Nitrate removal performances of a new aerobic denitrifier, Acinetobacter haemolyticus ZYL, isolated from domestic wastewater

Optimization of degradation conditions and analysis of degradation mechanism for nitrite by Bacillus aryabhattai 47

Excessive nitrite levels cause significant damage to aquaculture, making it crucial to explore green and reliable nitrite removal technologies. In this study, A Bacillus aryabhattai (designated as the strain 47) isolated from aquaculture wastewater was used as the experimental strain. The nitrite degradation conditions of the strain 47 were optimized, and the optimal conditions are: glucose was 12.74 g/L, fermented special soybean meal was 21.27 g/L, MgCl2 369 mg/L, pH 7.0, incubated at 30 °C with the inoculum size of 2 % and the rotation speed of 170 rpm. Under the optimal conditions, the nitrite concentration of the culture solution was 200 mg/L, and the nitrite removal rate reached 91.4 %. Meanwhile, the mechanism by which Mg2+ enhanced the nitrite degradation ability of the strain 47 was investigated by transcriptomics. An operon structure directed cellular trafficking of Mg2+, and then, the Mg2+-mediated catalytic reaction of multiple enzymes enhanced and improved cellular metabolic processes (e.g. the transport and metabolism of nitrite, central carbohydrate metabolism oxidative phosphorylation). At the same time, with the progress of cell metabolism, cells secreted a series of enzymes related to nitrite transport and metabolism to promote the metabolism of nitrite. And the process of the assimilated nitrate reduction pathway of nitrite degradation in the strain 47 was elaborated at the transcriptome level. This study provided a new insight into nitrite treatment mediated by microbial organisms.

Thauera sp. for efficient nitrate removal in continuous denitrifying moving bed biofilm reactor

Thauera is the most widely found dominant denitrifying genus in wastewater. In earlier study, MBBR augmented with a specially developed denitrifying five-membered bacterial consortium (DC5) where Thauera was found to be the most abundant and persistent genus. Therefore, to check the functional potential of Thauera in the removal of nitrate-containing wastewater in the present study Thauera sp.V14 one of the member of the consortium DC5 was used as the model organism. Thauera sp.V14 exhibited strong hydrophobicity, auto-aggregation ability, biofilm formation and denitrification ability, which indicated its robust adaptability short colonization and nitrate removal efficiency. Continuous reactor studies with Thauera sp.V14 in 10 L dMBBR showed 91% of denitrification efficiency with an initial nitrate concentration of 620 mg L-1 within 3 h of HRT. Thus, it revealed that Thauera can be employed as an effective microorganism for nitrate removal from wastewater based on its performance in the present studies.

Three Novel Marine Species of Paracoccus, P. aerodenitrificans sp. nov., P. sediminicola sp. nov. and P. albus sp. nov., and the Characterization of Their Capability to Perform Heterotrophic Nitrification and Aerobic Denitrification

Heterotrophic nitrification-aerobic denitrification (HN-AD) is an efficient nitrogen removal process and the genus Paracoccus is one important group of the HN-AD bacteria. During an investigation of the microbial diversity in marine ranching of the Pearl River Estuary (PR China), three bacterial strains, designated SCSIO 75817^T, SCSIO 76264^T and SCSIO 80058^T, were isolated from sediments. Phylogenetic analyses based on 16S rRNA gene sequences indicated that the three strains belonged to the genus Paracoccus and their closest neighbors were P. isoporae DSM 22220^T (97.6-98.0%), P. aurantiacus CGMCC 1.13898^T (97.3-97.6%) and P. xiamenensis MCCC 1A16381^T (97.1-97.4%), respectively. The analysis results of 16S rRNA gene similarity, ANI, AAI and dDDH showed that the pairwise similarities between these three strains and their closest neighbors were 97.4-98.5%, 76.9-81.0%, 75.5-79.6% and 20.3-23.3%, respectively. Polyphasic taxonomic data of the phylogenetic, phenotypic and chemotaxonomic analyses indicate that these strains represent three novel species in the genus Paracoccus, for which the names Paracoccus aerodenitrificans sp. nov., Paracoccus sediminicola sp. nov. and Paracoccus albus sp. nov. are proposed, respectively. The study also demonstrated the heterotrophic nitrification-aerobic denitrification (HN-AD) ability of the novel species P. aerodenitrificans SCSIO 75817^T. When it was aerobically cultivated at 28 °C using NH₄⁺-N, NO₃^--N and NO₂^--N as the sole nitrogen sources, the nitrogen removal efficiencies were 73.4, 55.27 and 49.2%, respectively, and the maximum removal rates were 3.05, 1.82 and 1.63 mg/L/h, respectively. The results suggest that it has promising potential for wastewater treatment.

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.

Genomics and nitrogen metabolic characteristics of a novel heterotrophic nitrifying-aerobic denitrifying bacterium Acinetobacter oleivorans AHP123

A novel aerobic strain of Acinetobacter oleivorans AHP123 was isolated from activated sludge, which could conduct heterotrophic nitrification and denitrification simultaneously. This strain has excellent NH₄⁺-N removal ability, with 97.93% removal rate at 24-hour. To identify the metabolic pathways of this novel strain, genes of gam, glnA, gdhA, gltB, nirB, nasA, nar, nor, glnK and amt were detected by genome analysis. Through RT-qPCR, it was found that the expression of key genes confirmed two possible ways of nitrogen removal in strain AHP123: nitrogen assimilation and heterotrophic nitrification aerobic denitrification (HNAD). However, the absence of some common HNAD genes (amo, nap and nos) suggested that strain AHP123 might have a different HNAD pathway from other HNAD bacteria. Nitrogen balance analysis revealed that strain AHP123 assimilated most of the external nitrogen sources into intracellular nitrogen.

A review: Manganese-driven bioprocess for simultaneous removal of nitrogen and organic contaminants from polluted waters

Water pollutants, such as nitrate and organics have received much attention for their harms to ecological environment and human health. The redox transformation between Mn(Ⅱ) and Mn(Ⅳ) for nitrogen and organics removal have been recognized for a long time. Mn(Ⅱ) can act as inorganic electron donor to drive autotrophic denitrification so as to realize simultaneous removal of Mn(Ⅱ), nitrate and organic pollutants. Mn oxides (MnOx) also play an important role in the adsorption and degradation of some organic contaminants and they can change or create new oxidation pathways in the nitrogen cycle. Herein, this paper provides a comprehensive review of nitrogen and organic contaminants removal pathways through applying Mn(Ⅱ) or MnOx as forerunners. The main current knowledge, developments and applications, pollutants removal efficiency, as well as microbiology and biochemistry mechanisms are summarized. Also reviewed the effects of factors such as the carbon source, the environmental factors and operation conditions have on the process. Research gaps and application potential are further proposed and discussed. Overall, Mn-based biotechnology towards advanced wastewater treatment has a promising prospect, which can achieve simultaneous removal of nitrogen and organic contaminants, and minimize sludge production.

Insight into sulfamethoxazole effects on aerobic denitrification by strain Pseudomonas aeruginosa PCN-2: From simultaneous degradation performance to transcriptome analysis

It is a well-established fact that aerobic denitrifying strains are profoundly affected by antibiotics, but bacterium performing simultaneous aerobic denitrification and antibiotic degradation is hardly reported. Here, a typical aerobic denitrifying bacterium Pseudomonas aeruginosa PCN-2 was discovered to be capable of sulfamethoxazole (SMX) degradation. The results showed that nitrate removal efficiency was decreased from 100% to 88.12%, but the resistance of strain PCN-2 to SMX stress was enhanced with the increment of SMX concentration from 0 to 100 mg/L. Transcriptome analysis revealed that the down-regulation of energy metabolism pathways rather than the denitrifying functional genes was responsible for the suppressed nitrogen removal, while the up-regulation of antibiotic resistance pathways (e.g., biofilm formation, multi-drug efflux system, and quorum sensing) ensured the survival of bacterium and the carrying out of aerobic denitrification. Intriguingly, strain PCN-2 could degrade SMX during aerobic denitrification. Seven metabolites were identified by the UHPLC-MS, and three degradation pathways (which includes a new pathway that has never been reported) was proposed combined with the expressions of drug metabolic genes (e.g., cytP450, FMN, ALDH and NAT). This work provides a mechanistic understanding of the metabolic adaption of strain PCN-2 under SMX stress, which provided a broader idea for the treatment of SMX-containing wastewater.

Organic and inorganic nitrogen removals by an ureolytic heterotrophic nitrification and aerobic denitrification strain Acinetobacter sp. Z1: Elucidating its physiological characteristics and metabolic mechanisms

Although heterotrophic nitrification-aerobic denitrification (HN-AD) is promising in nitrogen removal, it remains unclear for most HN-AD strains in physiological characteristics and metabolic mechanisms. In this study, a newly isolated strain Acinetobacter sp. Z1 converted not only inorganic nitrogen, but also organic nitrogen to N₂. Among them, urea was the preferential nitrogen substrate. Single-factor experiments showed that efficient HN-AD process occurred with acetate as carbon source, C/N ratios of 12 for NH₄⁺-N and 15 for NO₃^--N, pH 8, 30 °C, DO of ∼5.8 mg/L and salinity less than 1.5 %. Subsequently, response surface analysis was applied to predict the optimal growth conditions. Its complete genome annotation in combination with enzymatic activity assay and nitrogen balance calculation showed that at least four pathways involved in nitrogen metabolism. This work indicates that ureolytic strain Z1 could be prepared as bacterial agents with other HN-AD strains to treat urea-containing wastewater like urine from urban community.

Efficient remediation of Mn2+ and NH4+-N in co-contaminated water and soil by Acinetobacter sp. AL-6 synergized with grapefruit peel biochar: Performance and mechanism

Electrolysis manganese slag produced in industrial manganese production causes massive leachate containing heavy metal Mn²⁺ and inorganic NH₄⁺-N, which causes serious hazard to the water body and soil. A cost-effective alternative to address the multiple pollution is urgently needed. This study investigated the synergy of grapefruit peel biochar (BC) and strain AL-6 to remediate Mn²⁺ and NH₄⁺-N in sequencing batch bioreactor (SBR) and soil column. The results showed that, in SBR, under the condition of C/N 5, temperature 30°C, BC and strain AL-6 showed fabulous performance to remove Mn²⁺ (99.3%) and NH₄⁺-N (97.7%). The coexisting ions Mg²⁺ and Ca²⁺ had no effects on the removal of Mn²⁺ and COD, however, 23.3% removal efficiency of NH₄⁺-N was curtailed. Characterization found that the presence of MnCO₃ confirmed the adsorption of Mn²⁺ by functional groups action, and gas chromatography indicated that BC and strain AL-6 promoted the reduction of N₂O and organic carbon. In addition, BC and strain AL-6 helped to immobilize 799.41 mg L^-1 of Mn²⁺ and 320 mg L^-1 of NH₄⁺-N after 45 d in the soil column. And the determination of TOC, CEC, pH, Eh, soil enzymatic activity (catalase and urease), and microbial diversity and abundance confirmed that BC and strain AL-6 increased the soil fertility and bioavailability of pollutants. Totally, BC and strain AL-6 possess great potential to remediate Mn²⁺ and NH₄⁺-N pollution in water and soil.

Denitrification strategy of Pantoea sp. MFG10 coupled with microbial dissimilatory manganese reduction: Deciphering the physiological response based on extracellular secretion

In this study, the manganese (Mn) reduction-coupled denitrification strategy of dissimilatory Mn reducing bacteria was insightfully investigated. Different parameters (MnO₂ level, pH, and temperature) were optimized by kinetic fitting to improve denitrification and Mn reduction effects. The 300 mg L^-1 MnO₂ addition achieved 98.72% NO₃^--N removal in 12 h, which was 54.62% higher than blank group without MnO₂. Scale-up studies showed that the metabolic activity of the bacteria was effectively enhanced by the addition of MnO₂. Besides the deepening of humification in the system, tryptophan-like protein and polysaccharide as potential electron donor precursors revealed remarkable contributions to the extracellular secretion-dependent denitrification process of DMRB. The effect of EPS on Mn reduction depends mainly on the capture of MnO₂ by the LB-EPS layer versus its dissolution in the TB-EPS layer. Ultimately, the EPS possess a dual effect of accelerated denitrification and Mn reduction efficiency due to the enhanced EET process.

Phenol and 17β-estradiol removal by Zoogloea sp. MFQ7 and in-situ generated biogenic manganese oxides: Performance, kinetics and mechanism

The pollution of multifarious pollutants such as heavy metal, organic compounds, and nitrate are a hot research topic at present. In this study, the functions of Zoogloea sp. MFQ7 and its biological precipitation formed during bacterial manganese oxidation on the removal of phenol and 17β-estradiol (E2) were investigated. Strain MFQ7, a manganese-oxidizing bacteria, can remove 98.34% of phenol under pH of 7.1, a temperature of 30 ℃ and Mn²⁺ concentration of 24.34 mg L^-1, additionally, the optimum E2 removal by strain MFQ7 was 100.00% at pH of 7.1, temperature of 28 ℃ and Mn²⁺ concentration of 28.45 mg L^-1 by using response surface methodology (RSM) based on Box-Behnken design (BBD) model. The maximum adsorption capacity of bio-precipitation for phenol and E2 was 201.15 mg g^-1 and 65.90 mg g^-1, respectively. Furthermore, adsorption kinetics and isotherms analysis, XPS, FTIR spectra, Mn(III) trapping experiments elucidated chemical adsorption and Mn(III) oxidation contribute to the removal of phenol and E2 by biogenic manganese oxides. These findings indicated that the adsorption and oxidation of manganese are expected to be one of the effective means to remove these typical organic pollutants containing phenol and E2.

Heterotrophic ammonium assimilation: An important driving force for aerobic denitrification of Rhodococcus erythropolis strain Y10

Studies on microbial ammonium removal have focused on the heterotrophic nitrification of microorganisms and have rarely studied the role of ammonium assimilation. In this study, Rhodococcus erythropolis strain Y10 with the capacity of aerobic denitrification was screened from the surface flow constructed wetlands that treat high-strength ammonium swine wastewater. Instead of through nitrification, this strain removed ammonium through heterotrophic ammonium assimilation, with the removal rate of 9.69 mg/L/h. The KEGG nitrogen metabolism pathway analysis combined with nitrogen balance calculation manifested that the removal of nitrate and nitrite by R. erythropolis Y10 was achieved through two pathways: 1) assimilation reduction to biomass nitrogen and 2) aerobic denitrification reduction to gaseous nitrogen. Ammonium addition improved the aerobic denitrification rate of nitrate and nitrite. The maximal reduction rates of nitrate and nitrite increased from 7.82 and 7.23 mg/L/h to 9.09 and 8.09 mg/L/h respectively, when 100 mg/L ammonium was separately added to 150 mg/L nitrate and nitrite. Furthermore, the removal efficiency of total nitrogen increased from 69.80% and 77.65% to 89.19% and 91.88%, respectively. Heterotrophic ammonium assimilation promoted the aerobic denitrification efficiency of Rhodococcus erythropolis strain Y10.

Characterization of Acinetobacter indicus ZJB20129 for heterotrophic nitrification and aerobic denitrification isolated from an urban sewage treatment plant

The Acinetobacter indicus strain ZJB20129 isolated from an urban sewage treatment plant demonstrated the heterotrophic nitrification-aerobic denitrification (HN-AD) ability. Strain ZJB20129 could remove 98.73% of ammonium-N, 97.26% of nitrite-N and 96.55% of nitrate-N, and the maximum removal rate was 3.66, 4.62 and 5.21 mg/L/h, respectively. Ammonium was preferentially used during simultaneous nitrification and denitrification. Strain ZJB20129 exhibited highest ammonium removal capability when carbon source was sodium succinate, C/N ratio was 15, pH was 8.0, and temperature was 35 ℃. Key enzymes involved in HN-AD including hydroxylamine oxidase, periplasmic nitrate reductase and nitrite reductase as well as their encoding genes were detected, and the metabolic pathway of HN-AD was subsequently predicted. Our results suggested that Acinetobacter indicus ZJB20129 displayed superior nitrogen removal performance on actual wastewater and thus made it have a good application prospect in wastewater biological treatment.

Simultaneous removal of nitrate, manganese, and tetracycline by Zoogloea sp. MFQ7: Adsorption mechanism of tetracycline by biological precipitation

A Mn(II) oxidizing-denitrifying and tetracycline (TC) removal bacterium Zoogloea sp. MFQ7 was isolated in this study. Nitrogen removal was 83.49% by nitrogen balance experiment. The maximum removal efficiencies of nitrate, Mn(II), and TC by strain MFQ7 within 96 h was 100.00, 74.56, and 63.59% at C/N of 2.0, pH of 7.0, Mn(II) of 20 mg L^-1, temperature of 30.0 °C, and TC of 0.2 mg L^-1. SEM illustrated that biogenic manganese oxides (BMO) was petal-like, XRD and XPS analyses confirmed that MnO₂ was the main component of BMO. Besides, the maximum adsorption capacity of BMO for TC was 52.21 mg g^-1. FTIR detected the changes in TC adsorption by BMO. Pseudo-second-order model (R² = 0.994) explained the adsorption kinetics of TC on BMO and Langmuir isotherm model (R² = 0.983) suggested that it was homogeneous adsorption, thermodynamics data (ΔG < 0, ΔH = 18.31 kJ mol^-1, ΔS = 72.8 J (mol*K)^-1) confirmed that adsorption was endothermic and spontaneous.

Characteristics of a novel heterotrophic nitrification-aerobic denitrification yeast, Barnettozyma californica K1

Yeast strain K1, isolated from surface sediment, was identified as Barnettozyma californica. The strain showed efficient heterotrophic nitrification and aerobic denitrification (HN-AD) at initial ammonium, nitrite and nitrate concentrations of 14-140 mg/L. Additionally, the optimum carbon source for its growth and nitrogen removal activity was sucrose, followed by glucose, acetate and citrate. The maximum removal efficiencies of ammonium, nitrite and nitrate were 99.11%, 99.13% and 98.84% under 48 h of culture with sucrose at 140 mg/L nitrogen and the corresponding removal efficiencies of total nitrogen were 90.16%, 86.65% and 81.48%, respectively. The optimum conditions for the inorganic nitrogen removal and growth of strain K1 were a C/N of 18 and a salinity of 5-15 ppt. The amoA, nirK and nosZ genes of K1 were detected. All the results suggest that B. californica K1 is capable of HN-AD and has the potential to remove inorganic nitrogen from wastewater.