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Intercellular electron transfer (IET) refers to the process within which electrons being indirectly or directly transferred to the exterior of cells and eventually delivered to the electron acceptors around cells. IET widely exists in nature, especially when electron acceptor are deficient. IET can be divided into two categories: indirect IET and direct IET. Indirect IET (intercellular substrate transfer) always occurs with electron transfer of hydrogen, formate, and other metabolites. Direct intracellular electron transfer is achieved by the coupling of intracellular and extracellular electron transfer. IET boosts the activity of cellular substrate metabolism and expands the acting space of cells. Moreover, IET generates electric current which provides driving-power for energy sharing between bacteria and transformation of extracellular material (such as heavy metals and humus). There is no doubt that IET has physiological and ecological significance. This review summarized recent advances, making a systematic analysis of the process, characteristics, mechanism and eco-physiological significance of IET.

Physical and chemical characteristics of PM2.5 and its toxicity to human bronchial cells BEAS-2B in the winter and summer.

With the increasing occurrence of haze during the summer, the physicochemical characteristics and toxicity differences in PM2.5 in different seasons are of great concern. Hangzhou is located in an area that has a subtropical monsoon climate where the humidity is very high during both the summer and winter. However, there are limited studies on the seasonal differences in PM2.5 in these weather conditions. In this test, PM2.5 samples were collected in the winter and summer, the morphology and chemical composition of PM2.5 were analyzed, the toxicity of PM2.5 to human bronchial cells BEAS-2B was compared, and the correlation between PM2.5 toxicity and the chemical composition was discussed. The results showed that during both the winter and summer, the main compounds in the PM2.5 samples were water-soluble ions, particularly SO42-, NO3-, and NH4+, followed by organic components, while heavy metals were present at lower levels. The higher the mass concentration of PM2.5, the greater its impact on cell viability and ROS levels. However, when the mass concentration of PM2.5 was similar, the water extraction from the summer samples showed a greater impact on BEAS-2B than that from the winter samples. The cytotoxicity of PM2.5 was closely associated with heavy metals and organic pollutants but less related to water-soluble ions.

Anaerobic methane oxidation coupled to nitrite reduction can be a potential methane sink in coastal environments.

In the current study, we investigated nitrite-dependent anaerobic methane oxidation (N-DAMO) as a potential methane sink in the Hangzhou Bay and the adjacent Zhoushan sea area. The potential activity of the N-DAMO process was primarily observed in Hangzhou Bay by means of (13)C-labeling experiments, whereas very low or no potential N-DAMO activity could be detected in the Zhoushan sea area. The measured potential N-DAMO rates ranged from 0.2 to 1.3 nmol (13)CO2 g(-1) (dry sediment) day(-1), and the N-DAMO potentially contributed 2.0-9.4 % to the total microbial methane oxidation in the examined sediments. This indicated that the N-DAMO process may be an alternative pathway in the coastal methane cycle. Phylogenetic analyses confirmed the presence of Candidatus Methylomirabilis oxyfera-like bacteria in all the examined sediments, while the group A members (the dominant bacteria responsible for N-DAMO) were found mainly in Hangzhou Bay. Quantitative PCR showed that the 16S rRNA gene abundance of Candidatus M. oxyfera-like bacteria varied from 5.4 × 10(6) to 5.0 × 10(7) copies g(-1) (dry sediment), with a higher abundance observed in Hangzhou Bay. In addition, the overlying water NO3 (-) concentration and salinity were identified as the most important factors influencing the abundance and potential activity of Candidatus M. oxyfera-like bacteria in the examined sediments. This study showed the evidence of N-DAMO in coastal environments and indicated the importance of N-DAMO as a potential methane sink in coastal environments.

Vertical distribution of nitrite-dependent anaerobic methane-oxidising bacteria in natural freshwater wetland soils.

Nitrite-dependent anaerobic methane oxidation (n-damo) is a recently discovered process that is catalysed by "Candidatus Methylomirabilis oxyfera". In the present study, the vertical distribution (0-10, 20-30, 50-60 and 90-100 cm) of M. oxyfera-like bacteria was investigated in Xiazhuhu wetland, the largest natural wetland on the southern Yangtze River (China). Phylogenetic analyses showed that group A of M. oxyfera-like bacteria and pmoA genes occurred primarily at depths of 50-60 and 90-100 cm. Quantitative PCR further confirmed the presence of M. oxyfera-like bacteria in soil cores from different depths, with the highest abundance of 5.1 × 10(7) copies g(-1) dry soil at depth of 50-60 cm. Stable isotope experiments demonstrated that the n-damo process occurred primarily at depths of 50-60 and 90-100 cm, with the potential rates ranging from 0.2 to 14.5 nmol CO2 g(-1) dry soil d(-1). It was estimated that the methane flux may increase by approximately 2.7-4.3% in the examined wetland in the absence of n-damo. This study shows that the deep wetland soils (50-60 and 90-100 cm) are the preferred habitats for M. oxyfera-like bacteria. The study also highlights the potential importance of these bacteria in the methane and nitrogen cycles in deep wetland soils.

Evidence for the cooccurrence of nitrite-dependent anaerobic ammonium and methane oxidation processes in a flooded paddy field.

Anaerobic ammonium oxidation (anammox) and nitrite-dependent anaerobic methane oxidation (n-damo) are two of the most recent discoveries in the microbial nitrogen cycle. In the present study, we provide direct evidence for the cooccurrence of the anammox and n-damo processes in a flooded paddy field in southeastern China. Stable isotope experiments showed that the potential anammox rates ranged from 5.6 to 22.7 nmol N2 g(-1) (dry weight) day(-1) and the potential n-damo rates varied from 0.2 to 2.1 nmol CO2 g(-1) (dry weight) day(-1) in different layers of soil cores. Quantitative PCR showed that the abundance of anammox bacteria ranged from 1.0 × 10(5) to 2.0 × 10(6) copies g(-1) (dry weight) in different layers of soil cores and the abundance of n-damo bacteria varied from 3.8 × 10(5) to 6.1 × 10(6) copies g(-1) (dry weight). Phylogenetic analyses of the recovered 16S rRNA gene sequences showed that anammox bacteria affiliated with "Candidatus Brocadia" and "Candidatus Kuenenia" and n-damo bacteria related to "Candidatus Methylomirabilis oxyfera" were present in the soil cores. It is estimated that a total loss of 50.7 g N m(-2) per year could be linked to the anammox process, which is at intermediate levels for the nitrogen flux ranges of aerobic ammonium oxidation and denitrification reported in wetland soils. In addition, it is estimated that a total of 0.14 g CH4 m(-2) per year could be oxidized via the n-damo process, while this rate is at the lower end of the aerobic methane oxidation rates reported in wetland soils.

Evidence for nitrite-dependent anaerobic methane oxidation as a previously overlooked microbial methane sink in wetlands.

The process of nitrite-dependent anaerobic methane oxidation (n-damo) was recently discovered and shown to be mediated by "Candidatus Methylomirabilis oxyfera" (M. oxyfera). Here, evidence for n-damo in three different freshwater wetlands located in southeastern China was obtained using stable isotope measurements, quantitative PCR assays, and 16S rRNA and particulate methane monooxygenase gene clone library analyses. Stable isotope experiments confirmed the occurrence of n-damo in the examined wetlands, and the potential n-damo rates ranged from 0.31 to 5.43 nmol CO2 per gram of dry soil per day at different depths of soil cores. A combined analysis of 16S rRNA and particulate methane monooxygenase genes demonstrated that M. oxyfera-like bacteria were mainly present in the deep soil with a maximum abundance of 3.2 × 10(7) gene copies per gram of dry soil. It is estimated that ∼0.51 g of CH4 m(-2) per year could be linked to the n-damo process in the examined wetlands based on the measured potential n-damo rates. This study presents previously unidentified confirmation that the n-damo process is a previously overlooked microbial methane sink in wetlands, and n-damo has the potential to be a globally important methane sink due to increasing nitrogen pollution.

Transient and long-term effects of bicarbonate on the ANAMMOX process.

In this study, the effects of both transient and long-term inorganic carbon (IC) addition on the anaerobic ammonium oxidation (ANAMMOX) process under pseudo-steady-state and substrate inhibitions were analyzed using reactor performance and measures of sludge activity. Compared with the nitrogen removal rate (NRR) of 3.42 kg N m(-3) day(-1) in the control bioreactor (ICDR) without IC, the peak NRR reached 21.0 kg N m(-3) day(-1) in the reactor (ICAR) with sufficient IC added. It was revealed that the long-term addition of bicarbonate significantly enhanced the performance of the ANAMMOX reactor. The optimum HCO3 (-)/TN ratio was considered to be 1.20, which is lower than that in normal conditions. The IC concentration affected biomass activity, and the transient addition or removal of IC to differing sludge media caused a significant loss of activity. Sufficient addition of IC alleviated the inhibition of excess substrates, while the inhibition was aggravated by the IC limitation. The half-maximal (50 %) inhibitory concentrations of substrate for the sludge were 295 mg L(-1) NO2 (-)-N and 361 mg L(-1) NH4 (+)-N with 120 mg L(-1) of fixed HCO3 (-) and 346 mg L(-1) NO2 (-)-N and 456 mg L(-1) NH4 (+)-N with unlimited IC, respectively. Changing the HCO3 (-)/TN (in milligrams per milligram) ratio resulted in the variation of ANAMMOX stoichiometric ratios. Sludge characterization parameters in the ICDR, including biomass, extracellular polymeric substances, heme C, and so on, were lower than those in ICAR. Filamentous bacteria and spherical bacteria were also observed in the reactor with limited IC.

Distribution and diversity of nitrite-dependent anaerobic methane-oxidising bacteria in the sediments of the Qiantang River.

Nitrite-dependent anaerobic methane oxidation (n-damo) process was reported to be mediated by "Candidatus Methylomirabilis oxyfera", which belongs to the candidate phylum NC10. M. oxyfera-like bacteria have been detected in lake ecosystems, while their distribution, diversity and abundance in river ecosystems have not been well studied. In this study, both the 16S rRNA and the pmoA molecular biomarkers confirmed the presence of diverse NC10 phylum bacteria related to M. oxyfera in a river ecosystem-the Qiantang River, Zhejiang Province (China). Phylogenetic analysis of 16S rRNA genes demonstrated that the recovered M. oxyfera-like sequences could be grouped into several distinct clusters that exhibited 89.8% to 98.9% identity to the M. oxyfera 16S rRNA gene. Similarly, several different clusters of pmoA gene sequences were observed, and these clusters displayed 85.1-95.4% sequence identity to the pmoA gene of M. oxyfera. Quantitative PCR showed that the abundance of M. oxyfera-like bacteria varied from 1.32 ± 0.16 × 10(6) to 1.03 ± 0.12 × 10(7) copies g (dry weight)(-1). Correlation analysis demonstrated that the total inorganic nitrogen content, the ammonium content and the organic content of the sediment were important factors affecting the distribution of M. oxyfera-like bacterial groups in the examined sediments. This study demonstrated the distribution of diverse M. oxyfera-like bacteria and their correlation with environmental factors in Qiantang River sediments.

Broad distribution of diverse anaerobic ammonium-oxidizing bacteria in chinese agricultural soils.

Anaerobic ammonium-oxidizing (anammox) bacteria have been detected in many marine and freshwater ecosystems. However, little is known about the distribution, diversity, and abundance of anammox bacteria in terrestrial ecosystems. In this study, anammox bacteria were found to be present in various agricultural soils collected from 32 different locations in China. Phylogenetic analysis of the 16S rRNA genes showed "Candidatus Brocadia," "Candidatus Kuenenia," "Candidatus Anammoxoglobus," and "Candidatus Jettenia" in the collected soils, with "Candidatus Brocadia" being the dominant genus. Quantitative PCR showed that the abundance of anammox bacteria ranged from 6.38 × 10(4) ± 0.42 × 10(4) to 3.69 × 10(6) ± 0.25 × 10(6) copies per gram of dry weight. Different levels of diversity, composition, and abundance of the anammox bacterial communities were observed, and redundancy analysis indicated that the soil organic content and the distribution of anammox communities were correlated in the soils examined. Furthermore, Pearson correlation analysis showed that the diversity of the anammox bacteria was positively correlated with the soil ammonium content and the organic content, while the anammox bacterial abundance was positively correlated with the soil ammonium content. These results demonstrate the broad distribution of diverse anammox bacteria and its correlation with the soil environmental conditions within an extensive range of Chinese agricultural soils.

Enrichment of an anammox bacterial community from a flooded paddy soil.

This study describes the enrichment of anammox bacteria in a column simulating oxygen limited flooded paddy soils, which are important man-made ecosystems that receive substantial amounts of fixed nitrogen. The upper 50 cm of the paddy soil, containing a high amount of ammonium [1.6-10.4 mmol N kg (dry weight)(-1)], was selected as the inoculum for anammox enrichment. After 18 months of incubation with freshwater from the paddy soil ecosystem, the enrichment culture consumed approximately 4 mmol ammonium l(-1) day(-1) and 5 mmol nitrite l(-1) day(-1). The maximum specific anammox activity of the culture was 35.7 µmol N g (dry weight)(-1) h(-1). Fluorescence in situ hybridization indicated that anammox cells constituted 50% ± 10% of the enrichment culture. The phylogenetic analyses of 16S rRNA and the diagnostic hydrazine synthase (hzsA) genes showed that two dominant anammox species were enriched from paddy soil. The enriched Candidatus Anammoxoglobus-like organisms showed a 16S rRNA gene similarity of 97.5-99.2% to Candidatus Anammoxoglobus propionicus and the Candidatus Jettenia-like organisms showed 92.1-93.1% 16S rRNA gene identity to Candidatus Jettenia asiatica. Real-time quantitative PCR of hzsA gene suggested that up to 10(10) copies g (dry weight)(-1) of soil anammox bacteria were present in the enrichment culture.

Microbiology, ecology, and application of the nitrite-dependent anaerobic methane oxidation process.

Nitrite-dependent anaerobic methane oxidation (n-damo), which couples the anaerobic oxidation of methane to denitrification, is a recently discovered process mediated by "Candidatus Methylomirabilis oxyfera." M. oxyfera is affiliated with the "NC10" phylum, a phylum having no members in pure culture. Based on the isotopic labeling experiments, it is hypothesized that M. oxyfera has an unusual intra-aerobic pathway for the production of oxygen via the dismutation of nitric oxide into dinitrogen gas and oxygen. In addition, the bacterial species has a unique ultrastructure that is distinct from that of other previously described microorganisms. M. oxyfera-like sequences have been recovered from different natural habitats, suggesting that the n-damo process potentially contributes to global carbon and nitrogen cycles. The n-damo process is a process that can reduce the greenhouse effect, as methane is more effective in heat-trapping than carbon dioxide. The n-damo process, which uses methane instead of organic matter to drive denitrification, is also an economical nitrogen removal process because methane is a relatively inexpensive electron donor. This mini-review summarizes the peculiar microbiology of M. oxyfera and discusses the potential ecological importance and engineering application of the n-damo process.

Performance and robustness of an ANAMMOX anaerobic baffled reactor subjected to transient shock loads.

The impacts of transient overloads on the performance of a laboratory-scale anaerobic ammonium oxidation (ANAMMOX) anaerobic baffled reactor was studied by increasing the substrate concentration or inflow rate to 1.5-3.0 times above normal values. These shocks, with the exception of the highest substrate shock, weakened the nitrogen removal efficiency (NRE) but improved the nitrogen removal rate by 0.01-0.18 g l(-1) h(-1). The communities and the location of the sludge may be altered by distinct types of shocks. The substrate vibration data showed that the reactor was unresponsive to hydraulic shocks but sensitive to substrate shocks and the former compartments were more susceptible to the shocks. In the inhibition period, the pH and NRE of the reactor were related to the residual ammonium and free ammonia (FA) and FA was a factor in the reactor fluctuations. The Gaussian model proposed to describe the shocks response fits the experimental data well.

Metabolic properties of a mixed culture of aerobic ammonia oxidizers and its optimal reaction conditions.

The aerobic ammonia oxidation is an important process for nitrogen removal from wastewater with high ammonia concentration. Here, we investigated the metabolic properties of a mixed culture of aerobic ammonia oxidizers and determined its optimal reaction conditions. The maximum specific rate of NO(2)(-)-N formation of the culture was 14.9 mg N mg(protein)(-1) d(-1). The ammonia oxidation capacity was positively correlated with the microbial biomass concentration. Haldane model showed that the half-saturation constant (K(s)) for NH(4)(+)-N of the culture was 78.5 mg L(-1), and the inhibition constant (K(i)) for NH(4)(+)-N was 393.4 mg L(-1). The acetic acid and beef extract had significant inhibitory effects on ammonia oxidation, while there was little effect of methanol and glucose on ammonia oxidation. Orthogonal experiments with range analysis, variance analysis, factor contribution analysis and response surface analysis confirmed the optimal reaction conditions for ammonia oxidation to be 30-32 °C, pH 7.8-8.0, and 150-200 mg L(-1) NH(4)(+)-N concentration.

Hydrazine synthase, a unique phylomarker with which to study the presence and biodiversity of anammox bacteria.

Anaerobic ammonium-oxidizing (anammox) bacteria play an important role in the biogeochemical cycling of nitrogen. They derive their energy for growth from the conversion of ammonium and nitrite into dinitrogen gas in the complete absence of oxygen. Several methods have been used to detect the presence and activity of anammox bacteria in the environment, including 16S rRNA gene-based approaches. The use of the 16S rRNA gene to study biodiversity has the disadvantage that it is not directly related to the physiology of the target organism and that current primers do not completely capture the anammox diversity. Here we report the development of PCR primer sets targeting a subunit of the hydrazine synthase (hzsA), which represents a unique phylogenetic marker for anammox bacteria. The tested primers were able to retrieve hzsA gene sequences from anammox enrichment cultures, full-scale anammox wastewater treatment systems, and a variety of freshwater and marine environmental samples, covering all known anammox genera.

Distribution and diversity of anaerobic ammonium-oxidizing bacteria in the sediments of the Qiantang River.

Anaerobic ammonium oxidation (anammox) is an important process in the marine nitrogen cycle. However, little is known about the distribution, diversity and abundance of anammox bacteria in inland river ecosystems. Here, we found the presence of diverse anammox bacteria in a freshwater river - the Qiantang River, Zhejiang Province (China). The phylogenetic analysis of 16S rRNA genes showed that Brocadia genus, Kuenenia genus, Scalindua genus and three new anammox bacterial clusters could be detected together in Qiantang River sediments, suggesting a higher anammox bacterial diversity in the Qiantang River ecosystem than in open ocean environments where only Scalindua genus was detected. Brocadia and Kuenenia appeared to be the most common anammox bacterial genera in the Qiantang River. Redundancy analysis showed that the sediment organic carbon (OrgC) content had significant influence on the distribution of anammox bacteria in Qiantang River sediments. Pearson correlation analyses showed that OrgC content significantly influenced the anammox bacterial diversity. The results of real-time quantitative PCR showed spatial variations of anammox bacterial abundances which were highly correlated with the sediment total inorganic nitrogen content. These results demonstrated the distribution of diverse anammox bacteria and the influences of environmental factors on anammox bacterial communities in Qiantang River sediments.

Anaerobic ammonium oxidation (anammox) in different natural ecosystems.

Anammox (anaerobic ammonium oxidation), which is a reaction that oxidizes ammonium to dinitrogen gas using nitrite as the electron acceptor under anoxic conditions, was an important discovery in the nitrogen cycle. The reaction is mediated by a specialized group of planctomycete-like bacteria that were first discovered in man-made ecosystems. Subsequently, many studies have reported on the ubiquitous distribution of anammox bacteria in various natural habitats, including anoxic marine sediments and water columns, freshwater sediments and water columns, terrestrial ecosystems and some special ecosystems, such as petroleum reservoirs. Previous studies have estimated that the anammox process is responsible for 50% of the marine nitrogen loss. Recently, the anammox process was reported to account for 9-40% and 4-37% of the nitrogen loss in inland lakes and agricultural soils respectively. These findings indicate the great potential for the anammox process to occur in freshwater and terrestrial ecosystems. The distribution of different anammox bacteria and their contribution to nitrogen loss have been described in different natural habitats, demonstrating that the anammox process is strongly influenced by the local environmental conditions. The present mini-review summarizes the current knowledge of the ecological distribution of anammox bacteria, their contribution to nitrogen loss in various natural ecosystems and the effects of major influential factors on the anammox process.

New anaerobic, ammonium-oxidizing community enriched from peat soil.

Anaerobic ammonium-oxidizing (anammox) bacteria have been recognized as an important sink for fixed nitrogen and are detected in many natural environments. However, their presence in terrestrial ecosystems has long been overlooked, and their contribution to the nitrogen cycling in natural and agricultural soils is currently unknown. Here we describe the enrichment and characterization of anammox bacteria from a nitrogen-loaded peat soil. After 8 months of incubation with the natural surface water of the sampling site and increasing ammonium and nitrite concentrations, anammox cells constituted 40 to 50% of the enrichment culture. The two dominant anammox phylotypes were affiliated with "Candidatus Jettenia asiatica" and "Candidatus Brocadia fulgida." The enrichment culture converted NH(4)(+) and NO(2)(-) to N(2) with the previously reported stoichiometry (1:1.27) and had a maximum specific anaerobic ammonium oxidation rate of 0.94 mmol NH(4)(+)·g (dry weight)(-1)·h(-1) at pH 7.1 and 32°C. The diagnostic anammox-specific lipids were detected at a concentration of 650 ng·g (dry weight)(-1), and pentyl-[3]-ladderane was the most abundant ladderane lipid.

Identification and quantification of anammox bacteria in eight nitrogen removal reactors.

Various studies have revealed anaerobic ammonium oxidation (anammox) as a very attractive alternative process suitable for nitrogen removal from wastewater. Here we investigated anammox bacteria in eight different nitrogen removal reactors. The diversity and abundance of anammox bacteria were determined by the 16S rRNA gene analysis, fluorescence in situ hybridization with specific probes and real-time quantitative PCR (qPCR). In these reactors, at least eight unique near full length anammox 16S rRNA gene sequences were detected, which were distributed over two genera; Candidati Brocadia and Kuenenia. FISH results confirmed that only one anammox bacterium dominated the community in each of the eight reactors investigated in this study. qPCR analysis revealed that anammox bacteria were present in seven of the reactors in the order of 10(9) cells/ml and 10(7) cells/ml in reactor A1. The dominant and divergent Brocadia-like anammox phylotype in one reactor represented a novel species for which we propose the name Candidatus Brocadia sinica. Taken together, these results indicated that a single seeding source could be used to seed anammox reactors designed to treat different types of wastewater, which could lead to a faster start-up of bioreactors.

Influence of substrates on nitrogen removal performance and microbiology of anaerobic ammonium oxidation by operating two UASB reactors fed with different substrate levels.

Both ammonium and nitrite act as substrates as well as potential inhibitors of anoxic ammonium-oxidizing (Anammox) bacteria. To satisfy demand of substrates for Anammox bacteria and to prevent substrate inhibition simultaneously; two strategies, namely high or low substrate concentration, were carefully compared in the operation of two Anammox upflow anaerobic sludge blanket (UASB) reactors fed with different substrate concentrations. The reactor working at relatively low influent substrate concentration (NO(2)(-)-N, 240 mg-NL(-1)) was shown to avoid the inhibition caused by nitrite and free ammonia. Using the strategy of low substrate concentration, a record super high volumetric nitrogen removal rate of 45.24 kg-Nm(-3) day(-1) was noted after the operation of 230 days. To our knowledge, such a high value has not been reported previously. The evidence from transmission electron microscopy (TEM) showed that the morphology and ultrastructure of the Anammox cells in both the reactor enrichments was different.

Enrichment features of anammox consortia from methanogenic granules loaded with high organic and methanol contents.

Vigorous anaerobic ammonium oxidation (anammox) activity was realized by seeding with diverse sludge contents. Granules taken from a 2-year old methanogenic reactor loaded with high organic and methanol contents were used as inoculum to enrich anammox biomass in a 1.1L upflow anaerobic sludge blanket reactor. Anammox activity appeared after an operation of 83 d resulting in the final nitrogen removal rate of 11.7 kg N m(-3) d(-1) with the efficient granulation of anammox sludge. The analysis based on 16S rDNA sequencing confirmed that Candidatus "Brocadia" was the dominant population in the enriched biomass.