Nitrospira-like Nitrite-oxidizing Bacteria Research Articles

Effects of Nitrogen Fertilizer on Nitrospira- and Nitrobacter-like Nitrite-Oxidizing Bacterial Microbial Communities under Mulched Fertigation System in Semi-Arid Area of Northeast China

The accumulation of nitrite is frequently overlooked, despite the fact that nitrification is the most essential phase of the entire nitrogen (N) cycle and that nitrifying bacteria play a significant role in nitrification. At present, the effects of different N application rates on soil nitrite-oxidizing bacteria (NOB) abundance, community composition, diversity, and its main influencing factors are still unclear. In this study, five N fertilizer application rates under film mulching and a drip irrigation system were studied in the semi-arid area of Northeast China. The treatments were 0 kg ha−1 (N0), 90 kg ha−1 (N1), 150 kg ha−1 (N2), 210 kg ha−1 (N3), and 270 kg ha−1 (N4). Fluorescent quantitative PCR and Illumina Miseq sequencing were used to analyze the abundance and community structure of NOB under different amounts of N application. The results showed that the increase in amounts of N application was strongly accompanied by an increase in the content of soil organic matter (SOM), total nitrogen (TN), nitrate nitrogen (NO3−-N), and ammonium nitrogen (NH4+-N), while the pH significantly reduced with an increase in N fertilization. N fertilization significantly increased soil nitrite oxidoreductase (NXR) activity, soil nitrification potential (PNR), and soil nitrite oxidation potential (PNO). A high N application rate significantly heightened the abundance of Nitrospira- and Nitrobacter-like NOB. N fertilizer considerably raised the Shannon index of Nitrospira-like NOB. The N application amount was the key factor affecting the community structure of Nitrospira-like NOB, and available nitrogen (AN) had the dominant influence on the community structure of Nitrospira-like NOB. N fertilizer can cause soil acidification, which affects NOB abundance and diversity. Nitrospira-like NOB may promote nitrite oxidation in different N application rates under a mulched fertigation system. The findings offered a crucial scientific foundation for further investigation into how nitrite-oxidizing bacteria respond to N fertilizer management strategies in farmland soil under film mulching drip irrigation in Northeast China.

Soil nitrogen dynamics drive regional variation in nitrogen use efficiency in rice: A multi‐scale study

AbstractNortheast and East China account for ~36% of the Chinese rice cultivation area, yet considerable spatial disparities in nitrogen use efficiency (NUE) exist between these regions. The underlying causes remain poorly understood. Herein, we conducted a case study in two sample sites from two regions, Wuchang and Changshu, using multi‐scale evidence chains spanning macro‐ and micro‐ processes to identify the determinants of spatial NUE variability. Field studies showed higher NUE (partial factor productivity, PFP, and agronomic efficiency, AE) but lower ammonia volatilisation in Wuchang paddy soil. By separating edaphic factors from climatic conditions, soil replacement pot studies between Wuchang and Changshu revealed that both apparent (AE and recovery efficiency, RE) and 15N‐traced NUE were higher, whereas 15N fertilizer losses were lower in Wuchang‐soil than Changshu‐soil irrespective of site, suggesting soil type contributed to differences in soil N retention capacity and NUE of the soils. Process‐scale results showed that greater rates of gross N mineralizsation (13‐fold higher), gross nitrification (93% higher), and denitrification (52% higher) in Changshu‐soil compared to Wuchang‐soil corresponded to functional gene relative abundance, signifying larger reactive N losses and reduced soil N retention capacity. Microbial community analysis suggested that the differential N transformations were caused by differences in ammonia‐oxidizing archaea (AOA) family nitrososphaeraceae and Nitrospira‐like nitrite‐oxidizing bacteria (NOB). This highlights the importance of specific efficiency‐enhanced strategies tailored to the edaphic characteristics of cropping regions, such as increasing soil N retention capacity using enhanced‐efficiency fertilizer in East China, while implementing conservation management strategies in Northeast China.Highlights Field‐scale studies revealed higher NUE and lower NH3 volatilisation in Wuchang site. Soil replacement pot studies showed higher NUE in Wuchang‐soil regardless of sites. Process‐scale results unravelled high N losses and low soil N retention in Changshu‐soil. Varying NUE partially correlated with Nitrososphaeraceae AOA and Nitrospira‐like NOB.

Ammonia- and Nitrite-Oxidizing Bacteria are Dominant in Nitrification of Maize Rhizosphere Soil Following Combined Application of Biochar and Chemical Fertilizer.

Autotrophic nitrification is regulated by canonical ammonia-oxidizing archaea (AOA) and bacteria (AOB) and nitrite-oxidizing bacteria (NOB). To date, most studies have focused on the role of canonical ammonia oxidizers in nitrification while neglecting the NOB. In order to understand the impacts of combined biochar and chemical fertilizer addition on nitrification and associated nitrifiers in plant rhizosphere soil, we collected rhizosphere soil from a maize field under four different treatments: no fertilization (CK), biochar (B), chemical nitrogen (N) + phosphorus (P) + potassium (K) fertilizers (NPK), and biochar + NPK fertilizers (B + NPK). The potential nitrification rate (PNR), community abundances, and structures of AOA, AOB, complete ammonia-oxidizing bacteria (Comammox Nitrospira clade A), and Nitrobacter- and Nitrospira-like NOB were measured. Biochar and/or NPK additions increased soil pH and nutrient contents in rhizosphere soil. B, NPK, and B + NPK treatments significantly stimulated PNR and abundances of AOB, Comammox, and Nitrobacter- and Nitrospira-like NOB, with the highest values observed in the B + NPK treatment. Pearson correlation and random forest analyses predicted more importance of AOB, Comammox Nitrospira clade A, and Nitrobacter- and Nitrospira-like NOB abundances over AOA on PNR. Biochar and/or NPK additions strongly altered whole nitrifying community structures. Redundancy analysis (RDA) showed that nitrifying community structures were significantly affected by pH and nutrient contents. This research shows that combined application of biochar and NPK fertilizer has a positive effect on improving soil nitrification by affecting communities of AOB and NOB in rhizosphere soil. These new revelations, especially as they related to understudied NOB, can be used to increase efficiency of agricultural land and resource management.

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.

Enhanced biological nitrogen removal under low dissolved oxygen in an anaerobic-anoxic-oxic system: Kinetics, stoichiometry and microbial community

A lab-scale anaerobic-anoxic-oxic system was used to investigate the nitrogen removal mechanism under low dissolved oxygen (DO) conditions. When DO was decreased from 2 to 0.5 mg L−1, chemical oxygen demand (COD) and NH4+ removals were not influenced, while total nitrogen removal increased from 69% to 79%. Further batch tests indicated that both the specific nitrification rate and denitrification rate greatly increased under low DO conditions. When DO was decreased from 2 to 0.5 mg L−1, the oxygen half saturation constant value for ammonia oxidizing bacteria (AOB) decreased from 0.39 to 0.29 mg-O2 L−1, and for nitrite oxidizing bacteria (NOB), it reduced from 0.29 to 0.09 mg-O2 L−1. Correspondingly, the observed yield coefficients increased from 0.05 to 0.10 mg-cell mg−1-N for AOB, and from 0.02 to 0.06 mg-cell mg−1-N for NOB. High-throughput sequencing revealed that the relative abundances of AOB increased from 6.13% to 6.54%, Nitrospira-like NOB increased from 3.67% to 6.50%, and denitrifiers increased from 2.84% to 7.04%. Improved simultaneous nitrification and denitrification under low DO conditions contributed to the enhanced nitrogen removal.

Influences of nitrogen forms on abundances and community structures of ammonia and nitrite oxidizers in a slightly alkaline upland soil

ABSTRACT Nitrogen addition can significantly affect soil nitrification capacity through driving soil nitrifiers. However, the roles of nitrogen forms on nitrifiers are rarely known. This study assessed the effects of nitrogen addition forms (NH4 +-N and NO3 –-N) on nitrifiers’ abundances and community structures in a slightly alkaline upland soil by means of a short-term microcosms experiment. Nitrospira-like nitrite-oxidizing bacteria (NOB) numerically dominated nitrifiers’ community. Ammonia-oxidizing archaea (AOA) abundance positively correlated to Nitrospira-like NOB abundance, and ammonia-oxidizing bacteria (AOB) abundance positively linked to Nitrobacter-like NOB abundance. NH4 +-N addition significantly increased AOB and Nitrobacter-like NOB abundances, whereas the abundances of tested four groups of nitrifiers were relatively insensitive to NO3 –-N addition. AOA and Nitrobacter-like NOB community structures were significantly changed only upon NH4 +-N addition, but AOB and Nitrospira-like NOB community structures were obviously altered by both NH4 +-N and NO3 –-N addition, with stronger impacts by the former. Overall, our results confirmed that not only NH4 +-N but also NO3 –-N addition obviously affected soil nitrifiers’ community. The findings obtained here highlight distinct physiological potentials of nitrifiers’ subgroups to upland soil nitrification.

Successive phytoextraction alters ammonia oxidation and associated microbial communities in heavy metal contaminated agricultural soils

Phytoextraction is an attractive strategy for remediation of soils contaminated by heavy metal (HM), yet the effects of this practice on biochemical processes involved in soil nutrient cycling remain unknown. Here we investigated the impact of successive phytoextraction with a Cd/Zn co-hyperaccumulator Sedum alfredii (Crassulaceae) on potential nitrification rates (PNRs), abundance and composition of nitrifying communities and functional genes associated with nitrification using archaeal and bacterial 16S rRNA gene profiling and quantitative real-time PCR. The PNRs in rhizosphere were significantly (P < 0.05) lower than in the unplanted soils, and decreased markedly with planting time. The decrease of PNR was more paralleled by changes in numbers of copy and transcript of archaeal amoA gene than the bacterial counterpart. Phylogenetic analysis revealed that phytoextraction induced shifts in community structure of soil group 1.1b lineage-dominated ammonia-oxidizing archaea (AOA), Nitrosospira cluster 3-like ammonia-oxidizing bacteria (AOB) and Nitrospira-like nitrite-oxidizing bacteria (NOB). A strong positive correlation was observed between amoA gene transcript numbers and PNRs, whereas root exudates showed negative effect on PNR. This effect was further corroborated by incubation test with the concentrated root exudates of S. alfredii. Partial least squares path model demonstrated that PNR was predominantly controlled by number of AOA amoA gene transcripts which were strongly influenced by root exudation and HM level in soil. Our result reveals that successive phytoextraction of agricultural soil contaminated by HMs using S. alfredii could inhibit ammonia oxidation and thereby reduce nitrogen loss.

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.

The transformation from anammox granules to deammonification granules in micro-aerobic system by facilitating indigenous ammonia oxidizing bacteria

Granular deammonification process is a good way to retain aerobic and anaerobic ammonia oxidizing bacteria (AOB and anammox bacteria) and exhaust flocculent nitrite oxidizing bacteria (NOB). In this study, to facilitate indigenous AOB growth on anammox granules, by stepwise reducing influent nitrite, anammox granules were effectively transformed into deammonification granules in a micro-aerobic EGSB in 100 days. Total nitrogen removal efficiency of 90% and nitrogen removal rate of 2.3 g N/L/d were reached at stable deammonification stage. High influent FA and limited oxygen supply contributed suppression for Nitrospira-like NOB. In transition stages, Proteobacteria and Chloroflexi were always dominated. Anammox abundance decreased, while AOB abundance grew fast. Anammox bacteria and AOB were dominated by Brocadia fulgida and Nitrosomonas europaea, respectively. Denitrification activity and bacteria existed although without influent organic. The final AOB abundance was about 4.55–13.8 times more than anammox bacteria abundance, with almost equal potential activities.

High-rate nitrification of electronic industry wastewater by using nitrifying granules.

Nitrifying granules have a high sedimentation property and an ability to maintain a large amount of nitrifying bacteria in a reaction tank. Our group has examined the formation process of nitrifying granules and achieved high-rate nitrification for an inorganic synthetic wastewater using these granules. In this research, a pilot-scale test plant with an 850-liter reaction tank was assembled in a semiconductor manufacturing factory in order to conduct a continuous water conduction test using real electronics industry wastewater. The aim was to observe the formation of nitrifying granules and determine the maximum ammonia removal rate. The average granule diameter formed during the experiment was 780 μm and the maximum ammonia removal rate was observed to be 1.5 kgN·m-3·day-1 at 20 °C, which is 2.5-5 times faster than traditional activated sludge methods. A fluorescence in situ hybridization analysis showed that β-proteobacterial ammonia oxidizing bacteria and the Nitrospira-like nitrite-oxidizing bacteria dominate the bacteria population in the granules, and their strong aggregation capacity might confer some benefits to the formation of these nitrifying granules.

Soil pH and plant diversity drive co-occurrence patterns of ammonia and nitrite oxidizer in soils from forest ecosystems

In this study, we investigated how co-occurrence patters of ammonia and nitrite oxidizers, which drive autotrophic nitrification, are influenced by tree species composition as well as soil pH in different forest soils. We expected that a decline of ammonia oxidizers in coniferous forests, as a result of excreted nitrification inhibitors and at acidic sites with low availability of ammonia, would reduce the abundance of nitrite-oxidizing bacteria (NOB). To detect shifts in co-occurrence patterns, the abundance of key players was measured at 50 forest plots with coniferous respectively deciduous vegetation and different soil pH levels in the region Schwabische Alb (Germany). We found ammonia-oxidizing archaea (AOA) and Nitrospira-like NOB (NS) to be dominating in numbers over their counterparts across all forest types. AOA co-occurred mostly with NS, while bacterial ammonia oxidizers (AOB) were correlated with Nitrobacter-like NOB (NB). Co-occurrence patterns changed from tight significant relationships of all ammonia and nitrite oxidizers in deciduous forests to a significant relationship of AOB and NB in coniferous forests, where AOA abundance was reduced. Surprisingly, no co-occurrence structures between ammonia and nitrite oxidizers could be determined at acidic sites, although abundances were correlated to the respective nitrogen pools. This raises the question whether interactions with heterotrophic nitrifiers may occur, which needs to be addressed in future studies.

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.

Effects of 44 years of chronic nitrogen fertilization on the soil nitrifying community of permanent grassland

Chronic nutrient addition to grassland soils can strongly influence the composition and abundance of nitrifying microbial communities. Despite the fact that nitrifying microbes play a crucial role in regulating ecosystem nitrogen (N) cycling, our understanding of how long-term N fertilization might influence nitrifying microbial groups is still limited. Here we used soil from a 44-year-old grassland fertilization experiment and performed high-throughput pyrosequencing analyses (and real-time quantitative PCR) to determine whether and how the identity and abundance of nitrifying microbes has changed in response to chronic inorganic (chemical fertilizer) and organic (cattle slurry) N additions. We found that the amoA genes of ammonia-oxidizing archaea (AOA) significantly increased under organic N additions, whereas ammonia-oxidizing bacteria (AOB) increased with the addition of inorganic N. Proportional changes of AOA, AOB and nitrite-oxidizing bacteria (NOB) demonstrate that nitrifying phylotypes are influenced by chronic N additions. We also found that AOA/AOB ratios increased with higher application rates of cattle slurry suggesting that AOA may affect N cycling more in soils receiving animal manures, whereas AOB are functionally more important in chemically fertilized soils. Phylogenetic analysis shows that shifts in AOA and AOB community structure occurred through time across N fertilization treatments. For example, (a) fosmid 29i4-like AOA, (b) Nitrosospira cluster 3-like AOB, and (c) Nitrospira-like NOB dominated nitrifying communities in fertilized soils. Finally, high-throughput pyrosequencing of 16S rRNA genes show that N fertilization (either inorganic or organic) increased the abundance of Actinobacteria in soils while it decreased the abundance of Proteobacteria. Our study is one of the first to show that long-term N additions to soils can greatly affect nitrifying communities, and that phylogenetically and functionally distinct nitrifiers have developed through time in response to chronic N fertilization.

Keys to Cultivating Uncultured Microbes: Elaborate Enrichment Strategies and Resuscitation of Dormant Cells

Keys to Cultivating Uncultured Microbes: Elaborate Enrichment Strategies and Resuscitation of Dormant Cells

Stability and nitrite-oxidizing bacteria community structure in different high-rate CANON reactors

In completely autotrophic nitrogen removal over nitrite (CANON) process, the bioactivity of nitrite-oxidizing bacteria (NOB) should be effectively inhibited. In this study, the stability of four high-rate CANON reactors and the effect of free ammonia (FA) and organic material on NOB community structure were investigated using DGGE. Results suggested that with the increasing of FA, the ratio of total nitrogen removal to nitrate production went up gradually, while the biodiversity of Nitrobacter-like NOB and Nitrospira-like NOB both decreased. When the CANON reactor was transformed to simultaneous partial nitrification, anammox and denitrification (SNAD) reactor by introducing organic material, the denitrifiers and aerobic heterotrophic bacteria would compete nitrite or oxygen with NOB, which then led to the biodiversity decreasing of both Nitrobacter-like NOB and Nitrospira-like NOB. The distribution of Nitrobacter-like NOB and Nitrospira-like NOB were evaluated, and finally effective strategies for suppressing NOB in CANON reactors were proposed.

Interactions between Thaumarchaea, Nitrospira and methanotrophs modulate autotrophic nitrification in volcanic grassland soil.

Ammonium/ammonia is the sole energy substrate of ammonia oxidizers, and is also an essential nitrogen source for other microorganisms. Ammonia oxidizers therefore must compete with other soil microorganisms such as methane-oxidizing bacteria (MOB) in terrestrial ecosystems when ammonium concentrations are limiting. Here we report on the interactions between nitrifying communities dominated by ammonia-oxidizing archaea (AOA) and Nitrospira-like nitrite-oxidizing bacteria (NOB), and communities of MOB in controlled microcosm experiments with two levels of ammonium and methane availability. We observed strong stimulatory effects of elevated ammonium concentration on the processes of nitrification and methane oxidation as well as on the abundances of autotrophically growing nitrifiers. However, the key players in nitrification and methane oxidation, identified by stable-isotope labeling using (13)CO2 and (13)CH4, were the same under both ammonium levels, namely type 1.1a AOA, sublineage I and II Nitrospira-like NOB and Methylomicrobium-/Methylosarcina-like MOB, respectively. Ammonia-oxidizing bacteria were nearly absent, and ammonia oxidation could almost exclusively be attributed to AOA. Interestingly, although AOA functional gene abundance increased 10-fold during incubation, there was very limited evidence of autotrophic growth, suggesting a partly mixotrophic lifestyle. Furthermore, autotrophic growth of AOA and NOB was inhibited by active MOB at both ammonium levels. Our results suggest the existence of a previously overlooked competition for nitrogen between nitrifiers and methane oxidizers in soil, thus linking two of the most important biogeochemical cycles in nature.

Long-Term Low DO Enriches and Shifts Nitrifier Community in Activated Sludge

In the activated sludge process, reducing the operational dissolved oxygen (DO) concentration can improve oxygen transfer efficiency, thereby reducing energy use. The low DO, however, may result in incomplete nitrification. This research investigated the long-term effect of low DO on the nitrification performance of activated sludge. Results indicated that, for reactors with 10 and 40 day solids retention times (SRTs), complete nitrification was accomplished after a long-term operation with a DO of 0.37 and 0.16 mg/L, respectively. Under long-term low DO conditions, nitrite oxidizing bacteria (NOB) became a better oxygen competitor than ammonia oxidizing bacteria (AOB) and, as a result, no nitrite accumulated. Real-time PCR assays indicated that the long-term low DO enriched both AOB and NOB in activated sludge, increasing the sludge nitrification capacity and diminishing the adverse effect of low DO on the overall nitrification performance. The increase in the population size of nitrifiers was likely resulted from the reduced nitrifier endogenous decay rate by a low DO. Under long-term low DO conditions, Nitrosomonas europaea/eutropha remained as the dominant AOB, whereas the number of Nitrospira-like NOB became much greater than Nitrobacter-like NOB, especially for the 40 day SRT sludge. The enrichment and shift of the nitrifier community reduced the adverse effect of low DO on nitrification; therefore, low DO operation of a complete nitrification process is feasible.