Nitrate removal by alkali-resistant Pseudomonas sp. XS-18 under aerobic conditions: Performance and mechanism

Efficient nitrogen removal by the aerobic denitrifying bacterium Pseudomonas stutzeri RAS-L11 under triple stresses of high alkalinity, high salinity, and tetracycline: From performance to mechanism

Efficient aerobic denitrification bacteria are rarely reported under triple stresses of high alkalinity, high salinity, and tetracycline. Here, strain Pseudomonas stutzeri RAS-L11 was isolated, under the optimal reaction conditions of C/N = 6, sodium acetate as carbon source, and pH 7.0-11.0. Moreover, RAS-L11 showed perfect nitrogen removal performance under dual and triple stresses. Specifically, the mean removal efficiency of total dissolved nitrogen for different medium (nitrate, nitrite, ammonia, nitrate and ammonia, and nitrite and ammonia) reached 92.35 %, 66.85 %, 71.33 %, 89.42 %, and 68.76 % under triple stresses. Nitrogen balance results indicated that biomass nitrogen accounted for a small percentage (4.48 % to 20.79 %). Furthermore, the nitrogen metabolism pathways and tetracycline, salinity, and alkaline tolerance-associated genes were also confirmed. Strain RAS-L11 achieved 42.67-70.72 % NO3--N and 83.72-88.53 % NH4+-N removal efficiencies in both sterilized and actual systems treating pharmaceutical wastewater. Our characterization of the RAS-L11 provides a reference for nitrogen removal of pharmaceutical wastewater.

Nitrogen removal characteristics and salt tolerance mechanisms of the novel bacterium Halomonas sp. W07 in saline wastewater treatment

The extremely high osmotic pressure that frequently emerges in industrial wastewater will notably impact microorganisms' survival and nitrogen removal efficiency. A newly isolated Halomonas sp. strain W07 demonstrated the ability to efficiently remove nitrate and nitrite at an average rate of 4.68 and 5.56 mg/L/h, respectively, under an 8 % salinity condition. Whole-genome sequencing and nitrogen balance analysis revealed that W07 utilize the dissimilatory nitrate reduction to ammonium (DNRA) and ammonium assimilation pathways, including genes nap, nar, nasA, nir, glnA, gltBD, and gdhA2, to accomplish efficient nitrogen assimilation and removal in a high-salt environment. Furthermore, the expression of genes associated with salinity tolerance in W07 suggested that the strain can withstand osmotic stress by enhancing extracellular polymer secretion and facilitating the transport and synthesis of compatible solutes. The notable nitrogen removal efficiency and high salinity tolerance exhibited by strain W07 make it a promising candidate for nitrate removal under high-salt conditions.

Biocontrol potential of four Pseudomonas strains against tobacco black shank disease

Tobacco black shank is a significant disease that poses a severe threat to tobacco production. To identify effective biocontrol agents for combating tobacco black shank disease, a screening of 39 putative Pseudomonas strains was conducted utilizing the plate confrontation assay. Four strains exhibiting inhibitory effects were selected and further evaluated for their disease control potential in pot trials. The effects of the strains on the growth of tobacco seedlings were detected using the root-irrigation method. The results demonstrated that four Pseudomonas strains exhibited significant inhibitory effects against tobacco black shank disease. The inhibition rates of strains YC2140, YC2090, YC2202, and Tr157 against P. nicotianae were determined to be 77.20%, 73.43%, 73.07%, and 32.46%, respectively. Pot trials showed that the biocontrol efficiency of Tr157, YC2090, YC2140, YC2202 against tobacco black shank disease was 96.30%, 66.67%, 62.96%, 62.96%, respectively. In addition, the strain Tr157 was found to be capable of producing indole-3-acetic acid (IAA). Meanwhile, Tr157, YC2140, and YC2202 demonstrated the ability to solubilize phosphorus, while all the four strains were capable of solubilizing potassium and producing siderophores. These strains also promoted tobacco growth increasing the total fresh weight by 146.33%, 153.21%, 87.16% and 239.91%, respectively. Overall, this study underscores the potential of the four Pseudomonas strains as effective biocontrol agents against tobacco black shank disease, offering an eco-friendly and sustainable alternative to chemical fungicides in agriculture.

New Insight Into the Mechanism of Nitrite Enhancement on Heterotrophic Nitrification and Aerobic Denitrification Bacterium in Gene Expression

The growth and nitrogen metabolism of heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria are affected by nitrite, but the mechanisms underlying this for strain Acinetobacter johnsonii EN-J1 are unclear. In this study, the addition of 10 mg/L nitrite increased the reduction rate of ammonium by 1.0 mg/L/h, and 20 mg/L nitrite increased the reduction rate of nitrate by 3.9 mg/L/h. Compared with the control, the nitrate reductase activity, electron transfer activity, and adenosine triphosphate content of EN-J1 were enhanced by 142.0%, 278.0% and 279.0%, respectively, in the nitrate removal process after the addition of 20 mg/L nitrite. The whole genome was annotated with nitrogen removal genes such as narGHI, narK, nsrR, nirBD, nasA, glnA, gltB, gdhA and amt. Transcriptome analysis showed that nitrite triggered significant upregulation of several key pathways, including nitrogen metabolism, the tricarboxylic acid cycle, and amino acid metabolism for enhancing denitrification. The expression of key denitrification genes (narG, narK, hmp, nirBD, glnA and nasA) was detected by real-time quantitative polymerase chain reaction. These results suggested that nitrite enhances denitrification by increasing the expression of denitrification genes, electron transfer and adenosine triphosphate levels, which is important for elucidating the mechanism of nitrite promotion of biological nitrogen removal efficiency.

Simultaneous removal of methane and high nitrite from the wastewater by Methylomonas sp. with soluble methane monooxygenase

Aerobic methanotrophs play a crucial role in controlling methane emission in wastewater treatment. However, the high nitrite produced during ammonium oxidation, nitrate assimilation, and denitrification hinders methane oxidation and nitrogen removal. In this study, Methylomonas sp. HYX-M1, possessing two methane monooxygenase and multiple nitrite reductase genes, demonstrated efficient methane oxidation, coupled with nitrite removal abilities up to 6 mM. Strain HYX-M1 presented methane oxidation rate of 0.05 mmol/d and nitrite removal rate of 0.53 mM/d under low-oxygen conditions. Assimilation and denitrification mainly accounted for 94.6-96.06 % and 3.10-5.03 % of nitrite removal. Methane monooxygenase genes, pmoA and mmoX expressed in different nitrite concentrations. Meanwhile, the nirB and nirD of strain HYX-M1 upregulated by 2.7- and 8.5-fold in 6 mM, respectively. The sod and ahpC genes upregulated, contributing to the survival of strain HYX-M1 in high nitrite. These findings provide a new strategy for the application of aerobic methanotrophs in regulating methane emission of wastewater with high nitrite.

Efficient ammonia oxidation by Pseudomonas citronellolis strain YN-21 under strongly acidic conditions: Performance and mechanism

Ammonia oxidation microorganisms generally tend to have low rates of ammonia oxidation under acidic conditions, as the protonated ammonia is not a substrate for ammonia monooxygenase. In this work, heterotrophic ammonia oxidation bacteria (HAOB) Pseudomonas citronellolis strain YN-21 showed high efficiency in removing NH4+ (12.7 mg/L/h) even at initial pH 4.5. The potential acid resistance mechanisms (H+ efflux, H+ consumption, and production of alkaline substances) maintained intracellular pH neutrality. Transcriptome analysis showed that genes involved in amino acid metabolism, carbohydrate metabolism, ABC transporter and nitrogen metabolism were significantly up-regulated, which facilitated the rapid removal of NH4+ in an acidic environment. Moreover, urea could be used as an alternative nitrogen source for YN-21 in a strongly acidic environment, and the production of NH3 from urea hydrolysis provided a substrate for ammonia oxidation. These results provide new insights into efficient ammonia oxidation in acidic environments.

Tapping into haloalkaliphilic bacteria for sustainable agriculture in treated wastewater: insights into genomic fitness and environmental adaptation

The increasing salinity and alkalinity of soils pose a global challenge, particularly in arid regions such as Tunisia, where about 50% of lands are sensitive to soil salinization. Anthropogenic activities, including the use of treated wastewater (TWW) for irrigation, exacerbate these issues. Haloalkaliphilic bacteria, adapted to TWW conditions and exhibiting plant-growth promotion (PGP) and biocontrol traits, could offer solutions. In this study, 24 haloalkaliphilic bacterial strains were isolated from rhizosphere sample of olive tree irrigated with TWW for more than 20 years. The bacterial identification using 16S rRNA gene sequencing showed that the haloalkaliphilic isolates, capable of thriving in high salinity and alkaline pH, were primarily affiliated to Bacillota (Oceanobacillus and Staphylococcus). Notably, these strains exhibited biofertilization and enzyme production under both normal and saline conditions. Traits such as phosphate solubilization, and the production of exopolysaccharide, siderophore, ammonia, and hydrogen cyanide were observed. The strains also demonstrated enzymatic activities, including protease, amylase, and esterase. Four selected haloalkaliphilic PGPR strains displayed antifungal activity against Alternaria terricola, with three showing tolerances to heavy metals and pesticides. The strain Oceanobacillus picturea M4W.A2 was selected for genome sequencing. Phylogenomic analyses indicated that the extreme environmental conditions probably influenced the development of specific adaptations in M4W.A2 strain, differentiating it from other Oceanobacillus picturae strains. The presence of the key genes associated with plant growth promotion, osmotic and oxidative stress tolerance, antibiotic and heavy metals resistance hinted the functional capabilities might help the strain M4W.A2 to thrive in TWW-irrigated soils. By demonstrating this connection, we aim to improve our understanding of genomic fitness to stressed environments. Moreover, the identification of gene duplication and horizontal gene transfer events through mobile genetic elements allow the comprehension of these adaptation dynamics. This study reveals that haloalkaliphilc bacteria from TWW-irrigated rhizosphere exhibit plant-growth promotion and biocontrol traits, with genomic adaptations enabling their survival in high salinity and alkaline conditions, offering potential solutions for soil salinization issues.

Changes in microbial communities during high-rate microbial selenate reduction in an up-flow anaerobic fluidized bed reactor

Biological fluidized bed reactor (FBR) is a promising treatment option for removing selenium oxyanions from wastewater by converting them into elemental selenium. The process can achieve high rates and be efficiently operated at low hydraulic retention times (HRT). However, the effects of HRT on the changes in microbial community in the FBR process have not been previously explored. In this study, dynamic changes of microbial communities both on biofilm carrier and in suspension of a selenate-reducing FBR were explored at various HRTs (0.3-120 h). Based on partial 16S rRNA gene sequencing of the microbial communities, alpha diversity of microbial communities in suspension rather than in the biofilm were impacted by low HRTs (0.3 h-3 h). Members from genera Geobacter, Geoalkalibacter, and Geovibrio were the main selenate-reducing bacteria on carrier throughout the FBR process. Genus Geobacter was dominant in FBR carrier at HRT of 24 h-120 h, whereas Geoalkalibacter and Geovibrio dominated at low HRT of 0.3 h-6 h. Suspended microbial communities detected in the FBR effluent were more sensitive to HRT changes than that in biofilm. "Shock loading" at HRT of 0.3 h had a great impact on microbial community compositions both in the biofilm and effluent. Reactor operation in batch mode and long HRT of 24 h helped recover the community from "shock loading" and improved selenite reduction and ethanol oxidation. Redundancy analysis revealed that HRT, influent pH and selenate loading were key operational parameters impacting both the FBR performance and the composition of microbial communities associated with both the FBR carrier and effluent. Overall, the microbial communities in FBR biofilm flexibly responded to the changes of HRT and showed resilience to the temporary shock loading, enabling efficient selenate removal.

Inhibition of phosphorus removal performance in activated sludge by Fe(III) exposure: transitions in dominant metabolic pathways

Introduction

Simultaneous chemical phosphorus removal process using iron salts (Fe(III)) has been widely utilized in wastewater treatment to meet increasingly stringent discharge standards. However, the inhibitory effect of Fe(III) on the biological phosphorus removal system remains a topic of debate, with its precise mechanism yet to be fully understood.

Methods

Batch and long-term exposure experiments were conducted in six sequencing batch reactors (SBRs) operating for 155 days. Synthetic wastewater containing various Fe/P ratios (i.e., Fe/P = 1, 1.2, 1.5, 1.8, and 2) was slowly poured into the SBRs during the experimental period to assess the effects of acute and chronic Fe(III) exposure on polyphosphate-accumulating organism (PAO) growth and phosphorus metabolism.

Results

Experimental results revealed that prolonged Fe(III) exposure induced a transition in the dominant phosphorus removal mechanism within activated sludge, resulting in a diminished availability of phosphorus for bio-metabolism. In Fe(III)-treated groups, intracellular phosphorus storage ranged from 3.11 to 7.67 mg/g VSS, representing only 26.01 to 64.13% of the control. Although the abundance of widely reported PAOs (Candidatus Accumulibacter) was 30.15% in the experimental group, phosphorus release and uptake were strongly inhibited by high dosage of Fe(III). Furthermore, the abundance of functional genes associated with key enzymes in the glycogen metabolism pathway increased while those related to the polyphosphate metabolism pathway decreased under chronic Fe(III) stress.

Discussion

These findings collectively suggest that the energy generated from polyhydroxyalkanoates oxidation in PAOs primarily facilitated glycogen metabolism rather than promoting phosphorus uptake. Consequently, the dominant metabolic pathway of communities shifted from polyphosphate-accumulating metabolism to glycogen-accumulating metabolism as the major contributor to the decreased biological phosphorus removal performance.

Functional analysis and comparative genomics of Rahnella perminowiae S11P1 and Variovorax sp. S12S4, two plant growth-promoting rhizobacteria isolated from Crocus sativus L. (saffron) rhizosphere

BACKGROUND

Rahnella perminowiae S11P1 and Variovorax sp. S12S4 are two plant growth-promoting rhizobacteria that were previously isolated from the rhizosphere of Crocus sativus L. (saffron), and have demonstrated interesting PGP activities and promising results when used as inoculants in field trials. To further elucidate the molecular mechanisms underlying their beneficial effects on plant growth, comprehensive genome mining of S11P1 and S12S4 and comparative genomic analysis with closely related strains were conducted.

RESULTS

Functional annotation of the two strains predicted a large number of genes involved in auxin and siderophore production, nitrogen fixation, sulfur metabolism, organic acid biosynthesis, pyrroloquinoline quinone production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, volatile organic compounds production, and polyamine biosynthesis. In addition, numerous genes implicated in plant-bacteria interactions, such as those involved in chemotaxis and quorum sensing, were predicted. Moreover, the two strains carried genes involved in bacterial fitness under abiotic stress conditions. Comparative genomic analysis revealed an open pan-genomic structure for the two strains. COG annotation showed that higher fractions of core and accessory genes were involved in the metabolism and transport of carbohydrates and amino acids, suggesting the metabolic versatility of the two strains as effective rhizosphere colonizers. Furthermore, this study reports the first comparison of Multilocus sequence analysis (MLSA) and core-based phylogenies of the Rahnella and Variovorax genera.

CONCLUSIONS

The present study unveils the molecular mechanisms underlying plant growth promotion and biocontrol activity of S11P1 and S12S4, and provides a basis for their further biotechnological application in agriculture.

Genomics and metabolic characteristics of simultaneous heterotrophic nitrification aerobic denitrification and aerobic phosphorus removal by Acinetobacter indicus CZH-5

This study provides for the first time a systematic understanding of Acinetobacter indicus CZH-5 performance, metabolic pathway and genomic characteristics for aerobic nitrogen (N) and phosphorus (P) removal. Acinetobacter indicus CZH-5 showed promising performance in heterotrophic nitrification aerobic denitrification and aerobic phosphorus removal. Under optimal conditions, the maximum ammonia-N, total nitrogen and orthophosphate-P removal efficiencies were 90.17%, 86.33%, and 99.89%, respectively. The wide tolerance range suggests the strong environmental adaptability of the bacteria. The complete genome of this strain was reconstructed. Whole genome annotation was used to re-construct the N and P metabolic pathways, and related intracellular substance metabolic pathways were proposed. The transcription levels of related functional genes and enzyme activities further confirmed these metabolic mechanisms. N removal was achieved via the nitrification-denitrification pathway. Furthermore, CZH-5 exhibited significant aerobic P uptake, with phosphate diesters as the main species of intracellular P.

Integration of ammonium assimilation with denitrifying phosphorus removal for efficient nutrient management in wastewater treatment

Nutrient removal from sewage is transitioning to nutrient recovery. However, biological treatment technologies to remove and recover nutrients from domestic sewage are still under investigation. This study delved into the integration of ammonium assimilation with denitrifying phosphorus removal (DPR) as a method for efficient nutrient management in sewage treatment. Results indicated this approach eliminated over 80 % of the nitrogen in the influent, simultaneously recovering over 60 % of the nitrogen as the activated sludge through ammonia assimilation, and glycerol facilitated this process. The nitrification/denitrifying phosphorus removal ensured the stability of both nitrogen and phosphorus removal. The phosphorus removal rate exceeded 96 %, and the DPR rate reached over 90 %. Network analysis highlighted a stable community structure with Proteobacteria and Bacteroidota driving ammonium assimilation. The synergistic effect of fermentation bacteria, denitrifying glycogen-accumulating organisms, and denitrifying phosphorus-accumulating organisms contributed to the stability of nitrogen and phosphorus removal. This approach offers a promising method for sustainable nutrient management in sewage treatment.

Nitrogen removal characteristics of novel bacterium Klebsiella sp. TSH15 by assimilatory/dissimilatory nitrate reduction and ammonia assimilation

A novel strain with heterotrophic nitrification and aerobic denitrification was screened and identified as Klebsiella sp. TSH15 by 16S rRNA. The results demonstrated that the ammonia-N and nitrate-N removal rates were 2.99 mg/L/h and 2.53 mg/L/h under optimal conditions, respectively. The analysis of the whole genome indicated that strain TSH15 contained the key genes involved in assimilatory/dissimilatory nitrate reduction and ammonia assimilation, including nas, nar, nir, nor, glnA, gltB, gdhA, and amt. The relative expression levels of key nitrogen removal genes were further detected by RT-qPCR. The results indicated that the N metabolic pathways of strain TSH15 were the conversion of nitrate or nitrite to ammonia by assimilatory/dissimilatory nitrate reduction (NO3-→NO2-→NH4+) and further conversion of ammonia to glutamate (NH4+-N → Glutamate) by ammonia assimilation. These results indicated that the strain TSH15 had the potential to be applied to practical sewage treatment in the future.

Enhanced photocarrier separation in Br substitution-induced [W(VI)O6-x] units for highly efficient photocatalytic nitrate reduction under alkaline conditions

Photocatalytic nitrate (NO3-) reduction is considered a promising green and non-polluting technology to solve the nitrate pollution of groundwater and surface water. Herein, a novel Br-substituted Bi2WO6-x ultrathin nanosheets were prepared by a simple hydrothermal method in a strong acid environment containing sixteen alkyl three methyl bromide (CTAB). The catalytic system solves the problems of low carrier separation efficiency, poor performance under alkaline conditions, and a hard-to-activate N = O bond, achieving efficient NO3- removal under alkaline conditions along with high N2 selectivity. It was confirmed that Br-substituted Bi2WO6-x produced the [W(VI)O6-x] units with a strong electron-withdrawing property by changing the polarity of the O-W-O bond. As a result, the effective space charge separation caused by the change of the W valence state and the spontaneous fracture behavior of the N = O bond improved the carriers utilization efficiency and distinctly reduced the reaction energy consumption, synergistically achieving excellent performance.

Roxarsone biotransformation by a nitroreductase and an acetyltransferase in Pseudomonas chlororaphis, a bacterium isolated from soil

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, Rox), a widely used organoarsenical feed additive, can enter soils and be further biotransformed into various arsenic species that pose human health and ecological risks. However, the pathway and molecular mechanism of Rox biotransformation by soil microbes are not well studied. Therefore, in this study, we isolated a Rox-transforming bacterium from manure-fertilized soil and identified it as Pseudomonas chlororaphis through morphological analysis and 16S rRNA gene sequencing. Pseudomonas chlororaphis was able to biotransform Rox to 3-amino-4-hydroxyphenylarsonic acid (3-AHPAA), N-acetyl-4-hydroxy-m-arsanilic acid (N-AHPAA), arsenate [As(V)], arsenite [As(III)], and dimethylarsenate [DMAs(V)]. The complete genome of Pseudomonas chlororaphis was sequenced. PcmdaB, encoding a nitroreductase, and PcnhoA, encoding an acetyltransferase, were identified in the genome of Pseudomonas chlororaphis. Expression of PcmdaB and PcnhoA in E. coli Rosetta was shown to confer Rox(III) and 3-AHPAA(III) resistance through Rox nitroreduction and 3-AHPAA acetylation, respectively. The PcMdaB and PcNhoA enzymes were further purified and functionally characterized in vitro. The kinetic data of both PcMdaB and PcNhoA were well fit to the Michaelis-Menten equation, and nitroreduction catalyzed by PcMdaB is the rate-limiting step for Rox transformation. Our results provide new insights into the environmental risk assessment and bioremediation of Rox(V)-contaminated soils.

Multi-omics analysis to reveal key pathways involved in low C/N ratio stress response in Pseudomonas sp. LW60 with superior nitrogen removal efficiency

In practical engineering, nitrogen removal at low temperatures or low C/N ratios is difficult. Although strains can remove nitrogen well at low temperatures, there is no research on the performance and deep mechanism of strains under low C/N ratio stress. In this study, Pseudomonas sp. LW60 with superior nitrogen removal efficiency under low C/N ratio stress was isolated at 4 °C. With a C/N ratio of 2-10, the NH4+-N removal efficiency was 40.02 %-100 % at 4 °C. Furthermore, the resistance mechanism of Pseudomonas sp. LW60 to low C/N ratio stress was deeply investigated by multi-omics. The results of transcriptome, proteome, and metabolome revealed that the resistance of strain LW60 to low C/N ratio stress was attributed to enhanced central carbon metabolism, amino acid metabolism, and ABC transporters, rather than nitrogen removal pathways. This study isolated a strain with low C/N ratio tolerance and deeply explored its tolerance mechanism by multi-omics.

Removal of nitrate nitrogen by Pseudomonas JI-2 under strong alkaline conditions: Performance and mechanism

The nitrate nitrogen removal characteristics of Pseudomonas JI-2 under strong alkaline conditions and the composition and functional groups of extracellular polymeric substance were analyzed. Furthermore, nontargeted metabonomics and bioinformatics technology were used to investigate the alkaline tolerance mechanism. JI-2 removed 11.05 mg N/(L·h) of nitrate with the initial pH, carbon to nitrogen ratio and temperature were 11.0, 8 and 25 °C respectively. Even when the pH was maintained at 11.0, JI-2 could still effectively remove nitrate. JI-2 contains a large number of Na+/H+ antiporters, such as Mrp, Mnh (mnhACDEFG) and Pha (phaACDEFG), which can stabilize the intracellular acid-base environment, and SlpA can enable quick adaptation to alkaline conditions. Moreover, JI-2 responds to the strong alkaline environment by secreting more polysaccharides, acidic functional groups and compatible solutes and regulating key metabolic processes such as pantothenate and CoA biosynthesis and carbapenem biosynthesis. Therefore, JI-2 can survive in strong alkaline environments and remove nitrate efficiently.

The performance and mechanism of tetracycline and ammonium removal by Pseudomonas sp. DX-21

To remove ammonium and tetracycline (TC) from wastewater, a new strain, DX-21, was isolated and exhibited simultaneous removal ability. The performance of DX-21 in TC removal, its removal mechanism, and the potential toxicities of the degradation products were investigated with genomics, mass spectrometry, density functional theory calculations, quantitative structure-activity relationship analyses, and Escherichia coli exposure experiments. DX-21 exhibited removal of ammonium (9.64 mg·L-1·h-1) via assimilation, and TC removal (0.85 mg·L-1·h-1) primarily occurred through cell surface bio-adsorption and biodegradation. Among the 12 identified degradation products, the majority exhibited lower toxicities than TC. Moreover, potential degradation pathways were proposed, including hydroxylation and deamination. Furthermore, DX-21 possessed TC resistance genes, various oxygenases and peroxidases that could potentially contribute to TC degradation. DX-21 colonized activated sludge and significantly enhanced the biodegradation of TC. Therefore, DX-21 showed potential for treating wastewater containing both ammonium and TC.

Start-up of solid-phase denitrification process for treatment of nitrate-rich water in recirculating mariculture system: Carbon source selection and nitrate removal mechanism

Efficient nitrate removal from recirculating mariculture system (RMS) water is of significance since high concentration of nitrate would cause chronic health effects on aquatic organisms and eutrophication. Solid-phase denitrification (SPD) is a safer and more sustainable approach than conventional heterotrophic denitrification by dosing liquid carbon sources. Thus, its application for treating nitrate-rich RMS water was investigated in this study. Poly 3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) was identified with the best nitrate removal among four kinds of carbon sources. PHBV-filled reactors started with mariculture, municipal and mixing sludges (at the ratio of 1:1) and fed with 200 mg L-1 nitrate-rich RMS water all achieved over 81% nitrate removals with a HRT of 4 days. The dissolved organic carbon concentrations of the reactors were in the range of 3-9 mg L-1. Arcobacter, Halomonas, and Psedomonas were dominant genera responsible for nitrate removal in different reactors. Metagenomic analyses indicate that both denitrification and assimilatory nitrate reduction (ANR) are the main contributors to nitrate removals. Metagenomic results illustrated nirB/D cooperated with nasA may perform ANR pathway, which transformed nitrate to ammonia for biosynthesis. These results indicate that SPD could be a safer alternative for treating nitrate-rich RMS water, and provide new insights into nitrogen metabolism pathways in SPD process.

A novel hypothermic strain, Pseudomonas reactans WL20-3 with high nitrate removal from actual sewage, and its synergistic resistance mechanism for efficient nitrate removal at 4 °C

Nitrate can be well removed by bacteria at 25-30 °C. However, nitrate removal almost ceases at temperatures lower than 5 °C. In this study, a novel hypothermic strain, Pseudomonas reactans WL20-3 exhibited an excellent aerobic nitrate removal ability at 4 °C. It had high capability for the removal of nitrate, total dissolved nitrogen (TDN), and dissolved organic carbon (DOC) at 4 °C, achieving removal efficiencies of 100%, 87.91%, and 97.48%, respectively. The transcriptome analysis revealed all genes involved in the nitrate removal pathway were significantly up-regulated. Additionally, the up-regulation of ABC transporter genes and down-regulation of respiratory chain genes cooperated with the nitrate metabolism pathway to resist low-temperature stress. In actual sewage, inoculated with WL20-3, the nitrate removal efficiency was found to be 70.70%. Overall, these findings demonstrated the impressive capacity of the novel strain WL20-3 to remove nitrate and provided novel insights into the synergistic resistance mechanism of WL20-3 at low temperature.

Simultaneous denitrification and electricity generation in a methane-powered bioelectrochemical system

Bioelectrochemical system is a novel method for controlling down nitrate pollution, yet the feasibility of using methane as the electron donors for denitrification in this system remains unknown. In this study, using the effluent from mother BESs as inocula, a denitrifying anaerobic methane oxidation bioelectrochemical system was successfully started up in 92 days. When operated with 50 mmol/L phosphate buffer solution at pH 7 and 30°C, the maximum methane consumption, nitrate, and total nitrogen removal load reached 0.23 ± 0.01 mmol/d, 551.0 ± 22.1 mg N/m3 /d, and 64.0 ± 18.8 mg N/m3 /d, respectively. Meanwhile, the peak voltage of 93 ± 4 mV, the anodic coulombic efficiency of 6.99 ± 0.20%, and the maximum power density of 219.86 mW/m3 were obtained. The metagenomics profiles revealed that the dominant denitrifying bacteria in the cathodic chamber reduced most nitrate to nitrite through denitrification and assimilatory reduction. In the anodic chamber, various archaea including methanotrophs and methanogens converted methane via reverse methanogenesis to form formate (or H2 ), acetate, and methyl compounds, which were than utilized by electroactive bacteria to generate electricity. PRACTITIONER POINTS: A denitrifying anaerobic methane oxidation BES was successfully started up in 92 d. Simultaneous removal of methane and nitrate was achieved in the DAMO-BES. Functional genes related to AMO and denitrification were detected in the DAMO-BES. Methylocystis can mediate AMO in the anode and denitrification in the cathode.

Efficient nitrogen removal by a novel extreme strain, Pseudomonas reactans WL20-3 under dual stresses of low temperature and high alkalinity: Characterization, mechanism, and application

Although many studies report the resistance of heterotrophic nitrification-aerobic denitrification (HN-AD) strains to single environmental stress, there is no research on its resistance to dual stresses of low temperature and high alkalinity. A novel bacterium Pseudomonas reactants WL20-3 isolated in this study showed removal efficiencies of 100%, 100%, and 97.76% for ammonium, nitrate, and nitrite, respectively, at 4 °C and pH 11.0. Transcriptome analysis revealed that the resistance of strain WL20-3 to dual stresses was attributed not only to the regulation of genes in the nitrogen metabolic pathway, but also to genes in other pathways such as the ribosome, oxidative phosphorylation, amino acid metabolism, and ABC transporters. Additionally, WL20-3 removed 83.98% of ammonium from actual wastewater at 4 °C and pH 11.0. This study isolated a novel strain WL20-3 with superior nitrogen removal under dual stresses and provided a molecular understanding of its tolerance mechanism to low temperature and high alkalinity.

The Slaughterhouse as Hotspot of CC1 and CC6 Listeria monocytogenes Strains with Hypervirulent Profiles in an Integrated Poultry Chain of Italy

In Europe, very few studies are available regarding the diversity of Listeria monocytogenes (L. monocytogenes) clonal complexes (CCs) and sequence types (ST) in poultry and on the related typing of isolates using whole genome sequencing (WGS). In this study, we used a WGS approach to type 122 L. monocytogenes strains isolated from chicken neck skin samples collected in two different slaughterhouses of an integrated Italian poultry company. The studied strains were classified into five CCs: CC1-ST1 (21.3%), CC6-ST6 (22.9%), CC9-ST9 (44.2%), CC121-ST121 (10.6%) and CC193-ST193 (0.8%). CC1 and CC6 strains presented a virulence gene profile composed of 60 virulence genes and including the Listeria Pathogenicity Island 3, aut_IVb, gltA and gltB. According to cgMLST and SNPs analysis, long-term persistent clusters belonging to CC1 and CC6 were found in one of the two slaughterhouses. The reasons mediating the persistence of these CCs (up to 20 months) remain to be elucidated, and may involve the presence and the expression of stress response and environmental adaptation genes including heavy metals resistance genes (cadAC, arsBC, CsoR-copA-copZ), multidrug efflux pumps (mrpABCEF, EmrB, mepA, bmrA, bmr3, norm), cold-shock tolerance (cspD) and biofilm-formation determinants (lmo0673, lmo2504, luxS, recO). These findings indicated a serious risk of poultry finished products contamination with hypervirulent L. monocytogenes clones and raised concern for the consumer health. In addition to the AMR genes norB, mprF, lin and fosX, ubiquitous in L. monocytogenes strains, we also identified parC for quinolones, msrA for macrolides and tetA for tetracyclines. Although the phenotypical expression of these AMR genes was not tested, none of them is known to confer resistance to the primary antibiotics used to treat listeriosis The obtained results increase the data on the L. monocytogenes clones circulating in Italy and in particular in the poultry chain.

Characterization and metabolic pathway of Pseudomonas fluorescens 2P24 for highly efficient ammonium and nitrate removal

The ammonium and nitrate removal performance and metabolic pathways of a biocontrol strain, Pseudomonas fluorescens 2P24, were investigated. Strain 2P24 could completely remove 100 mg/L ammonium and nitrate, with removal rates of 8.27 mg/L/h and 4.29 mg/L/h, respectively. During these processes, most of the ammonium and nitrate were converted to biological nitrogen via assimilation, and only small amounts of nitrous oxide escaped. The inhibitor allylthiourea had no impact on ammonium transformation, and diethyl dithiocarbamate and sodium tungstate did not inhibit nitrate removal. Intracellular nitrate and ammonium were detectable during the nitrate and ammonium transformation process, respectively. Moreover, the nitrogen metabolism functional genes (glnK, nasA, narG, nirBD, nxrAB, nirS, nirK, and norB) were identified in the strain. All results highlighted that P. fluorescens 2P24 is capable of assimilatory and dissimilatory nitrate reduction, ammonium assimilation and oxidation, and denitrification.

Enhanced heterotrophic nitrification and aerobic denitrification performance of Glutamicibacter arilaitensis EM-H8 with different carbon sources

Different carbon sources for Glutamicibacter arilaitensis EM-H8 were evaluated for ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N) and nitrite nitrogen (NO₂^--N) removal. Strain EM-H8 could rapidly remove NH₄⁺-N, NO₃^--N and NO₂^--N. The highest removal rates measured for different forms of nitrogen with different carbon sources were 5.94 mg/L/h for NH₄⁺-N with sodium citrate, 4.25 mg/L/h for NO₃^--N with sodium succinate, and 3.88 mg/L/h for NO₂^--N with sucrose. The Nitrogen balance showed that strain EM-H8 could convert 77.88% of the initial nitrogen into nitrogenous gas when NO₂^--N was selected as the sole nitrogen source. The presence of NH₄⁺-N increased the removal rate of NO₂^--N from 3.88 to 4.02 mg/L/h. In an enzyme assay, ammonia monooxygenase, nitrate reductase and nitrite oxidoreductase were detected at 0.209, 0.314, and 0.025 U/mg protein, respectively. These results demonstrate that strain EM-H8 performs well for nitrogen removal, and shows excellent potential for simple and efficient removal of NO₂^--N from wastewater.

The coexistence of copper ions and TC affected the binding ability and the reaction order between extracellular polymeric substances of aerobic granular sludge and exogenous substances

As a barrier against external toxic effects, extracellular polymeric substances (EPSs) directly affect the toxicity and removal efficiency of exogenous substances. The reaction of EPSs with exogenous substances has been taken into consideration. The contents of EPSs in sludge cultivated by different influent water vary greatly, which leads to great differences in the binding ability and reaction sequence between EPSs and exogenous substances. However, the results in this respect are very limited. In this study, the binding characteristics between exogenous tetracycline (TC)/copper ions (Cu²⁺) and EPSs from aerobic granular sludge cultured under single and coexisting TC/Cu²⁺ were assessed by three-dimensional fluorescence-parallel factor analysis. The pollutants in the influent water could directionally induce microorganisms to secrete more EPSs, while fluorescence substances in EPSs could combine with the exogenous substances to lessen their effects. In the presence of coexisting TC and Cu²⁺ in the influent water, the ability of fluorescence substances in EPSs to combine with exogenous TC or Cu²⁺ weakened, and humic substances in EPSs were more susceptible than protein substances to binding with exogenous substances. However, the reaction order between EPSs components and exogenous TC or Cu²⁺ was opposite, and the ability of fluorescence substances in EPSs to combine with exogenous TC or Cu²⁺ was enhanced under individual TC or Cu²⁺ existing in the influent water. This study provided new insights into the interaction between EPSs and exogenous substances.

Klebsiella oxytoca (EN-B2): A novel type of simultaneous nitrification and denitrification strain for excellent total nitrogen removal during multiple nitrogen pollution wastewater treatment

The poor total nitrogen (TN) removal rate achieved using microorganisms to treat wastewater polluted with multiple types of nitrogen was improved using a novel simultaneous nitrification and denitrification strain (Klebsiella oxytoca EN-B2). Strain EN-B2 rapidly eliminated ammonium, nitrate, and nitrite, giving maximum elimination rates of 4.58, 7.46, and 7.83 mg/(L h), respectively, equivalent to TN elimination rates of 4.35, 6.92, and 7.11 mg/(L h), respectively. The simultaneous nitrification and denitrification system gave ammonium and nitrite elimination rates of 7.14 and 9.17 mg/(L h), respectively, and a TN elimination rate ≥ 9.0 mg/(L h). Nitrogen balance calculations indicated that 51.22 %, 31.62 % and 46.82 % of TN in systems containing only ammonium, nitrite, and nitrate, respectively, were lost as nitrogenous gases. The ammonia monooxygenase, hydroxylamine oxidoreductase, nitrate reductase and nitrite reductase enzyme activities were determined. The results indicated that strain EN-B2 can be used to treat wastewater polluted with multiple types of nitrogen.

Performance and mechanism of nitrate removal by the aerobic denitrifying bacterium JI-2 with a strong autoaggregation capacity

Here, a new strain JI-2 of the strongly autoaggregating aerobic denitrifying bacteria was screened. The nitrate removal ability and autoaggregation mechanism of JI-2 were analyzed using the nitrogen balance and genomics technology. The nitrate removal rate was 27.05 mg N/(L·h) at pH 9.0 and C/N 8.0. The strain JI-2 removes nitrate via the aerobic denitrification and dissimilation pathways and removes ammonium via the assimilation pathway. 66.81 % nitrate was converted to cellular components under aerobic conditions. Complex nitrogen metabolism genes were detected in strain JI-2. C-di-GMP mediates the motility behavior of JI-2 by binding the FleQ and PilZ proteins, and regulating the expression of PslA. Furthermore, the mechanism of autoaggregation was verified by extracellular polymeric substance analysis. Meanwhile, the nitrate removal rates of strain JI-2 was 11.13-12.50 mg N/(L·h) in wastewater. Thus, strain JI-2 has good prospects for application in the treatment of nitrate wastewater.

Evidence for Assimilatory Nitrate Reduction as a Previously Overlooked Pathway of Reactive Nitrogen Transformation in Estuarine Suspended Particulate Matter

Suspended particulate matter (SPM) contributes to the loss of reactive nitrogen (Nr) in estuarine ecosystems. Although denitrification and anaerobic ammonium oxidation in SPM compensate for the current imbalance of global nitrogen (N) inputs and sinks, it is largely unclear whether other pathways for Nr transformation exist in SPM. Here, we combined stable isotope measurements with metagenomics and metatranscriptomics to verify the occurrence of dissimilatory nitrate reduction to ammonium (DNRA) in the SPM of the Pearl River Estuary (PRE). Surprisingly, the conventional functional genes of DNRA (nirBD) were abundant and highly expressed in SPM, which was inconsistent with a low potential rate. Through taxonomic and comparative genomic analyses, we demonstrated that nitrite reductase (NirBD) in conjunction with assimilatory nitrate reductase (NasA) performed assimilatory nitrate reduction (ANR) in SPM, and diverse alpha- and gamma-proteobacterial lineages were identified as key active heterotrophic ANR bacteria. Moreover, ANR was predicted to have a relative higher occurrence than denitrification and DNRA in a survey of Nr transformation pathways in SPM across the PRE spanning 65 km. Collectively, this study characterizes a previously overlooked pathway of Nr transformation mediated by heterotrophic ANR bacteria in SPM and has important implications for our understanding of N cycling in estuaries.

Ball milling potassium ferrate activated biochar for efficient chromium and tetracycline decontamination: Insights into activation and adsorption mechanisms

Herein, novel Fe-biochar composites (MBC_BM500 and MBC_BM700) were synthesized through K₂FeO₄ co-pyrolysis and ball milling, and were used to eliminate Cr(VI)/TC from water. Characterization results revealed that higher temperature promoted formation of zero-valent iron and Fe₃C on MBC_BM700 through carbothermal reduction between K₂FeO₄ and biochar. The higher specific surface area and smaller particle size of MBC_BM500/700 stemmed from the corrosive functions of K and the ball milling process. And the maximal uptake amount of MBC_BM700 for Cr(VI)/TC was 117.49/90.31 mg/g, relatively higher than that of MBC_BM500 (93.86/84.15 mg/g). Furthermore, ion exchange, pore filling, precipitation, complexation, reduction and electrostatic attraction were proved to facilitate the adsorption of Cr(VI), while hydrogen bonding force, pore filling, complexation and π-π stacking were the primary pathways to eliminate TC. This study provide a reasonable design of Fe-carbon materials for Cr(VI)/TC contained water remediation, which required neither extra modifiers nor complex preparation process.

Performance and mechanism of tetracycline removal by the aerobic nitrate-reducing strain Pseudomonas sp. XS-18 with auto-aggregation

The coexistence of multiple pollutants has become a distinctive feature of water pollution. However, there are a few strains that can remove nitrate and tetracycline (TC). Here, the efficiency of strain XS-18 in removing nitrate and TC was analyzed, and the mechanism of tolerance and removal of TC was investigated by infrared spectroscopy, three-dimensional fluorescence spectroscopy, and genome analysis. XS-18 could efficiently remove TC (0.40 mg·L^-1·h^-1) at pH 7.0-11.0 with auto-aggregation. TC was removed via extracellular polymeric substance (EPS) (55.90%) and cell surface (44.10%) adsorption. TC (10 mg/L) could stimulate XS-18 to secrete more polysaccharides and hydrophobic proteins to improve its auto-aggregation ability. The findings also confirmed that TC resistance genes were present. Furthermore, the bacterial flagellum, signal transduction of the chemotactic system and regulatory genes were shown to be related to the auto-aggregation of the strain. XS-18 has potential applications in the treatment of wastewater containing nitrate and TC.

Atypical Serogroup IVb-v1 of Listeria monocytogenes Assigned to New ST2801, Widely Spread and Persistent in the Environment of a Pork-Meat Producing Plant of Central Italy

In this study, we characterized 84 Listeria monocytogenes (Lm) strains having an atypical IVb-v1 profile and isolated in a meat producing plant of Central Italy. They were assigned to the new MLST type ST2801 (CC218). The new ST was widespread in the food-producing environment where it was able to persist for over a year even after cleaning and sanitation. Cluster analysis identified three main clusters genetically close to each other (0-22 allelic differences and 0-28 SNPs) from two different cgMLST types, suggesting a common source. The coexistence of closely related clusters over time could be the result of a different evolution path starting from a common ancestor first introduced in the plant and/or the consequence of the repetitive reintroduction of closely related clones probably by raw materials. All the strains presented several determinants for heavy metals resistance, stress response, biofilm production, and multidrug efflux pumps with no significant differences among the clusters. A total of 53 strains carried pLI100 and the j1776 plasmids, while in one strain, the pLM33 was found in addition to pLI100. Only the strains carrying plasmids presented cadA and cadC for cadmium resistance and the mco gene encoding a multicopper oxidase and gerN for an additional Na+/H+-K+ antiporter. All the strains presented a virulence profile including a full-length inlA gene and the additional LIPI-3. The isolation of a new ST with a large pattern of stress-adaptation genes and able to persist is an important contribution to deepening the current knowledge on the uncommon IVb-v1 and in general on the genomic diversity of Lm.

Effect of sulfamethoxazole on nitrate removal by simultaneous heterotrophic aerobic denitrification

The increase in mariculture activities worldwide has not only led to a rise of nitrogen compounds in the ecosystem but has also intensified the accumulation of antibiotics in both terrestrial and marine environments. This study focused on the effect of typical antibiotics, specifically sulfamethoxazole (SMX) on nitrate removal from mariculture wastewater by aerobic denitrification process; an aerobic denitrification system feeding with 148.2 mg/L COD, 8.59 mg/L nitrate, 0.72 mg/L nitrite, and 4.75 mg/L ammonium was set up. The hydraulic retention time (HRT) was 8 h. As the aerobic bioreactor started up successfully without SMX dosage, an excellent removal of ammonium, nitrite, and nitrate was achieved at 91.35%, 93.33%, and 88.51%, respectively; the corresponding effluent concentrations were 0.41 mg/L, 0.048 mg/L, and 0.96 mg/L. At the influent SMX doses of 0, 1, 5, and 10 mg/L, the COD removal reached 96.91%, 96.27%, 88.69%, and 85.89%, resulting in effluent concentrations of 4.53, 5.45, 17.38, and 20.6 mg/L, respectively. Nitrification was not inhibited by SMX dosage. However, aerobic denitrification was inhibited by 10 mg/L SMX. Proteobacteria was the most abundant phylum, and surprisingly its abundance increased with the increase in SMX concentration. An excellent SMX degradation was noted at initial SMX dosages of 1, 5, and 10 mg/L; the removal rate was 100%,100%, and 99.8%, respectively. The SMX degrading genera Comamonas sp., Acinetobacter sp., and Thauera sp. are of great validity to wastewater engineers because they have demonstrated efficiency in simultaneous heterotrophic aerobic denitrification and antibiotic degradation as well as COD removal. PRACTITIONER POINTS: Nitrification was not inhibited by increase in SMX dosage. An increase in SMX dosage inhibited aerobic denitrification. COD removal was not affected by increased SMX dosage. Comamonas, Acinetobacter, and Thauera had high efficiency in COD removal and SMX degradation.