Number Of Ammonia-oxidizing Bacteria Research Articles

Impact of salinity and organic matter on the ammonia-oxidizing archaea and bacteria in treating hypersaline industrial wastewater: amoA gene abundance and ammonia removal contributions.

Studies publishedrecently proposed that ammonia-oxidizing archaea (AOA) may bebeneficial for hypersaline (salinity > 50g NaCl L-1) industrial wastewater treatment. However, knowledge of AOA activity in hypersaline bioreactors is limited. This study investigated the effects of salinity, organic matter, and practical pickled mustard tuber wastewater (PMTW) on AOA and ammonia-oxidizing bacteria (AOB) in two sequencing batch biofilm reactors (SBBRs). Results showed that despite observed salinity inhibition (p < 0.05), both AOA and AOB contributed to high ammonia removal efficiency at a salinity of 70 g NaCl L-1 in the two SBBRs. The ammonia removal efficiency of SBBR2 did not significantly differ from that of SBBR1 in the absence of organic matter (p > 0.05). Batch tests and quantitative real-time PCR (qPCR) reveal that salinity and organic matter inhibition resulted in a sharp decline in specific ammonia oxidation rates and amoA gene copy numbers of AOA and AOB (p < 0.05). AOA demonstrated higher abundance and more active ammonia oxidation activity in hypersaline and high organic matter environments. Salinity was positively correlated with the potential ammonia oxidation contribution of AOA (p < 0.05), resulting in a potential transition from AOB dominance to AOA dominance in SBBR1 as salinity levels rose. Moreover, autochthonous AOA in PMTW promoted the abundance and ammonia oxidation activities of AOA in SBBR2, further elevating the nitrification removal efficiency after feeding the practical PMTW. AOA demonstrates greater tolerance tothe challenging hypersaline environment, making it a valuable candidate for the treatment of practical industrial wastewater with high salinity and organic content.

Biochar Amendment in Vermi-Wetland for Enhancing Nitrification during Excess Sludge Recycling

Vermi-wetland is a sustainable technology for recycling excess sludge in small-town areas. Although biochar (BC) amendment into the vermi-wetland could considerably boost the effectiveness of treating sludge, its impact on the nitrogen transformation in vermi-wetland remains unclear. Hence, this study aimed to explore the mechanism and performance of BC amendment into the vermi-wetland for enhancing nitrogen transformation during excess sludge recycling. The semi-aquatic plant Acorus calamus and the earthworm Eisenia fetida were planted in the designed vertical vermi-reactor, with corncob BC added to the upper and lower layers of one vermi-reactor, in comparison with the vermi-reactor without BC. The vermi-reactor with BC significantly lowered (p &lt; 0.05) ammonia nitrogen (NH4+-N) and nitrite nitrogen (NO2−-N) in the effluent by 1.63 and 4.85-fold, respectively, and increased considerably nitrate nitrogen (NO3−-N) in the effluent by 1.5-fold. The numbers of ammonia-oxidizing bacteria (AOB) and archaea (AOA) in the vermi-reactor with BC were greatly enriched by 6 and 1.42-fold, compared with their counterparts (p &lt; 0.05). Moreover, nirS and nirK gene copies in the vermi-reactor with BC were considerably improved (p &lt; 0.05) by 2.03 and 1.82-fold, respectively. BC significantly enhanced the growth of earthworms by 6.92-fold and promoted plant growth by 1.28-fold. In addition, the AOB members like Nitrosomonas and Nitrosospira and the AOA members like Crenarchaeota and Thaumarchaeota cohabited in BC. Overall, these results suggest that a vermi-reactor amended with BC could enhance the nitrification processes of excess sludge, thereby improving the treatment performance of vermi-wetland.

PH Dynamics in Aquaponic Systems: Implications for Plant and Fish Crop Productivity and Yield

The pH range of 7.0 to 7.2 is recommended to ensure reasonable nitrification rates in aquaponics; however, this range is conducive neither to nitrification, a critical process that occurs at pH 8.0, nor to plant growth. To determine the effects of pH in an aquaponic system, Swiss chard (Beta vulgaris L.), kale (Brassica oleracea L.), mustard green (Brassica juncea L.), cilantro (Coriandrum sativum L.), lettuce (Lactuca sativa L.), and arugula (Eruca vesicaria L.) were cultured with tilapia (Oreochromis niloticus) in 5-year-old coupled aquaponic systems at three pH levels, 6.0, 6.5, and 7.0, in comparison with hydroponics. Morphological and physiological growth parameters of vegetable and fish crops were measured regularly, and the ammonia-oxidizing bacteria (AOB) in the aquaponic system were analyzed by qPCR at the end of the production. This study found that feed conversion ratio, fish biomass, and copy number of AOB were not affected by different pH, but similar to hydroponic systems, lower pH in aquaponic systems increased fresh and dry mass and nutrient levels of all plant species tested. This study suggests that pH has a significant impact on plant performance and yield in both aquaponic and hydroponic systems and that, similar to hydroponics, a pH of 6 is desirable for aquaponic systems to improve plant crop yield without compromising nitrification activity and fish yield.

Influence of ammonia and NaCl on nitrifying community and activity: Implications for formulating nitrifying culture augmentation

Bioaugmentation of nitrifying cultures can accelerate nitrification during startup and transition periods of recirculating aquaculture system (RAS) operations. To formulate nitrifying cultures for RASs, impacts of ammonia and salinity (NaCl) on culturing nitrifying microorganisms were comprehensively investigated by including currently known groups of nitrifying microorganisms (ammonia oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), comammox, Nitrospira, and Nitrobacter). By varying ammonia loading rate (ALRs of 1.6, 8, 20, 40, 60 and 150 mgN/L/d) of continuous-flow bioreactors fed with inorganic medium experimented for culture preparation, cultures containing distinct patterns of nitrifying communities were produced. Operating the reactors at the ALRs of ≤40 mgN/L/d, resulting in the effluent total ammonia nitrogen (TAN) and nitrite concentrations of ≤2.64 and ≤0.53 mgN/L, respectively, delivered the consortia consisting of a broad spectrum of substrate affinity nitrifying microorganisms. At the lower ranges of these ALRs (≤8 mgN/L/d), the most desirable consortia comprising comparable numbers of AOB, AOA, and comammox could be produced (the effluent TAN concentrations of ≤0.20 mgN/L), which would be resilient for applying in various RAS types. Enriching the cultures at the ALRs of ≥60 mgN/L/d allowed only the nitrifying microorganisms with low substrate affinity to dominate, incongruent with the consortia found in actual RASs. AOB were adaptable at all salinity studied (2, 15, and 30 g/L), while AOA and comammox were sensitive to elevated salinity (15 and 30 g/L, respectively). The ammonia removal rate of a culture prepared at 2 g/L salinity decreased largely when applied at 15 and 30 g/L. In contrast, those prepared at 15 and 30 g/L were more robust to different salinity. Separately preparing the cultures at different salinity for uses in freshwater-low salinity and brackish-marine RASs is recommended. The findings of this work enhance our understanding on how to formulate nitrifying culture augmentation for used in different RAS types.

Surface Ammonia-Oxidizer Abundance During the Late Summer in the West Antarctic Coastal System.

Marine ammonia oxidizers that oxidize ammonium to nitrite are abundant in polar waters, especially during the winter in the deeper mixed-layer of West Antarctic Peninsula (WAP) waters. However, the activity and abundance of ammonia-oxidizers during the summer in surface coastal Antarctic waters remain unclear. In this study, the ammonia-oxidation rates, abundance and identity of ammonia-oxidizing bacteria (AOB) and archaea (AOA) were evaluated in the marine surface layer (to 30 m depth) in Chile Bay (Greenwich Island, WAP) over three consecutive late-summer periods (2017, 2018, and 2019). Ammonia-oxidation rates of 68.31 nmol N L−1 day−1 (2018) and 37.28 nmol N L−1 day−1 (2019) were detected from illuminated 2 m seawater incubations. However, high ammonia-oxidation rates between 267.75 and 109.38 nmol N L−1 day−1 were obtained under the dark condition at 30 m in 2018 and 2019, respectively. During the late-summer sampling periods both stratifying and mixing events occurring in the water column over short timescales (February–March). Metagenomic analysis of seven nitrogen cycle modules revealed the presence of ammonia-oxidizers, such as the Archaea Nitrosopumilus and the Bacteria Nitrosomonas and Nitrosospira, with AOA often being more abundant than AOB. However, quantification of specific amoA gene transcripts showed number of AOB being two orders of magnitude higher than AOA, with Nitrosomonas representing the most transcriptionally active AOB in the surface waters. Additionally, Candidatus Nitrosopelagicus and Nitrosopumilus, phylogenetically related to surface members of the NP-ε and NP-γ clades respectively, were the predominant AOA. Our findings expand the known distribution of ammonium-oxidizers to the marine surface layer, exposing their potential ecological role in supporting the marine Antarctic system during the productive summer periods.

Nutrient-Limited Enrichments of Nitrifiers From Soil Yield Consortia of Nitrosocosmicus-Affiliated AOA and Nitrospira-Affiliated NOB.

The discovery of ammonia-oxidizing archaea (AOA) and complete ammonia-oxidizing (comammox) bacteria widespread in terrestrial ecosystems indicates an important role of these organisms in terrestrial nitrification. Recent evidence indicated a higher ammonia affinity of comammox bacteria than of terrestrial AOA and ammonia-oxidizing bacteria (AOB), suggesting that comammox bacteria could potentially represent the most low-nutrient adapted nitrifiers in terrestrial systems. We hypothesized that a nutrient-limited enrichment strategy could exploit the differences in cellular kinetic properties and yield enrichments dominated by high affinity and high yield comammox bacteria. Using soil with a mixed community of AOA, AOB, and comammox Nitrospira, we compared performance of nutrient-limited chemostat enrichment with or without batch culture pre-enrichment in two different growth media without inhibitors or antibiotics. Monitoring of microbial community composition via 16S rRNA and amoA gene sequencing showed that batch enrichments were dominated by AOB, accompanied by low numbers of AOA and comammox Nitrospira. In contrast, nutrient-limited enrichment directly from soil, and nutrient-limited sub-cultivation of batch enrichments consistently yielded high enrichments of Nitrosocosmicus-affiliated AOA associated with multiple canonical nitrite-oxidizing Nitrospira strains, whereas AOB numbers dropped below 0.1% and comammox Nitrospira were lost completely. Our results reveal competitiveness of Nitrosocosmicus sp. under nutrient limitation, and a likely more complex or demanding ecological niche of soil comammox Nitrospira than simulated in our nutrient-limited chemostat experiments.

How silicon fertilizer improves nitrogen and phosphorus nutrient availability in paddy soil?

In order to reveal the mechanism of silicon (Si) fertilizer in improving nitrogen (N) and phosphorus (P) nutrient availability in paddy soil, we designed a series of soil culture experiments by combining application of varying Si fertilizer concentrations with fixed N and P fertilizer concentrations. Following the recommendations of fertilizer manufacturers and local farmers, we applied Si in concentrations of 0, 5.2, 10.4, 15.6, and 20.8 μg/kg. At each concentration of added Si, the availability of soil N and P nutrients, soil microbial activity, numbers of ammonia-oxidizing bacteria and P-decomposing bacteria which means that the organic P is decomposed into inorganic nutrients which can be absorbed and utilized by plants, and urease and phosphatase activity first increased, and then decreased, as Si was added to the soil. These indicators reached their highest levels with a Si application rate of 15.6 μg/kg, showing values respectively 19.78%, 105.09%, 8.34%, 73.12%, 130.36%, 28.12%, and 20.15% higher than those of the controls. Appropriate Si application (10.4 to 15.6 µg/kg) could significantly increase the richness of the soil microbial community involved in cycling of N and P nutrients in the soil. When the Si application rate was 15.6 μg/kg, parameters for characterizing microbial abundance such as sequence numbers, operational taxonomic unit (OTU) number, and correlation indices of microbial community richness such as Chao1 index, the adaptive coherence estimator (ACE) index, Shannon index, and Simpson index all reached maximum values, with amounts increased by 14.46%, 10.01%, 23.80%, 30.54%, 0.18%, and 2.64%, respectively, compared with the control group. There is also a good correlation between N and P mineralization and addition of Si fertilizer. The correlation coefficients between the ratio of available P/total P (AP/TP) and the number of ammonia-oxidizing bacteria, AP/TP and acid phosphatase activity (AcPA), AP/TP and the Shannon index, the ratio of available N/total amount of N (AN/TN) and the number of ammoniated bacteria, and AN/TN and AcPA were 0.9290, 0.9508, 0.9202, 0.9140, and 0.9366, respectively. In summary, these results revealed that enhancement of soil microbial community structure diversity and soil microbial activity by appropriate application of Si is the key ecological mechanism by which application of Si fertilizer improves N and P nutrient availability.

Variation, distribution, and diversity of canonical ammonia-oxidizing microorganisms and complete-nitrifying bacteria in highly contaminated ecological restoration regions in the Siding mine area

Canonical ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB) and complete-nitrifying bacteria (comammox) exist in a variety of ecosystems. However, little is known about AOA, AOB and comammox or their contributions to nitrification in the soils of heavily degraded and acidic mine regions. In the present study, the activity, richness, diversity and distribution patterns of AOA, AOB and comammox in the Siding mine area were investigated. Nemerow's multifactor pollution index (PN) values indicated that the soil in all three areas in the Siding mine area was highly contaminated by Cd, Pb, Zn, Mn and Cu. The AOA, AOB and comammox amoA gene copy numbers exhibited significant positive correlations with Pb and Zn levels and PN values, which indicated that the populations of AOA, AOB and comammox underwent adaptation and reproduction in response to pollution from multiple metals in the Siding mine area. Among them, the abundance of AOA was the highest, and AOA may survive better than AOB and comammox under such severely pollution-stressed and ammonia-limited conditions. The phyla Thaumarchaeota and Crenarchaeota may play vital roles in the soil ammonia oxidation process. Unlike AOA, AOB may use soil available phosphorus to help them compete for NH3 and other limiting nutrients with AOA and heterotrophs. Moreover, soil organic matter was the main factor influencing the species diversity of AOB, the β-diversity of AOB and comammox, and the community composition of AOA, AOB and comammox. Our research will help to explain the role and importance of AOA, AOB and comammox in the different ecological restoration regions in the Siding mine area.

Acidification in corn monocultures favor fungi, ammonia oxidizing bacteria, and nirK-denitrifier groups

Agricultural practices of no-till and crop rotations are critical to counteract the detrimental effects of monocultures and tillage operations on ecosystem services related to soil health such as microbial N cycling. The present study explored the main steps of the microbial N cycle, using targeted gene abundance as a proxy, and concerning soil properties, following 19 and 20 years of crop monocultures and rotations of corn (Zea mays L.), and soybean [Glycine max (L.) Merr.], either under no-till or chisel tillage. Real-time quantitative polymerase chain reaction (qPCR) was implemented to estimate phylogenetic groups and functional genes related to the microbial N cycle: nifH (N2 fixation), amoA (nitrification) and nirK, nirS, and nosZ (denitrification). Our results indicate that long-term crop rotation and tillage decisions affect soil health as it relates to soil properties and microbial parameters. No-till management increased soil organic matter (SOM), decreased soil pH, and increased copy numbers of AOB (ammonia oxidizing bacteria). Crop rotations with more corn increased SOM, reduced soil pH, reduced AOA (ammonia oxidizing archaea) copy numbers, and increased AOB and fungal ITS copy numbers. NirK denitrifier groups were also enhanced under continuous corn. Altogether, the more corn years included in a crop rotation multiplies the amount of N needed to sustain yield levels, thereby intensifying the N cycle in these systems, potentially leading to acidification, enhanced bacterial nitrification, and creating an environment primed for N losses and increased N2O emissions.

Abundance and activity of ammonia oxidizing archaea and bacteria in bulk water and biofilm in water supply systems practicing chlorination and chloramination: Full and laboratory scale investigations.

The abundance and nitrification activity of ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) in bulk water and biofilm in chloraminated and chlorinated water supply systems were investigated. The abundance of AOB varied between cold and warm periods while that was the case for AOA only in biofilm. Lower ammonia concentrations favored the abundance of AOA over AOB. AOA and AOB were found more in distal zones of the distribution system (DS). Higher numbers of AOA and AOB were observed in DS associated with chloramination compared to those associated with chlorination. Significant positive correlations between ammonia-N in bulk water and AOA indicate a possibility of involvement of AOA in nitrification in DS. A separate laboratory-based experiment simulating DS condition was conducted to understand the effects of chlorine and chloramine dosages and temperature on AOA and AOB. AOA were inhibited less than AOB in the presence of lower concentrations of chlorine and chloramine (1.5 and 2.0mg/L chlorine; 0.05-0.1 and 0.3-0.4mg/L chloramine) while both of them were not detected at higher dosages (2.5mg/L chlorine and 1.5-1.6mg/L chloramine). At a low temperature (10-12°C), chloramine and chlorine provided similar inhibition trends in which AOB were inhibited more than AOA. At a high temperature (25°C), chloramine was less inhibitory to AOA and AOB than chlorine.

Response of ammonia-oxidizing Bacteria and Archaea to long-term saline water irrigation in alluvial grey desert soils

Soil nitrification via ammonia oxidation is a key ecosystem process in terrestrial environments, but little is known of how increasing irrigation of farmland soils with saline waters effects these processes. We investigated the effects of long-term irrigation with saline water on the abundances and community structures of ammonia-oxidizing bacteria (AOB) and archaea (AOA). Irrigation with brackish or saline water increased soil salinity (EC1:5) and NH4-N compared to irrigation with freshwater, while NO3-N, potential nitrification rates (PNR) and amoA gene copy numbers of AOA and AOB decreased markedly under irrigation regimes with saline waters. Moreover, irrigation with brackish water lowered AOA/AOB ratios. PNR was positively correlated with AOA and AOB amoA gene copy numbers across treatments. Saline and brackish water irrigation significantly increased the diversity of AOA, as noted by Shannon index values, while saline water irrigation markedly reduced AOB diversity. In addition, irrigation with brackish or fresh waters resulted in higher proportions of unclassified taxa in the AOB communities. However, irrigation with saline water led to higher proportions of unclassified taxa in the AOA communities along with the Candidatus Nitrosocaldus genus, as compared to soils irrigated with freshwater. AOA community structures were closely associated with soil salinity, NO3−N, and pH, while AOB communities were only significantly associated with NO3−N and pH. These results suggest that salinity was the dominant factor affecting the growth of ammonia-oxidizing microorganisms and community structure. These results can provide a scientific basis for further exploring the response mechanism of ammonia-oxidizing microorganisms and their roles in nitrogen transformation in alluvial grey desert soils of arid areas.

Variability of the nitrifying bacteria in the biofilm and water column of a recirculating aquaculture system for tilapia ( Oreochromis niloticus ) production

The aim of this study was to evaluate variability of nitrifying bacterial community in the biofilm and in the water of a recirculating aquaculture systems (RAS) in a tilapia farming in order to determine if nitrification process is dependent, or not, of nitrifying bacteria abundance. Biofilm and water samples were collected periodically for 30 days and analysed with the fluorescent in situ hybridization (FISH) technique, used to quantify ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). Ammonia presented the peak in the first week, while the nitrite's maximum was recorded in the second week. Nitrate increased steadily, indicating nitrification activity. Total bacterial abundance in biofilm increased continuously, while in water, it did not change significantly. In the biofilm, number of AOB was high at beginning, decreased after few days and increased again following augment of ammonia. Number of NOB also showed an increase in abundance in biofilm following the increment of nitrite and nitrate. In water, AOB and NOB did not show major variability. Relative abundance of nitrifying bacteria represented more than 30% of total bacteria in biofilm at beginning of the experiment. Their contribution decreased to >3% in last days. It indicates that nitrifying bacteria are biofilm colonizers, and that their activity seems to be directly related to the concentration of nitrogen compounds. However, contribution of nitrifying bacteria did not vary much along the time. We may conclude that the biofilm-nitrifying bacteria plays major role in nitrification process in RAS and that the activity of these organisms is dependent of their abundance in response to the concentration of nitrogen compounds.

Organic Matter Regulates Ammonia-Oxidizing Bacterial and Archaeal Communities in the Surface Sediments of Ctenopharyngodon idellus Aquaculture Ponds.

Ammonia-oxidizing bacteria (AOB) and archaea (AOA) play important roles in nitrogen removal in aquaculture ponds, but their distribution and the environmental factors that drive their distribution are largely unknown. In this study, we collected surface sediment samples from Ctenopharyngodon idellus ponds in three different areas in China that practice aquaculture. The community structure of AOB and AOA and physicochemical characteristics in the ponds were investigated. The results showed that AOA were more abundant than AOB in all sampling ponds except one, but sediment AOB and AOA numbers varied greatly between ponds. Correlation analyses indicated a significant correlation between the abundance of AOB and arylsulfatase, as well as the abundance of AOA and total nitrogen (TN) and arylsulfatase. In addition, AOB/AOA ratio was found to be significantly correlated with the microbial biomass carbon. AOB were grouped into seven clusters affiliated to Nitrosospira and Nitrosomonas, and AOA were grouped into six clusters affiliated to Nitrososphaera, Nitrososphaera sister group, and Nitrosopumilus. AOB/AOA diversity in the surface sediments of aquaculture ponds varied according to the levels of total organic carbon (TOC), and AOB and AOA diversity was significantly correlated with arylsulfatase and β-glucosidase, respectively. The compositions of the AOB communities were also found to be significantly influenced by sediment eutrophic status (TOC and TN levels), and pH. In addition, concentrations of acid phosphatase and arylsulfatase in surface sediments were significantly correlated with the prominent bacterial amoA genotypes, and concentrations of TOC and urease were found to be significantly correlated with the prominent archaeal amoA genotype compositions. Taken together, our results indicated that AOB and AOA communities in the surface sediments of Ctenopharyngodon idellus aquaculture ponds are regulated by organic matter and its availability to the microorganisms.

Bio-geochemical Circulation of Nitrogen in Lakes and the Role of Microorganisms

In this paper, the nitrogen forms of lacustrine sediments and their roles in biogeochemical cycles were studied. The effects of nitrogen on water-sediments - physical, chemical and biological processes in submerged plant systems, and understanding the physiological and ecological effects and feedback mechanism of submerged macrophytes on eutrophic water bodies can provide a scientific basis for lake endogenous pollution control. The in situ experiments were used to analyze the spatial distribution of ammonia nitrogen concentration, total organic carbon concentration, nitrification activity and the number of ammonia-oxidizing bacteria in Shahe reservoir and the Yangwa depression. Combined with the pollution characteristics and actual characteristics of the two sections, it is found that the concentration of nitrogen and the nitrifying active water at the two gates of Shahe reservoir and Yangwa gate are similar.

Ammonia-oxidizers’ diversity in wastewater treatment processes

ABSTRACTThe diversity of ammonia-oxidizing bacteria (AOB) within the beta-subclass of Proteobacteria was investigated by genus- and family-specific real-time quantitative PCR (qPCR) assays on samples drawn from wastewater treatment systems. The 16S rRNA gene copy numbers ranged from 7.0 × 103 to 6.8 × 106, 1.1 × 107 to 1.8 × 107, and 2.9 × 105 to 1.5 × 107 copies/mL, respectively. Volumetric ammonium load (VAL) in the wastewater treatment systems calculated using the AOB numbers was in the range of 2.1–12.6 mM/d. Distribution patterns of eutrophic (i.e. Nitrosomonas europaea and Nitrosomonas nitrosa clusters) and oligotrophic (i.e. Nitrosomonas cryotolerans cluster) AOB groups were correlated with the VAL values. A high possibility of potential false-positive detection by family-specific qPCR assays was established by evaluating theoretical specificity in in silico and experimental investigations. The specificities of genus-specific qPCR assays were confirmed by amoA PCR, followed by cloning and sequencing. VAL must be the factor influencing the inclusion of AOB species. However, there was no significant correlation between the volatile suspended solid concentration representing chemical oxygen demand and N. europaea’s community population, indicating that the degree of ammonia oxidation influenced the community cluster of Nitrosomonas relatively more.

Nitrification in Activated Sludge Exposed to Static Magnetic Field

The study investigated wastewater treatment in an aerobic reactor with activated sludge exposed to static magnetic field (SMF) with mean induction of 8.1 mT. The efficiency of chemical oxygen demand removal was about 90% in a control reactor and an SMF-exposed reactor. Although the nitrification efficiency was higher than 95% in both reactors, the activity of ammonia-oxidizing bacteria was higher in the SMF-exposed reactor. This resulted in shortening of nitrification time to 4 h compared to 8 h in the control reactor. Higher number of ammonia-oxidizing bacteria in the SMF-exposed reactor might result from increased oxygen penetration into the liquid exposed to SMF, which favored growth of these bacteria. The results indicate that SMF enhanced nitrification, the most sensitive process from the biological nitrogen transformations. SMF influenced the overall biomass content that was 14% higher in the SMF-exposed reactor than in the control reactor.

Diversity, abundance and activity of ammonia-oxidizing microorganisms in fine particulate matter

Increasing ammonia emissions could exacerbate air pollution caused by fine particulate matter (PM2.5). Therefore, it is of great importance to investigate ammonia oxidation in PM2.5. This study investigated the diversity, abundance and activity of ammonia oxidizing archaea (AOA), ammonia oxidizing bacteria (AOB) and complete ammonia oxidizers (Comammox) in PM2.5 collected in Beijing-Tianjin-Hebei megalopolis, China. Nitrosopumilus subcluster 5.2 was the most dominant AOA. Nitrosospira multiformis and Nitrosomonas aestuarii were the most dominant AOB. Comammox were present in the atmosphere, as revealed by the occurrence of Candidatus Nitrospira inopinata in PM2.5. The average cell numbers of AOA, AOB and Ca. N. inopinata were 2.82 × 104, 4.65 × 103 and 1.15 × 103 cell m−3 air, respectively. The average maximum nitrification rate of PM2.5 was 0.14 μg (NH4+-N) [m3 air·h]−1. AOA might account for most of the ammonia oxidation, followed by Comammox, while AOB were responsible for a small part of ammonia oxidation. Statistical analyses showed that Nitrososphaera subcluster 4.1 was positively correlated with organic carbon concentration, and Nitrosomonas eutropha showed positive correlation with ammonia concentration. Overall, this study expanded our knowledge concerning AOA, AOB and Comammox in PM2.5 and pointed towards an important role of AOA and Comammox in ammonia oxidation in PM2.5.

Responses of bacterial community and functional marker genes of nitrogen cycling to biochar, compost and combined amendments in soil.

Biochar and compost are seen as two attractive waste management options and are used for soil amendment and pollution remediation. The interaction between biochar and composting may improve the potential benefits of biochar and compost. We investigated soil physicochemical properties, bacterial community, bacterial 16S rRNA, and functional marker genes of nitrogen cycling of the soil remedied with nothing (S), compost (SC), biochar (SB), a mixture of compost and biochar (SBC), composted biochar (SBced), and a composted mixture of biochar and biomass (SBCing). The results were that all amendments (1) increased the bacterial community richness (except SB) and SBCing showed the greatest efficiency; (2) increased the bacterial community diversity (SBCing > SBC > SC > SBced > SB > S); and (3) changed the gene copy numbers of 16S rRNA, nirK, nirS, and nosZ genes of bacteria, ammonia-oxidizing archaea (AOA), and ammonia-oxidizing bacteria (AOB). All amendments (except SB) could increase the gene copy number of 16S rRNA, and SBCing had the greatest efficiency. The changes of soil bacterial community richness and diversity and the gene copy numbers of 16S rRNA, nirK, nirS, nosZ, AOA, and AOB would affect carbon and nitrogen cycling of the ecosystem and also implied that BCing had the greatest efficiency on soil amendment.

The effects of salinity on nitrification using halophilic nitrifiers in a Sequencing Batch Reactor treating hypersaline wastewater.

With annual increases in the generation and use of saline wastewater, the need to avoid environmental problems such as eutrophication is critical. A previous study identified ways to start up a halophilic sludge domesticated from estuarine sediments to remove nitrogen from wastewater with a salinity of 30 g/L. This investigation expands that work to explore the impact of salinity on nitrogen removal. This study demonstrated that the mixed halophilic consortia removed nitrogen from wastewater with a salinity of 30–85 g/L. A kinetic analysis showed that halophilic nitrifiers selected based on hypersalinity were characterized by low Ks, μmax and specific ammonium oxidization rates. This explains the decrease in ammonium removal efficiency in the high salinity operational phases. Salinity inhibited ammonia oxidizing bacteria (AOB) activity, as well as the number of dominant AOB, but did not significantly affect the AOB dominant species. Three most dominant AOB lineages in the halophilic sludge were Nitrosomonas marina, Nitrosomonas europaea, and Nitrosococcus mobilis. Nitrosomonas europaea and Nitrosococcus mobilis were mainly affected by salinity, while nitrite accumulation and ammonia loading played the key role in determining the abundance of Nitrosococcus mobilis and Nitrosococcus europaea. The study contributes insights about shifts in halophilic nitrifying bacterial populations.

Microbial Diversity of Ammonia Oxidizing and Other Bacteria of Activated Sludge

Microbial diversity and large quantity of ammonia-oxidizing bacteria (AOB) in activated sludge were compared using PCR-DGGE and real-time PCR assays. Activated sludge samples were collected from different types of wastewater treatment plants (WWTPs). The composition of total bacteria determined by PCR-DGGE was highly diverse between the samples, whereas the community of AOB was similar across all the investigated activated sludge. Total bacterial numbers and AOB numbers in the aerated mixed liquor were in the range of 1.2×10<SUP>9</SUP> to 2.8×10<SUP>12</SUP> and 1.9×10<SUP>7</SUP> to 2.7×10<SUP>10</SUP> copies/l, respectively. Activated sludge from livestock, textile, and sewage treating WWTPs contained relatively high amoA gene copies (more than 10<SUP>5</SUP> copies/l), whereas activated sludge from food and paper WWTPs revealed a low number of the amoA gene (less than 10<SUP>3</SUP> copies/l). The value of the amoA gene copy effectively showed the difference in composition of bacteria in different activated sludge samples and this was better than the measurement with the AOB 16S rRNA or total 16S rRNA gene. These results suggest that the quantification of the amoA gene can help monitor AOB and ammonia oxidation in WWTPs.