Nitrite-oxidizing Bacteria Community Research Articles

Influencing factors on the activity of an enriched Nitrospira culture with granular morphology

ABSTRACT Nitrospira is a common genus of nitrite-oxidising bacteria (NOB) found in wastewater treatment plants (WWTPs). To identify the key factors influencing the composition of NOB communities, research was conducted using both sequencing batch reactor (SBR) and continuous flow reactor under different conditions. High-throughput 16S rRNA gene sequencing revealed that Nitrospira (18.79% in R1 and 25.77% in R3) was the dominant NOB under low dissolved oxygen (DO) and low nitrite ( NO 2 − -N) concentrations, while Nitrobacter (21.26% in R2) was the dominant NOB under high DO and high NO 2 − -N concentrations. Flocculent and granule sludge were cultivated with Nitrospira as the dominant genus. Compared to Nitrospira flocculent sludge, Nitrospira granule sludge had higher inhibition threshold concentrations for free ammonia (FA) and free nitrous acid (FNA). It was more likely to resist adverse environmental disturbances. Furthermore, the effects of environmental factors such as temperature, pH, and DO on the activity of Nitrospira granular sludge were also studied. The results showed that the optimum temperature and pH for Nitrospira granular sludge were 36°C and 7.0, respectively. Additionally, Nitrospira granular sludge showed a higher dissolved oxygen half-saturation constant (Ko) of 3.67 ± 0.71 mg/L due to its morphological characteristics. However, the majority of WWTPs conditions do not meet the conditions for the Nitrospira granular sludge. Thus, it can be speculated that future development of aerobic partial nitrification granular sludge may automatically eliminate the influence of Nitrospira. This study provides a theoretical basis for a deeper understanding of Nitrospira and the development of future water treatment processes.

Nitrite oxidizing bacteria, Nitrobacter and Nitrospira, are differently influenced by season, fertilizer, and tillage in long-term maize culture

Nitrite (NO2−) oxidation is the second step in nitrification, following ammonia (NH3) oxidation, and catalyzed by nitrite oxidizing bacteria (NOB). Their activity is critical in preventing toxic accumulation of NO2−. The two major NOB genera in soil are Nitrobacter and Nitrospira. This study investigated how N fertilization and tillage management influenced these two NOB communities in long-term (>40 years) maize (Zea mays L.) cropping. To evaluate NOB community changes we used PCR and denaturing gradient gel electrophoresis (DGGE) to analyze Nitrobacter and Nitrospira NO2− oxidoreductase genes (nxr). Season, fertilizer rate, and tillage all influenced Nitrobacter and Nitrospira communities, but differentially for the two genera. Nitrobacter was more diverse in summer, whereas Nitrospira was more diverse in winter. Nitrobacter was more diverse in N-fertilized samples, whereas Nitrospira diversity decreased with increasing fertilizer rate in winter but not summer. Nitrobacter diversity was not significantly influenced by tillage, whereas no-tillage samples had more diverse Nitrospira, compared to plow tillage samples. In addition to providing evidence for better understanding the relationship between soil management and NOB communities, this study also helped to suggest linkages between ammonia oxidizing bacteria and Nitrobacter and between ammonia oxidizing archaea and Nitrospira that may facilitate future studies concerning ammonia-oxidizing nitrifiers and NOB.

Microbial response on the first full-scale DEMON® biomass transfer for mainstream deammonification

Sidestream partial nitritation and deammonification (pN/A) of high-strength ammonia wastewater is a well-established technology. Its expansion to the mainstream is, however mainly impeded by poor retention of anaerobic ammonia oxidizing bacteria (AnAOB), insufficient repression of nitrite oxidizing bacteria (NOB) and difficult control of soluble chemical oxygen demand and nitrite levels.At the municipal wastewater treatment plant in Strass (Austria) the microbial consortium was exhaustively monitored at full-scale over one and a half year with regular transfer of sidestream DEMON® biomass and further retention and enrichment of granular anammox biomass via hydrocyclone operation.Routine process parameters were surveyed and the response and evolution of the microbiota was followed by molecular tools, ex-situ activity tests and further, AnAOB quantification through particle tracking and heme measurement.After eight months of operation, the first anaerobic, simultaneous depletion of ammonia and nitrite was observed ex-situ, together with a direction to higher nitrite generation (68% of total NOx-N) as compared to nitrate under aerobic conditions. Our dissolved oxygen (DO) scheme allowed for transient anoxic conditions and had a strong influence on nitrite levels and the NOB community, where Nitrobacter eventually dominated Nitrospira. The establishment of a minor but stable AnAOB biomass was accompanied by the rise of Chloroflexi and distinct emergence of Chlorobi, a trend not seen in the sidestream system. Interestingly, the most pronounced switch in the microbial community and noticeable NOB repression occurred during unfavorable conditions, i.e. the cold winter season and high organic load. Further abatement of NOB was achieved through bioaugmentation of aerobic ammonia oxidizing bacteria (AerAOB) from the sidestream-DEMON® tank. Performance of the sidestream pN/A was not impaired by this operational scheme and the average volumetric nitrogen removal rate of the mainstream even doubled in the second half of the monitoring campaign. We conclude that a combination of both, regular sidestream-DEMON® biomass transfer and granular SRT increase via hydrocyclone operation was crucial for AnAOB establishment within the mainstream.

Nitrifier community assembly and species co-existence in forest and meadow soils across four sites in a temperate to tropical region

Nitrification is a central process in terrestrial N cycling. However, the role of diversity of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB) in shaping nitrifier communities remains underexplored. This study deciphered the nitrifier community assembly by analyzing amplicon sequence variants (ASVs) of amoA and nxrB genes from soil microbiomes in forest and meadow ranging from the temperate monsoon to the tropic monsoon climate areas. The abundance, α-diversity, and β-diversity of AOA, AOB, Nitrobacter, and Nitrospira were dominantly distinguished by geographical variation and less by vegetation type. The overall environmental factors, including the soil properties and climate factors, significantly correlated with the β-diversity of AOA and Nitrospira, but not with AOB and Nitrobacter community. The assembly process of AOA was dominated by heterogeneous selection, while that of AOB, Nitrobacter, and Nitrospira by dispersal limitation. We found that AOA and Nitrospira dominated the combined nitrifier network, and several phylotypes exhibited extensive segregation between different modules, suggesting niche partition was present within subgroups or lineages of AOA, AOB, and Nitrospira. Links between different functional groups might reflect functional coupling, while links between the same lineage or subgroup could result from niche overlap or unknown mechanisms. As network connectors, some AOA and Nitrospira belonged to generalists, which could be essential to keep the stability of the network. Nitrospira inopinata-like node in module 24 suggested that comammox might not be an ecologically isolated bacterium in nitrification. We hypothesized that a balance between species sorting in AOA and dispersal limitation in AOB and NOB communities determined the species co-existence in the forest and meadow soils from temperate to tropical regions. This study might enhance our understanding of contemporary co-existence in different functional groups driving nitrification.

Conversion of grassland to cropland altered soil nitrogen-related microbial communities at large scales

Land-use changes may dramatically disturb underground microbial biodiversity, especially in the fragile ecological areas. However, the impact of conversion of grassland to cropland on soil nitrogen (N)-related microbial communities is not fully understood in the farming-pastoral ecotone of northern China. Therefore, 24 paired grassland and cropland soil samples were collected in this region to investigate the community structure and assembly processes of soil N-related microorganisms via amplicon sequencing of nifH, archaeal and bacterial amoA, and nxrB genes. The results showed higher ammonia-oxidizing bacteria (AOB) alpha diversity but a lower nitrite-oxidizing bacteria (NOB) diversity in cropland soil compared to grassland soil. Non-metric multidimensional scaling ordinations revealed that diazotroph, AOB and NOB communities differed considerably between grassland and cropland soil. Soil microbial co-occurrence networks showed that conversion of grassland to cropland significantly lowered the average degree, average clustering coefficient, total nodes and links, resulting in less complex microbial networks in cropland soil. Land-use change altered AOB community assembly processes, resulting from a stochasticity-dominated process in grassland soil to a determinism-dominated process in cropland soil. In contrast, deterministic processes were dominant in diazotroph community assembly, whereas stochastic processes were dominant in constructing ammonia-oxidizing archaea and NOB communities in both grassland and cropland soil. These results provide novel evidence that the conversion of grassland to cropland altered the diversity and assembly processes of soil microbial communities involved in soil N-cycling processes, which has important implications for the potential changes in soil functions under land-use changes.

A successful start-up of an anaerobic membrane bioreactor (AnMBR) coupled mainstream partial nitritation-anammox (PN/A) system: A pilot-scale study on in-situ NOB elimination, AnAOB growth kinetics, and mainstream treatment performance

In this pilot-scale study, an innovative mainstream treatment process that couples the anaerobic membrane reactor (AnMBR) with a one-stage PN/A system was proposed for advancing the concept of carbon neutrality in the municipal wastewater treatment plant. This work demonstrates the start-up procedure of a pilot-scale one-stage PN/A system for mainstream treatment. The 255-day start-up of the one-stage PN/A system involved the cultivation of ammonium-oxidizing bacteria (AOB) from the activated sludge, suppression of nitrite-oxidizing bacteria (NOB), investigation of in-situ growth kinetics of anammox bacteria (AnAOB), and the 50-day operation of the pilot-scale AnMBR-PN/A process for natural mainstream treatment. It is verified in the pilot-scale system for the first time that the in-situ free ammonia (FA) and free nitrous acid (FNA) exposure could effectively eliminate the Nitrospira (the NOB genus) while retaining the Nitosonomas (the AOB genus) community in the suspended sludge. NOB community rebounding was not detected even at the mainstream conditions with low nitrogen concentrations (Influent ammonium concentration=38±6 mg-NH4+-N/L) by intermittent aeration to control the system dissolved oxygen (DO) below 0.5 mg/L. The results of the mainstream treatment showed that the average effluent total nitrogen (TN) in the coupled process was generally lower than 10 mg-N/L, which meets the discharge limits of most prefectures in Japan. The investigated results of the in-situ anammox bacteria (AnAOB) growth kinetics suggested that the promoted start-up strategy of taking advantage of the warm months with higher mainstream temperature to achieve the rapid in-situ growth of the AnAOB is applicable in the investigated regions. From the perspective of the removal performance of the TN and organic substance, the AnMBR-PN/A process has great potential as the layouts of the carbon-neutral mainstream wastewater treatment plants.

Effects of Different Land Use Types on Active Autotrophic Ammonia and Nitrite Oxidizers in Cinnamon Soils.

Land use types with different disturbance gradients show many variations in soil properties, but the effects of different land use types on soil nitrifying communities and their ecological implications remain poorly understood. Using 13CO2-DNA-based stable isotope probing (DNA-SIP), we examined the relative importance and active community composition of ammonia-oxidizing archaea (AOA) and bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in soils under three land use types, forest, cropland, and greenhouse vegetable soil, representing three interference gradients. Soil net nitrification rate was in the order forest soil > cropland soil > greenhouse vegetable soil. DNA-SIP showed that active AOA outcompeted AOB in the forest soil, whereas AOB outperformed AOA in the cropland and greenhouse vegetable soils. Cropland soil was richer in NOB than in AOA and AOB. Phylogenetic analysis revealed that ammonia oxidation in the forest soil was predominantly catalyzed by the AOA Nitrosocosmicus franklandus cluster within the group 1.1b lineage. The 13C-labeled AOB were overwhelmingly dominated by Nitrosospira cluster 3 in the cropland soil. The active AOB Nitrosococcus watsonii lineage was observed in the greenhouse vegetable soil, and it played an important role in nitrification. Active NOB communities were closely affiliated with Nitrospira in the forest and cropland soils, and with Nitrolancea and Nitrococcus in the greenhouse vegetable soil. Canonical correlation analysis showed that soil pH and organic matter content significantly affected the active nitrifier community composition. These results suggest that land use types with different disturbance gradients alter the distribution of active nitrifier communities by affecting soil physicochemical properties. IMPORTANCE Nitrification plays an important role in the soil N cycle, and land use management has a profound effect on soil nitrifiers. It is unclear how different gradients of land use affect active ammonia-oxidizing archaea and bacteria and nitrite-oxidizing bacteria. Our research is significant because we determined the response of nitrifiers to human disturbance, which will greatly improve our understanding of the niche of nitrifiers and the differences in their physiology.

Unravelling adaptation of nitrite-oxidizing bacteria in mainstream PN/A process: Mechanisms and counter-strategies

Stable suppression of nitrite-oxidizing bacteria (NOB) is still a major challenge for the implementation of partial nitritation and anammox (PN/A) in mainstream treatment. Despite numerous suppression strategies demonstrated, it is increasingly recognized that NOB could develop resistance to these strategies, threatening the long-term stability of the mainstream PN/A process. This study aims to understand adaption mechanisms and develop counter-strategies to overcome the adaptation. To this end, three previously-demonstrated suppression strategies, including NOB inactivation via side stream sludge treatment with free ammonia (FA), the use of low dissolved oxygen (DO), and the use of anammox to scavenge nitrite, were stepwise applied, over a period of 800 days, to a laboratory-scale reactor treating effluent from a high-rate activated sludge (HRAS) plant. FA sludge treatment alone sustained nitrite accumulation for about two months, after which NOB adaptation occurred causing PN to fail. The FA adaptation was induced by a shift in the NOB community from Nitrospira to Ca. Nitrotoga. The latter was found to have higher resistance to FA and also a higher maximum specific growth rate. Low DO at 0.2–0.4 mg O2 L−1 was then applied, in conjunction with FA treatment, which successfully eliminated Ca. Nitrotoga and re-established PN. However, new and unidentified NOB with a higher apparent oxygen affinity emerged in three months, again leading to PN failure. Lastly, as the third strategy for NOB suppression, anammox was introduced as an in-situ nitrite-scavenger. The combo-strategy delivered reliable NOB suppression with no further adaptation in the remaining experimental period (eight months). The resulted one-stage PN/A reactor achieved a nitrogen removal efficiency of 84.2 ± 5.37%. A control reactor, operated in parallel under the same conditions but without FA treatment, only achieved 10.4 ± 4.6% nitrogen removal, with anammox completely outcompeted by NOB in the last phase.

Changes in alpine grassland type drive niche differentiation of nitrifying communities on the Qinghai‒Tibetan Plateau

Nitrification is a critical process of nitrogen (N) cycling performed by ammonia-oxidizing archaea (AOA) and bacteria (AOB), nitrite-oxidizing bacteria (NOB), and complete ammonia oxidation (comammox). However, the performance of these nitrifying groups in alpine grasslands has rarely been documented. This study investigated their abundance and community structure in four alpine grasslands on the Qinghai‒Tibetan Plateau with quantitative PCR and high-throughput sequencing. Potential ammonia oxidation (PAO) was measured and partitioned by inhibitor method. PAO was mainly dominated by AOA. PAO and potential nitrite oxidation (PNO) significantly decreased, while the apparent half-saturation constant (Km) had no significant change along a grassland degradation gradient. Phylogenetic analyses revealed that the predominant AOA, AOB, and NOB were Nitrososphaera, Nitrosospira, and Nitrospira lineages, respectively. Network analyses revealed that the alpine nitrifying co-occurrence network had a modular structure that was mainly shaped by taxonomic relatedness and environmental relationships, indicating different nitrifying species occupy disparate niches. Soil pH, ammonium, and moisture were the main drivers for variation in AOA, AOB, and NOB communities, respectively. Here, we provide evidence of niche differentiation in nitrifying communities with changes in grassland type. Moreover, these findings support a theoretical foundation for predicting the repercussions of grassland degradation on soil nitrifying communities in alpine ecosystems.

Responses of nitrite-oxidizing bacteria community to excessive nitrogen application and straw incorporation under intensive cultivation

ABSTRACT N fertilization and straw incorporation often disturb the soil and may affect nitrite oxidation (NO); however, the underlying mechanism remains unclear. Here, we collected soil samples through a 4-year field experiment including no N fertilization, normal N application, excess N application (EN), and EN plus straw incorporation (ES) treatments. We measured the community composition, abundance, and activity of Nitrobacter-like and Nitrospira-like nitrite-oxidizing bacteria (NOB). N application and straw incorporation significantly enhanced potential NO activity (PNO). PNO was affected by the abundance of Nitrobacter but not Nitrospira and the community compositions of both NOB. With increasing N application rate, Nitrobacter abundance increased from 1.0 to 11.8 × 104 copies g−1 dry weight soil, whereas Nitrospira abundance increased initially then subsequently decreased, ranged from 2.1 to 5.2 × 106 copies g−1 dry weight soil. Moreover, N application and straw incorporation markedly affected the NOB community composition. Soil pH and organic C were the key factors shaping the NOB community composition. Overall, N fertilization combined with straw incorporation can affect NO by altering the Nitrobacter abundance and NOB community composition. These findings expand our understanding of mechanisms underlying the effects of straw incorporation on nitrification, particularly under N enrichment.

Effects of cadmium on soil nitrification in the rhizosphere of Robinia pseudoacacia L. seedlings under elevated atmospheric CO2 scenarios

The individual impacts of elevated CO2 and heavy metals on soil nitrification have been widely reported. However, studies on the combined effects of elevated CO2 and heavy metals on soil nitrification are still limited. Here, a 135-day growth chamber experiment was conducted to investigate the impacts of elevated CO2 and cadmium (Cd) levels on soil nitrification in the rhizosphere of Robinia pseudoacacia L. seedlings. Elevated CO2 combined with Cd pollution generally stimulated ammonia monooxygenase (AMO), hydroxylamine oxidase (HAO), and nitrite oxidoreductase (NXR) activities. Compared to the control, the abundance of ammonia-oxidizing bacteria (AOB) at day 135 and ammonia-oxidizing archaea (AOA) increased significantly (p < 0.05) and the abundance of AOB at days 45 and 90 and that of the nitrite-oxidizing bacteria (NOB) decreased under elevated CO2 + Cd. Elevated CO2 mostly led to a significant (p < 0.05) decrease in soil nitrification intensity in the rhizosphere of R. pseudoacacia exposed to Cd. The effects of Cd, CO2, and their interaction on HAO and NXR activities were significant (p < 0.01). Soil pH, the C/N ratio, water-soluble organic carbon, water-soluble organic nitrogen (WSON), and total carbon were the dominant factors (p < 0.05) affecting nitrifying enzyme activities and nitrification intensity in rhizosphere soils. Elevated CO2 clearly affected AOA, AOB, and NOB community structures and dominant genera by shaping C/N ratio, pH, and Cd and WSON contents in rhizosphere soils under Cd exposure. Overall, the responses of pH, C/N ratio, WSON, and Cd to elevated CO2 led to changes in rhizosphere soil nitrification under the combination of elevated CO2 and Cd pollution.

Community assembly mechanisms and co-occurrence patterns of nitrite-oxidizing bacteria communities in saline soils

Nitrite-oxidizing bacteria (NOB) catalyze the second step of nitrification by oxidizing nitrite to nitrate, which is a key process in the biogeochemical nitrogen cycling. However, little is known about the co-occurrence patterns and assembly processes of NOB communities in agricultural soils with different salinities. Here, we explored the effects of salinity on Nitrobacter and Nitrospira community using high-throughput sequencing and multivariate statistical analyses. Our results showed that high salinity significantly inhibited the nitrite oxidation rates and decreased the abundance of Nitrobacter and Nitrospira. Extreme salty conditions significantly altered the diversity and composition of Nitrospira community but had little effect on Nitrobacter community. Nitrobacter network in high salinity soils was more closely connected while the connectivity of Nitrospira network became weak. Nitrobacter and Nitrospira community exhibited distinct assembly processes at different salinity levels. Stochastic processes were dominant in the Nitrobacter community assembly in both low and high salinity soils. Interestingly, the assembly of Nitrospira community was governed by stochastic and deterministic processes in low and high salinity soils, respectively. To our knowledge, our study provides the first description of the co-occurrence patterns and assembly processes of NOB communities in agricultural soils with different salinities. These results can help us understand the NOB ecological roles and improve the nitrite oxidation activity in a high salinity environment.

The limited effects of carbonaceous material amendments on nitrite-oxidizing bacteria in an Alfisol

Carbonaceous materials are soil conditioners that affect nitrogen cycles. However, how carbonaceous materials influence nitrite-oxidizing bacteria (NOB) is yet unclear. In this study, we investigated the NOB community and its potential activities under different treatments (control, biochar, straw, limestone, biochar + limestone, and straw + limestone) in an Alfisol, a type of arable soil depleted in calcium carbonate but enriched in aluminum- and iron-bearing minerals. Treatments with limestone increased soil pH, and straw inputs caused an increment of available potassium (AK). Ammonia (NH4+) was inversely changed under the straw and biochar + limestone amendments. None of the treatments significantly impacted the abundance of Nitrobacter (nxrA) or the potential nitrite oxidation activity (PNO). The abundance of Nitrospira (nxrB) increased in the biochar + limestone-treated samples and was significantly correlated with PNO, pH, and AK. High-throughput sequencing results showed that the α-diversity of NOB did not change in response to the treatments. The dominant Nitrobacter OTUs were affiliated within the Clusters 3, 4, 8, and 9 (a new cluster named in this study), while those of Nitrospira were in the lineage II and Namibian soil cluster 2. The limited compositional variation for Nitrobacter was explained by pH, and that for Nitrospira by pH, TN, and NH4+. Among all available data in this study, the richness of Nitrospira was the most important predictor (73%) for PNO. Therefore, we assumed that the community of nitrite oxidizers (Nitrospira) could be relatively redundant in function, supported by the observation that the carbonaceous inputs did not impact either the potential activity or the α-diversity but did affect the abundance and community composition.

Fertilization rather than aggregate size fractions shape the nitrite-oxidizing microbial community in a Mollisol

How nitrite-oxidizing bacteria (NOB) respond to long-term fertilization and variations in soil aggregate levels remains unclear. In this study, the potential nitrite oxidation activity (PNO), abundance, diversity, and community compositions of Nitrobacter- and Nitrospira-like NOB were examined in three aggregate fractions (2000–250, macroaggregate; 250–53, microaggregate; <53 μm, silt + clay) of a Mollisol under four fertilization regimes. NOB abundances were higher in macro- and micro-aggregates, and best explained by aggregate size variation. The PNO, Shannon diversity index and community composition of NOB were more affected by the fertilization regimes. We found PNO significantly correlated with the structure of Nitrospira-like NOB, followed by the abundances and Shannon diversity indexes of NOB. Soil aggregate phosphorus level, total potassium and NH4+ were associated with the NOB community structure. Our results suggested that PNO directly link to the variations for the abundance, diversity and community structure of NOB, which are regulated by the nutrient level in the microhabitat.

Shifts in Nitrobacter- and Nitrospira-like nitrite-oxidizing bacterial communities under long-term fertilization practices

Nitrite-oxidizing bacteria (NOB) are key players in the second step of nitrification, which is an important process in the soil nitrogen (N) cycle. However, the ecology of nitrite oxidizers and their response to disturbances such as long-term fertilization practices are scarcely known in agricultural ecosystems. We used samples from a Red soil subject to a long-term chemical and organic fertilization experiment, including control without fertilizer (CK), swine manure (M), chemical fertilization (NPK), and chemical/manure combined fertilization (MNPK) treatment, to explore how agricultural practices impact the community structure, abundance, and potential activity of nitrite oxidizers (PNO). The abundance of Nitrobacter was significantly increased in the M and MNPK plots, whereas the abundance of Nitrospira was significantly reduced in the M and NPK treatment plots and less inhibited in the MNPK treatment. The PNO showed a similar trend to that for Nitrobacter abundance. The diversity of Nitrobacter increased in the M-treated plots, while that of Nitrospira increased in the M and MNPK plots and decreased in the NPK plots. Non-metric multidimensional scaling (NMDS) revealed that the Nitrobacter- and Nitrospira-like NOB community was shift in these four fertilization treatments. Redundancy analysis showed that pH+SOC (soil organic carbon) and pH+TN (total nitrogen) significantly explained the variation in the composition of Nitrobacter and Nitrospira, respectively. In addition, the Nitrospira/Nitrobacter abundance ratio and community structure of Nitrobacter- and Nitrospira-like NOB are responsible for the changes of soil PNO. Collectively, these data suggest that the nitrite-oxidation process in the red soil is possibly controlled by both Nitrospira and Nitrobacter-like NOB, which were shaped by pH+TN and pH+SOC, respectively.

Sulfide inhibition of nitrite oxidation in activated sludge depends on microbial community composition

Increasingly, technologies that use sulfide as an electron donor are being considered for nitrogen removal; however, our understanding of how sulfide affects microbial communities in nitrifying treatment processes is limited. In this study, we used batch experiments to quantify sulfide inhibition of both ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) using activated sludge from two full-scale treatment plants with distinct treatment processes. The batch experiments showed that NOB were more vulnerable to sulfide inhibition than AOB, and that inhibition constants (KI) for NOB were distinct between the two treatment plants, which also had distinct nitrite oxidizing microbial communities. A Nitrospira-rich, less diverse NOB community was inhibited more by sulfide than a more diverse community rich in Nitrotoga and Nitrobacter. Therefore, sulfide-induced nitritation may be more successful in less diverse, Nitrospira-rich communities. Additionally, sulfide significantly influenced the activity of non-nitrifying microbial community members, as measured by 16S rRNA cDNA sequencing. Overall, these results indicate that sulfide has a strong impact on both nitrification and the activity of the underlying microbial communities, and that the response is community-specific.

Effect of free ammonia inhibition on NOB activity in high nitrifying performance of sludge.

The inhibition of free ammonia (FA) on nitrite-oxidizing bacteria (NOB) was investigated using an enriched NOB community with high nitrifying performance. A continuous-flow reactor was operated for the enrichment of the bacterial community. High-throughput sequencing analysis showed that Nitrospira (NOB) using in batch experiments was extended from 4.78% to 12.08% during the under continuous-flow operation for 27 days. For each batch experiments, an ammonia injection at the start-up resulted in the desired initial FA concentration (at pH = 8.1–8.2, T = 25 °C), and a continuous ammonia feeding stream allowed for a relatively stabilized FA levels as much as the initial one. Results indicated that FA inhibition on NOB was not instantaneous but occurred gradually at a certain reaction time. Low concentrations of FA (18.08–24.95 mg L−1) had a limited inhibition on NOB with increasingly high nitrate production rates, whereas high FA levels (36.06–50.66 mg L−1) exerted a significant negative impact on the NOB. Also, strong adaptation happened in these high levels of FA inhibition on NOB, which resulted in an overall low NOB activity during the whole aerobic operation.

Nitrospira are more sensitive than Nitrobacter to land management in acid, fertilized soils of a rapeseed-rice rotation field trial

Nitrite oxidation is recognized as an essential process of biogeochemical nitrogen cycling in agricultural ecosystems. How nitrite-oxidizing bacteria (NOB) respond to land managements (the effect from the long-term straw incorporation and environmental variability caused by the shift from the upland stage to the paddy stage) in a rapeseed-rice rotation field remains unclear. We found the nitrite oxidation (NO) in soils increased from the upland stage to the paddy stage. An inhibitory effect of the long-term straw incorporation on NO was detectable in the upland stage. The abundance of Nitrospira was always greater than Nitrobacter, and it was affected by the rice-growing and straw incorporation while Nitrobacter was not. NO correlated positively with the abundance of Nitrospira and with soluble sulfate (SO42−), soil moisture, pH and NH4+. The high-throughput sequencing analysis of the nitrite oxidoreductase nxrA and nxrB genes for Nitrobacter- and Nitrospira-like NOB was performed respectively. The dominating (relative abundance>1%) operational taxonomic units (OTUs) from Nitrobacter were closely related to Nitrobacter hamburgensis, whereas those from Nitrospira were affiliated with or related to lineage II, lineage V and several unknown groups. Heatmap analysis showed that a few dominant Nitrobacter OTUs were affected by the straw treatment or the rice-growing, and half of the dominant Nitrospira ones were explained by at least one of the variables. Multi-response permutation procedure (MRPP) and redundancy analyses showed that the Nitrospira-like NOB community changes were significantly shaped by the land managements and the soil chemical properties, including pH, moisture and NH4+, whereas that of the Nitrobacter-like NOB community was not. These results suggested that Nitrospira are more sensitive than Nitrobacter to land management in acid and fertilized soils of a rapeseed-rice rotation field trial.

Effect of inorganic carbon concentration on the stability and nitrite-oxidizing bacteria community structure of the CANON process in a membrane bioreactor

ABSTRACTIn the completely autotrophic nitrogen removal over nitrite (CANON) process, the nitrite-oxidizing bacteria (NOB) should be effectively suppressed or thoroughly washed out. In this study, the nitrate production and the structure of NOB community under different inorganic carbon (IC) concentrations were investigated using denaturing gradient gel electrophoresis (DGGE) in a membrane bioreactor (MBR). Results showed that IC decrease correspondingly lowered the nitrogen removal, and simultaneously induced the nitrate production by NOB. DGGE results indicated the IC deficit led to the biodiversity increasing of both Nitrobacter-like NOB and Nitrospira-like NOB. An equation fitted between the ratio of nitrate production to ammonia consumption () and the ratio of influent IC to ammonia concentration () indicated the influent should be controlled between 1.6 and 2.3 to ensure the stable operation of the CANON process. A small amount addition of organic material could be used as an effective strategy to suppress NOB when the ratio was not appropriate.

Long-term straw returning affects Nitrospira-like nitrite oxidizing bacterial community in a rapeseed-rice rotation soil.

Nitrospira are the most widespread and well known nitrite-oxidizing bacteria (NOB) and putatively key nitrite-oxidizers in acidic ecosystems. Nevertheless, their ecology in agriculture soils has not been well studied. To understand the impact of straw incorporation on soil Nitrospira-like bacterial community, a cloned library analysis of the nitrite oxidoreductase gene-nxrB was performed for a long-term rapeseed-rice rotation system. In this study, most members of the Nitrospira-like NOB in the paddy soils from the Wuxue field experiment station were phylogenetically related with Nitrospira lineages II. The Shannon diversity index possessed a decrease trend in the straw applied soils. The relative abundances of 16 OTUs (accounting 72% of the total OTUs, including 11 unique OTUs and 5 shared OTUs) were different between in the straw applied and control soils. These data suggested a selection effect from the long-term straw fertilization. Canonical correspondence analysis data showed that a centralized group of Nitrospira-like NOB OTUs in the community was partly explained by the soil ammonium, nitrate, available phosphorus, and the available potassium. This could suggest that straw fertilization led to the soil Nitrospira-like NOB community shift, which was correlated with the change of available nutrients in the bulk soil.