Search

Biological filters effectively remove ammonium from drinking water via nitrification. In a pilot-scale upflow biological contact filter (U-BCF), complete ammonia oxidizers (comammox), which are capable of oxidizing ammonia to nitrate in one cell, were more abundant than ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). However, little information is available on the contribution of comammox to nitrification. In this study, we evaluated the autotrophic growth activity of comammox associated with biological activated carbon (BAC) in a U-BCF by DNA-stable isotope probing (DNA-SIP). BAC samples collected from the U-BCF were continuously fed mineral medium containing 0.14 mg N L−1 ammonium and 12C- or 13C-labeled bicarbonate for 20 days. DNA-SIP analysis revealed that comammox (clades A and B) as well as AOA assimilated bicarbonate after 10 days of incubation, proving that dominant comammox could contribute to nitrification. Contrarily, AOB remained inactive throughout the observation period. Amplicon sequencing of the 13C-labeled DNA fractions of comammox revealed that specific genotypes other than the most dominant genotype in the original sample were more enriched under the incubation condition for the DNA-SIP experiment. Thus, dominant genotypes of comammox in a U-BCF might utilize organic nitrogen to fuel nitrification in ammonia-limited environments. [ABSTRACT FROM AUTHOR]

Lead (Pb) contamination is one of the major environmental problems on a global scale. Bacterial endophytes have been accepted as a promising technique to assist phytoremediation. In this study, three Pb-tolerant endophytic bacteria were isolated from the roots of Pityrogramma calomelanos. Based on partial 16S rRNA gene sequencing analysis, all isolates were similar to Pseudomonas and tolerated Pb concentration up to 1850mg/L, producing siderophores and solubilized phosphate. Among them, Pc isolate closely related to Pseudomonas psychrophila showed the highest water-soluble Pb in solution (Pb solubilization) and in contaminated soil. This isolate was chosen to study the effects on Pb accumulation in the roots of Acacia mangium and Eucalyptus camaldulensis by a hydroponic experiment. The results showed that, in the Hoagland nutrient solution with no Pb spiking, the roots showed no significant difference (p > 0.05), and the concentration of Pb ranged from 10 to 89 mg/kg. In the nutrient solution in the presence of 30 mg/L Pb, there were no significant changes in Pb contents in roots. However, A. mangium showed an increase in Pb concentration in the roots (6829 ± 697 mg/kg), compared to non-inoculation (6242 ± 272 mg/kg). E. camaldulensis inoculation showed a decrease in Pb content (3763 ± 592 mg/kg), compared to non-inoculation (4233 ± 264 mg/kg). These results suggest that the Pc isolate closely related to P. psychrophila was effective in promoting the phytoremediation potential of A. mangium, but it was not useful for E. camaldulensis. [ABSTRACT FROM AUTHOR]

Ammonia-oxidizing archaea (AOA) have recently been proposed as potential players for ammonia removal in wastewater treatment plants (WWTPs). However, there is little evidence directly showing the contribution of AOA to ammonia oxidation in these engineered systems. In this study, DNA-stable isotope probing (DNA-SIP) with labeled 13C-HCO3− was introduced to sludge from a municipal WWTP. Quantitative PCR demonstrated that AOA amoA genes outnumbered AOB amoA genes in this WWTP sludge. AOA amoA gene sequence analysis revealed that AOA present in this WWTP were specific to one subcluster within the group 1.1b Thaumarchaeota. When ammonia was supplied to DNA-SIP incubation, the DNA-SIP profiles demonstrated the incorporation of the 13C into AOA and AOB. However, the 13C was not found to be assimilated into both microorganisms in the incubation without ammonia. Specific primers were designed to target amoA genes of AOA belonging to the subcluster found in this WWTP. Applying the primers to DNA-SIP experiment revealed that AOA of this subcluter most likely utilized inorganic carbon during ammonia oxidation under the studied conditions. [ABSTRACT FROM AUTHOR]

Most bioremediation studies on volatile organic compounds (VOCs) have focused on a single contaminant or its derived compounds and degraders have been identified under single contaminant conditions. Bioremediation of multiple contaminants remains a challenging issue. To identify a bacterial consortium that degrades multiple VOCs (dichloromethane (DCM), benzene, and toluene), we applied DNA-stable isotope probing. For individual tests, we combined a C-labeled VOC with other two unlabeled VOCs, and prepared three unlabeled VOCs as a reference. Over 11 days, DNA was periodically extracted from the consortia, and the bacterial community was evaluated by next-generation sequencing of bacterial 16S rRNA gene amplicons. Density gradient fractions of the DNA extracts were amplified by universal bacterial primers for the 16S rRNA gene sequences, and the amplicons were analyzed by terminal restriction fragment length polymorphism (T-RFLP) using restriction enzymes: HhaI and MspI. The T-RFLP fragments were identified by 16S rRNA gene cloning and sequencing. Under all test conditions, the consortia were dominated by Rhodanobacter, Bradyrhizobium/ Afipia, Rhizobium, and Hyphomicrobium. DNA derived from Hyphomicrobium and Propioniferax shifted toward heavier fractions under the condition added with C-DCM and C-benzene, respectively, compared with the reference, but no shifts were induced by C-toluene addition. This implies that Hyphomicrobium and Propioniferax were the main DCM and benzene degraders, respectively, under the coexisting condition. The known benzene degrader Pseudomonas sp. was present but not actively involved in the degradation. [ABSTRACT FROM AUTHOR]

Isolation of complex dissolved organic matter (DOM) from environmental water is a major challenge for unknown screening analysis by high-resolution mass spectrometry. In this study, DOM in process water during advanced drinking water treatment was fractionated sequentially by three solid-phase extraction (SPE) cartridges based on the polarity and charge of DOM molecules. By sequential SPE with unknown screening analysis, over 3000 DOM features were found in raw water, whereas around 2000 were obtained by a single SPE. The hydrophobic neutral (HPON) fraction contained CHO features with highest averaged molecular weight followed by hydrophobic acid (HPOA) and then hydrophilic acid (HPIA). The average degree of carbon double bond equivalents and carbon oxidation states indicated that the HPON fraction contained molecules that were more unsaturated and less oxidized than those of the HPOA and HPIA fractions. Ozone selectively decomposed (1) more unsaturated and less oxidized HPON features, (2) more unsaturated HPOA compounds, and (3) less oxidized HPIA molecules. Oxidation by-products were mostly HPON and HPIA compounds that were more oxidized than the decomposed molecules. During biological activated carbon (BAC) filtration, less oxidized HPON were preferentially removed, whereas HPOA were removed without selectivity. HPON and HPIA molecules with more oxidized character were found to be refractory to BAC treatment. HPON with more unsaturated and HPIA with more oxidized characters were decomposed by chlorine. Many types of HPIA decomposed during chlorination were the oxidation by-products of ozonation that were refractory to BAC treatment. Sequential SPE with unknown screening analysis provided previously unknown details of the molecular characteristics of DOM and its changes during advanced water treatment. • Sequential solid-phase extraction effectively recovers dissolved organic matter (DOM). • Ozone preferentially decomposes more unsaturated and less oxidized DOM. • Ozone oxidation by-products are found as highly oxidized hydrophobic neutral (HPON) and hydrophilic acid (HPIA). • Biological activated carbon filtration removes less oxidized HPON and hydrophobic acid (HPOA). • Chlorine selectively reacts with HPON and HPIA species. [ABSTRACT FROM AUTHOR]

Granular activated carbon (GAC) has been widely introduced to advanced drinking water purification plants to remove organic matter and ammonium. Backwashing, which is the routine practice for GAC maintenance, is an important operational factor influencing the performance of GAC and its microbial biomass. In this study, the effects of backwashing on the ammonium removal potential of GAC were evaluated. In addition, abundances of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) on GAC were analyzed. GAC samples before and after backwashing were collected from a full-scale drinking water purification plant. Samplings were conducted before and after implementation of prechlorination of raw water. The results showed that the ammonium removal potential of the GAC increased by 12% after backwashing before prechlorination (p < 0.01). After implementing the prechlorination, the ammonium removal potential of the GAC decreased by 12% even after backwashing (p < 0.01). The AOA was predominant on the GAC in the two samplings. Regardless of prechlorination, the amounts of the AOA and the AOB remained at the same level before and after backwashing. Analysis of the backwashing water indicated that the amounts of the AOA and AOB washed out from the GAC were negligible (0.08%–0.26%) compared with their original amounts on the GAC. These results revealed the marginal role of backwashing on the biomass of ammonia oxidizers on GAC. However, the results also revealed that backwashing could have a negative impact on the ammonium removal potential of GAC during prechlorination. [ABSTRACT FROM AUTHOR]

The increasing organic contamination of surface water hinders the conventional tap water treatment process. Membrane bioreactors (MBRs) are a promising alternative technology for recovering water from polluted surface water. In this study, the composition changes of dissolved organic matters (DOMs) in MBR and ultraviolet/ozone (UV/O 3)-MBR systems for polluted surface water treatment were investigated using Orbitrap mass spectrometry analysis with unknown screening. The intense DOM ions within a mass-to-charge ratio range of 100–500 was detected, and 2340 molecular formulae from 5743 peaks were assigned to the two systems. The most abundant components were formulae with C, H, O, N, and CHO only classes. The highest formulae decrease including CHO, CHON, CHOS, and CHONS were attributed to the bio-carrier used in both systems. Results showed that bioprocess was the main contributor in the DOM reduction, and the integration of UV/O 3 into the MBR improved the DOM composition changes. Biodegradable components with low O/C ratio in the CHO and CHON classes remarkably increased in the UV/O 3 -MBR system. The integration of UV/O 3 as a polishing step in the recirculation stream of MBR system was effective in improve the DOM removal. Image 1 • Orbitrap MS was used to detect dissolved organic matter changes in membrane bioreactor for treating polluted surface water. • 2340 molecular formulae out of total peaks 5743 were assigned. • The main change was taken place in carrier side of membrane bioreactor system. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) have been reported as precursors of disinfection byproducts (DBPs) and its molecular characteristics are rarely investigated due to its complexity. In this study, changes in the characteristics of DOM were investigated in the lower Phong River in Thailand in dry season and after the first rain in rainy season, using a non-targeted analysis with Orbitrap mass spectrometry. The river was rich with CHO features dominated by lignin-like molecules, while lipid-like molecules increase after domestic wastewater discharges. Wastewater discharge released DOM with higher molecular weight (MW) that was less oxygenated (low O/C) and less oxidized (low carbon oxidation state [C os ]). A lake affected by anthropogenic activities contributed more oxidized DOM into the river, while surface runoff carried DOM that is more oxygenated (high O/C), less hydrogenated (low H/C), and more oxidized (high C os) to the stream. Water treatment further modified DOM to be lower MW. Approximately three hundred Cl-containing features (CHOCl) detected upstream were also found downstream. Disinfection by chlorine (Cl 2) or chlorine dioxide (ClO 2) formed both CHO and CHOCl DBPs. Low chlorine dosage applied to upstream and downstream samples resulted in many common unknown DBPs while increasing chlorine dosage resulted in more unique DBPs. At the same dosage, Cl 2 reacted with DOM more than ClO 2 , including more oxidized molecules that are refractory to ClO 2. Both Cl 2 and ClO 2 produced chlorinated and non-chlorinated DBPs, and some DBPs were commonly found by both disinfections. Cl 2 -produced DBPs were more unsaturated (higher [DBE–O]/C) and oxidized (higher C os) than ClO 2 -DBPs. Image 1 • Molecular changes in dissolved organic matter (DOM) along the river were tracked. • Domestic discharges release DOM with high molecular weight (MW) and less oxidized. • A natural lake contributed more oxidized DOM into the river. • Water treatment further modified DOM to be lower MW. • Unique and shared CHO and CHOCl disinfection byproducts (DBPs) were found by chlorine or chlorine dioxide. [ABSTRACT FROM AUTHOR]

• Kouleothrix abundance caused low activated sludge settleability in municipal plants. • Denitrification at feeding stage is a promising selection pressure for Kouleothrix. • Dissolved oxygen control may be also a promising way to suppress Kouleothrix growth. Kouleothrix (Type 1851) filamentous bacteria associated with bulking incidents were investigated for their quantitative correlations with sludge settleability in municipal wastewater treatment plants (WWTPs) around Japan. Factors affecting their abundance were also explored by statistical analyses with the aim of controlling bulking by suppressing their growth. Real-time quantitative PCR assays showed Kouleothrix spp. mainly ranged from 104−105 copies ng-DNA−1 in WWTPs. They were not always abundant in every WWTP, but their abundance (>105 copies ng-DNA−1) almost always coincided with low activated sludge settleability. Their abundance in nitrogen removal processes was always low (1.08 − 3.83 × 104 copies ng-DNA−1). Denitrification process at the feeding stage may be a useful selection pressure for Kouleothrix spp., leading to their suppression. A stepwise multiple regression analysis revealed that the increase of dissolved oxygen (DO) and pH in an aeration tank have a negative influence, while NH 4 + increase in the influent has a positive influence on the Kouleothrix spp. abundance. The three-variable model was significant and accounted for approximately 45% of the variance in the dependent variable (i.e., Kouleothrix spp.). The DO increase had the greatest influence on the Kouleothrix spp. decrease, and thus, the DO control may be a promising way to suppress their growth in WWTPs. [ABSTRACT FROM AUTHOR]

An improved assessment of environmental risks to public water bodies requires screening a large number of micropollutants. This study reports the development of a novel target screening method based on solid-phase extraction (SPE), HPLC, and high-resolution Orbitrap MS for the analysis of micropollutants with diverse chemical properties. First, target compounds were screened for their detectability by Orbitrap MS. An optimized SPE cartridge and HPLC column maximized recovery and separated most target compounds. The sensitivity and repeatability of the method was validated by determining the detection limits and relative standard deviation (RSD). Eighty-four compounds with highly diverse properties were simultaneously detected with detection limits of 0.1–100 ng/L. Of these compounds, 52 were quantitated, with R2 ≥ 0.99 by linearity analysis and SPE recovery ratios of ≥50%. The remaining 32 compounds were qualitatively detected, with R2 < 0.99 or SPE recovery ratio of <50%. Satisfactory repeatability was obtained (RSD < 13.5%). This method was applied to the surveillance of the Arakawa River in Japan in 2019. Thirty-two compounds, including pesticides, surfactants, plasticizers, adhesives, and industrial solvents, were detected in the river. The measured concentrations of 13 compounds were compared with their predicted no effect concentrations (PNECs). Decanoic acid showed a higher concentration than the corresponding PNEC value, suggesting that its risk to the Arakawa water environment required further evaluation. The concentrations of dicyclohexylamine, 1,3-diphenylguanidine, and 2,4-dichlorophenoxyacetic acid were higher than their corresponding PNEC/10 values, demonstrating that these compounds were of higher priority than other compounds. [Display omitted] • Development of a quantification method using SPE-HPLC-Orbitrap MS. • Simultaneous detection of 84 micropollutants with high reliability. • Mostly lower method quantification limits than conventional analytical methods. • Method applicability: screening analysis of micropollutants in water environment. [ABSTRACT FROM AUTHOR]

This study aimed to classify the possible molecular formulas of precursors for disinfection by-products (DBPs) in raw, coagulated, and chlorinated water samples from the U-Tapao Canal, Songkhla, Thailand. The molecular formulas of DBPs in chlorinated water were investigated. Polyaluminum chloride (PACl) was employed as a coagulant. Orbitrap Fourier transform-mass spectrometry was able to estimate the composition of dissolved organic matter (DOM) with the carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S) elements contained and DBPs at the molecular level. The molecular formulas of the DOM in the raw water primarily consisted of CHO and CHON when extracted by lichrolut EN. The CHO and CHON species were rich in lignin-, tannin-, and condensed aromatic-like substances. The DOM with high-molecular-weight from 300 to 500 Da were preferentially removed by coagulation. The PACl coagulation decreased the abundances of lignin-, tannin-, and condensed aromatic-like substances in the CHO formulas, while lignin- and condensed aromatic-like substances in the CHON formulas remained. The remaining precursors corresponded to CHON molecules in the coagulated water, which may result in the formation of some chlorine (Cl)-containing molecules. Several DBPs among the CHOCl and CHONCl species were produced in the chlorinated water through the addition reaction of chlorine. New chlorinated N-DBPs of 21 formulas were detected. Image 1 • The LiEN is selective for trapping DOM in a wide mass range (100–500 Da). • The non-targeted DBP precursors were evaluated by the Orbitrap mass spectrometry. • PACl coagulation mostly removed DOM with MW ranging from 300 to 500 Da. • Formation of CHOCl and CHONCl species corresponded to their putative precursors. [ABSTRACT FROM AUTHOR]

Isotope dilution techniques (IDT) and sequential extraction procedures (SEPs) were compared to apprehend the differences between two techniques in determining metal exchangeability and vulnerability to pollute the urban groundwater. For this purpose, soil (n = 2), "soakaway" sediment deposited in the artificial infiltration facilities (AIF) (n = 4), and road dust (n = 2) were sampled from Tokyo metropolitan. Sorption coefficients of four metals (Cu, Zn, Cd and Pb) were assessed through isotopic exchangeability (E-value) and potential mobile pool i.e. addition of exchangeable, reducible and oxidizable fraction obtained by Community Bureau of Reference (BCR)-procedures. The E-value for the three samples were found smaller than the potential mobile pool but were higher than BCR-exchangeable fractions. The use of strong extractants are likely to play an active role in the disagreement between SEPs and IDT. IDT accounts for the isotopic exchangeability while BCR provides information of vulnerability of metals associated with different fractions that can leach under different environmental conditions. Sorption coefficients measured in soakaway sediment was found comparable to soil thus likely to retain metals. However, as variability in environmental conditions is likely to affect Kd, the soakaway sediment may become an active metal source in future rather than acting as the permanent sink. The study concludes that there is the possibility of errors while predicting metal vulnerability to groundwater with both techniques and thus a model compliance integrating the virtue of both techniques will be a way forward. Image 1 • Better compliance amid isotope dilution and sequential extraction for high metal loading. • Isotopic exchangeability (E-value) was smaller than extracted potential mobile pool. • Coupling of IDT with BCR provide better estimate of leaching vulnerability for metals. • IDT accounts for actual exchangeability while SEPs provide leaching vulnerability. [ABSTRACT FROM AUTHOR]

In premise plumbing, microbial water quality may deteriorate under certain conditions, such as stagnation. Stagnation results in a loss of disinfectant residual, which may lead to the regrowth of microorganisms, including opportunistic pathogens. In the present study, microbial regrowth was investigated at eight faucets in a building over four seasons in one year. Water samples were obtained before and after 24 h of stagnation. In the first 100‍ ‍mL after stagnation, total cell counts measured by flow cytometry increased 14- to 220-fold with a simultaneous decrease in free chlorine from 0.17-0.36‍ ‍mg L -1 to <0.02‍ ‍mg L -1 . After stagnation, total cell counts were not significantly different among seasons; however, the composition of the microbial community varied seasonally. The relative abundance of Pseudomonas spp. was dominant in winter, whereas Sphingomonas spp. were dominant in most faucets after stagnation in other seasons. Opportunistic pathogens, such as Legionella pneumophila, Mycobacterium avium, Pseudomonas aeruginosa, and Acanthamoeba spp., were below the quantification limit for real-time quantitative PCR in all samples. However, sequences related to other opportunistic pathogens, including L. feeleii, L. maceachernii, L. micdadei, M. paragordonae, M. gordonae, and M. haemophilum, were detected. These results indicate that health risks may increase after stagnation due to the regrowth of opportunistic pathogens.

Current challenges in the anaerobic bioremediation of benzene are the lack of capable cultures and limited knowledge on the biodegradation pathway. Under methanogenic conditions, benzene may be mineralized by syntrophic interactions between microorganisms, which are poorly understood. The present study developed an optimized formula for anoxic medium to successfully promote the growth of the putative benzene degrader Deltaproteobacterium Hasda-A and enhance the benzene degradation activity of methanogenic enrichment cultures. Within 70‍ ‍d of incubation, the benzene degradation activity and relative abundance of Hasda-A in cultures in the new defined medium increased from 0.5 to >3‍ ‍mg L -1 d -1 and from 2.5% to >17%, respectively. Together with Hasda-A, we found a strong positive relationship between the abundances of superphylum OD1 bacteria, three methanogens (Methanoregula, Methanolinea, and Methanosaeta) and benzene degradation activity. The syntrophic relationship between these microbial taxa and Hasda-A was then demonstrated in a correlation analysis of longitudinal data. The involvement of methanogenesis in anaerobic benzene mineralization was confirmed by inhibition experiments. The high benzene degradation activity and growth of Hasda-A were quickly recovered in successive dilutions of enrichment cultures, proving the feasibility of using the medium developed in the present study to produce highly capable cultures. The present results will facilitate practical applications in bioremediation and research on the molecular mechanisms underlying benzene activation and syntrophic interactions in benzene mineralization.

An improved assessment of environmental risks to public water bodies requires screening a large number of micropollutants. This study reports the development of a novel target screening method based on solid-phase extraction (SPE), HPLC, and high-resolution Orbitrap MS for the analysis of micropollutants with diverse chemical properties. First, target compounds were screened for their detectability by Orbitrap MS. An optimized SPE cartridge and HPLC column maximized recovery and separated most target compounds. The sensitivity and repeatability of the method was validated by determining the detection limits and relative standard deviation (RSD). Eighty-four compounds with highly diverse properties were simultaneously detected with detection limits of 0.1-100 ng/L. Of these compounds, 52 were quantitated, with R 2  ≥ 0.99 by linearity analysis and SPE recovery ratios of ≥50%. The remaining 32 compounds were qualitatively detected, with R 2  < 0.99 or SPE recovery ratio of <50%. Satisfactory repeatability was obtained (RSD < 13.5%). This method was applied to the surveillance of the Arakawa River in Japan in 2019. Thirty-two compounds, including pesticides, surfactants, plasticizers, adhesives, and industrial solvents, were detected in the river. The measured concentrations of 13 compounds were compared with their predicted no effect concentrations (PNECs). Decanoic acid showed a higher concentration than the corresponding PNEC value, suggesting that its risk to the Arakawa water environment required further evaluation. The concentrations of dicyclohexylamine, 1,3-diphenylguanidine, and 2,4-dichlorophenoxyacetic acid were higher than their corresponding PNEC/10 values, demonstrating that these compounds were of higher priority than other compounds., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

A dissimilatory nitrate reduction to ammonium (DNRA) microbial community was developed under a high organic carbon to nitrate (C/NO 3 - ) ratio in an anoxic semi-continuous sequencing batch reactor (SBR) fed with glucose as the source of carbon and NO 3 - as the electron acceptor. Activated sludge collected from a municipal wastewater treatment plant with good denitrification efficiency was used as the inoculum to start the system. The aim of this study was to examine the microbial populations in a high C/NO 3 - ecosystem for potential DNRA microorganisms, which are the microbial group with the ability to reduce NO 3 - to ammonium (NH 4 + ). A low C/NO 3 - reactor was operated in parallel for direct comparisons of the microbial communities that developed under different C/NO 3 - values. The occurrence of DNRA in the high C/NO 3 - SBR was evidenced by stable isotope-labeled nitrate and nitrite ( 15 NO 3 - and 15 NO 2 - ), which proved the formation of NH 4 + from dissimilatory NO 3 - /NO 2 - reduction, in which both nitrogen oxides induced DNRA activity in a similar manner. An analysis of sludge samples with Illumina MiSeq 16S rRNA sequencing showed that the predominant microorganisms in the high C/NO 3 - SBR were related to Sulfurospirillum and the family Lachnospiraceae, which were barely present in the low C/NO 3 - system. A comparison of the populations and activities of the two reactors indicated that these major taxa play important roles as DNRA microorganisms under the high C/NO 3 - condition. Additionally, a beta-diversity analysis revealed distinct microbial compositions between the low and high C/NO 3 - SBRs, which reflected the activities observed in the two systems.

Nitrification, the microbial oxidation of ammonia to nitrate via nitrite, occurs in a wide range of acidic soils. However, the ammonia-oxidizing bacteria (AOB) that have been isolated from soil to date are acid-sensitive. Here we report the isolation and characterization of an acid-adapted AOB from an acidic agricultural soil. The isolated AOB, strain TAO100, is classified within the Gammaproteobacteria based on phylogenetic characteristics. TAO100 can grow in the pH range of 5-7.5 and survive in highly acidic conditions until pH 2 by forming cell aggregates. Whereas all known gammaproteobacterial AOB (γ-AOB) species, which have been isolated from marine and saline aquatic environments, are halophiles, TAO100 is not phenotypically halophilic. Thus, TAO100 represents the first soil-originated and non-halophilic γ-AOB. The TAO100 genome is considerably smaller than those of other γ-AOB and lacks several genes associated with salt tolerance which are unnecessary for survival in soil. The ammonia monooxygenase subunit A gene of TAO100 and its transcript are higher in abundance than those of ammonia-oxidizing archaea and betaproteobacterial AOB in the strongly acidic soil. These results indicate that TAO100 plays an important role in the nitrification of acidic soils. Based on these results, we propose TAO100 as a novel species of a new genus, Candidatus Nitrosoglobus terrae.