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This study elucidates the impact of fluctuating influent conditions and in situ ultrasonic wave exposure on the stability of aerobic granular sludge (AGS) in the treatment of simulated wastewater emanating from rare earth mining operations. During a stable influent period spanning from Day 1 to Day 95, the seed granules underwent an initial disintegration followed by a re-granulation phase. The secondary granulation was achieved on Day 80 and Day 40 for the ultrasonic reactor (R1) and the control reactor (R2), respectively. Notably, granules formed in R1 exhibited a more porous structure compared to those generated in R2. Subsequently, when the ammonia nitrogen in the influent oscillated between 100 and 500 mg/L during Days 96-140, both reactors yielded compact and densely structured granules. Nitrogen removal profiles were comparable between the two reactors: the removal efficiencies for ammonia nitrogen and total inorganic nitrogen escalated from 95% and 80%, respectively, during Days 1-95, to 95% and 90%, respectively, post-Day 140. A suite of performance metrics indicated that steady-state granules from R1 outperformed those from R2 across several parameters. Specifically, the nitrification/denitrification rates, and relative abundance of denitrifying bacteria were all higher in granules from R1. Conversely, the relative abundance of nitrifying bacteria was comparable between granules from both reactors. However, R1 granules demonstrated lower sludge concentration and smaller average particle size than their R2 counterparts. In conclusion, the AGS system demonstrated robust resilience to fluctuating ammonia nitrogen, and the application of ultrasonic waves significantly enhanced granular activity while achieving in situ sludge reduction. [ABSTRACT FROM AUTHOR]

The transmembrane nitrate reductase (Nar) is the first enzyme in the dissimilatory alternate anaerobic nitrate respiratory chain in denitrifying bacteria. To date, there has been no real-time method to determine its specific activity embedded in its native membrane; here, we describe such a new method, which is useful with the inside-out membranes of Paracoccus denitrificans and other denitrifying bacteria. This new method takes advantage of the native coupling of the endogenous NADH dehydrogenase or Complex I with the reduction of nitrate by Nar through the quinone pool of the inner membranes of P. denitrificans. This is achieved under previously reached anaerobic conditions. Inner controls confirming the specific Nar activity determined by this new method were made by the total inhibition of the Nar enzyme by sodium azide and cyanide, well-known Nar inhibitors. The estimation of the Michaelis–Menten affinity of Nar for NO3− using this so-called Nar-JJ assay gave a Km of 70.4 μM, similar to previously determined values. This new Nar-JJ assay is a suitable, low-cost, and reproducible method to determine in real-time the endogenous Nar activity not only in P. denitrificans, but in other denitrifying bacteria such as Brucella canis, and potentially in other entero-pathogenic bacteria. [ABSTRACT FROM AUTHOR]

Iron–carbon galvanic-cell-supported autotrophic denitrification (IC-ADN) is a burgeoning efficient and cost-effective process for low-carbon wastewater treatment. This study revealed the influence of organic carbon (OC) and dissolved oxygen (DO) on IC-ADN in terms of functional and microbiological characteristics. The nitrogen removal efficiency increased to 91.6% and 94.7% with partial organic carbon source addition to COD/TN of 1 and 3, respectively. The results of 16S rRNA high-throughput sequencing with nirS and cbbL clone libraries showed that Thiobacillus was the predominant autotrophic denitrifying bacteria (ADB) in the micro-electrolysis-based autotrophic denitrification, which obtained nitrogen removal efficiency of 80.9% after 96 h. The ADBs shifted gradually to heterotrophic denitrifying bacteria Thauera with increasing COD/TN ratio. DO concentration of 0.8 rarely affected the denitrification efficiency and the denitrifying communities. When the DO concentration increased to 2.8 mg/L, the nitrogen removal efficiency decreased to 69.1%. These results demonstrated that autotrophic denitrification was notably affected by COD/TN and high DO concentration, which could be used to acquire optimum conditions for nitrogen removal. These results provided an in-depth understanding of the influential factors for galvanic-cell-based denitrification and helped us construct a stable and highly efficient treatment process for insufficient carbon source wastewater. [ABSTRACT FROM AUTHOR]

Background: Lake Bonney, which is divided into a west lobe (WLB) and an east lobe (ELB), is a perennially ice-covered lake located in the McMurdo Dry Valleys of Antarctica. Despite previous reports on the microbial community dynamics of ice-covered lakes in this region, there is a paucity of information on the relationship between microbial genomic diversity and associated nutrient cycling. Here, we applied gene- and genome-centric approaches to investigate the microbial ecology and reconstruct microbial metabolic potential along the depth gradient in Lake Bonney. Results: Lake Bonney is strongly chemically stratified with three distinct redox zones, yielding different microbial niches. Our genome enabled approach revealed that in the sunlit and relatively freshwater epilimnion, oxygenic photosynthetic production by the cyanobacterium Pseudanabaena and a diversity of protists and microalgae may provide new organic carbon to the environment. CO-oxidizing bacteria, such as Acidimicrobiales, Nanopelagicales, and Burkholderiaceae were also prominent in the epilimnion and their ability to oxidize carbon monoxide to carbon dioxide may serve as a supplementary energy conservation strategy. In the more saline metalimnion of ELB, an accumulation of inorganic nitrogen and phosphorus supports photosynthesis despite relatively low light levels. Conversely, in WLB the release of organic rich subglacial discharge from Taylor Glacier into WLB would be implicated in the possible high abundance of heterotrophs supported by increased potential for glycolysis, beta-oxidation, and glycoside hydrolase and may contribute to the growth of iron reducers in the dark and extremely saline hypolimnion of WLB. The suboxic and subzero temperature zones beneath the metalimnia in both lobes supported microorganisms capable of utilizing reduced nitrogens and sulfurs as electron donors. Heterotrophs, including nitrate reducing sulfur oxidizing bacteria, such as Acidimicrobiales (MAG72) and Salinisphaeraceae (MAG109), and denitrifying bacteria, such as Gracilimonas (MAG7), Acidimicrobiales (MAG72) and Salinisphaeraceae (MAG109), dominated the hypolimnion of WLB, whereas the environmental harshness of the hypolimnion of ELB was supported by the relatively low in metabolic potential, as well as the abundance of halophile Halomonas and endospore-forming Virgibacillus. Conclusions: The vertical distribution of microbially driven C, N and S cycling genes/pathways in Lake Bonney reveals the importance of geochemical gradients to microbial diversity and biogeochemical cycles with the vertical water column. [ABSTRACT FROM AUTHOR]

A novel aerobic denitrifying bacterium Bacillus cereus J1 was isolated from a sewage treatment plant. Its characteristics under two distinct nitrogen sources were systematically investigated. According to the results of whole-genome sequencing, we inferred that strain J1 removes nitrogen through processes such as aerobic denitrification, dissimilatory nitrate reduction to ammonium, and ammonium assimilation. The degradation process of COD and total inorganic nitrogen (TIN) correlated to the zero-order degradation kinetics equation, and the maximum removal rate of NO3−−N reached 3.17 mg/L/h and that of NH4+−N was 3.79 mg/L/h. Utilizing single-factor experiments and response surface methodology, the optimal conditions for nitrate removal were determined as a shaking speed of 115 rpm, COD/nitrogen mass (C/N ratio) of 12.25, and salinity of 3.44 g/L, with the C/N ratio exerting the most significant influence. Similarly, for the maximum ammonium removal, the ideal conditions involved a shaking speed of 133 rpm, C/N ratio of 29, and salinity of 13.30 g/L, with the shaking speed exerting the most significant influence. These findings demonstrate that large amounts of ammonium and nitrate can be quickly removed with the help of Bacillus cereus J1, indicating that strain J1 may be applied to alleviate nitrogen pollution in aquatic environments. [ABSTRACT FROM AUTHOR]

Variation in the condition of marine sediments provides selective preservation milieus, which act as a key determinant for the abundance and distribution of dinoflagellate resting cysts in natural sediments. Microbial degradation is an understudied biological factor of potential importance in the processes. However, gaps remain in our knowledge about the fundamental information of the bacterial consortia associated with dinoflagellate resting cysts both in laboratory cultures and in the field. Here we used Scrippsiella acuminata as a representative of cyst-producing dinoflagellates to delineate the diversity and composition of bacterial microbiomes co-existing with the laboratory-cultured resting cysts, and to explore possible impacts of low temperature, darkness, and anoxia (the mock conditions commonly observed in marine sediments) on the associated bacterial consortia. Bacterial microbiome with high diversity were revealed associated with S. acuminata at resting stage. The mock conditions could significantly shift bacterial community structure and exert notably inhibitory effects on growth-promoting bacteria. Resting cysts under conditions typically observed in marine sediments fostered bacterial microbiomes with more diverse trophic strategies, characteristic of prominently enriched anaerobic chemotrophic bacteria generating energy via respiration with several different terminal electron acceptors, which yielded more acidic milieu unfavorable for the preservation of calcareous resting cysts. Our findings suggest that there is complex and dynamic interaction between dinoflagellates resting cysts and the associated bacterial consortia in natural sediments. This intrinsic interaction may influence the maintenance and/or accumulation of dinoflagellate resting cysts with potential of germination and initiation blooms in the field. [ABSTRACT FROM AUTHOR]

Veillonella spp. are nitrate-reducing bacteria with anaerobic respiratory activity that reduce nitrate to nitrite. They are obligate anaerobic, Gram-negative cocci that ferment lactate as the main carbon source and produce short-chain fatty acids (SCFAs). Commensal Veillonella reside in the human body site where lactate level is, however, limited for Veillonella growth. In this study, nitrate was shown to promote the anaerobic growth of Veillonella in the lactate-deficient media. We aimed to investigate the underlying mechanisms and the metabolism involved in nitrate respiration. Nitrate (15 mM) was demonstrated to promote Veillonella dispar growth and viability in the tryptone-yeast extract medium containing 0.5 mM L-lactate. Metabolite and transcriptomic analyses revealed nitrate enabled V. dispar to actively utilize glutamate and aspartate from the medium and secrete tryptophan. Glutamate or aspartate was further supplemented to a medium to investigate individual catabolism during nitrate respiration. Notably, nitrate was demonstrated to elevate SCFA production in the glutamate-supplemented medium, and further increase tryptophan production in the aspartate-supplemented medium. We proposed that the increased consumption of glutamate provided reducing power for nitrate respiration and aspartate served as a substrate for fumarate formation. Both glutamate and aspartate were incorporated into the central metabolic pathways via reverse tricarboxylic acid cycle and were linked with the increased production of acetate, propionate, and tryptophan. This study provides further understanding of the promoted growth and metabolic mechanisms by commensal V. dispar utilizing nitrate and specific amino acids to adapt to the lactate-deficient environment. [ABSTRACT FROM AUTHOR]

The objective of our study was to assess the effect of nitrate-reducing bacteria and natural nitrate source on the sensory properties of dried meat biltong. Appearance, colour on the cut, aroma, taste and juiciness, acidity, sweetness, and consistency were evaluated. The members of the panel gave their ratings between 1 and 5 according to the characteristics of the samples, with 1 being the lowest rating and 5 being the best rating. In the sensory evaluation of dried meat samples without oxygen absorber packaging, the group (P2) with bacterial culture, celery powder, and NaCl showed the highest scores for appearance, taste, juiciness, acidity, and consistency. Notably, P3 samples had significantly lower consistency scores compared to P2. Additionally, sample P1, with bacterial culture and NaCl, improved the colour on the cut compared to the negative control (C) with only NaCl. The best aroma and sweetness results were in the P3 group with curing salt, although these differences were not statistically significant (P = 0.05). The sensory evaluation of dried meat samples packaged with an oxygen absorber revealed that the combination of bacterial culture, celery powder, and NaCl (AP2) had the most positive influence on appearance, colour on the cut, and consistency. The group with the absorber and curing salt (AP3) showed improved aroma, taste, and juiciness. Acidity was primarily affected by the addition of bacterial culture and NaCl (AP1), as well as by AP2 and AP3. The most pleasing sweetness was achieved by adding bacterial culture and NaCl to samples with the absorber (AP1). Samples with the best consistency when packaged with the absorber were those with bacterial culture and celery powder (AP2). In summary, among dried meat samples with oxygen absorber, those with added curing salt (AP3) had the best overall sensory evaluation compared to the negative control with NaCl (AC). For samples without an oxygen absorber, the highest overall sensory scores were in the group with bacterial culture and celery powder, surpassing the control with NaCl (C). The use of an oxygen absorber and curing salt proved to be effective in the production of biltong, but replacing the curing salt with NaCl and the addition of celery powder and bacterial culture significantly improved the sensory evaluation compared to the other groups (except AP3). [ABSTRACT FROM AUTHOR]

Simple Summary: The nitrogen cycling process in alpine wetlands is profoundly affected by precipitation changes. Utilizing high-throughput sequencing analysis of nirS-type functional genes, this study delved into the dynamic response mechanism of nirS-type denitrifiers to precipitation changes in the alpine wetland of Qinghai Lake. The findings revealed that a 50% increase in rainfall shifted the community assembly process of denitrifiers from deterministic to stochastic. Dominant microflora at the genus level responded significantly to precipitation changes, with aer-obic bacteria comprising the majority of differentially abundant taxa. As precipitation in-creased, the complexity of the microbial interaction network decreased. Precipitation notably emerged as the primary regulator of nirS-type denitrifiers, accounting for 51% of the variation in community composition. In summary, this study offers a fresh perspective for investigating the ecological processes of nitrogen cycling in alpine ecosystems. The nitrogen cycling process in alpine wetlands is profoundly affected by precipitation changes, yet the dynamic response mechanism of denitrifiers to long-term precipitation shifts in the alpine wetland of the Qinghai-Tibet Plateau remains enigmatic. Utilizing high-throughput sequencing analysis of nirS-type functional genes, this study delved into the dynamic response mechanism of nirS-type denitrifiers to precipitation changes in the alpine wetland of Qinghai Lake. The findings revealed that nirS-type denitrifiers in the alpine wetland of Qinghai Lake were primarily Proteobacteria, and Alpha diversity exhibited a negative correlation with the precipitation gradient, with deterministic processes predominating in the community assembly of denitrifying microbes. A 50% increase in rainfall shifted the community assembly process of denitrifiers from deterministic to stochastic. Dominant microflora at the genus level responded significantly to precipitation changes, with aerobic bacteria comprising the majority of differentially abundant taxa (55.56%). As precipitation increased, the complexity of the microbial interaction network decreased, and a 25% reduction in precipitation notably elevated the relative abundance of three key functional groups: chemoheterotrophic, aerobic chemoheterotrophic, and nitrogen fixation. Precipitation notably emerged as the primary regulator of nirS-type denitrifiers in the alpine wetland of Qinghai Lake, accounting for 51% of the variation in community composition. In summary, this study offers a fresh perspective for investigating the ecological processes of nitrogen cycling in alpine ecosystems by examining the diversity and community composition of nirS-type denitrifiers in response to precipitation changes. [ABSTRACT FROM AUTHOR]

The single-cycle transient high-concentration organic load shock test was conducted on the micropressure swirl reactor (MPSR) and sequencing batch reactor (SBR) to assess their capability to different levels of transient organic load shock (OLS), including pollutant removal, sludge characteristics, and microbial characteristics. The results indicated that the impact-resistance of biological treatment systems was related to reactor structure and microbial community distribution. When subjected to transient chemical oxygen demand (COD) load of 0.81, 1.28, and 1.70 g / (L · d a y) , respectively, both reactors exhibited effective organic removal capabilities. Compared with MPSR, within a certain shock range, nitrification in the SBR was less affected by shock and had a higher effect on nitrogen and phosphorus removal. However, when shock load reached 1.70 gCOD/(L·day) , the denitrification was sufficient in the MPSR, and microorganisms continued to secrete polysaccharides (PS), which was beneficial for adsorbing pollutants and resisting impacts. Under steady-state conditions, the SBR exhibited excellent nitrification with a relative abundance of 60.7% for nitrifying functional groups such as Thiothrix. Compared with the SBR, the MPSR displayed a higher microbial community diversity, with a variety of phosphorus-removing bacteria and denitrifying bacteria genera occupying aerobic and anoxic partitions within the same space, which was profitable for effective denitrification and phosphorus removal under high OLS. Besides, the enrichment of Flavobacterium and Zoogloea sp. at high concentrations significantly enhanced the MPSR's resistance to OLS. This study provides a theoretical basis for effective measures by different processes in response to organic load shocks. [ABSTRACT FROM AUTHOR]

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Copyright of Journal of Chongqing University of Technology (Natural Science) is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Tetracycline and copper ion are common pollutants in wastewater, and the effects of mixed pollutants on microorganisms in wastewater biological treatment have been less studied. In order to reveal the effects of mixed pollutants of tetracycline and copper ion on the microorganisms during the biological phosphorus removal, three ratios of tetracycline and copper ions were designed by the direct equipartition ray method. The relative abundance and diversity of microbial community were investigated, and the microbial interactions were revealed through microbiological methods. The results demonstrated that, for three different ratios, the inhibitory effect of specific phosphorus uptake rate became more significant with the increase of the tetracycline-copper ions concentration and the reaction time. The microbial community decreased with the increase of the proportion of tetracycline in different ratios. The relative abundance of Acinetobacter decreased with the increase of the proportion of tetracycline, while the relative abundance of Ca.Competibacter was higher under the conditions of low mixtures concentrations. Positive interactions and symbiotic relationships among microorganisms were predominant for three different ratios. However, as the proportion of tetracycline increased, the community structure of microorganisms shifted from phosphate-accumulating organisms to glycogen accumulating organisms and denitrifying bacteria. This study can provide a reference for the effect of mixed pollutants on microorganisms and the mechanism of wastewater treatment. [ABSTRACT FROM AUTHOR]

This paper investigated the effect of nitrogen loading rates (NLRs) on the stability of aerobic granular sludge (AGS) for treating simulated ionic rare earth mine wastewater with high ammonia nitrogen and extremely low organic content. Mature AGS from a sequencing batch reactor (SBR) was seeded into five identical SBRs (R1, R2, R3, R4 and R5). The five reactors were operated with different NLRs (0.2, 0.4, 0.8, 1.2 and 1.6 kg/m3·d). After 30 days of operation, R1, R2 and R5 were dominated by broken granules, while most of the granules in R3 and R4 still maintained a complete structure. The properties of granules from R1, R2, R3, R4 and R5 deteriorated to varying degrees, while the granules from R3 and R4 showed better stability than that from R1, R2 and R5. In R1, R2, R3 and R4, the steady-state ammonia nitrogen removal efficiencies were all greater than 90%, and the steady-state removal efficiencies of total inorganic nitrogen (TIN) were approximately 30%. In R5, the removal efficiencies of ammonia nitrogen and TIN were both approximately 70%. The dominant nitrifying and denitrifying bacterial genera of the granules from the five reactors were Nitrosomonas and Thauera, respectively, and their relative abundance was much higher in granules from R3 and R4. The results demonstrated that a relative equilibrium between the growth and metabolism of nitrifying/denitrifying bacteria was achieved when NLR was between 0.8 and 1.2 kg/m3·d, which could provide technical support for the stability maintenance of AGS in the treatment of ionic rare earth mine wastewater. [ABSTRACT FROM AUTHOR]

This study aims to examine the nitrogen removal characteristics and microbial community variation at low hydraulic retention time (HRT) in a shallow constructed wetland (SCW) using iron–carbon (Fe–C) porous filter material (PFM) as substrate. Effects of influent nitrogen forms and chemical oxygen demand (COD)/N ratio on nitrogen removal performance at HRT of 1 day were investigated. Results showed that total nitrogen (TN) removal declined with the decrease of influent NH4+‐N‐to‐NO3−‐N ratio. When the influent NH4+‐N/NO3−‐N ratio was 0.1, TN removal decreased by 15.4% compared with that at ratio of 2.0. The increase of influent COD/N ratio enhanced NO3−‐N reduction, and TN removal reached 74.5% at influent COD/N ratio 7.0. The microbial community was analyzed for the biofilm samples on Fe–C PFM at front (WF), middle (WM), and back (WB) of SCW. Proteobacteria, Bacteroidetes, Chloroflexi, and Firmicutes were dominant bacteria phyla. The relative abundance of genera involved in the nitrification and denitrification decreased with the influent flow. The iron autotrophic denitrifying and macromolecular organics degrading bacteria were abundant in the middle and back of SCW. Microbial nitrification and denitrification, plant uptake, and plant synergism contributed to 86.3%, 7.41%, and 19.9% of N removal, respectively. These results demonstrated that the SCW with Fe–C PFM as substrate was efficient in nitrogen removal at low HRT. [ABSTRACT FROM AUTHOR]

Bacillus velezensis M3-1 strain isolated from the sediment of Myriophyllum aquatium constructed wetlands was found to efficiently convert NO 3 −-N to NO 2 −-N, and the requirements for carbon source addition were not very rigorous. This work demonstrates, for the first time, the feasibility of using the synergy of anammox and Bacillus velezensis M3-1 microorganisms for nitrogen removal. In this study, the possibility of M3-1 that converted NO 3 −-N produced by anammox to NO 2 −-N was verified in an anaerobic reactor. The NO 3 −-N reduction ability of M3-1 and denitrifying bacteria in coupling system was investigated under different C/N conditions, and it was found that M3-1 used carbon sources preferentially over denitrifying bacteria. By adjusting the ratio of NH 4 +-N to NO 2 −-N, it was found that the NO 2 −-N converted from NO 3 −-N by M3-1 participated in the original anammox.The nitrogen removal efficacy (NRE) of the coupled system was increased by 12.1%, compared to the control group anammox system at C/N = 2:1. Functional gene indicated that it might be a nitrate reducing bacterium.This study shows that the nitrate reduction rate achieved by the Bacillus velezensis M3-1 can be high enough for removing nitrate produced by anammox process, which would enable improve nitrogen removal from wastewater. [ABSTRACT FROM AUTHOR]

Vallisneria spinulosa Yan (V.spinulosa Yan) with good ability of water purification is often used for ecological restoration of polluted water bodies. However, it is difficult to survive in turbid water bodies due to the low lighting condition. This study explored the feasibility of introducing artificial underwater light source into water bodies with high turbidity to strengthen the water restoration by V.spinulosa Yan. Addition of underwater light source promoted the clonal reproduction ability of V.spinulosa Yan, thus enhancing the removal loads of total nitrogen (TN), total phosphorus (TP), and nitrate nitrogen ( NO 3 − - N ) by 1.60–3.43 × 10−2, 1.49–3.49 × 10−3, and 0.80–2.06 × 10−2 g m−2 d−1, respectively. Underwater light source significantly reduced the abundance of microbial community on V.spinulosa Yan leaves, as well as most nitrifying bacteria (Nitrosomonadaceae) and denitrifying bacteria (Nitrospira, Comamonadaceae, and Rhodocyclaceae) in the system. But the attachment of some Cyanophyta (Chloroplast and Cyanobacteria) and Photosynthetic bacteria (Rhodobacter) onto the leaves and the growth of Methyloligellaceae in water and sediments were promoted. Nitrogen and phosphorus removal by the growth system of V.spinulosa Yan without underwater light source mainly depended on the biological processes by functional bacteria, while the absorption and co-assimilation effect of V.spinulosa Yan with underwater light source. [ABSTRACT FROM AUTHOR]

Denitrification and nitrate-ammonification are the responsible processes for nitrate removal in the estuaries. Temperature, nitrate and organic carbon availability are key factors controlling a rate of the nitrate reduction processes. This mixed cultures chemostat study investigates the competition ability and their nitrate reduction end-products of the bacteria isolated from an estuary at different temperatures. This study will help us to understand the seasonal nitrate reduction processes in an estuary. The experiments showed that a nitrate-ammonifier was the predominant process in the steady-state chemostat at high temperature. While a facultative denitrifier-nitrate ammonifier was the predominant process at low temperature. However, the main end products of nitrate reduction at high temperature were up to 61% N2 indicating a denitrifier still had an important role in the end products of nitrate reduction in the estuary. The data also showed that a nitrite respiring bacterium reduced nitrite to N2, that responsible for approximately 6-9% of total N2 produced in the culture. This study confirmed that nitrate ammonifiers out-compete denitrifiers at high temperature, however, denitrifiers still had an important role in end products of nitrate reduction. [ABSTRACT FROM AUTHOR]

A proton exchange membrane increases the electrical performance of a microbial fuel cell (MFC). New inexpensive materials should be sought, especially in a constructed wetland microbial fuel cell (CW-MFC). Here, in a laboratory-scale system of five CW-MFCs, wet clay, wet earth or mud, and non-woven cloth were used as inexpensive separators with long-term stability. The five CW-MFCs were planted with Typha latifolia, fed with synthetic wastewater, and packed with natural porous material. Graphite felt was used as electrodes and the experimental system had a hydraulic residence time of 3 days, operating under shade and natural conditions of temperature and light. Electrodes were connected to current collectors (copper wire) and to an external resistance, with a change every 20 days, starting in open-circuit and following with 20000, 18000, 15000, 10000, 5600, 1000, 560, and 10 Ω. These laboratory-scale CW-MFCs reduced concentrations of nitrates, ammonium ion, and sulfates without inhibiting electricity production. Microbiological analyses indicated that anaerobic, facultative, aerobic, and denitrifying bacteria may have caused these reductions. The reactor with the live plant and with the wet earth or mud separator achieved the highest production of electricity (22.6 mW/m2), and may be worth further attention. [ABSTRACT FROM AUTHOR]

Derived from the denitrifying bacterium Aromatoleum aromaticum EbN1 (Azoarcus sp.), the enzyme S-1-(4-hydroxyphenyl)-ethanol dehydrogenase (S-HPED) belongs to the short-chain dehydrogenase/reductase family. Using research techniques like UV-Vis spectroscopy, dynamic light scattering, thermal-shift assay and HPLC, we investigated the catalytic and structural stability of S-HPED over a wide temperature range and within the pH range of 5.5 to 9.0 under storage and reaction conditions. The relationship between aggregation and inactivation of the enzyme in various pH environments was also examined and interpreted. At pH 9.0, where the enzyme exhibited no aggregation, we characterized thermally induced enzyme inactivation. Through isothermal and multitemperature analysis of inactivation data, we identified and confirmed the first-order inactivation mechanism under these pH conditions and determined the kinetic parameters of the inactivation process. Additionally, we report the positive impact of glucose as an enzyme stabilizer, which slows down the dynamics of S-HPED inactivation over a wide range of pH and temperature and limits enzyme aggregation. Besides characterizing the stability of S-HPED, the enzyme's catalytic activity and high stereospecificity for 10 prochiral carbonyl compounds were positively verified, thus expanding the spectrum of substrates reduced by S-HPED. Our research contributes to advancing knowledge about the biocatalytic potential of this catalyst. [ABSTRACT FROM AUTHOR]

Despite recent interest in functional food merits of dietary nitrate, there is a paucity of information on its utility as a pre-biotic for the enrichment of health-promoting oral bacteria. The objective of this investigation was to observe the dynamic change in the denitrifying oral microbiome of healthy human volunteers following supplementation of nitrate enriched diet for a period of two-weeks. The study involved isolation, identification and comparison of nitrate-reducing oral bacteria of five human volunteers before and after supplementation of a nitrate-rich diet. This was further correlated with salivary nitrite contents to understand denitrification efficacy with prolonged dietary nitrate supplementation. A total of 153 bacterial strains were isolated from baseline (BSL) samples of healthy participants, i.e. before supplementation and after dietary nitrate supplementation (ADNS); 32 out of these isolates could be confirmed to be nitrate-reducers. Although members of Firmicutes viz., Streptococcus salivarius, Streptococcus parasanguinis and Actinobacteria viz., Rothia mucilaginosa were present in both BSL and ADNS samples, the relative abundance of Actinobacteria was higher and Firmicutes was lower in ADNS in comparison to BSL samples. Moreover, Proteobacteria were found only in ADNS and not BSL samples. Interestingly, these changes in nitrate-reducing microbiome were correlated with higher salivary nitrite levels on day 14 in comparison to day 1 following acute supplementation of dietary NO3−. Thus, it is being hypothesized that Rothia, Neisseria and Streptococcus spp. which appeared following 14 days of nitrate supplementation, could be more efficient towards reducing nitrate and boosting salivary nitrite levels. [ABSTRACT FROM AUTHOR]

Due to its widespread presence in groundwater, nitrate contamination has become a major global concern. Identifying the different sources of this contamination, particularly those related to agricultural practices, is therefore crucial to assess its negative impacts. The European Nitrates Directive (91/676/EEC) requires the protection of all natural freshwater resources with a maximum nitrate concentration threshold of 50 mgNO3+L-1, applicable to all groundwater, regardless of its intended use. Many studies have used a chemical approach to identify these contaminations, but one of the possible approaches to identify contamination and the source of the contamination is a microbiological approach. An aquifer's unique groundwater fingerprint: its hydrology, chemistry, and geology are shaped by the communities of heterotrophic bacteria that thrive in this underground environment. The present study carries out an evaluation of the impact of nitrate and ammonia on the bacterial community of groundwater, in particular by studying the correlations between the two chemical forms analyzed and some of the native species most present in nitrifying and denitrifying groundwater. These evaluations make it possible to identify the microbial species subject to the variation of ammonia and nitrate concentrations and to evaluate the extent of variation in the natural environment, providing useful information on the variation of the chemical compound, validating the innovative thesis of being used as a natural tracer for the identification of potential direct or indirect contamination. [ABSTRACT FROM AUTHOR]

Three ecological restoration systems vegetated with Vallisneria natans, containing ceramisite (VC), bio-carrier and ceramisite (BVC) or Fe/C filler, bio-carrier and ceramisite (FBVC) as functional substrates were constructed for black and odorous water restoration. The average ammonia nitrogen (NH4+ -N) conversion rate of FBVC (90.51 %) was similar to that of BVC (88.49 %) and significantly higher than that of VC (53.35 %). However, the average total nitrogen (TN) removal rate of FBVC (84.93 %) was much higher than that of BVC (73.02 %) and VC (52.06 %). Additionally, the average COD removal efficiencies for VC, BVC and FBVC were 52.54 %, 71.84 % and 80.59 %, respectively; while they were 69.72 %, 74.79 % and 97.38 % for total phosphorus (TP). Highthroughput sequencing revealed that the richness and diversity of autotrophic denitrifying bacteria, such as Pseudomonas, Pseudoxanthomonas, Arenimonas and Hydrogenophaga increased significantly in FBVC, while the plant growth-promoting bacterium Rhodobacter was dominant. Overall, this study demonstrated that a Vallisneria natans based ecological restoration system coupled with Fe/C internal electrolysis (Fe/C-IE) effectively improved the quality of black and odorous water. In addition, the mechanism of nitrogen, phosphorus and carbon removal was proposed. [ABSTRACT FROM AUTHOR]

Immobilized microorganisms technology has been explored as a promising wastewater treatment method. To further increase the activity of the immobilized microorganisms, a porous membrane which was composed of poly (lactic acid) (PLA) and poly (ethylene glycol) (PEG) was designed for microorganism encapsulation. The plane membrane and the spherical membrane were prepared respectively. The morphology, mechanical properties, nitrate permeability, and biodegradability of the plane membranes were investigated to determine an optimized formulation. And then, denitrifying bacteria was encapsulated by the spherical membrane and its denitrification performance in synthetic wastewater was explored. The mean pore size of the PLA/PEG plane membranes ranged from 2.09 ± 0.63 μm to 3.15 ± 1.32 μm. PEG stimulated interconnected pore structure of the PLA/PEG plane membrane. Compare with neat PLA membrane, the tensile strength of the PLA/50%PEG plane membrane decreased by about 53.2% and elongation at break increased by about 103.5%. Nitrate permeability attained a maximum of 188.95 ± 4.59 mg·L−1·m−2·h−1 for PLA/50%PEG plane membrane. The denitrifying active sludge enclosed with the spherical membrane showed good denitrification performance in a short start-up time. The nitrate removal rate reached 51.14% on the 4th day and 82.53% on the 17th day. This porous PLA/50%PEG membrane was good for the diffusion of substrates and nutrients, which enabled the encapsulated microorganism recovered activity in a short time. The spraying method made the microorganism encapsulation could be designed according to the different microorganisms and different user environments, which expanded the application scope of microorganism encapsulation technology. [ABSTRACT FROM AUTHOR]

Unique worldwide, nitrate/iodine deposits (NIDs) are located along a 700 km geological belt in the Atacama Desert, Chile. They serve as the primary source of mineral ores for the extraction of iodine, sodium, and potassium nitrates. NIDs have been relatively underexplored from a biological perspective. To address this, we collected sixteen soil samples from abandoned mines in Oficinas Pissis and Savona for chemical, mineralogical, and metagenomic analyses. The soils primarily consisted of halite and darapskite, with only one sample being predominantly composed of thenardite. Deliquescence and water activity measurements yielded values ranging from 0.02% to 0.40% and 0.47 to 0.62, respectively. To investigate the presence, identification, relative abundance, and diversity of microbial life in NID soils, we employed MiSeq high-throughput sequencing and bioinformatic tools. The dominant phyla observed were Firmicutes and Proteobacteria, with Actinobacteria and Cyanobacteria being predominant in two soil samples. Furthermore, we detected nitrate/perchlorate-reducing bacterial activity in enriched cultures from the soil samples. This study sheds light on the resilience of microbial life in the Atacama Desert NIDs, providing compelling evidence for its existence and offering insight into factors that could facilitate it within this unique environment. [ABSTRACT FROM AUTHOR]

Wastewater treatment using microbial fuel cells (MFCs) is a potentially useful technology due to its low cost, environmental friendliness, and low sludge production. In this study, a single-chambered air cathode MFC (SCMFC) was developed and investigated regarding its performance and microbial community evolution following nitrate exposure. During long-term operation, diverse denitrifiers accumulated on the electrodes to form a denitrifying MFC (DNMFC) with stable activity for nitrate reduction. The DNMFC presented considerably higher electroactivity, stability, and denitrification rates than the SCMFC. Though energy recovery decreased in the DNMFC by partial organics utilized for heterotrophic denitrification, the electron transfer efficiency increased. Geobacter as the absolutely dominant genus in the SCMFC anode was eliminated and replaced by Azonexus and Pseudomonas in the DNMFC. Furthermore, the biomass of Pseudomonas (151.0 ng/μL) in the DNMFC cathode was five-fold higher than that in the SCMFC, although the bacterial community compositions were quite similar. The DNMFC with highly abundant Pseudomonas exhibited much better performance in terms of electrochemical activity and nitrate removal. The evolution process of functional bacteria from the SCMFC to the DNMFC comprehensively reveals the significant role of denitrifying electroactive bacteria in a bioelectrochemical system for nitrogen-containing wastewater treatment. [ABSTRACT FROM AUTHOR]

Purpose: Reduce the climate cost of plastic mulch is an important issue for the sustainable development of dryland. Previous studies suggest plastic mulch has risk to increase nitrous oxide emission, but how this produced by the complex interaction between soil properties and microbial is still an unsolved problem and need to research to develop targeted practice. Methods: To address this question, molecular ecology tools, including real-time quantitative and high-throughput sequencing were employed to explore how plastic mulch induced change on soil environment and then stimulates denitrification. Three mulching treatments were compared, including no mulching, spring and autumn mulching. Results: Plastic mulch induced significant increase in the richness and diversity of nir-containing denitrifiers. The nirS and nirK-gene abundance was the greatest under the autumn mulching, and a more conspicuous change in the community structure and abundance was observed for nirK gene than for nirS denitrifiers. The most differentially abundant taxa in the autumn mulching were Anaeromyxobacter, Terriglobus, Edwardsiella, Catenulispora and Acidobacterium for nirK genes and Cupriavidus for nirS genes. Mulching increased the potential denitrification enzyme activity by 58% and 29% for autumn and spring mulching, respectively, and this effect was mirrored by the abundance of nirK, but not by nirS denitrifiers. The nirK gene was significantly correlated to variations in soil moisture, temperature, and nitrate nitrogen. Conclusion: Plastic mulch stimulates denitrification by inducing higher moisture, temperature and nitrate nitrogen content and structural change in the community of nirK denitrifying bacteria in dryland agroecosystems. [ABSTRACT FROM AUTHOR]

Non-fermentative nitrite reduction to ammonium, resulting in the release of ammonium in the environment, can be performed by a variety of enzymes found among bacteria and archaea. NrfA-dependent ammonifiers are phylogenetically diverse and are present in terrestrial and aquatic environments, and for the latter especially in sediments. NrfA-dependent ammonifiers often carry genes involved in denitrification and redox reactions with sulfur or iron compounds, suggesting that they play a role in multiple biogeochemical cycles. In most aquatic and terrestrial environments, denitrifiers dominate over nitrate ammonifiers, and denitrification is the dominating process of nitrate reduction. However, nitrate ammonification rates can be significant under certain redox conditions. Nitrate ammonifiers are a taxonomically diverse group of microorganisms that reduce nitrate to ammonium, which is released, and thereby contribute to the retention of nitrogen in ecosystems. Despite their importance for understanding the fate of nitrate, they remain a largely overlooked group in the nitrogen cycle. Here, we present the latest advances on free-living microorganisms using NrfA to reduce nitrite during ammonification. We describe their diversity and ecology in terrestrial and aquatic environments, as well as the environmental factors influencing the competition for nitrate with denitrifiers that reduce nitrate to gaseous nitrogen species, including the greenhouse gas nitrous oxide (N 2 O). We further review the capacity of ammonifiers for other redox reactions, showing that they likely play multiple roles in the cycling of elements. [ABSTRACT FROM AUTHOR]

[Objective] The paper aimed to study the effects of biochar application on the quality of cured tobacco, soil mutrients and soil microbial community structure. (Method) A randomised block group field experiment was conducted using Yunyan 87 as the experimental mate rial. Four treatments were set up (SWT1: Conventional fertilization; SWT2: Conventional fertilization biochar 1500 kg/hm²; SWT3: Conventional fertilization + biochar 2250 kg/hm²; SWT4: Conventional fertilization biochar 3000 kg/hm²) to determine the chemical composition, sensory quality of cured tobacco and the soil nutrients, rhizosphere soil hacterial diversity of the cured tobacco at maturity. [Result] The application of biochar had no significant influence on the soil nutrients and chemical composition of cured tobacco. Compared with the SWTI treatment, the sensory quality of cured tobacco was significantly improved in all treatments of biochar application, among which SWT3 treat- ment showed the best performance with 13.85%,6.56%,10.87%,8.70%,4.62%,12.31% and 6.25% improvement in amma quality, aroma amount, concentration, strength, impurities, usage value, and total score, respectively. With the increase of biochar application rate, the bacterial richness (Chaol index), diversity (Shannon indes), total ASV number and unique ASV number in the rhizosphere soil of flue- cured tobacco showed a decreasing trend. Compared with SWT1 treatment, the difference in microbial community structure composition incre aed with the increase of biochar application rate. The dominant phyla of each treatment were Proteobacteria, Acidobacteria and Actinobacte ria, At the phylum classification level, there was no significant difference in the community structure composition among different treatments. The application of biochar increased the relative abundance of f Rhizobiaceae, g Allorhizobium, Neorhizobium, g Pararhizobium, g Rhizobium and other nitrogen fixing bacteria, as well as funcultured_Actinobacterium, f Burkholderiaceae, Pseudomonadaceae, o Pseudomonadale, g Pseudomonas, g Sphingopyxis, & Dyella, g Massilin and other growth promoting bacteria. The application of biochar decreased the relative abundance of denitrifying bacteria such as sunclassified_Anaerolinencrar and g unclassified Caulobacteracene. At the ASV classification level, AN was the dominant factor affecting the changes in soil bacterial community structure. [Conclusion] The application of biochar improve the sensory quality of cured tobacco leaves, with SWT3 treatment (2250 kg/hm²) performing the best. The application of biochar reduce thizosphere soil bacteria a-diversity, and increase the relative abundance of beneficial hacteria such as nitrogen fixing bacteria, growth promoting bacteria, and denitrifying bacteria in the thizosphere soil, which is beneficial for increasing soil nutrients and promoting plant growth. [ABSTRACT FROM AUTHOR]

The biodegradable polymer poly-β-hydroxybutyrate (PHB) is a promising carbon source for biological mitigation of nitrogen pollution, a significant problem in aquaculture that physical and chemical methods have not provided a comprehensive solution. Here we investigated the impact of PHB on the zero-water-change largemouth bass culture by 30- and 40-day experiments. PHB loaded into the filter circulation pump at 4 g L−1, optimum value determined by the first experiment, significantly reduced the levels of nitrate by 99.65%, nitrite by 95.96%, and total nitrogen by 85.22% compared to the control without PHB. PHB also significantly increased denitrifying bacteria (e.g., Proteobacteria and Fusobacteria) and expression of denitrification genes (e.g., nirK and nirS) in the microbial community, improving growth and health parameters of largemouth bass. While the impact may vary in other culture systems, PHB thus demonstrated its remarkable utility in aquaculture, highlighting ecological assessment and application to larger aquaculture operations as future considerations. [ABSTRACT FROM AUTHOR]

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The electrochemical reduction of nitrate to ammonia (ENRA) provides an efficient approach to remove nitrate pollution and achieve ammonia production simultaneously. Herein, inspired by bio-enzyme in denitrifying bacteria, a carbon-coated nickel phosphide (NiPC) nanosheet derived from metal-organic frameworks (MOFs) is proposed as an efficient catalyst for ENRA. Through electron engineering, controllable Niδ+ in nickel phosphide is achieved by regulating the degree of phosphating, which enhances its activity for the hydrogenation of nitrate. As the result, Niδ+ becomes one of dominating factors determining the efficiency of the ENRA reaction in nickel phosphide. The optimal NiPC catalyst exhibits impressive property toward ENRA: NH4+ Faraday efficiency of 96.68%, NH4+ selectivity of 99.04%, and nitrate conversion rate of 90.43% under low nitrate concentration (200 mgL−1). This work opens a new avenue for the design of next-generation catalysts through electron engineering for ENRA. [ABSTRACT FROM AUTHOR]

In order to solve the problems of difficult selection of carbon sources and high cost of dosage in advanced treatment of wastewater treatment plant, denitrification biological filter was used to explore the denitrification performance of different carbon sources. In this study, the denitrification performance of three carbon sources (sodium acetate, ethanol and methanol) at different hydraulic retention time (HRT), nitrogen ratio (C/N) and influent NH4+-N concentration and the microbial community structure at different heights of the reactor were investigated. The results showed that under the condition of low carbon nitrogen ratio, as the HRT increased, the removal efficiency of NH4+-N and NO3--N in the effluent of three systems with sodium acetate ethanol and methanol as carbon sources gradually increased, and the accumulation of NO2--N in methanol system was the lowest in the three systems. With the gradual increase of carbon to C/N, the concentration of NH4+-N and NO3--N in the three systems gradually decreased. The effluent TN concentration of sodium acetate and methanol system was less than 1.5 mg/L when C/N was 6 and 5, which met the Class W of Environmental Quality Standard for Surface Water. With the increase of influent NH4+-N concentration, it led to the increase of NO2--N accumulation degree, resulting in the increase of effluent TN concentration. Carbon sources led to significant differences in the abundance of the three systems at the phylum level. The differences at the genus level were more obvious, and the total relative abundance of denitrifying bacteria was in the order of sodium acetate system > ethanol system > methanol system. The results of this study can provide a theoretical reference for the selection of carbon source and the use of dosage in waste-water treatment plants. [ABSTRACT FROM AUTHOR]

Global riverine nitrous oxide (N2O) emissions have increased more than 4-fold in the last century. It has been estimated that the hyporheic zones in small streams alone may contribute approximately 85% of these N2O emissions. However, the mechanisms and pathways controlling hyporheic N2O production in stream ecosystems remain unknown. Here, we report that ammonia-derived pathways, rather than the nitrate-derived pathways, are the dominant hyporheic N2O sources (69.6 ± 2.1%) in agricultural streams around the world. The N2O fluxes are mainly in positive correlation with ammonia. The potential N2O metabolic pathways of metagenome-assembled genomes (MAGs) provides evidence that nitrifying bacteria contain greater abundances of N2O production-related genes than denitrifying bacteria. Taken together, this study highlights the importance of mitigating agriculturally derived ammonium in low-order agricultural streams in controlling N2O emissions. Global models of riverine ecosystems need to better represent ammonia-derived pathways for accurately estimating and predicting riverine N2O emissions. NH4+-derived pathways, rather than NO3--derived pathway, are the dominant hyporheic N2O sources in lower-order streams. These findings provide insights into better estimation of N2O emissions in global models of riverine ecosystems and emphasize the importance of managing ammonium. [ABSTRACT FROM AUTHOR]

Most reduced organic matter entering activated sludge systems is particulate (1–100-µm diameter) or colloidal (0.001–1-µm diameter), yet little is known about colonization of particulate organic matter by activated sludge bacteria. In this study, colonization of biopolymers (chitin, keratin, lignocellulose, lignin, and cellulose) by activated sludge bacteria was compared with colonization of glass beads in the presence and absence of regular nutrient amendment (acetate and ammonia). Scanning electron microscopy and quantitative PCR revealed chitin and cellulose were most readily colonized followed by lignin and lignocellulose, while keratin and glass beads were relatively resistant to colonization. Bacterial community profiles on particles compared to sludge confirmed that specific bacterial phylotypes preferentially colonize different biopolymers. Nitrifying bacteria proved adept at colonizing particles, achieving higher relative abundance on particles compared to bulk sludge. Denitrifying bacteria showed similar or lower relative abundance on particles compared to sludge. Key points: • Some activated sludge bacteria colonize natural biopolymers more readily than others. • Nitrifying bacteria are overrepresented in natural biopolymer biofilm communities. • Biopolymers in wastewater likely influence activated sludge community composition. [ABSTRACT FROM AUTHOR]

During pregnancy, all major physiological systems undergo remarkable changes, driven largely by alterations in the maternal hormonal milieu. In healthy pregnancies, maternal cardiovascular and metabolic adaptation to pregnancy occurs to support fetal growth and maternal well-being. Impaired maternal adaptation to pregnancy is associated with a range of pregnancy complications, including gestational diabetes and preeclampsia. There is growing recognition of the importance of different maternal microbiota, including in the gut, vagina and oral cavity, in supporting normal maternal adaptations to pregnancy as well as evidence for microbial disturbances associating with pregnancy pathologies. Here, we aim to summarise emerging evidence demonstrating that differences in maternal microbiota associate with pregnancy outcomes and discuss potential therapeutic approaches under development that might restore an 'optimal' microbiome. In particular, we highlight recent work by ourselves and others exploring the role of the oral microbiome in pregnancy, given established links between poor oral health (e.g. periodontitis) and adverse pregnancy outcomes. Our research has focussed on specific nitrate-reducing oral bacteria which play a role in the generation of nitric oxide (NO) and other bioactive nitrogen oxides associated with cardiovascular health and maternal cardiovascular adaption to pregnancy. Ongoing research aims to define whether altered microbial profiles have clinical utility in the prediction of pregnancy pathologies, and whether interventions designed to optimise specific maternal microbiota could help prevent future complications. [ABSTRACT FROM AUTHOR]

Stable and efficient partial nitrification reaction and nitrite accumulation are essential for the operation of partial nitrification-anaerobic ammonia oxidation process. This paper investigated the changes in the performance of a partial nitrification bioreactor during the domestication process. After 40 days of domestication, the partial nitrification reaction remained stable, the nitrite accumulation rate (NAR) increased significantly to 85.7%, and the NO2--N/NH4+-N ratio stabilized at 1.25 ± 0.04. Both diversity indices (Simpson and Shannon) and richness indices (Ace and Chao1) tend to decrease with domestication. Nitrosomonas as a typical ammonia oxidizing bacterium it increased its relative abundance in the reactor from 0.02 ± 0.007% at P1 to 11.6 ± 2.2% at P2, and at P3 stage the denitrifying functional bacteria norank_f_AKYH76, Dokdonella and unclassified_f_Comamonadaceae reached 33.4 ± 12.5%, 18.8 ± 1.8%, and 10.1 ± 1.3%, respectively, and the increase in the relative abundance of these functional species was also consistent with the accumulation of nitrite nitrogen in the reactor. [ABSTRACT FROM AUTHOR]

Understanding the bacteria associated with nitrification and denitrification is crucial for comprehending the processes that lead to nitrous oxide emissions in agricultural greenhouse soils. Therefore, it is important to determine their abundance and expression to gain insight into these processes. The aim of this study was to explore the bacterial communities associated with denitrification in a greenhouse agricultural soil amended with crop residues and manure for six years. For this purpose, we proceeded to detect and quantify the genes nirK and nirS and the gene nosZ through clone library construction, sequencing, phylogenetic analysis, and quantitative polymerase chain reaction (qPCR). Sequence analysis based on the clone library revealed that many of the nirS or nirK genes detected were not closely related to known denitrifier bacteria, but some of the nosZ sequences were related to the genera such as Pseudomonas, Halomonas, and Marinobacter. Furthermore, the qPCR revealed a high abundance of DNA copies in nirK, 6.08 × 109 ± 1.16 × 109, while nirS and nosZ showed lower values, 9.05 × 106 ± 1.65 × 106 and 8.71 × 106 ± 1.44 × 106, respectively. However, the highest expression rate was observed for nirS (mRNA/DNA ratio = 3.10 × 10− 3), while nirK and nosZ showed 10-fold lower expression rates (4.4 × 10− 4 and 3.5 × 10− 4, respectively). The results of this work provide a preliminary overview of the diversity, abundance and expression of key genes associated with the denitrification process in this type of soil and are a starting point for further studies to understand how this type of soil management can influence the denitrification process. [ABSTRACT FROM AUTHOR]

Nitrate attenuation during river bank infiltration is the key process for reducing nitrogen pollution. Temperature is considered to be an important factor affecting nitrate attenuation. However, the magnitude and mechanism of its impact have not been clear for a long time. In this study, the effects of temperature and temperature gradient on the nitrate denitrification rate were investigated via static batch and dynamic soil column simulation experiments. The results showed that temperature had a significant effect on the denitrification rate. Temperature effects were first observed in denitrifying bacteria. At low temperatures, the microorganism diversity was low, resulting in a lower denitrification rate constant. The static experimental results showed that the denitrification rate at 19 °C was approximately 2.4 times that at 10 °C. The dynamic soil column experiment established an exponential positive correlation between the nitrate denitrification decay kinetic constant and temperature. The affinity of denitrifying enzymes for nitrate in the reaction substrate was ordered as follows: decreasing temperature gradient (30 °C → 10 °C) > zero temperature gradient (10 °C) > increasing temperature gradient condition (0 °C → 10 °C). This study provides a theoretical basis for the biogeochemical processes underlying river bank infiltration, which will help aid in the development and utilization of groundwater resources. [ABSTRACT FROM AUTHOR]

An innovative inbuilt moving bed biofilm reactor (MBBR) was created to protect fish from nitrogen in a household aquarium. During the 90 experimental days, the ammonia nitrogen (NH4 +-N) concentration in the aquarium with the inbuilt MBBR was always below 0.5mg/L, which would not threaten the fish. Concurrently, nitrite and nitrate nitrogen concentrations were always below 0.05mg/L and 4.5mg/L, respectively. However, the blank contrast aquarium accumulated 1.985mg/L NH4 +-N on the 16th day, which caused the fish to die. The suspended biofilms could achieve the specific NH4 +-N removal rate of 45.43g/m³/d. Biofilms presented sparsely with filamentous structures and showed certain degrees of roughness. The bacterial communities of the suspended biofilms and the sediment were statistically different (p <0.05), reflected in denitrifying and nitrifying bacteria. In particular, the relative abundance of Nitrospira reached 1.4%, while the genus was barely found in sediments. The suspended biofilms showed potentials for nitrification function with the predicted sequence numbers of ammonia monooxygenase [1.14.99.39] and hydroxylamine dehydrogenase [EC:1.7.2.6] of 220 and 221, while the values of the sediment were only 5 and 1. This study created an efficient NH4 +-N removal inbuilt MBBR for household aquariums and explored its mechanism to afford a basis for its utilization. [ABSTRACT FROM AUTHOR]

Comparative analysis of the effects of different filling rates of polypropylene filler on the operational effectiveness, microbial abundance and diversity, and metabolism of the AA‐MBBR system for the treatment of domestic wastewater. The results showed that under the condition of the optimal filling rate of 40%, the average removal rates of BOD5, COD, NH3‐N, TN, and TP in the AA‐MBBR system were 93.63%, 90.02%, 81.25%, 80.07%, and 74.51%, respectively, and the effluent COD was 143.05 mg/L and the effluent NH3‐N was 37.03 mg/L; the number of operational taxonomic units (OTUs) in the AA‐MBBR system with the optimal fill rate was 595, which was higher than 10%, 20%, 30%, and 50%, and it was also found that the relative abundance of denitrifying bacteria (DNB) and polyphosphate bacteria (Paos) increased with the increase of biofilm fill rate, DNB increased by about 32.9% at TCL (fill rate) 40 compared to TCL10, Paos increased by about 21.6% at TCL30 compared to TCL10. the AA‐MBBR system with a fill rate of 40% showed better pollutant removal than the other systems with other fill rates The bacterial diversity was higher than that of the systems with other filling rates. [ABSTRACT FROM AUTHOR]

Abstract Denitrifying bacteria harboring the nitrate reductase S (nirS) gene convert active nitrogen into molecular nitrogen, and alleviate eutrophication in aquaculture water. Suspended particulate matter (SPM) is an important component of aquaculture water and a carrier for denitrification. SPM with different particle sizes were collected from a coastal high-altitude aquaculture pond in Maoming City, China. Diversity, community structure, abundance of nirS-type denitrifying bacteria on SPM and environmental influencing factors were studied using high-throughput sequencing, fluorescence quantitative PCR, and statistical analysis. Pseudomonas, Halomonas, and Wenzhouxiangella were the dominant genera of nirS-type denitrifying bacteria on SPM from the ponds. Network analysis revealed Pseudomonas and Halomonas as the key genera involved in the interaction of nirS-type denitrifying bacteria on SPM in the ponds. qPCR indicated a trend toward greater nirS gene abundance in progressively larger SPM. Dissolved oxygen, pH, temperature, and SPM particle size were the main environmental factors influencing changes in the nirS-type denitrifying bacterial community on SPM in coastal high-altitude aquaculture pond water. These findings increase our understanding of the microbiology of nitrogen cycle processes in aquaculture ecosystem, and will help optimize aquatic tailwater treatment strategies.

A strain D5 with excellent partial denitrification performance was screened from paddy soil. The bacteria were identified as Klebsiella pneumoniae by morphological observation and 16S r DNA sequence analysis. The denitrification ability of strain D5 under different environmental factors （carbon source，C/N ratio and temperature） were investigated using single-factor experiments. The results showed that various environmental factors had obvious influence on partial denitrification of strain D5. The optimal conditions for partial denitrification activity of strain D5 were carbon source of sodium citrate， C/N ratio of 3，temperatures of 25 ℃ and 35 ℃. The results showed that strain D5 had excellent partial denitrification performance，and the optimal partial denitrification effect could be achieved by regulating environmental conditions.

An in situ integrated system, consisting of ecological floating islands (EFI), ecological riverbeds (ER), and ecological filter dams (EFD), was built in a ditch only receiving the effluent of sewage plant; the effect of in situ technologies on the distribution of aquatic pathogen was investigated. The results showed the aquatic pathogen decreased along the ditch. Specifically, the relative abundance of Legionella, Aeromonas, and Acinetobacter decreased from 0.032, 0.035, and 0.26 to 0.026%, 0.012%, and 0.08%, respectively. Sedimentation, filtration, and sorption (provided by plant roots and biofilms on substrates) were principal processes for the removal. The nitrogen removal bacteria to prevent the potential risk of eutrophication were also evaluated. The EFI and ER were the dominant sites for Nitrosomonas (34.96%, 32.84%) and Nitrospira (35.74%, 54.73%) enrichment, while EFI and EFD facilitated the enrichment of denitrification bacteria. Notably, the relative abundance of endogenous denitrifiers (DNB-en) (including Dechloromonas at 9.72%, Thermomonas at 0.58%, and Saccharibacteria at 2.55%) exceeded those of exogenous denitrifiers (DNB-ex) (Thauera at 0.20%, Staphylococcus at 0.005%, and Rhodobacter at 0.27%). This study demonstrated that the in situ integrated system was effective in reducing the abundance of pathogens in the drainage channel, and the deficiency of DNB-ex and carbon sources made nitrate removal difficult. [ABSTRACT FROM AUTHOR]

Microorganisms are notoriously known to cause local corrosion and stress corrosion cracking (SCC), which seriously endangers the materials service safety. Cu can enhance antibacterial function of the material and reduce the vulnerability to hydrogen embrittlement (HE). However, the dilemma of how much Cu content generates the best resistance to microbiological corrosion and SCC arises. Here, we modified the Cu content in pipeline steel to obtain the best antibacterial effect to nitrate reducing bacteria Bacillus cereus and HE resistance. The findings offer a fresh perspective on how to design and prepare a steel that are both resistant to microbiological corrosion and SCC. [ABSTRACT FROM AUTHOR]

The cultivation systems of Coffea spp. in a cooperative society in Puebla, Mexico, include Rustic, Traditional Polyculture, Commercial Polyculture, Unshaded Monoculture and Shaded Monoculture. In this work, the properties of the soil were analyzed through physical, chemical and biological analyses to determine its nutritional status. Composite sample analyses were conducted to determine physical, chemical and microbiological parameters (fungi, actinomycetes, mesophilic bacteria, nitrifying and denitrifying bacteria). Leaf nutrients were determined. Rustic was the cropping system with the highest amount of K in the soil and nutrient assimilation in the leaf (N, P, K and Fe) (p = 0.001); in addition, it had high populations of mesophilic bacteria, fungi and actinomycetes and very low nitrification and denitrification rates. The principal component analyses (PCA) (>3.25%) indicated that actinomycetes and K in soil favor the assimilation of Fe, K and P. This Coffea spp. cultivation system generated a lower impact on soil health than the rest of the systems and favored forest ecosystem conservation. [ABSTRACT FROM AUTHOR]

The primary objective of the present study is to enhance the denitrification process in constructed wetlands (CWs), employed as an ecological and natural technology for wastewater treatment. Eco-friendly approaches have been tested to improve the nitrate removal efficiency in pilot-scale subsurface flow CWs. Initially, the system's performance was enhanced by using a natural substrate, namely cork, as a filter medium. Another approach is bio-inoculation into the rhizosphere of a bacterial strain with the potential capacity for nitrate removal, thereby reinforcing the synergy between the plant and microorganisms. Finally, the approaches were combined, and nitrate removal was assessed. The main results showed that the most effective nitrate removal from wastewater was achieved with cork (80%) compared to gravel (60%). Bio-inoculation into the rhizosphere of denitrifying bacteria significantly improved nitrate removal. Indeed, the nitrate removal rate by the inoculated CW filled with gravel, was higher than the non-inoculated system, with rates of 78% and 60%, respectively. Moreover, the highest removal rate of 99.77% was obtained with the inoculated system filled with cork. [ABSTRACT FROM AUTHOR]

Purpose: This study was to explore the environmental driving factors and the assembly mechanisms of aerobic denitrifying bacteria community with different seasons and rarity in the sediments of Baiyangdian Lake. Materials and methods: Sediment samples were collected from 16 locations in Baiyangdian Lake. Microbial community composition and diversity were measured by napA gene sequencing. Redundancy analysis (RDA) and Mantel analysis were used to study the environmental factors that drive subcommunities with different rarity in summer and winter. Based on network analysis, the symbiotic relationship of subcommunities with different rarity in summer and winter was discussed. The assembly mechanism of subcommunities with different rarity in summer and winter was investigated by null model analysis. The influence factor of different rarity subcommunity diversity in summer and winter was studied based on structural equation modeling (SEM). Results and discussion: We found that the α-diversity of winter was higher than that of summer, and the α-diversity of rare taxa (RT) was higher than that of abundant taxa (AT). Nitrate (NO3−-N) was the most critical factor affecting AT in two seasons; temperature (T) and CODMn were the most critical environmental factors affecting RT in summer and winter, respectively. All taxa were significantly affected by dissolved oxygen (DO) in winter. The network analysis showed that symbiotic relationships were dominant among species, and the interrelationship between groups was closer in winter. RT was more crucial for preserving the stability of the bacterial community's overall composition and structure, but AT had stronger environmental adaptability. The null model revealed that dispersal limitation predominated in the community assembly of AT and RT. With the increase of rarity, the contribution of undominated and homogeneous dispersal to microbial subcommunity aggregation increases. The SEM revealed a significant detrimental impact of NO3−-N and NO2−-N on β-diversity of AT and RT in summer (P = 0.009, n = 16 and P = 0.002, n = 16) but promoted β-diversity of AT and RT in winter. CODMn, Mn, pH, and DO had the greatest influence on β-diversity of AT and RT in winter. Conclusion: In conclusion, our study enhances the understanding of aerobic denitrifying bacterial community diversity, assemblage patterns, and environmental driving mechanisms, and provides important implications for microbial ecology. Moreover, these results provide strategies for the subsequent screening of aerobic denitrifying bacteria in natural water, which is of great significance for the realization of in situ nitrogen removal in natural water. [ABSTRACT FROM AUTHOR]

Preventing the rebound of black and odorous water bodies is critical for improving the ecological environment of water bodies. This study examined the effect and underlying mechanism of in-situ improvement of the sediment microenvironment by nitrate in the tailwater of wastewater treatment plants combined with aerobic denitrifying bacteria under low-DO regulation (TailN + CFM + LDO). On the 60th day of remediation, the levels of dissolved oxygen and oxidation–reduction potential in the overlying water rose to 5.6 mg/L and 300 mV, respectively, the concentration of acid volatile sulfide within the sediment significantly decreased by 70.4%, and the organic matter content in the sediment was reduced by 62.7%, in which the heavy fraction organic matter was degraded from 105 g/kg to 56 g/kg, and the potential risk of water reverting to black and odorous conditions significantly decreased. Amplicon sequencing analysis revealed that the relative abundance of the electroactive bacteria Thiobacillus and Pseudomonas with denitrification capacity was found to be significantly higher in the TailN + CFM + LDO group than in the other remediation groups. Functional prediction of the 16S sequencing results indicated that both the quantity and activity of critical microbial enzymes involved in nitrification and denitrification processes could be enhanced in the TailN + CFM + LDO group. These results improved our understanding of the improvement of the sediment microenvironment and could thus facilitate its application. [ABSTRACT FROM AUTHOR]

Aha Lake artificial reservoir wetland, Niangniang Mountain karst mountain wetland, and Caohai plateau lake wetland are typical karst wetlands in Guizhou Province with unique topography and geomorphic features. They were selected as research objects in this study to explore microorganisms and functional genes in nitrogen metabolism adopting macro-genome sequencing technology. It was found that Proteobacteria, Actinobacteria, and Acidobacteria were the dominant phyla in nitrogen metabolism in these three wetlands, similar to previous studies. However, at the genus level, there was a significant difference, with the dominant bacteria being Bradyrhizobium, Methylocystis, and Anaeromyxobacter. Six nitrogen metabolism pathways, including nitrogen fixation, nitrification, denitrification, dissimilatory nitrate reduction, assimilatory nitrate reduction, and complete nitrification, comammox, were revealed, but anaerobic ammonia oxidation genes were not detected. Nitrogen metabolism microorganisms and pathways were more affected by SOM, pH, NO3−, and EC in karst wetlands. This study further discussed microorganisms and functions of nitrogen metabolism in karst wetlands, which was of great significance to nitrogen cycles of karst wetland ecosystems. [ABSTRACT FROM AUTHOR]