Methanogenic Community Structure Research Articles

Stochastic processes drive the diversity and composition of methanogenic community in a natural mangrove ecosystem

Methanogens are considered to be crucial components of mangrove ecosystems with ecological significance. However, understanding the assembly processes of methanogenic communities in mangrove ecosystems is relatively insufficient. In the current study, a natural mangrove in a protection zone was employed to investigate the diversity and assembly processes of methanogenic community by using amplicon high-throughput sequencing, a null model as well as a neutral community model. The results showed that methanogenic community in mangrove sediments were highly diverse, with the predominance of methylotrophic Methanolobus, and hydrogenotrophic Methanogenium, Methanospirillum. The diversity, composition, and gene abundance varied obviously across the mangrove sampling sites, whereas the measured environmental variables exhibited a negligible effect. Null model showed that the values of beta nearest-taxon index were mostly between −2 and 2, indicating that stochastic processes contributed more than deterministic processes driving the methanogenic community assembly in mangrove sediments. Neutral community model revealed a high estimated migration rate of methanogenic community, further substantiating the significance of stochastic processes. Among the keystone species identified in network analysis, methanogens affiliated to hydrogenotrophic Methanospirillum may have a crucial role in maintaining the structure and function of methanogenic community. Notably, these keystone species were almost unaffected by measured environmental factors, indicating that the methanogenic community in mangrove sediments is more likely to be affected by stochastic processes. This study deepens the understanding of the diversity and assembly of methanogenic community in mangrove sediments, and provides clues to maintain mangrove ecosystem functioning.

Composition of the rumen archaeal community of growing camels fed different concentrate levels.

Understanding the rumen fermentation and methanogenic community in camels fed intensively is critical for optimizing rumen fermentation, improving feed efficiency, and lowering methane emissions. Using Illumina MiSeq sequencing, quantitative real-time PCR, and high-performance liquid chromatography, this study evaluates the influence of different concentrate supplement levels in the diet on rumen fermentation as well as the diversity and structure of the rumen methanogenic community for growing dromedary camels. Twelve growing camels were divided into three groups and given three levels of concentrate supplement, 0.7% (C1), 1% (C2), and 1.3% (C3) based on their body weight. All animals were fed alfalfa hay ad libitum. The levels of total volatile fatty acid, rumen ammonia, and methanogen copy number were unaffected by the supplementation level. Increasing the concentrate supplement level increased the proportion of propionic acid while decreasing the proportion of acetic acid. Increasing the level of concentrate in the diet had no effect on alpha diversity metrics or beta diversity of rumen methanogens. Methanobrevibacter and Methanosphaera predominated the methanogenic community and were declined as concentrate supplement level increased. This study sheds new light on the effect of concentrate supplement level in growing camels' diet on rumen fermentation and methanogenic community, which could help in the development of a strategy that aimed to reduce methane emissions and enhance feed efficiency.

Differences in Methanogenic Pathways and Communities in Paddy Soils Under Three Typical Cropping Modes

AbstractThe methane (CH4) production process in paddy fields varies depending on different cropping modes. However, there is limited knowledge on the changes in anaerobically produced CH4 isotopic ratios (δ13CH4), the methanogenic pathways, and the dominant communities of methanogens in paddy soils under different modes. To address this, we conducted experiments using anaerobic incubation methods, stable carbon isotope fractionation through inhibition studies with fluoromethane, and high‐throughput sequencing. These methods allowed us to measure the CH4 production potential (MPP), the relative contribution of acetoclastic methanogenesis to CH4 production (fac), and the composition of the methanogen community in paddy soils under three typical cropping modes: Rice‐Wheat (RW), Rice‐Fallow (RF), and Double‐Rice (DR) in China. The results showed that MPP was 30.7 μg CH4 g−1 d−1 in DR soil, around 57% and 66% higher than that in RW and RF soils, respectively, possibly due to the lower pH, clay content, and higher abundance of the mcrA gene. Moreover, RF soil had the highest value of produced δ13CH4 (−43.9‰) but the lowest value of produced δ13CO2 (−26.3‰). Based on the carbon isotope fractionation associated with methanogenesis via H2/CO2 reduction (1.049–1.062), the values of fac estimated in the RF soil (80%–98%) were much higher than that in the RW (39%–60%) and DR soils (52%–75%). This could be supported by the finding showing that Methanosarcina, the acetoclastic methanogens, were dominant in RF soil, while Methanosarcina and Methanobacterium (the hydrogenotrophic methanogens) dominated in RW and DR soils. Redundancy analysis revealed that the community structure of methanogens was significantly affected by soil pH. The findings suggest that differences in the abundance and composition of methanogens, possibly driven by soil pH, play a key role in regulating methanogenesis in the paddy soils, and further provide valuable insights into the process of CH4 production in different cropping modes.

Water table level controls methanogenic and methanotrophic communities and methane emissions in a Sphagnum-dominated peatland.

Peatlands are important sources of the greenhouse gas methane emissions equipoised by methanogens and methanotrophs. However, knowledge about how microbial functional groups associated with methane production and oxidation respond to water table fluctuations has been limited to date. Here, methane-related microbial communities and the potentials of methane production and oxidation were determined along sectioned peat layers in a subalpine peatland across four Sphagnum-dominated sites with different water table levels. Methane fluxes were also monitored at these sites. The results showed that mcrA gene copies for methanogens were the highest in the 10- to 15-cm peat layer, which was also characterized by the maximum potential methane production (24.53 ± 1.83 nmol/g/h). Copy numbers of the pmoA gene for type Ia and Ib methanotrophs were enriched in the 0-5 cm peat layer with the highest potential methane oxidation (43.09 ± 3.44 nmol/g/h). For the type II methanotrophs, the pmoA gene copies were higher in the 10- to 15-cm peat layer. Hydrogenotrophic methanogens and type II methanotrophs dominated the methane functional groups. Deterministic process contributed more to methanogenic and methanotrophic community assemblages in comparison with stochastic process. The level of water table significantly shaped methanogenic and methanotrophic community structures and regulated methane fluxes. Compared with vascular plants, Sphagnum mosses significantly reduced the methane emissions in peatlands. Collectively, these findings enhance a comprehensive understanding of the effect of the water table level on methane functional groups, with consequential implications for reducing methane emissions within peatland ecosystems.IMPORTANCEThe water table level is recognized as a critical factor in regulating methane emissions, which are largely dependent on the balance of methanogens and methanotrophs. Previous studies on peat methane emissions have been mostly focused on spatial-temporal variations and the relationship with meteorological conditions. However, the role of the water table level in methane emissions remains unknown. In this work, four representative microhabitats along a water table gradient in a Sphagnum-dominated peatland were sampled to gain an insight into methane functional communities and methane emissions as affected by the water table level. The changes in methane-related microbial community structure and assembly were used to characterize the response to the water table level. This study improves the understanding of the changes in methane-related microbial communities and methane emissions with water table levels in peatlands.

Methanogenic and methanotrophic communities determine lower CH4 fluxes in a subtropical paddy field under long-term elevated CO2

Clarifying the effects of elevated CO2 concentration (e[CO2]) on CH4 emissions from paddy fields and its mechanisms is a crucial part of the research on agricultural systems in response to global climate change. However, the response of CH4 fluxes from rice fields to long-term e[CO2] (e[CO2] duration >10 years) and its microbial mechanism is still lacking. In this study, we used a long-term free-air CO2 enrichment experiment to examine the relationship between CH4 fluxes and the methanogenic and methanotrophic consortia under long- and short-term e[CO2]. We demonstrated that contrary to the effect of short-term e[CO2], long-term e[CO2] decreased CH4 fluxes. This may be associated with the reduction of methanogenic abundance and the increase of methanotrophic abundance under long-term e[CO2]. In addition, long-term e[CO2] also changed the community structure and composition of methanogens and methanotrophs compared with short-term e[CO2]. Partial least squares path modeling analysis showed that long-term e[CO2] also could affect the abundance and composition of methanogens and methanotrophs indirectly by influencing soil physical and chemical properties, thereby ultimately altering CH4 fluxes in paddy soils. These findings suggest that current estimates of short-term e[CO2]-induced CH4 fluxes from paddy fields may be overestimated. Therefore, a comprehensive assessment of climate‑carbon cycle feedbacks may need to consider the microbial regulation of CH4 production and oxidation processes in paddy ecosystems under long-term e[CO2].

Conversion of natural coastal wetlands to mariculture ponds dramatically decreased methane production by reducing substrate availability

Coastal wetlands are increasingly being converted into aquaculture ponds to meet growing global demand for fish protein. Coastal wetlands conversion has been predicted to result in significant carbon (C) emissions; however, a mechanistic understanding of the effects of coastal wetland conversion on soil’s capacity to produce greenhouse gases remains lacking. Here, integrated biogeochemical investigations on methanogenic substrates, community structures, and activities were conducted in a coastal Spartina alterniflora saltmarsh and three saltmarsh-converted mariculture ponds aged 6, 13, and 20 years. Saltmarsh conversion into mariculture ponds decreased CH4 production potential from 353 to 16.3–78.3 µg CH4 kg−1 d−1. The concentrations of dissolved organic C and non-competitive methanogenic substrate, trimethylamine, were reduced by 84.8% and 79.7%, respectively, whereas methanogens abundance decreased by 43.7%, probably due to the decreased C input following conversion. Among the ponds, CH4 production potential, methanogenic substrates (acetate and trimethylamine), and methanogen abundance decreased with conversion chronosequence. However, the dominant methanogen group did not shift after land conversion, and the potential methylamine-utilizing Methanosarcinaceae accounted for 86.5% and 85.3–89.7% of the total populations in the S. alterniflora saltmarsh and mariculture ponds, respectively, implying that methylotrophic methanogenesis was the predominant pathway of CH4 production in both ecosystems. The results indicated that the conversion of natural coastal saltmarsh to mariculture ponds decreased CH4 production by reducing substrate availability and methanogen abundance, and CH4 production potential in mariculture ponds was more efficiently suppressed with conversion chronosequence.

Response of methanogenic community and their activity to temperature rise in alpine swamp meadow at different water level of the permafrost wetland on Qinghai-Tibet Plateau.

Wetlands are an important source of atmospheric methane (CH4) and are sensitive to global climate change. Alpine swamp meadows, accounting for ~50% of the natural wetlands on the Qinghai-Tibet Plateau, were considered one of the most important ecosystems. Methanogens are important functional microbes that perform the methane producing process. However, the response of methanogenic community and the main pathways of CH4 production to temperature rise remains unknown in alpine swamp meadow at different water level in permafrost wetlands. In this study, we investigated the response of soil CH4 production and the shift of methanogenic community to temperature rise in the alpine swamp meadow soil samples with different water levels collected from the Qinghai-Tibet Plateau through anaerobic incubation at 5°C, 15°C and 25°C. The results showed that the CH4 contents increased with increasing incubation temperature, and were 5-10 times higher at the high water level sites (GHM1 and GHM2) than that at the low water level site (GHM3). For the high water level sites (GHM1 and GHM2), the change of incubation temperatures had little effect on the methanogenic community structure. Methanotrichaceae (32.44-65.46%), Methanobacteriaceae (19.30-58.86%) and Methanosarcinaceae (3.22-21.24%) were the dominant methanogen groups, with the abundance of Methanotrichaceae and Methanosarcinaceae having a significant positive correlation with CH4 production (p < 0.01). For the low water level site (GHM3), the methanogenic community structure changed greatly at 25°C. The Methanobacteriaceae (59.65-77.33%) was the dominant methanogen group at 5°C and 15°C; In contrast, the Methanosarcinaceae (69.29%) dominated at 25°C, and its abundance showed a significant positive correlation with CH4 production (p < 0.05). Collectively, these findings enhance the understanding of methanogenic community structures and CH4 production in permafrost wetlands with different water levels during the warming process.

Variations of methane fluxes and methane microbial community composition with soil depth in the riparian buffer zone of a sponge city park

Riparian buffers benefit both natural and man-made ecosystems by preventing soil erosion, retaining soil nutrients, and filtering pollutants. Nevertheless, the relationship between vertical methane fluxes, soil carbon, and methane microbial communities in riparian buffers remains unclear. This study examined vertical methane fluxes, soil carbon, and methane microbial communities in three different soil depths (0–5 cm, 5–10 cm, and 10–15 cm) within a riparian buffer of a Sponge City Park for one year. Structural equation model (SEM) results demonstrated that vertical methane fluxes varied with soil depths (λ = −0.37) and were primarily regulated by methanogenic community structure (λ = 0.78). Notably, mathematical regression results proposed that mcrA/pmoA ratio (R2 = 0.8) and methanogenic alpha diversity/methanotrophic alpha diversity ratio (R2 = 0.8) could serve as valid predictors of vertical variation in methane fluxes in the riparian buffer of urban river. These findings suggest that vertical variation of methane fluxes in riparian buffer soils is mainly influenced by carbon inputs and methane microbial abundance and community diversity. The study's results quantitatively the relationship between methane fluxes in riparian buffer soils and abiotic and biotic factors in the vertical direction, therefore contributing to the further development of mathematical models of soil methane emissions.

A joint role of iron oxide and temperature for methane production and methanogenic community in paddy soils

Microbial methanogenesis in paddy soils contributes approximately one-fifth of global anthropogenic methane (CH4) release, creating severe negative climate feedback. The dynamics of iron oxides in flooded paddy fields, as well as temperature changes, have an impact on CH4 production. However, the relationship between the two, as well as their interactive mechanisms in influencing CH4 production and microbial communities in paddy soils, is not yet clear. Therefore, we investigated the interactive effects of temperature (15, 25 and 35 °C) and iron oxide (ferrihydrite) on CH4 production and methanogenic community structure in two Chinese paddy soils, one subtropical and one temperate. We characterized shifts in microbial communities using high-throughput sequencing of bacteria, archaea and methanogenic mcrA genes following an anaerobic incubation for 90 days. Our results showed that temperature significantly promoted Fe reduction in paddy soils, and both together regulated CH4 production by reducing the number of methanogens. Additionally, the temperature sensitivity of methanogenesis was higher in the temperate than in the subtropical paddy soil. We also demonstrated that ferrihydrite can inhibit methanogenesis by reducing the relative abundance of Methanosarcinales and altering the community patterns of methanogens in these paddy soils. Likewise, increases in temperature changes the relative abundance of Methanosarcinales and Methanobacteriales, promoting methanogenesis. Overall, our results provide new insights into the role of iron oxides and temperature in regulating greenhouse gas emissions from paddy soils.

Effect of extreme pH conditions on methanogenesis: Methanogen metabolism and community structure

The control of pH is effective for inhibiting methanogenesis in the chain elongation fermentation (CEF) system. However, obscure conclusions exist especially with regard to the underlying mechanism. This study comprehensively explored the responses of methanogenesis in granular sludge at various pH levels, ranging from 4.0 to 10.0, from multiple aspects including methane production, methanogenesis pathway, microbial community structure, energy metabolism and electron transport. Results demonstrated that compared with that at pH 7.0, pH at 4.0, 5.5, 8.5 and 10.0 triggered a 100%, 71.7%, 23.8% and 92.1% suppression on methanogenesis by the end of 3 cycles lasting 21 days. This might be explained by the remarkably inhibited metabolic pathways and intracellular regulations. To be more specific, extreme pH conditions decreased the abundance of the acetoclastic methanogens. However, obligate hydrogenotrophic and facultative acetolactic/hydrogenotrophic methanogens were significantly enriched by 16.9%-19.5 fold. pH stress reduced the gene abundance and/or activity of most enzymes involved in methanogenesis such as acetate kinase (by 81.1%–93.1%), formylmethanofuran dehydrogenase (by 10.9%–54.0%) and tetrahydromethanopterin S-methyltransferase (by 9.3%–41.5%). Additionally, pH stress suppressed electron transport via improper electron carriers and decreased electron amount as evidenced by 46.3%–70.4% reduced coenzyme F420 content and diminished abundance of CO dehydrogenase (by 15.5%–70.5%) and NADH:ubiquinone reductase (by 20.2%–94.5%). pH stress also regulated energy metabolism with inhibited ATP synthesis (e.g., ATP citrate synthase level reduced by 20.1%–95.3%). Interestingly, the protein and carbohydrate content secreted in EPS failed to show consistent responses to acidic and alkaline conditions. Specifically, when compared with pH 7.0, the acidic condition remarkably reduced the levels of total EPS and EPS protein while both levels were enhanced in the alkaline condition. However, the EPS carbohydrate content at pH 4.0 and 10.0 both decreased. This study is expected to promote the understanding of the pH control-induced methanogenesis inhibition in the CEF system.

Competitive Reactions during Ethanol Chain Elongation Were Temporarily Suppressed by Increasing Hydrogen Partial Pressure through Methanogenesis Inhibition.

Organic waste streams can be converted into high-value platform chemicals such as medium-chain carboxylic acids (MCCAs) using mixed microbial communities via chain elongation. However, the heterogeneity of waste streams and the use of complex microbial communities can lead to undesirable reactions, thus decreasing process efficiency. We explored suppressing excessive ethanol oxidation to acetate (EEO) by increasing the hydrogen partial pressure (PH2) through hydrogenotrophic methanogenesis inhibition by periodically adding 2-bromoethanesulfonate (2-BES) to an MCCA-producing bioreactor to reach 10 mM of 2-BES upon addition. The bioreactor was fed with pretreated food waste and brewery waste containing high concentrations of short-chain carboxylic acids and ethanol, respectively. While 2-BES addition initially reduced EEO, some methanogens (Methanobrevibacter spp.) persisted and resistant populations were selected over time. Besides changing the methanogenic community structure, adding 2-BES also changed the bacterial community structure due to its impact on PH2. While we demonstrated that PH2 could be manipulated using 2-BES to control EEO, methods that do not require the addition of a chemical inhibitor should be explored to maintain optimum PH2 for long-term suppression of EEO.

Interactions among heavy metals and methane-metabolizing microorganisms and their effects on methane emissions in Dajiuhu peatland.

Peatlands play a crucial role in mediating the emissions of methane through active biogeochemical cycling of accumulated carbon driven by methane-metabolizing microorganisms; meanwhile, they serve as vital archives of atmospheric heavy metal deposition. Despite many edaphic factors confirmed as determinants to modulate the structure of methanotrophic and methanogenic communities, recognition of interactions among them is limited. In this study, peat soils were collected from Dajiuhu peatland to assess the presence of heavy metals, and methanotrophs and methanogens were investigated via high-throughput sequencing for functional genes mcrA and pmoA. Further analyses of the correlations between methane-related functional groups were conducted. The results demonstrated that both methane-metabolizing microorganisms and heavy metals have prominent vertical heterogeneity upward and downward along the depth of 20cm. Pb, Cd, and Hg strongly correlated with methanotrophs and methanogens across all seasons and depths, serving as forceful factors in structural variations of methanogenic and methanotrophic communities. Particularly, Pb, Cd, and Hg were identified as excessive elements in Dajiuhu peatland. Furthermore, seasonal variations of networks among methane-related functional groups and environmental factors significantly affected the changes of methane fluxes across different seasons. Concretely, the complicated interactions were detrimental to methane emissions in the Dajiuhu peatland, leading to the minimum methane emissions in winter. Our study identified the key heavy metals affecting the composition of methane-metabolizing microorganisms and linkages between seasonal variations of methane emissions and interaction among heavy metals and methane-metabolizing microorganisms, which provided much new reference and theoretical basis for integrated management of natural peatlands.

Aquaculture drastically increases methane production by favoring acetoclastic rather than hydrogenotrophic methanogenesis in shrimp pond sediments

Emissions of methane (CH4), a major greenhouse gas, should be cut by at least 30% by 2030 according to the last Conference of the Parties, CoP26. Aquaculture pond is a major CH4 emitter, yet the microbial mechanisms ruling methanogenesis by degradation of organic matter in sediments remain unclear. In particular, the respective roles of hydrogenotrophic and acetoclastic methanogenesis, and the impact of aquaculture farming practices are unknown. We studied methanogenesis in the surface sediments from a freshwater and an oligohaline pond before, during, and after shrimp farming. Hydrogenotrophic and acetoclastic contributions were distinguished by acetoclastic inhibition with methylfluoride (CH3F), and by 13C-analysis of CO2 and CH4. We also monitored the methanogenic community structure, dissolved organic carbon (DOC) levels, carbon to nitrogen (C/N) ratios, and humification indices derived from Fourier transform infrared spectroscopy. The results reveal that aquaculture farming practices increased methanogenesis rates, and these increases were explained by higher levels of DOC and lower C/N ratios during farming. Of the total methane produced, 51%–78% was by hydrogenotrophic methanogenesis. However, the total methane contribution from acetoclastic methanogenesis increased from approximately 22% before farming to approximately 45% during and after farming, with a decreasing isotope fractionation factor αc and an increasing relative abundance of Methanosaeta acetoclastic methanogen. All humification indices decreased during and after farming compared to before farming due to the input of polysaccharide-rich aquafeed. The close relationship between the humification indices and methanogenesis pathways indicates that the changes in sediment substrate quality drove the variation in the methanogenesis pathways. Increases in salinity decreased the methanogenesis rates but did not change the methanogenesis pathways. Overall, our findings reveal that aquaculture farming practices increase methanogenesis rates and favor acetoclastic over hydrogenotrophic methanogenesis, and that adjusting shrimp diets, increasing salinity, and removing residual aquafeed could reduce methanogenesis.

Effect of short-term warming and drought on the methanogenic communities in degraded peatlands in Zoige Plateau

Peatlands in Qinghai-Tibetan are degrading with climate change and human activities. Peatland degradation and climate change affect methane emissions. Methanogens are key functional microbes during methane production; however, knowledge of methanogens in degraded peatlands is lacking. Here, we investigated the effects of short-term (1 year) warming (OTC), drought (20%), and their combination on methanogens in the degraded peatlands on the Zoige Plateau of China via qPCR and clone library analysis. The results showed that Methanomicrobiales and Methanobacteriales were predominant in all the treatments. Non-metric multidimensional scaling (NMDS) and PERMANOVA analyses showed that the methanogenic community structure among the climate change treatments was not significantly different. The relative abundance of methanogen communities showed insignificant variation among the climate change treatments. The copy number and Shannon diversity of methanogens were significantly different within the climate change treatments, and drought significantly decreased the copy number of methanogens when compared to the control. The Redundancy analysis (RDA) results and correlation analysis showed that the environmental variables measured had no significant effect on methanogenic community structure and Shannon diversity. These results indicate that methanogens are insensitive to short-term climate change in degraded peatlands. This study provides insight into methane emissions from the Zoige Plateau peatlands by focusing on the possible responses of the methanogens to climate-driven changes.

Densification pretreatment triggers efficient methanogenic performance and robust microbial community during anaerobic digestion of corn stover

The recalcitrant characteristics of lignocellulosic waste and difficulties in biomass transportation and storage severely limit bioenergy production through anaerobic digestion (AD). In this study, Densifying Lignocellulosic biomass with Chemicals (DLC) pretreatment was developed to address these issues. The results showed that DLC treated corn stover (CS) reached a cumulative methane yield of as high as 224.30 mL/g VS (Volatile Solids), which was 59.27 % higher than that of un-treated. The reduced scum formation in the reactor, increased components consumption of solid phase, and higher organic biodegradability of liquid phase in AD of DLC treated CS enhanced methane yield. Microbial analysis indicated that DLC pretreatment affected the bacterial and methanogenic community structure, and a co-network with Comamonas and Methanobacterium, etc. as hub microbes was constructed. This study proposed a promising technology that could be potentially applied to industrial AD of lignocellulosic biomass.

Impacts of cyanobacterial biomass and nitrate nitrogen on methanogens in eutrophic lakes

Methanogenesis is a key process in carbon cycling in lacustrine ecosystems. Knowledge of the methanogenic pathway is important for creating mechanistic models as well as predicting methane emissions. Due to low concentrations of methyl substrates in freshwater lakes, the proportion of methylotrophic methanogenesis is believed to be negligible in such environments. However, the high abundance of methylotrophic methanogens previously detected in Dianchi Lake suggests that methylotrophic methanogenesis may be underestimated in eutrophic lakes, whereas their influencing factors and mechanisms are not yet clear. In this study, the effects of cyanobacteria biomass (CB) or/and nitrate nitrogen on methanogenesis, especially methylotrophic pathway, in eutrophic lakes were investigated using microcosm simulation experiments combined with chemical analysis and high-throughput sequencing techniques. The results showed that either CB or nitrate nitrogen had significant effects on methane flux, the archaeal diversity and community structure of methanogens. Functional prediction, together with the result of chemical analysis, revealed that CB could promote methylotrophic methanogenesis by providing methyl organic substrates, while nitrate nitrogen increased the relative abundance of obligate methylotrophic methanogens by competitively inhibiting the other two methanogenic pathways. In eutrophic lake where both CB and nitrate present at a high concentration, methylotrophic methanogenesis could play a much more important role than previously believed.

Polyaniline-coated conductive media promotes direct interspecies electrons transfer (DIET) and kinetics enhancement of low-strength wastewater treatment in anaerobic fluidized bed membrane bioreactor (AFMBR)

Polyaniline (PANI) was applied as coating materials to develop conductive surface on polyethylene terephthalate (PET) bead and polyvinylidene fluoride (PVDF) pellet termed as C-PET and C-PVDF as fluidized media in anaerobic fluidized bed membrane bioreactor (AFMBR). Parallel operation with AFMBRs showed that the fouling rate was lower for the C-PET and C-PVDF media than uncoated ones to scour membrane, and this was more pronounced as the organic loading rate was higher. Methane production rate was about 50% faster for the C-PET and C-PVDF media, and their use in the AFMBR system promoted methane yield by 14 to 190% higher than uncoated ones. 16S rRNA gene analysis revealed predictable results for methanogenic archaeal community structure (high abundance in Methanothrix), in line with the reactor performance observed, and suggestive of known Direct Interspecies Electron Transfer (DIET) metabolism. The bacterial analysis revealed common syntrophic species typically seen in anaerobic reactors, however, few known DIET species were also found, suggesting that more works are needed to elucidate pathways and syntrophies which may be activated by the PANI coating. Our results supported that conductive polymeric fluidized media should have great potential to promote kinetic enhancement in AFMBR treating low-strength wastewater.

Methanogenic community linked to organic acids fermentation from root exudates are affected by rice intensification in rotational soil systems

Rice paddy soils are an important biogenic source of methane, a relevant greenhouse gas. Rice rotation with upland crops and pastures affects hydrolytic and fermentative bacteria and methanogenic archaea by sequential exposition to oxic and anoxic conditions. There are several ways to reduce methane emissions from rice paddy soils. Here we examine the effect of intensification in rice rotations with upland crops upon the microbial community structure and methanogenesis when dicarboxylic acids exudated by rice root were amended in microcosms assays. Soils under rotations rice-pasture, rice-soybean and continuous rice, with the last two more intensive systems recently installed in the field experiment, were sampled. Amplicon sequencing of 16S rRNA gene analysis showed that the rotation system was a main driver of the microbial community structure, explaining 33%, 38% and 55% of the differences in the structure of Bacteria, Archaea and methanogens, respectively. The density of mcrA gene copies was significantly higher in continuous rice soil than in other soils, and the relative abundance of methanogenic archaea was 33% for rice monoculture, whereas represented 15% and 14% for the rice-pasture and rice-soybean soils, respectively. The incubation of soils with tartrate and succinate confirmed functional differences among soils since rice monoculture showed similar or higher methane production and significantly less acetate and propionate accumulation than other soils. The T-RFLP analysis of mcrA gene in soils and incubated soils revealed that Rice Cluster I increased after incubation in all rotational soils, whereas Methanosarcinaceae and Methanobacteriaceae remained relevant after incubation. Furthermore, a more stable community of methanogenic archaea was established in soil under continuous rice, since T-RF profiles of soils and incubated soils with dicarboxylic acids grouped together with 62% similarity, while communities from other rotational soils experimented a great shift after incubation with these substrates. Altogether, these results showed that the conversion of rice-pasture rotational fields to a more intensive rice crop production strongly impacts the methanogenic community structure and their potential for methane emission.

Changes in sediment methanogenic archaea community structure and methane production potential following conversion of coastal marsh to aquaculture ponds

Widespread conversion of coastal wetlands into aquaculture ponds in coastal region often results in degradation of the wetland ecosystems, but its effects on sediment's potential to produce greenhouse gases remain unclear. Using field sampling, incubation experiments and molecular analysis, we studied the sediment CH4 production potential and the relevant microbial communities in a brackish marsh and the nearby aquaculture ponds in the Min River Estuary in southeastern China. Sediment CH4 production potential was higher in the summer and autumn months than in spring and winter months, and it was significantly correlated with sediment carbon content among all environmental variables. The mean sediment CH4 production potential in the aquaculture ponds (20.1 ng g−1 d−1) was significantly lower than that in the marsh (45.2 ng g−1 d−1). While Methanobacterium dominated in both habitats (41–59%), the overall composition of sediment methanogenic archaea communities differed significantly between the two habitats (p < 0.05) and methanogenic archaea alpha diversity was lower in the aquaculture ponds (p < 0.01). Network analysis revealed that interactions between sediment methanogenic archaea were much weaker in the ponds than in the marsh. Overall, these findings suggest that conversion of marsh land to aquaculture ponds significantly altered the sediment methanogenic archaea community structure and diversity and lowered the sediment's capacity to produce CH4.

Methanogenesis pathways of methanogens and their responses to substrates and temperature in sediments from the South Yellow Sea

Although coastal sediments are major contributors to the production of atmospheric methane, the effects of environmental conditions on methanogenesis and the community of methanogenic archaea are not well understood. Here, we investigated the methanogenesis pathways in nearshore and offshore sediments from the South Yellow Sea (SYS). Moreover, the effects of the supply of methanogenic substrates (H2/CO2, acetate, trimethylamine (TMA), and methanol) and temperature on methanogenesis and the community of methanogenic archaea were further determined. Methylotrophic, hydrogenotrophic and acetotrophic methanogenesis were found to be responsible for biogenic methane production in nearshore sediments. In the offshore sediments, methylotrophic methanogenesis was the predominant methanogenic pathway. The changes in methanogenic community structure under different substrate amendments were characterized. Lower diversities were detected in substrate-amended samples with methanogenic activity. Hydrogenotrophic Methanogenium, multitrophic Methanosarcina, methylotrophic Methanococcoide, Methanococcoide or methylotrophic Methanolobus were dominant in H2/CO2-, acetate-, TMA- and methanol-amended sediment slurries, respectively. PCoA showed that the methanogen community in H2/CO2 and acetate amendments exhibited greater differences than those in other treatments. Lower temperature (10 °C) limits hydrogenotrophic and acetoclastic methanogenesis, but methylotrophic methanogenesis is much less affected. The response of methanogen diversity to the incubation temperature varied among the different substrate-amended slurries. The multitrophic methanogen Methanosarcina became increasingly abundant in H2/CO2− and acetate-amended sediment slurries when the temperature increased from 10 to 30 °C.