Structure and distribution of nitrite-dependent anaerobic methane oxidation bacteria vary with water tables in Zoige peatlands

ABSTRACT The recently discovered nitrite-dependent anaerobic methane oxidation (n-damo) is an important methane sink in natural ecosystems performed by NC10 phylum bacteria. However, the effect of water table (WT) gradient due to global change on n-damo bacterial communities is not well studied in peatlands. Here, we analysed the vertical distribution (0–100 cm) of n-damo bacterial communities at three sites with different WTs of the Zoige peatlands in the Qinghai-Tibetan Plateau. Using an n-damo bacterial specific 16S rRNA gene clone library, we obtained 25 operational taxonomic units (OTUs) that could be divided into Groups A, B, C, D and E (dominated by A and B). The dominant group was Group B at the high (OTU14 and OTU20) and intermediate (OTU7 and OTU8) WT sites and Group A was dominant at the low WT site (OTU6 and OTU5). Using high-throughput sequencing, we observed that n-damo bacteria mainly distributed in subsurface soils (50–60 and 20–30 cm), and their relative abundances were higher at the low WT site than at the other two sites. In addition, we found that pH and nitrate were positively correlated with Group A, while total organic carbon, total nitrogen and ammonia were positively associated with Group B. Our study provides new insights into our understanding of the response of n-damo bacteria to WT gradient in peatlands, with important implications for global change.

Response mechanism of denitrifying anaerobic methane oxidation microorganisms to ammonia

Environmental contextDenitrifying anaerobic methane oxidation (DAMO) is a new process in wastewater treatment with the potential to provide cheap and sustainable development. To better apply this technology to the large scale, we studied the response mechanism of DAMO microorganisms to ammonia, the main form of nitrogen in the nitrogenous wastewater. The results can provide a theoretical basis for the stable and efficient operation of DAMO processes. AbstractThe dominant microorganisms in the denitrifying anaerobic methane oxidation (DAMO) process are primarily DAMO bacteria and DAMO archaea, which can simultaneously realise methane oxidation and denitrification. Ammonia is the primary form of nitrogen found in wastewater. This study focuses on a coexistence system that contains both DAMO bacteria and DAMO archaea (DAMO co-system). The short- and long-term effects of NH4+-N on the DAMO co-system were investigated at both the macro level (such as denitrification performance) and the micro level (such as microbial structure and community). Short-term experimental studies demonstrated that the safe concentration of ammonia for this system was 250mgNL−1. When the ammonia concentration was 500mgNL−1, the nitrogen removal efficiency was significantly inhibited. With an increase in concentration and an extension of time, the inhibitory effect of ammonia was enhanced. Long-term experimental studies showed that the nitrogen removal performance of DAMO was completely inhibited when the ammonia concentration reached 1000mgNL−1 and that ammonia had a toxic accumulation effect on the DAMO co-system. The results of the pH experimental study demonstrated that free ammonia (FA) was the limiting factor in the alkaline condition, while ionised NH4+ was the limiting factor in neutral and acidic conditions. Scanning electron microscopy (SEM) demonstrated that the microbes in the DAMO co-system shrank after short-term exposure and that the microorganisms shrank in the shape of polygons. High-throughput sequencing analysis demonstrated that the community structure of the DAMO co-system changed substantially, and the species diversity and abundance decreased distinctly after long-term inhibition. A genus analysis indicated that the reduction in Nitrospirae may be an internal reason for the decrease in the denitrification performance of the DAMO co-system.

Evidence for the Cooccurrence of Nitrite-Dependent Anaerobic Ammonium and Methane Oxidation Processes in a Flooded Paddy Field

ABSTRACTAnaerobic 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 N2g−1(dry weight) day−1and the potential n-damo rates varied from 0.2 to 2.1 nmol CO2g−1(dry weight) day−1in different layers of soil cores. Quantitative PCR showed that the abundance of anammox bacteria ranged from 1.0 × 105to 2.0 × 106copies g−1(dry weight) in different layers of soil cores and the abundance of n-damo bacteria varied from 3.8 × 105to 6.1 × 106copies g−1(dry weight). Phylogenetic analyses of the recovered 16S rRNA gene sequences showed that anammox bacteria affiliated with “CandidatusBrocadia” and “CandidatusKuenenia” and n-damo bacteria related to “CandidatusMethylomirabilis oxyfera” were present in the soil cores. It is estimated that a total loss of 50.7 g N m−2per 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 CH4m−2per 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.

Combined anaerobic ammonium and methane oxidation for nitrogen and methane removal

Anammox (anaerobic ammonium oxidation) is an environment-friendly and cost-efficient nitrogen-removal process currently applied to high-ammonium-loaded wastewaters such as anaerobic digester effluents. In these wastewaters, dissolved methane is also present and should be removed to prevent greenhouse gas emissions into the environment. Potentially, another recently discovered microbial pathway, n-damo (nitrite-dependent anaerobic methane oxidation) could be used for this purpose. In the present paper, we explore the feasibility of simultaneously removing methane and ammonium anaerobically, starting with granules from a full-scale anammox bioreactor. We describe the development of a co-culture of anammox and n-damo bacteria using a medium containing methane, ammonium and nitrite. The results are discussed in the context of other recent studies on the application of anaerobic methane- and ammonia-oxidizing bacteria for wastewater treatment.

Simultaneous Nitrite-Dependent Anaerobic Methane and Ammonium Oxidation Processes

ABSTRACTNitrite-dependent anaerobic oxidation of methane (n-damo) and ammonium (anammox) are two recently discovered processes in the nitrogen cycle that are catalyzed by n-damo bacteria, including “CandidatusMethylomirabilis oxyfera,” and anammox bacteria, respectively. The feasibility of coculturing anammox and n-damo bacteria is important for implementation in wastewater treatment systems that contain substantial amounts of both methane and ammonium. Here we tested this possible coexistence experimentally. To obtain such a coculture, ammonium was fed to a stable enrichment culture of n-damo bacteria that still contained some residual anammox bacteria. The ammonium supplied to the reactor was consumed rapidly and could be gradually increased from 1 to 20 mM/day. The enriched coculture was monitored by fluorescencein situhybridization and 16S rRNA andpmoAgene clone libraries and activity measurements. After 161 days, a coculture with about equal amounts of n-damo and anammox bacteria was established that converted nitrite at a rate of 0.1 kg-N/m3/day (17.2 mmol day−1). This indicated that the application of such a coculture for nitrogen removal may be feasible in the near future.