amidst urban landscape and can be utilised as a tool for biomonitoring.

Enhancement of dissimilatory nitrate/nitrite reduction to ammonium of Escherichia coli sp. SZQ1 by ascorbic acid: Mechanism and performance

Dissimilatory nitrate reduction to ammonium (DNRA) can be used for nitrogen recovery. However, due to the low conversion efficiency of the DNRA process of microorganisms, the process cannot be industrially applied. Ascorbic acid (ASA) can improve DNRA efficiency of Escherichia coli sp. SZQ1 (E. coli). Experimental studies suggest that 10 g L−1 ASA promoted DNRA process of E. coli at high concentrations of nitrite (10–20 mM). In the 5 g L−1 ASA system, 9.2 mM nitrite was reduced to 8.21 mM ammonium by E. coli in 120 h. Mechanistic studies reveal that ASA reduced the oxidation-reduction potential (ORP) of the system and scavenged reactive oxygen species (ROS) in the cell of E. coli. Meanwhile, ASA was utilized by E. coli as the sole carbon source and provided electrons to DNRA process through ASA metabolic pathways. This study proposes a new strategy for increasing the efficiency of DNRA.

Determination of Nitrate and Nitrite in Swiss Chard (Beta vulgaris L. subsp. vulgaris) and Wild Rocket (Diplotaxis tenuifolia (L.) DC.) and Food Safety Evaluations.

Nitrite and nitrate levels in vegetables are a matter of concern due to their toxicity at high levels and nitrate high accumulation. Moreover, there is a lack of knowledge about their levels in some types of widely consumed vegetables such as chard and rocket. In this study, 124 Swiss chard and wild rocket samples were analyzed for determining nitrite and nitrate using validated and accredited analytical methods by ion chromatography with conductivity detection. High nitrite concentrations, up to 219.5 mg kg−1 f.w., were detected in one Swiss chard and three wild rocket samples. One Margin of Safety (MoS) value was <1. Regarding nitrate, in Swiss chard samples the mean concentration (2522.6 mg kg−1) was slightly higher than those reported in the literature for spinach and lettuce. No MoS was <1, but 83% of values were <100. Nitrate concentrations higher than the legal limit were quantified in 11 rucola samples. The verification of 25% of wild rocket samples with nitrate concentration higher than the legal limit confirmed the need for official control. This study also suggests the introduction of legal limits for nitrite/nitrate in Swiss chard and nitrite in wild rocket.

Impact of nitrite on partial nitrification in aerobic sewage treatment reactors under mainstream conditions

Stable partial nitrification is still difficult to achieve under mainstream conditions. High and low nitrite concentrations were established in two identical, completely mixed, continuous aerobic reactors in parallel to determine the effect of nitrite on partial nitrification under mainstream conditions. Influent ammonium (NH4+-N) concentrations of 50 ± 3 and 10 ± 2 mg/L were used to create high and low nitrite concentrations. Partial nitrification in the two reactors was established through an influent NH4+-N loading of 0.12 kg/(m3·d) and dissolved oxygen (DO) levels of 0.1–0.3 mg/L. In a low nitrite-type reactor, the specific activity of nitrite-oxidizing bacteria (NOB) was 0.061 ± 0.005 kg/(kg volatile suspended solids [VSS]·d), which was lower than that in the high nitrite reactor (0.085 ± 0.010 kg/(kg VSS·d)). Real-time quantitative PCR showed a significant correlation between the percentage of NOB in the bacterial communities and nitrite levels in the reactor. Compared to the NOB percentage in the high nitrite reactor (0.074 %), a lower percentage (0.049 %) occurred in the low nitrite reactor. A supplementary mathematical simulation indicated that a low nitrite concentration was critical for NOB repression at DO concentrations of 0.2–0.3 mg/L. Finally, the feasibility of the low nitrite strategy was demonstrated in a PN-ANAMMOX reactor with effluent recycling. Ammonium conversion efficiencies > 40.6 % and nitrite accumulation efficiencies > 43.1 % could be achieved at recycling ratios of 250–300 %, which created low nitrite concentrations (below 1.5 mg/L) in the aerobic zone.

ARG2 single-nucleotide polymorphism rs3742879 affects plasma arginase 2 levels, nitric oxide formation and antihypertensive therapy response in preeclampsia.

Aim: This work examined whether ARG1 (rs2781659, rs2781667, rs2246012 and rs17599586) and ARG2 (rs3742879 and rs10483801) single-nucleotide polymorphisms (SNPs) are associated with antihypertensive therapy responsiveness in preeclampsia (PE) and their effects on arginase isoforms and nitrite concentrations in responsive and nonresponsive patients. Methods: SNP genotypes were determined by TaqMan assays. Plasma arginase levels were measured by ELISA and nitrite concentrations were measured using an ozone-based chemiluminescence assay. Results: The G allele for ARG2 rs3742879 (A>G) was less frequent in nonresponsive compared with responsive patients (15.5%vs 24.7%, respectively)and the G carriers of the nonresponsive subgroup had lower arginase 2 (9.2±7.5ng/mlvs 19.1±17.3ng/ml)and higher nitrite concentrations (110.2±52.8nMvs 78.5±37.9nM) than carriers of theAA genotype (all p<0.05). Conclusion: ARG2 SNP rs3742879 is associated with diminished arginase 2 levels and increased nitric oxide formation in nonresponsive PE patients.

A Model Assessment of the Occurrence and Reactivity of the Nitrating/Nitrosating Agent Nitrogen Dioxide (•NO2) in Sunlit Natural Waters.

Nitrogen dioxide (•NO2) is produced in sunlit natural surface waters by the direct photolysis of nitrate, together with •OH, and upon the oxidation of nitrite by •OH itself. •NO2 is mainly scavenged by dissolved organic matter, and here, it is shown that •NO2 levels in sunlit surface waters are enhanced by high concentrations of nitrate and nitrite, and depressed by high values of the dissolved organic carbon. The dimer of nitrogen dioxide (N2O4) is also formed in the pathway of •NO2 hydrolysis, but with a very low concentration, i.e., several orders of magnitude below •NO2, and even below •OH. Therefore, at most, N2O4 would only be involved in the transformation (nitration/nitrosation) of electron-poor compounds, which would not react with •NO2. Although it is known that nitrite oxidation by CO3•− in high-alkalinity surface waters gives a minor-to-negligible contribution to •NO2 formation, it is shown here that NO2− oxidation by Br2•− can be a significant source of •NO2 in saline waters (saltwater, brackish waters, seawater, and brines), which offsets the scavenging of •OH by bromide. As an example, the anti-oxidant tripeptide glutathione undergoes nitrosation by •NO2 preferentially in saltwater, thanks to the inhibition of the degradation of glutathione itself by •OH, which is scavenged by bromide in saltwater. The enhancement of •NO2 reactions in saltwater could explain the literature findings, that several phenolic nitroderivatives are formed in shallow (i.e., thoroughly sunlit) and brackish lagoons in the Rhône river delta (S. France), and that the laboratory irradiation of phenol-spiked seawater yields nitrophenols in a significant amount.

Pollution and substrate characteristics are correlated with intertidal macroalgal community structure on the eastern Libyan coast

ABSTRACT This pioneering investigation relates pollution indicators and substrate characteristics to algal diversity at seven sites along the eastern Libyan coast during autumn 2018 and spring 2019. Seawater chemical composition and algal diversity exhibited marked temporal and spatial variability. High concentrations of inorganic phosphorus (Pi), nitrite (NO2 −) and nitrate (NO3 −), along with low dissolved oxygen (DO) were used as indicators of water pollution. Water pollution status and nature of substrate were correlated with algal distribution and diversity. The algal community was dominated by rhodophytes followed by chlorophytes and ochrophytes, whereas cyanophytes and xanthophytes were rare. Interestingly, Xanthophyta was represented by the freshwater alga Vaucheria piloboloides. Chlorophytes, particularly Ulva spp, were associated with polluted sites, whereas rhodophytes and ochrophytes dominated the more pristine sites. Chlorophytes, rhodophytes and xanthophytes were more abundant in the cold season (October–December), whereas cyanophytes and ochrophytes were found in greater abundance in the warm season (March–May). In addition to the effect of pollution and climate, the nature of the substrate had a profound influence on algal diversity. The agreement between frequency of occurrence and percentage cover observed in cyanophytes, chlorophytes and ochrophytes was less evident in rhodophytes. The present work concludes that the enhanced urbanization at the eastern Libyan coast, with emergence of point source pollution mainly of municipal and industrial origins, has impacted the diversity of algal communities, leading to dominance of Chlorophyta, particularly Ulva spp, over the other algal groups at polluted sites.

Evaluation of short-term toxicity of ammonia and nitrite on the survival of whiteleg shrimp, Litopenaeus vannamei juveniles

The effects of short-term toxicity of total ammonia nitrogen (TAN) and nitrite were estimated in juveniles of Litopenaeus vannamei under laboratory conditions. In the first experiment, L. vannamei juveniles were exposed to different concentrations of ammonia (0, 5, 10, 15, 20, 30, and 40 mg of TAN L-1) or nitrite (0, 5, 10, 20, 30, 40, and 50 mg of NO2–N L-1), using the static renewal method at a salinity of 20 ppt and pH 8.2. The survival rates of juveniles significantly decreased when exposed to increased concentrations of ammonia or nitrite during the 96 h bioassays. The 24, 48, 72, and 96 h LC50 values of TAN in juveniles were 45.5, 30.1, 13.8, and 6.3 mg L-1, respectively, while the LC50 values of NO2–N at 24, 48, 72, and 96 h were 37.6, 16.7, 8.8, and 4.8 mg L-1, respectively. Experiment 2 evaluated the tolerance of L. vannamei juveniles at various salinities (5, 10, 15, and 20 ppt) under a high concentration of ammonia or nitrite (5 mg L-1). Results showed that the survival rates of L. vannamei at 5 ppt and 10 ppt were significantly lower than those at 20 ppt after 72 h and 96 h of exposure.

Investigation of a Methemoglobinemia Outbreak Caused by Eating Sausages with High Concentrations of Nitrates and Nitrites in Trang Province, Thailand, January 2022

In late January 2022, a cluster of methemoglobinemia cases across five provinces of Thailand was notified to the regional public health authorities. A joint investigation was conducted aiming to describe characteristics of the outbreak in one of the provinces, traceback the suspected food, and recommend prevention and control measures. We conducted a cross-sectional descriptive study, interviewing the cases, reviewing their medical records, and interviewing their parents and treating physicians. An active case finding was conducted. A probable case was defined as a person who presented with acute central cyanosis with oxygen saturation less than 92% by pulse oximetry. Suspected food samples were collected for nitrates and nitrites testing. Three cases (2 males, 1 female) were identified and there was no death. Their ages ranged from 8–12 years. The sausages came from the same source and were found to have high concentrations of nitrates (1,270.8–1,690.0 mg/kg) and nitrites (3,554.5–3,776.2 mg/kg). The sausages were identified as a likely cause of the outbreak. Government regulation, product liability laws, and food safety concerns among food retailers and customers are important to reduce the impact of consuming unsafe foods.

Startup strategies for mainstream anammox polishing in moving bed biofilm reactors

AbstractThis study evaluated startup strategies for mainstream polishing anammox moving bed biofilm reactors (MBBRs) without anammox bacterial (AMX) biomass inoculation. Two types of startups were tested: anammox only (no external carbon addition) and partial denitrification/anammox (PdNA) with glycerol addition. Reactors were started with either virgin carriers or carriers with a preliminary biofilm from a mainstream aerobic integrated fixed‐film activated sludge (IFAS) process. Three pilot‐scale startups were completed under the following conditions: anammox‐only with preliminary biofilm carriers, PdNA with preliminary biofilm carriers, and PdNA with virgin carriers. AMX presence was confirmed via quantitative polymerase chain reaction (qPCR) after 57, 57, and 77 days, respectively. Prior to AMX detection, average influent concentrations of ammonia and nitrite ranged from 1.7–2.7 mg/L and 0.98–1.8 mg/L, respectively. This study demonstrated that AMX can be grown on carriers without AMX seeding under mainstream conditions (temperature 17–29°C, low ammonia and nitrite), regardless of whether nitrite came from upstream or partial denitrification within the reactor. This study also showed that using preliminary biofilm carriers can decrease startup time by approximately 1 month. These results address critical questions for moving mainstream anammox processes to full‐scale implementation, and suggest that PdNA MBBRs are feasible and sustainable for full‐scale ammonia, nitrate, and nitrite polishing to meet stringent total nitrogen requirements.Practitioner Points This research will help utilities develop methods for starting up mainstream anammox MBBRs without the barrier of anammox biomass seeding. Preliminary biofilm carriers accelerated startup time in a PdNA MBBR, but a virgin carrier reactor started up in a similar timeframe, contrary to expectations. Also, contrary to expectations, high concentrations of ammonia and nitrite are not necessary for startup of an anammox or PdNA MBBR.

Technological characterization and flavor-producing potential of lactic acid bacteria isolated from traditional dry fermented sausages in northeast China

Thirty-seven lactic acid bacteria (LAB) strains were isolated from traditional dry sausages collected from Northeast China, including Latilactobacillus sakei (29 strains), Lactiplantibacillus plantarum (4 strains), Latilactobacillus curvatus (2 strains), Weissella hellenica (1 strain), and Lactococcus lactis (1 strain). Some LAB strains had tolerance to high concentrations of sodium chloride (6%), sodium nitrite (150 mg/L NaNO2), and acid (pH 4.0). They showed good growth and acidification properties and antimicrobial activity. Among them, five LAB strains that exhibited the best technological properties were selected and inoculated in the sausage model to explore their roles in flavor development. The contents of total free amino acids (FAAs) decreased ranging from 109.11 mg/g to 58.06 mg/g. A total of 46 volatile compounds were identified and the contents of volatile compounds increased in the sausage model during fermentation. Partial least squares regression analysis showed that Lb. sakei HRB10, Lb. plantarum MDJ2, W. hellenica HRB6, and Lc. lactis HRB0 promoted the generation of FAAs and volatile compounds in the sausage model. These findings demonstrated that the autochthonous LAB species are promising for the production of sausage with better flavor and fermentation performance.

Simultaneous nitrification and denitrification by Pseudomonas sp. Y-5 in a high nitrogen environment.

Pseudomonas sp. Y-5, a strain with simultaneous nitrification and denitrification (SND) capacity, was isolated from the Wuhan Municipal Sewage Treatment Plant. This strain could rapidly remove high concentrations of inorganic nitrogen. Specifically, Pseudomonas sp. Y-5 removed 103 mg/L of NH4+-N in 24 h without nitrate or nitrite accumulation when NH4+-N was its sole nitrogen source. The NH4+-N removal efficiency (RE) was 97.26%, and the average removal rate (RR) was 4.30 mg/L/h. Strain Y-5 also removed NO3--N and NO2--N even in aerobic conditions, with average RRs of 4.39 and 4.23 mg/L/h, respectively, and REs of up to 99.34% and 95.81% within 24 h. When cultured in SND medium (SNDM-1), strain Y-5 achieved an NH4+-N RE of up to 97.80% and a total nitrogen (TN) RE of 93.01%, whereas NO3--N was fully depleted in 48 h. Interestingly, high nitrite concentrations did not inhibit the nitrification capacity of Y-5 when grown in SNDM-2, the RE of NH4+-N and TN reached 96.29% and 94.26%, respectively, and nitrite was consumed completely. Strain Y-5 also adapted well to high concentrations of ammonia (~401.68 mg NH4+-N/L) or organic nitrogen (~315.12 mg TN/L). Our results suggested that Pseudomonas sp. Y-5 achieved efficient simultaneous nitrification and denitrification, thus demonstrating its potential applicability in the treatment of nitrogen-polluted wastewater.

Continuous monitoring of dissolved inorganic nitrogen (DIN) transformations along the waste-vadose zone - groundwater path of an uncontrolled landfill, using multiple N-species isotopic analysis

Landfill leachates contain a heavy load of dissolved inorganic nitrogen (DIN), posing a threat to water resources. Therefore, it is highly important to understand the processes that control its evolution (speciation, accumulation, or attenuation) during the percolation of leachates through the unsaturated zone, finally affecting the groundwater. However, tracking DIN transformations in this complex and inaccessible environment is challenging, and knowledge concerning this important topic under field conditions is scarce.The presented study used a unique monitoring system that allows sampling of repetitive samples from within the waste and the unsaturated zone. An array of 8 wells penetrating the underlying aquifer completed the spatial observation. Multiple N-species isotopic approach was applied to discern the dominating N-involving processes over the continuum - from the waste mound through the unsaturated zone and the underlying aquifer. Despite the considerable heterogeneity observed throughout the profile, the results provided a cohesive and valuable reflection of the evolution of the inorganic nitrogen pool in this highly contaminated environment.Leachates inside the waste had reducing characteristics with high accumulation of ammonium (up to 360 mg/l NH4+-N), and a distinct δ15N-NH4+ range (-3‰ to +10‰). The upper layers of the unsaturated zone underneath the landfill margins found to be aerated, promoting N oxidation which resulted in the accumulation of nitrate in the leachates (up to 490 mg/l NO3—N). Exceptionally high concentrations of nitrite (up to 126 mg/l NO2—N) were found as oxygen levels decreased in deeper sections of the vadose zone. Enrichment of δ15N-NO2− compared to δ15N-NO3− indicated the significance of autotropic nitrite reduction, controlling the DIN composition, correlated with NO2− accumulation and net DIN attenuation. The δ15N: δ18O ratio implied co-occurrence of denitrification in the leachates, even in the more oxidized sections, further contributing to N-attenuation in the unsaturated zone. In the aquifer, δ15N-NH4+ values and δ15N: δ18O ratio linked N contamination to the leachates source. The encounter with the oxidized groundwater promoted intensive nitrification. δ15N-NO2− values in the groundwater were lighter than both δ15N-NH4+ and δ15N-NO3− by 22‰ to 62‰, implying the co-occurrence of nitrification-denitrification processes. The effect of denitrification grew with decreasing dissolved oxygen (DO) levels below 0.5 mg/l towards the center of the plume, contributing to net DIN attenuation in the plume.The findings are significant for any consideration of the risk posed by DIN, as well as remediation measures, in a landfill environment and other sites with a heavy load of degrading organic matter.

Characterization of the facultative anaerobic Pseudomonas stutzeri strain HK13 to achieve efficient nitrate and nitrite removal

A new facultative anaerobic denitrifier was isolated from anoxic activated sludge and identified as Pseudomonas stutzeri strain HK13. Single-factor experiments indicated that the optimal conditions for nitrate removal were a C/N ratio of 8, an initial pH of 7–10, a shaking speed of 100 rpm, and a temperature of 30–40 °C. When 100 mg/L NO3--N and NO2--N were used separately as sole nitrogen sources, the strain exhibited efficient denitrification ability with total nitrogen (TN) removal efficiencies of 98.22% and 98.58%, respectively, in 15 h with the corresponding maximum removal rates of 20.03 and 21.77 mg/L/h. And there was no nitrite accumulation finally in the nitrate denitrification system. In addition, 97.42% total oxidized nitrogen (TON) was removed at 20 °C and 93.46% NO3--N was reduced at 45 °C, suggesting that strain HK13 had a wide range of temperature and pH to adapt to the environment. Moreover, strain HK13 exhibited a notable ability to tolerate high nitrate loading (initial NO3--N > 450 mg/L) with a TON removal amount of over 200 mg/L/day. These findings demonstrate that strain HK13 is effective for nitrogen removal in wastewaters containing high concentrations of nitrate and nitrite.

Nitrite Triggers Reprogramming of the Oral Polymicrobial Metabolome by a Commensal Streptococcus.

Commensal streptococci regulate health and homeostasis within oral polymicrobial communities. Remarkably, high salivary nitrite concentrations have also been associated with improved health in the oral cavity. We previously demonstrated that nitrite assists hydrogen peroxide-producing oral commensal streptococci in regulating homeostasis via the generation of reactive nitrogen species (RNS), which have antimicrobial activity on oral pathogens. However, it is unknown how nitrite and commensal streptococci work in concert to influence the metabolome of oral polymicrobial communities. In this study, we report that nitrite aids commensal streptococci in the inhibition of multi-kingdom pathogens that reside in distinct oral niches, which supports commensal dominance. More importantly, we show that commensal streptococci utilize nitrite to drive the metabolic signature of multispecies biofilms in a manner that supports commensal metabolism and resistance to RNS, and restricts metabolic processes that are required for pathogen virulence. Taken together, our study provides insight into how commensal streptococci use nitrite to trigger shifts in the oral polymicrobial metabolome to support health and homeostasis.

Strategy for rapid recovery of simultaneous sulfide and nitrite removal under high substrate inhibition

The paper deals with the strategy for a quick recovery of reactor treating sulfide and nitrite simultaneously under inhibition caused by high substrate concentration. For influent sulfide concentration of 360 mg S/L, respective sulfide and nitrite removal percentages dropped to 74.19% and 14.33% due to inhibition caused by high sulfide and nitrite concentrations. It was found that reduction in the influent substrate concentration (300 mg S/L) could not revive the nitrite removal performance in 4 days’ operation, which still showed a declining tendency from 47.16% to 18.52%. Regulating the influent pH around 6.70 ± 0.10, it only took 4 days to recover the performance for 300 mg S/L. Furthermore, at influent sulfide concentration increased to 360 mg S/L, respective sulfide and nitrite removal percentages were 99.76 ± 0.27% and 100.00%. The strategy of regulating influent pH could recover the process performance in a short term, which would provide great convenience for subsequent process research.

Genome-Resolved Metagenomic Insights into Massive Seasonal Ammonia-Oxidizing Archaea Blooms in San Francisco Bay.

ABSTRACTAmmonia-oxidizing archaea (AOA) are key for the transformation of ammonia to oxidized forms of nitrogen in aquatic environments around the globe, including nutrient-rich coastal and estuarine waters such as San Francisco Bay (SFB). Using metagenomics and 16S rRNA gene amplicon libraries, we found that AOA are more abundant than ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), except in the freshwater stations in SFB. In South SFB, we observed recurrent AOA blooms of “Candidatus Nitrosomarinus catalina” SPOT01-like organisms, which account for over 20% of 16S rRNA gene amplicons in both surface and bottom waters and co-occur with weeks of high nitrite concentrations (>10 μM) in the oxic water column. We observed pronounced nitrite peaks occurring in the autumn for 7 of the last 9 years (2012 to 2020), suggesting that seasonal AOA blooms are common in South SFB. We recovered two high-quality AOA metagenome-assembled genomes (MAGs), including a Nitrosomarinus-like genome from the South SFB bloom and another Nitrosopumilus genome originating from Suisun Bay in North SFB. Both MAGs cluster with genomes from other estuarine/coastal sites. Analysis of Nitrosomarinus-like genomes show that they are streamlined, with low GC content and high coding density, and harbor urease genes. Our findings support the unique niche of Nitrosomarinus-like organisms which dominate coastal/estuarine waters and provide insights into recurring AOA blooms in SFB.IMPORTANCE Ammonia-oxidizing archaea (AOA) carry out key transformations of ammonia in estuarine systems such as San Francisco Bay (SFB)—the largest estuary on the west coast of North America—and play a significant role in both local and global nitrogen cycling. Using metagenomics and 16S rRNA gene amplicon libraries, we document a massive, recurrent AOA bloom in South SFB that co-occurs with months of high nitrite concentrations in the oxic water column. Our study is the first to generate metagenome-assembled genomes (MAGs) from SFB, and through this process we recovered two high-quality AOA MAGs, one of which originated from bloom samples. These AOA MAGs yield new insight into the Nitrosopumilus and Nitrosomarinus-like lineages and their potential niches in coastal and estuarine systems. Nitrosomarinus-like AOA are abundant in coastal regions around the globe, and we highlight the common occurrence of urease genes, low GC content, and range of salinity tolerances within this lineage.

Gut microbiota mediated the toxicity of high concentration of dietary nitrite in C57BL/6 mice

Growing evidence indicates that exposure to high levels of nitrite for a prolonged time has adverse health effects. Although gut microbiota is responsible for the transformation of nitrite in the gut, the evidence concerning whether gut microbiota mediates the toxicity of nitrite is still lacking. The present study addressed the long-term effects of dietary nitrite on male C57BL/6 mice and employed fecal microbiota transplantation (FMT) to reveal whether gut microbiota mediated the effects of nitrite. Furthermore, the effect of azoxymethane (AOM) on gut microbiota was detected for mice drinking normal or nitrite-containing water. High nitrite had toxic effects on C57BL/6 mice. Meanwhile, high nitrite induced skin lesions in mice, accompanied with increased serum ALT, colon IL-6, TNF-α, and MDA levels, together with decreased serum Cr, colon sIgA, and T-AOC levels. After fecal microbiota was transplanted into the normal mice, the nitrite-regulated gut microbiota could also induce skin lesions, coupled with reduced serum Cr, and increased colon MDA. The high dose of nitrite caused the upregulations of Alistipes, Prevotella, and Ruminococcus, which could be transplanted into normal mice through FMT. Inversely, gut microbiota from normal mice reduced the effects of nitrite on serum ALT and Cr, together with colon sIgA and MDA. Gut microbiota from normal mice could also upregulate metabolic genes and downregulate stress genes in the nitrite-treated mice. It might due to the upregulation of Akkermansia and Parabacteroides caused by FMT from normal water-treated mice to nitrite-treated mice. In addition, AOM exhibited to be more toxic to the colon in the nitrite-treated mice in comparison with normal water-treated mice, and it might be due to the expression of Hspa1a and Hspa1b in the colon. Interestingly, gut microbiota was more influenced by AOM in the normal water-treated mice than the nitrite-treated mice. Overall, these data demonstrated that gut microbiota mediated the toxicity of a high concentration of dietary nitrite.

Specific Denitrifying and Dissimilatory Nitrate Reduction to Ammonium Bacteria Assisted the Recovery of Anammox Community From Nitrite Inhibition.

The anaerobic ammonium oxidation (anammox) by autotrophic anaerobic ammonia-oxidizing bacteria (AnAOB) is a biological process used to remove reactive nitrogen from wastewater. It has been repeatedly reported that elevated nitrite concentrations can severely inhibit the growth of AnAOB, which renders the anammox process challenging for industrial-scale applications. Both denitrifying (DN) and dissimilatory nitrate reduction to ammonium (DNRA) bacteria can potentially consume excess nitrite in an anammox system to prevent its inhibitory effect on AnAOB. However, metabolic interactions among DN, DNRA, and AnAOB bacteria under elevated nitrite conditions remain to be elucidated at metabolic resolutions. In this study, a laboratory-scale anammox bioreactor was used to conduct an investigation of the microbial shift and functional interactions of AnAOB, DN, and DNRA bacteria during a long-term nitrite inhibition to eventual self-recovery episode. The relative abundance of AnAOB first decreased due to high nitrite concentration, which lowered the system’s nitrogen removal efficiency, but then recovered automatically without any external interference. Based on the relative abundance variations of genomes in the inhibition, adaptation, and recovery periods, we found that DN and DNRA bacteria could be divided into three niche groups: type I (types Ia and Ib) that includes mainly DN bacteria and type II and type III that include primarily DNRA bacteria. Type Ia and type II bacteria outcompeted other bacteria in the inhibition and adaptation periods, respectively. They were recognized as potential nitrite scavengers at high nitrite concentrations, contributing to stabilizing the nitrite concentration and the eventual recovery of the anammox system. These findings shed light on the potential engineering solutions to maintain a robust and efficient industrial-scale anammox process.