亚硝酸盐型甲烷厌氧氧化及其功能微生物研究进展

亚硝酸盐型甲烷厌氧氧化（nitrite-dependent anaerobic methane oxidation,N-DAMO）是耦合氮循环和碳循环的关键环节,主要是由亚硝酸盐型甲烷厌氧氧化菌（Candidatus Methylomirabilis oxyfera）介导完成,对于研究全球氮和碳元素的生物地球化学循环具有重要意义。本文首先总结了国内外N-DAMO的影响因素和在不同自然生态系统中的分布;然后阐述了N-DAMO菌的生理生化特性及其富集培养优化实验和检测技术,最后探讨了N-DAMO技术的应用现状。本综述不仅有助于揭示全球碳氮循环的耦合作用机制,也为N-DAMO反应耦合其他厌氧生物处理过程应用到污水的除碳脱氮上提供了理论依据。     

Anaerobic methane oxidation in a coastal oxygen minimum zone: spatial and temporal dynamics

Coastal waters are a major source of marine methane to the atmosphere. Particularly high concentrations of this potent greenhouse gas are found in anoxic waters, but it remains unclear if and to what extent anaerobic methanotrophs mitigate the methane flux. Here we investigate the long-term dynamics in methanotrophic activity and the methanotroph community in the coastal oxygen minimum zone (OMZ) of Golfo Dulce, Costa Rica, combining biogeochemical analyses, experimental incubations and 16S rRNA gene sequencing over 3 consecutive years. Our results demonstrate a stable redox zonation across the years with high concentrations of methane (up to 1.7 μmol L⁻¹) in anoxic bottom waters. However, we also measured high activities of anaerobic methane oxidation in the OMZ core (rate constant, k, averaging 30 yr⁻¹ in 2018 and 8 yr⁻¹ in 2019–2020). The OPU3 and Deep Sea-1 clades of the Methylococcales were implicated as conveyors of the activity, peaking in relative abundance 5–25 m below the oxic–anoxic interface and in the deep anoxic water respectively. Although their genetic capacity for anaerobic methane oxidation remains unexplored, their sustained high relative abundance indicates an adaptation of these clades to the anoxic, methane-rich OMZ environment, allowing them to play major roles in mitigating methane fluxes.     

Non-linear dynamics of carbon and hydrogen isotopic signatures based on a biological kinetic model of nitrite-dependent methane oxidation by “Candidatus Methylomirabilis oxyfera”

System dynamics of nitrite-dependent anaerobic methane oxidation (N-DAMO) in a “Candidatus Methylomirabilis oxyfera” culture are described using a mathematical model based on chemical kinetics, microbial growth dynamics and equations for ¹³C and ²H isotopic fractionation. Experimental data for the N-DAMO model were taken from Rasigraf et al. (2012), who studied N-DAMO in a batch culture of “Ca. M. oxyfera” started at two different conditions with varying methane, nitrite and biomass concentrations. In the model, instead of using concentrations of each isotopologue (¹²C and ¹³C, ¹H and ²H), total concentrations and respective isotope ratios were considered as variables. The empirical Monod equations, which included methane and nitrite as two rate-limiting substrates, a threshold methane concentration CH _4min below which there was no biomass growth, and the same kinetic coefficients for the separate batch experiments, fitted the experimental data much better than apparent first-order kinetics that required rather different kinetic coefficients for the two experiments. Non-linear dynamics of ¹³C and ²H isotopic signatures were obtained based on the N-DAMO model. It was shown that rate limitation by methane or nitrite concentrations significantly affected the dynamics of carbon and hydrogen isotopic signatures. Fractionation rate increased at higher initial biomass concentration. The non-linear N-DAMO model satisfactorily described experimental data presented in the two-dimensional plot of hydrogen versus carbon stable isotopic signatures.     

Nitrogen source effects on the denitrifying anaerobic methane oxidation culture and anaerobic ammonium oxidation bacteria enrichment process

The co-culture system of denitrifying anaerobic methane oxidation (DAMO) and anaerobic ammonium oxidation (Anammox) has a potential application in wastewater treatment plant. This study explored the effects of permutation and combination of nitrate, nitrite, and ammonium on the culture enrichment from freshwater sediments. The co-existence of NO₃ ⁻, NO₂ ⁻, and NH₄ ⁺ shortened the enrichment time from 75 to 30 days and achieved a total nitrogen removal rate of 106.5 mg/L/day on day 132. Even though ammonium addition led to Anammox bacteria increase and a higher nitrogen removal rate, DAMO bacteria still dominated in different reactors with the highest proportion of 64.7% and the maximum abundance was 3.07 ± 0.25 × 10⁸ copies/L (increased by five orders of magnitude) in the nitrite reactor. DAMO bacteria showed greater diversity in the nitrate reactor, and one was similar to M. oxyfera; DAMO bacteria in the nitrite reactor were relatively unified and similar to M. sinica. Interestingly, no DAMO archaea were found in the nitrate reactor. This study will improve the understanding of the impact of nitrogen source on DAMO and Anammox co-culture enrichment.

     

NOB suppression and adaptation strategies in the partial nitrification–Anammox process for a poultry manure anaerobic digester

Poultry manure contains high levels of ammonia, which result in a suboptimal bioconversion to methane in anaerobic digesters (AD). A simultaneous process of nitrification, Anammox and denitrification (SNAD) in a continuous granular bubble column reactor to treat the anaerobically digested poultry manure was implemented. Thus, two strategies to achieve high efficiencies were proposed in this study: (1) ammonia overload to suppress nitrite oxidizing bacteria (NOB) and (2) gradual adaptation of the partial nitrification–Anammox (PN–A) biomass to organic matter. During the NOB-suppression stage, microbial and physical biomass characterizations were performed and the NOB abundance decreased from 31.3% to 3.3%. During the adaptation stage, with a nitrogen loading rate of 0.34 g L⁻¹ d⁻¹, a hydraulic retention time of 1.24 d and an influent COD/N ratio of 2.63 ± 0.02, a maximum ammonia and total nitrogen removal of 100% and 91.68% were achieved, respectively. The relative abundances of the aerobic and the anaerobic ammonia-oxidizing bacteria were greater than 35% and 40% respectively, during the study. These strategies provided useful design tools for the efficient removal of nitrogen species in the presence of organic matter.     

Decomposition processes in soil of a healthy and a declining Phragmites australis stand

Decomposition processes were investigated in the soil of a declining, more eutrophic and a healthy, less eutrophic freshwater reed (Phragmites australis (Cav.) Trin. ex Steudel) stand in the littoral zone of Rožmberk fishpond, Czech Republic. Soil and pore water were sampled five times from April to October 1998. Chemical properties, CO₂ production in oxic and anoxic conditions, CH₄ production, denitrifying enzyme activity (DEA) and bacterial biomass were measured under laboratory conditions in suspensions prepared from homogenised soil samples. The more eutrophic West stand was more anaerobic than the East stand, with lower redox potential, lower pH and with a higher amount of organic acids, mainly acetic and lactic acid. Mean seasonal concentrations of total nitrogen in pore water, nitrogen of amino acids and proteins, and reducing sugars were all higher in the soil at the more eutrophic stand. Higher nutrient status and more reduced conditions at the more eutrophic stand were accompanied by (i) a limitation of aerobic microbial activities (CO₂ production in oxic conditions: 0.35 versus 0.54 μmol CO₂ cm⁻³ h⁻¹); lower DEA (4.0 versus 20.2 nmol N₂O cm⁻³ h⁻¹) and a lower proportion of bacteria that were active in aerobic conditions; (ii) by a prevalence of anaerobic over aerobic microbial processes; (iii) by a higher rate of methanogenesis (15.0 versus 11.5 nmol CH₄ cm⁻³ h⁻¹) and (iv) by an overall lower rate of microbial processes as compared to less eutrophied stand. The shift from aerobic to anaerobic microbial metabolism, and a coinciding restriction of metabolic activities at the more eutrophic stand are indicative of an elevated oxygen stress in the soil, associated with accumulation of metabolites toxic to both the micro-organisms and the reed. Possible links between eutrophication, decomposition processes in the soil and reed decline are discussed.     

Anaerobic oxidation of methane by sulfate in hypersaline groundwater of the Dead Sea aquifer

Geochemical and microbial evidence points to anaerobic oxidation of methane (AOM) likely coupled with bacterial sulfate reduction in the hypersaline groundwater of the Dead Sea (DS) alluvial aquifer. Groundwater was sampled from nine boreholes drilled along the Arugot alluvial fan next to the DS. The groundwater samples were highly saline (up to 6300 mm chlorine), anoxic, and contained methane. A mass balance calculation demonstrates that the very low δ¹³C_DIC in this groundwater is due to anaerobic methane oxidation. Sulfate depletion coincident with isotope enrichment of sulfur and oxygen isotopes in the sulfate suggests that sulfate reduction is associated with this AOM. DNA extraction and 16S amplicon sequencing were used to explore the microbial community present and were found to be microbial composition indicative of bacterial sulfate reducers associated with anaerobic methanotrophic archaea (ANME) driving AOM. The net sulfate reduction seems to be primarily controlled by the salinity and the available methane and is substantially lower as salinity increases (2.5 mm sulfate removal at 3000 mm chlorine but only 0.5 mm sulfate removal at 6300 mm chlorine). Low overall sulfur isotope fractionation observed (³⁴ε = 17 ± 3.5‰) hints at high rates of sulfate reduction, as has been previously suggested for sulfate reduction coupled with methane oxidation. The new results demonstrate the presence of sulfate‐driven AOM in terrestrial hypersaline systems and expand our understanding of how microbial life is sustained under the challenging conditions of an extremely hypersaline environment.     

Sedimentary Organic Carbon and Nitrogen Sequestration Across a Vertical Gradient on a Temperate Wetland Seascape Including Salt Marshes,Seagrass Meadows and Rhizophytic Macroalgae Beds

Coastal wetlands are key in regulating coastal carbon and nitrogen dynamics and contribute significantly to climate change mitigation and anthropogenic nutrient reduction. We investigated organic carbon (OC) and total nitrogen (TN) stocks and burial rates at four adjacent vegetated coastal habitats across the seascape elevation gradient of Cádiz Bay (South Spain), including one species of salt marsh, two of seagrasses, and a macroalgae. OC and TN stocks in the upper 1 m sediment layer were higher at the subtidal seagrass Cymodocea nodosa (72.3 Mg OC ha⁻¹, 8.6 Mg TN ha⁻¹) followed by the upper intertidal salt marsh Sporobolus maritimus (66.5 Mg OC ha⁻¹, 5.9 Mg TN ha⁻¹), the subtidal rhizophytic macroalgae Caulerpa prolifera (62.2 Mg OC ha⁻¹, 7.2 Mg TN ha⁻¹), and the lower intertidal seagrass Zostera noltei (52.8 Mg OC ha⁻¹, 5.2 Mg TN ha⁻¹). The sedimentation rates increased from lower to higher elevation, from the intertidal salt marsh (0.24 g cm⁻² y⁻¹) to the subtidal macroalgae (0.12 g cm⁻² y⁻¹). The organic carbon burial rate was highest at the intertidal salt marsh (91 ± 31 g OC m⁻² y⁻¹), followed by the intertidal seagrass, (44 ± 15 g OC m⁻² y⁻¹), the subtidal seagrass (39 ± 6 g OC m⁻² y⁻¹), and the subtidal macroalgae (28 ± 4 g OC m⁻² y⁻¹). Total nitrogen burial rates were similar among the three lower vegetation types, ranging from 5 ± 2 to 3 ± 1 g TN m⁻² y⁻¹, and peaked at S. maritimus salt marsh with 7 ± 1 g TN m⁻² y⁻¹. The contribution of allochthonous sources to the sedimentary organic matter decreased with elevation, from 72% in C. prolifera to 33% at S. maritimus. Our results highlight the need of using habitat-specific OC and TN stocks and burial rates to improve our ability to predict OC and TN sequestration capacity of vegetated coastal habitats at the seascape level. We also demonstrated that the stocks and burial rates in C. prolifera habitats were within the range of well-accepted blue carbon ecosystems such as seagrass meadows and salt marshes.

     

Microbial nitrogen removal of ammonia wastewater in poly (butylenes succinate)-based constructed wetland: effect of dissolved oxygen

Constructed wetland (CW) is popular in wastewater treatment for its prominent advantage of low construction and operation cost. However, the nitrogen removal in conventional CW is usually limited by the low dissolved oxygen (DO) and insufficient electron donor. This paper investigated the nitrogen removal performance and mechanisms in the poly (butylenes succinate)-based CW (PBS-CW) while treating ammonia wastewater under different DO levels. The average DO contents in limited-aeration and full-aeration phases were 1.68 mg L⁻¹ and 5.71 mg L⁻¹, respectively. Results indicated that, with the ammonia nitrogen loading rate of 25 g N m⁻³ day⁻¹, total nitrogen removal ratios in the PBS-CW under the limited-aeration and full-aeration phases were 72% and 99%, respectively. Combined analyses revealed that simultaneous nitrification and denitrification (SND) via nitrite/nitrate were the main microbial nitrogen removal pathways in the aeration phase of the PBS-CW (> 89%). The microbial carrier of biodegradable material was believed to play a significant role in prompting SND performance while dealing with low C/N wastewater. Due to the coexistence of micro-anaerobic zone and carbon supply inside the coated biofilm, the high DO level in the PBS-CW increased the abundance of the nitrifying bacteria (amoA and nxrA), denitrifying bacteria (narG, nirK, nirS, and nosZ), and even anammox bacteria (anammox 16s rRNA). These features are beneficial to many microbial processes which require the simultaneous aerobic, anoxic, and anaerobic environment.

     

Latitudinal distribution of microbial communities in anaerobic biological stabilization ponds: effect of the mean annual temperature

Considering wide utilization and high methane fluxes from anaerobic biological stabilization ponds (ABSPs), understanding the methanogenesis in ABSPs is of fundamental importance. Here we investigated the variation and impact factors of methanogenesis in seven ABSPs that spanned from the north to the south of China. Results showed that methanogen abundance (7.7 × 10⁹–8.7 × 10¹⁰ copies g^?1 dry sediment) and methanogenic activities (2.2–21.2 μmol CH₄ g^?1 dry sediment h^?1) were considerable for all sediments. Statistical analysis demonstrated that compared with other factors (ammonium, pH, COD and TOC), mean annual temperature (MAT) showed the lowest P value and thus was the most important influencing factor for the methanogenic process. Besides, with the increasing MAT, methanogenic activity was enhanced mainly due to the shift of the dominant methanogenic pathway from acetoclastic (49.8–70.7%) in low MAT areas to hydrogenotrophic (42.0–54.6%) in high MAT areas. This shift of methanogenic pathway was also paralleled with changes in composition of bacterial communities. These results suggested that future global warming may reshape the composition of methanogen communities and lead to an increasing methane emission from ABSPs. Therefore, further research is urgently needed to globally estimate methane emissions from ABSPs and re‐examine the role of ABSPs in wastewater treatment.     

Rates of Microbial Production and Oxidation of Methane in the Bottom Sediments and Water Column of the Black Sea

Rates of biogeochemical (microbial) processes of methane production and methane oxidation were determined in the bottom sediments and water column of the Black Sea. Aerobic bacterial oxidation of methane was confined to the upper 20–30 cm of Holocene bottom sediments of the shelf (0.7–259 ng C/(dm³ day)) and to oxygenated waters (0.2–45 ng C/(dm³ day)). In reduced sediments of the deep-sea zone and in the hydrogen sulfide–containing water column, considerable rates of anaerobic methane oxidation were recorded, comparable to or exceeding the rates of methane oxidation in oxygenated layers. From one-fourth to one-half of the methane formed in bottom sediments was oxidized immediately therein. The major part of the remaining methane was oxidized in the water column, and a smaller portion arrived in the atmosphere.     

Leaf growth and population dynamics of intertidal Zostera japonica on the western coast of Korea

Leaf production and population dynamics of Zostera japonica were examined at three elevations of an intertidal transect in Seungbongdo Island on the western coast of Korea. Morphometrics, shoot density, biomass, leaf production, reproductive effort and environmental factors were monitored from October 2001 to October 2002. Z. japonica grew well in the lower intertidal zone from 0.2 to 1.0 m above mean chart datum. The upper station (St. 1) exhibited a finer sediment grain size and richer organic content than the middle (St. 2) and lower stations (St. 3). The size of shoots and leaves was significantly greater at St. 1 than at St. 3, whereas the rhizome internodes were longer at St. 3. Despite differences in morphological characteristics among three stations, seagrass biomass and shoot density were not significantly different among study sites. Shoot density, biomass, morphometrics and leaf productivity exhibited clear seasonal variations, which varied along with seasonal changes of water and air temperature. Leaf productivity measured by the clip and reharvest method was highest in September (4.3 g DW m⁻² d⁻¹) and lowest in February (0.2 g DW m⁻² d⁻¹). Reproductive shoots rapidly increased to maximum density along with the high water temperature in July to September. In the intertidal zone, Z. japonica exhibited faster vegetative growth on muddy sand than on sand, probably due to the difference in nutrient supply. The seasonal changes of water and air temperature were considered to play an important role in the seasonal leaf growth of Z. japonica.     

Copper enhances the activity and salt resistance of mixed methane-oxidizing communities

Effluents of anaerobic digesters are an underestimated source of greenhouse gases, as they are often saturated with methane. A post-treatment with methane-oxidizing bacterial consortia could mitigate diffuse emissions at such sites. Semi-continuously fed stirred reactors were used as model systems to characterize the influence of the key parameters on the activity of these mixed methanotrophic communities. The addition of 140 mg L⁻¹ NH₄⁺–N had no significant influence on the activity nor did a temperature increase from 28°C to 35°C. On the other hand, addition of 0.64 mg L⁻¹ of copper(II) increased the methane removal rate by a factor of 1.5 to 1.7 since the activity of particulate methane monooxygenase was enhanced. The influence of different concentrations of NaCl was also tested, as effluents of anaerobic digesters often contain salt levels up to 10 g NaCl L⁻¹. At a concentration of 11 g NaCl L⁻¹, almost no methane-oxidizing activity was observed in the reactors without copper addition. Yet, reactors with copper addition exhibited a sustained activity in the presence of NaCl. A colorimetric test based on naphthalene oxidation showed that soluble methane monooxygenase was inhibited by copper, suggesting that the particulate methane monooxygenase was the active enzyme and thus more salt resistant. The results obtained demonstrate that the treatment of methane-saturated effluents, even those with increased ammonium (up to 140 mg L⁻¹ NH₄⁺–N) and salt levels, can be mitigated by implementation of methane-oxidizing microbial consortia.     

Domoic acid in a marine pelagic food web: Exposure of southern right whales Eubalaena australis to domoic acid on the Península Valdés calving ground,Argentina

The gulfs that surround Península Valdés (PV), Golfo Nuevo and Golfo San José in Argentina, are important calving grounds for the southern right whale Eubalaena australis. However, high calf mortality events in recent years could be associated with phycotoxin exposure. The present study evaluated the transfer of domoic acid (DA) from Pseudo-nitzschia spp., potential producers of DA, to living and dead right whales via zooplanktonic vectors, while the whales are on their calving ground at PV. Phytoplankton and mesozooplankton (primary prey of the right whales at PV and potential grazers of Pseudo-nitzschia cells) were collected during the 2015 whale season and analyzed for species composition and abundance. DA was measured in plankton and fecal whale samples (collected during whale seasons 2013, 2014 and 2015) using liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS). The genus Pseudo-nitzschia was present in both gulfs with abundances ranging from 4.4 × 10² and 4.56 × 10⁵ cell l⁻¹. Pseudo-nitzschia australis had the highest abundance with up to 4.56 × 10⁵ cell l⁻¹. DA in phytoplankton was generally low, with the exception of samples collected during a P. australis bloom. No clear correlation was found between DA in phytoplankton and mesozooplankton samples. The predominance of copepods in mesozooplankton samples indicates that they were the primary vector for the transfer of DA from Pseudo-nitzschia spp. to higher trophic levels. High levels of DA were detected in four whale fecal samples (ranging from 0.30 to 710 μg g⁻¹ dry weight of fecal sample or from 0.05 and 113.6 μg g⁻¹ wet weight assuming a mean water content of 84%). The maximum level of DA detected in fecal samples (710 μg DA g⁻¹ dry weight of fecal sample) is the highest reported in southern right whales to date. The current findings demonstrate for the first time that southern right whales, E. australis, are exposed to DA via copepods as vectors during their calving season in the gulfs of PV.     

自然生境中亚硝酸盐型厌氧甲烷氧化细菌研究进展

随着功能微生物介导的亚硝酸盐型厌氧甲烷氧化(nitrite-dependent anaerobic methane oxidation,N-DAMO)过程被发现,人们对自然界的碳氮循环有了全新的认识,该过程成为自然生态系统中温室气体甲烷的汇,同时还是氮污染的消减途径。本文系统介绍了N-DAMO过程反应机理以及参与该过程的亚硝酸盐型厌氧甲烷氧化细菌(Candidatus Methylomirabilis oxyfera)的生理生化特征,并对研究该功能菌的分子微生物方法进行了汇总。通过对不同自然生境中该细菌的研究报道进行总结分析,揭示各生境中年均降水量、年均温度、所处不同自然区等大尺度宏观环境因子及碳源、氮源、pH和氧气含量等生存因子对其群落结构的潜在影响,最后在展望中提出此功能菌在未来可深入研究的方向,期望能厘清厌氧甲烷氧化过程及其功能菌在碳、氮循环中的生态学功能。     

Leaf growth and population dynamics of intertidal Zostera japonica on the western coast of Korea

Leaf production and population dynamics of Zostera japonica were examined at three elevations of an intertidal transect in Seungbongdo Island on the western coast of Korea. Morphometrics, shoot density, biomass, leaf production, reproductive effort and environmental factors were monitored from October 2001 to October 2002. Z. japonica grew well in the lower intertidal zone from 0.2 to 1.0 m above mean chart datum. The upper station (St. 1) exhibited a finer sediment grain size and richer organic content than the middle (St. 2) and lower stations (St. 3). The size of shoots and leaves was significantly greater at St. 1 than at St. 3, whereas the rhizome internodes were longer at St. 3. Despite differences in morphological characteristics among three stations, seagrass biomass and shoot density were not significantly different among study sites. Shoot density, biomass, morphometrics and leaf productivity exhibited clear seasonal variations, which varied along with seasonal changes of water and air temperature. Leaf productivity measured by the clip and reharvest method was highest in September (4.3 g DW m⁻² d⁻¹) and lowest in February (0.2 g DW m⁻² d⁻¹). Reproductive shoots rapidly increased to maximum density along with the high water temperature in July to September. In the intertidal zone, Z. japonica exhibited faster vegetative growth on muddy sand than on sand, probably due to the difference in nutrient supply. The seasonal changes of water and air temperature were considered to play an important role in the seasonal leaf growth of Z. japonica.     

Relationship between microbial activity and microbial community structure in six full-scale anaerobic digesters

High activity levels and balanced anaerobic microbial communities are necessary to attain proper anaerobic digestion performance. Therefore, this work was focused on the kinetic performance and the microbial community structure of six full-scale anaerobic digesters and one lab-scale co-digester. Hydrolytic (0.6–3.5 g COD g^?1 VSS d^?1) and methanogenic (0.01–0.84 g COD g^?1 VSS d^?1) activities depended on the type of biomass, whereas no significant differences were observed among the acidogenic activities (1.5–2.2 g COD g^?1 VSS d^?1). In most cases, the higher the hydrolytic and the methanogenic activity, the higher the Bacteroidetes and Archaea percentages, respectively, in the biomasses. Hydrogenotrophic methanogenic activity was always higher than acetoclastic methanogenic activity, and the highest values were achieved in those biomasses with lower percentages of Methanosaeta. In sum, the combination of molecular tools with activity tests seems to be essential for a better characterization of anaerobic biomasses.     

Start-up and stabilization of an Anammox process from a non-acclimatized sludge in CSTR

Development of an Anammox (anaerobic ammonium oxidation) process using non-acclimatized sludge requires a long start-up period owing to the very slow growth rate of Anammox bacteria. This article addresses the issue of achieving a shorter start-up period for Anammox activity in a well-mixed continuously stirred tank reactor (CSTR) using non-acclimatized anaerobic sludge. Proper selection of enrichment conditions and low stirring speed of 30 ± 5 rpm resulted in a shorter start-up period (82 days). Activity tests revealed the microbial community structure of Anammox micro-granules. Ammonia-oxidizing bacteria (AOB) were found on the surface and on the outer most layers of granules while nitrite-oxidizing bacteria (NOB) and Anammox bacteria were present inside. Fine-tuning of influent NO₂ ⁻/NH₄ ⁺ ratio allowed Anammox activity to be maintained when mixed microbial populations were present. The maximum nitrogen removal rate achieved in the system was 0.216 kg N/(m³ day) with a maximum specific nitrogen removal rate of 0.434 g N/(g VSS day). During the study period, Anammox activity was not inhibited by pH changes and free ammonia toxicity.     

Ecophysiological responses of the euhalophyte Suaeda salsa to the interactive effects of salinity and nitrate availability

Effects of salinity and nitrate nitrogen (NO₃⁻-N) on ion accumulation and chlorophyll fluorescence were monitored for two populations of Suaeda salsa grown from seeds in a greenhouse experiment. One population inhabits the intertidal zone and the other occurs on inland saline soils. Ion contents in soils and in leaves of the two populations were also investigated in field. In the greenhouse, seedlings were exposed to a NaCl concentration of 0.6 and 35.1 ppt, with 0.1 or 5 mM NO₃⁻-N treatments for 20 days. The contents of Na⁺ and Cl⁻ were higher, but NO₃⁻ was lower in soils of the intertidal zone than at the inland site. In the field, ion concentrations and the estimated contribution of these ions to osmotic potential in leaves showed no difference between the two populations, except that the estimated contribution of Na⁺ to osmotic potential in leaves of the intertidal population was lower than that in the inland population. In the greenhouse, in contrast, the concentration of Cl⁻ was lower, but NO₃⁻ concentration and the estimated contribution of NO₃⁻ to osmotic potential were higher, in the leaves of plants from the intertidal zone. Salinity had no effect on the maximal efficiency of PSII photochemistry (Fv/Fm) and the actual PSII efficiency (ΦPSII). The results indicated that S. salsa from the intertidal zone was better able to regulate Cl⁻ to a lower level, and accumulate NO₃⁻ even with low soil NO₃⁻ concentrations. Tolerance of the PSII machinery to high salinity stress may be an important characteristic for the studied species supporting growth in highly saline environments.     

Influence of electron acceptor availability and microbial community structure on sedimentary methane oxidation in a boreal estuary

Methane is produced microbially in vast quantities in sediments throughout the world’s oceans. However, anaerobic oxidation of methane (AOM) provides a near-quantitative sink for the produced methane and is primarily responsible for preventing methane emissions from the oceans to the atmosphere. AOM is a complex microbial process that involves several different microbial groups and metabolic pathways. The role of different electron acceptors in AOM has been studied for decades, yet large uncertainties remain, especially in terms of understanding the processes in natural settings. This study reports whole-core incubation methane oxidation rates along an estuarine gradient ranging from near fresh water to brackish conditions, and investigates the potential role of different electron acceptors in AOM. Microbial community structure involved in different methane processes is also studied in the same estuarine system using high throughput sequencing tools. Methane oxidation in the sediments was active in three distinct depth layers throughout the studied transect, with total oxidation rates increasing seawards. We find extensive evidence of non-sulphate AOM throughout the transect. The highest absolute AOM rates were observed below the sulphate-methane transition zone (SMTZ), strongly implicating the role of alternative electron acceptors (most likely iron and manganese oxides). However, oxidation rates were ultimately limited by methane availability. ANME-2a/b were the most abundant microbial phyla associated with AOM throughout the study sites, followed by ANME-2d in much lower abundances. Similarly to oxidation rates, highest abundances of microbial groups commonly associated with AOM were found well below the SMTZ, further reinforcing the importance of non-sulphate AOM in this system.