The Selenoproteome as a Dynamic Response Mechanism to Oxidative Stress in Hydrogenotrophic Methanogenic Communities.

Methanogenesis is a critical process in the carbon cycle that is applied industrially in anaerobic digestion and biogas production. While naturally occurring in diverse environments, methanogenesis requires anaerobic and reduced conditions, although varying degrees of oxygen tolerance have been described. Microaeration is suggested as the next step to increase methane production and improve hydrolysis in digestion processes; therefore, a deeper understanding of the methanogenic response to oxygen stress is needed. To explore the drivers of oxygen tolerance in methanogenesis, two parallel enrichments were performed under the addition of H2/CO2 in an environment without reducing agents and in a redox-buffered environment by adding redox mediator 9,10-anthraquinone-2,7-disulfonate disodium. The cellular response to oxidative conditions is mapped using proteomic analysis. The resulting community showed remarkable tolerance to high-redox environments and was unperturbed in its methane production. Next to the expression of pathways to mitigate reactive oxygen species, the higher redox potential environment showed an increased presence of selenocysteine and selenium-associated pathways. By including sulfur-to-selenium mass shifts in a proteomic database search, we provide the first evidence of the dynamic and large-scale incorporation of selenocysteine as a response to oxidative stress in hydrogenotrophic methanogenesis and the presence of a dynamic selenoproteome.

Anaerobic dihydrogen consumption of nutrient-limited aquifer sediment microbial communities examined by stable isotope analysis.

The biogeochemical consequences of dihydrogen (H2) underground storage in porous aquifers are poorly understood. Here, the effects of nutrient limitations on anaerobic H2 oxidation of an aquifer microbial community in sediment microcosms were determined in order to evaluate possible responses to high H2 partial pressures. Hydrogen isotope analyses of H2 yielded isotope depletion in all biotic setups indicating microbial H2 consumption. Carbon isotope analyses of carbon dioxide (CO2) showed isotope enrichment in all H2-supplemented biotic setups indicating H2-dependent consumption of CO2 by methanogens or homoacetogens. Homoacetogenesis was indicated by the detection of acetate and formate. Consumption of CO2 and H2 varied along the differently nutrient-amended setups, as did the onset of methane production. Plotting carbon against hydrogen isotope signatures of CH4 indicated that CH4 was produced hydrogenotrophically and fermentatively. The putative hydrogenotrophic Methanobacterium sp. was the dominant methanogen. Most abundant phylotypes belonged to typical ferric iron reducers, indicating that besides CO2, Fe(III) was an important electron acceptor. In summary, our study provides evidence for the adaptability of subsurface microbial communities under different nutrient-deficient conditions to elevated H2 partial pressures.

Effect of iron sources on methane production and phosphorous transformation in an anaerobic digestion system of waste activated sludge.

The iron materials are commonly employed to enhance resource recovery from waste activated sludge through anaerobic digestion (AD). The influence of different iron sources, such as Fe2O3, Fe3O4, and FeCl3 on methane production and phosphorus transformation in AD systems with thermal hydrolyzed sludge as the substrate was assessed in this study. The results indicated that iron oxides effectively promote methane yield and methane production rate in AD systems, resulting in a maximum increase in methane production by 1.6 times. Soluble FeCl3 facilitated the removal of 92.3% of phosphorus from the supernatant through the formation of recoverable precipitates in the sludge. The introduction of iron led to an increase in the abundance of bacteria responsible for hydrolysis and hydrogenotrophic methanogenesis. However, the enrichment of microbial communities varied depending on the specific irons used. This study provides support for AD systems that recover phosphorus and produce methane efficiently from waste sludge.

Enhancing methane production and interspecies electron transfer of anaerobic granular sludge by the immobilization of magnetic biochar.

Supplementation of conductive materials has been proved to be a promising approach for enhancing microbial interspecies electron transfer (IET) in anaerobic digestion systems. In this study, magnetic bamboo-based biochar was prepared at temperatures of 400-800 °C via a ball milling/carbonization method, and it immobilized in mature anaerobic granular sludge (AGS) aimed to enhance methane production by improving the IET process between syntrophic microbial communities in the AGS. Results showed that the AGS with magnetic biochar immobilization demonstrated increased glucotrophic and acetotrophic methane production by 69.54-77.56 % and 39.96-54.92 %, respectively. Magnetic biochar prepared at 800 °C with a relatively higher Fe content (0.37 g/g magnetic biochar) displayed a stronger electron charge/discharge capacity (36.66 F/g), and its immobilization into AGS promoted methane production most. The conductivity of AGS increased by 52.13-87.32 % after incorporating magnetic biochar. Furthermore, the extracellular polymeric substance (EPS) of AGS showed an increased capacitance and decreased electron transfer resistance possibly due to the binding of magnetic biochar and more riboflavin secretion in EPS, which could contribute to the accelerated IET process in the inner AGS. In addition, the immobilization of magnetic biochar could promote the production of volatile fatty acids by 15.36-22.50 %. All these improvements may jointly lead to the enhanced methane production capacity of AGS. This study provided a fundamental understanding of the role of incorporated magnetic biochar in AGS in promoting anaerobic digestion performance.

Cattle manure hydrochar posed a higher efficiency in elevating tomato productivity and decreasing greenhouse gas emissions than plant straw hydrochar in a coastal soil.

Rehabilitation of degraded soil health using high-performance and sustainable measures are urgently required for restoring soil primary productivity and mitigating greenhouse gas (GHG) emission of coastal ecosystems. However, the effect of livestock manure derived hydrochar on GHG emission and plant productivity in the coastal salt-affected soils, one of blue carbon (C) ecosystems, was poorly understood. Therefore, a cattle manure hydrochar (CHC) produced at 220 °C was prepared to explore its effects and mechanisms on CH4 and N2O emissions and tomato growth and fruit quality in a coastal soil in comparison with corresponding hydrochars derived from plant straws, i.e., sesbania straw hydrochars (SHC) and reed straw hydrochars (RHC) using a 63-day soil column experiment. The results showed that CHC posed a greater efficiency in reducing the global warming potential (GWP, 54.6 % (36.7 g/m2) vs. 45.5-45.6 % (22.2-30.6 g/m2)) than those of RHC and SHC. For the plant growth, three hydrochars at 3 % (w/w) significantly increased dry biomass of tomato shoot and fruit by 12.4-49.5 % and 48.6-165 %, respectively. Moreover, CHC showed the highest promotion effect on shoot and fruit dry biomass of tomato, followed by SHC ≈ RHC. Application of SHC, CHC and RHC significantly elevated the tomato sweetness compared with CK, with the order of CHC (54.4 %) > RHC (35.6 %) > SHC (22.1 %). Structural equation models revealed that CHC-depressed denitrification and methanogen mainly contributed to decreased GHG emissions. Increased soil phosphorus availability due to labile phosphorus supply from CHC dominantly accounted for elevated tomato growth and fruit production. Comparably, SHC-altered soil properties (e.g., decreased pH and increased total carbon content) determined variations of GHG emission and tomato growth. The findings provide the high-performance strategies to enhance soil primary productivity and mitigate GHG emissions in the blue C ecosystems.

Can freshwater plants and algae act as an effective feed supplement to reduce methane emissions from ruminant livestock?

Methane production by livestock is a substantial component of greenhouse gas emissions worldwide. The marine red algae, Asparagopsis taxiformis, has been identified as a possible supplement in livestock feeds due to its potent inhibition of methane production but currently is unable to be produced at scale. Finding additional taxa that inhibit methane production is therefore desirable. Here we provide foundational evidence of methanogenesis-inhibiting properties in Australian freshwater plants and algae, reviewing candidate species and testing species' chemical composition and efficacy in vitro. Candidate plant species and naturally-occurring algal mixes were collected and assessed for ability to reduce methane in batch testing and characterised for biochemical composition, lipids and fatty acids, minerals and DNA. We identified three algal mixes and one plant (Montia australasica) with potential to reduce methane yield in in vitro batch assay trials. All three algal mixes contained Spirogyra, although additional testing would be needed to confirm this alga was responsible for the observed activity. For the two samples that underwent multiple dose testing, Algal mix 1 (predominantly Spirogyra maxima) and M. australasica, there seems to be an optimum dose but sources, harvesting and storage conditions potentially determine their methanogenesis-inhibiting activity. Based on their compositions, fatty acids are likely to be acting to reduce methane in Algal mix 1 while M. australasica likely contains substantial amounts of the flavonoids apigenin and kaempferol, which are associated with methane reduction. Based on their mineral composition, the samples tested would be safe for livestock consumption at an inclusion rate of 20%. Thus, we identified multiple Australian species that have potential to be used as a feed supplement to reduce methane yield in livestock which may be suitable for individual farmers to grow and feed, reducing complexities of supply associated with marine alternatives and suggesting avenues for investigation for similar species elsewhere.

Effect of grape pomace supplement on growth performance, gastrointestinal microbiota, and methane production in Tan lambs.

Grape pomace (GP), a by-product in wine production, is nutritious and can be used as a feed ingredient for ruminants; however, its role in shaping sheep gastrointestinal tract (GIT) microbiota is unclear. We conducted a controlled trial using a randomized block design with 10 Tan lambs fed a control diet (CD) and 10 Tan lambs fed a pelleted diet containing 8% GP (dry matter basis) for 46 days. Rumen, jejunum, cecum, and colon bacterial and archaeal composition were identified by 16S rRNA gene sequencing. Dry matter intake (DMI) was greater (p < 0.05) in the GP than CD group; however, there was no difference in average daily gain (ADG, p < 0.05) and feed conversion ratio (FCR, p < 0.05) between the two groups. The GP group had a greater abundance of Prevotella 1 and Prevotella 7 in the rumen; of Sharpe, Ruminococcaceae 2, and [Ruminococcus] gauvreauii group in the jejunum; of Ruminococcaceae UCG-014 and Romboutsia in the cecum, and Prevotella UCG-001 in the colon; but lesser Rikenellaceae RC9 gut group in the rumen and cecum, and Ruminococcaceae UCG-005 and Ruminococcaceae UCG-010 in the colon than the CD group. The pathways of carbohydrate metabolism, such as L-rhamnose degradation in the rumen, starch and glycogen degradation in the jejunum, galactose degradation in the cecum, and mixed acid fermentation and mannan degradation in the colon were up-graded; whereas, the pathways of tricarboxylic acid (TCA) cycle VIII, and pyruvate fermentation to acetone in the rumen and colon were down-graded with GP. The archaeal incomplete reductive TCA cycle was enriched in the rumen, jejunum, and colon; whereas, the methanogenesis from H2 and CO2, the cofactors of methanogenesis, including coenzyme M, coenzyme B, and factor 420 biosynthesis were decreased in the colon. The study concluded that a diet including GP at 8% DM did not affect ADG or FCR in Tan lambs. However, there were some potential benefits, such as enhancing propionate production by microbiota and pathways in the GIT, promoting B-vitamin production in the rumen, facilitating starch degradation and amino acid biosynthesis in the jejunum, and reducing methanogenesis in the colon.

Improved methane production of two-phase anaerobic digestion by cobalt: Efficiency and mechanism.

Two-phase anaerobic digestion (AD) is a promising technology, but its performance is sensitive to methanogen. In this study, the effect of cobalt (Co) on two-phase AD was investigated and the enhanced mechanism was revealed. Though no obvious effect of Co2+ was observed in acidogenic phase, the activity of methanogens was significantly affected by Co2+ with an optimal Co2+ concentration of 2.0 mg/L. Ethylenediamine-N'-disuccinic acid (EDDS) was the most effective for improving Co bioavailability and increasing methane production. The role of Co-EDDS in improving methanogenic phase was also verified by operating three reactors for two months. The Co-EDDS supplement increased the level of Vitamin B12 (VB12) and coenzyme F420, and enriched Methanofollis and Methanosarcina, thereby successfully improving methane production and accelerating reactor recovery from ammonium and acid wastewater treatment. This study provides a promising approach to improve the efficiency and stability of anaerobic digester.

Effects of freeze-thaw cycles on methanogenic hydrocarbon degradation: Experiment and modeling.

Cold regions are warming much faster than the global average, resulting in more frequent and intense freeze-thaw cycles (FTCs) in soils. In hydrocarbon-contaminated soils, FTCs modify the biogeochemical and physical processes controlling petroleum hydrocarbon (PHC) biodegradation and the associated generation of methane (CH4) and carbon dioxide (CO2). Thus, understanding the effects of FTCs on the biodegradation of PHCs is critical for environmental risk assessment and the design of remediation strategies for contaminated soils in cold regions. In this study, we developed a diffusion-reaction model that accounts for the effects of FTCs on toluene biodegradation, including methanogenic biodegradation. The model is verified against data generated in a 215 day-long batch experiment with soil collected from a PHC contaminated site in Ontario, Canada. The fully saturated soil incubations with six different treatments were exposed to successive 4-week FTCs, with temperatures oscillating between -10 °C and +15 °C, under anoxic conditions to stimulate methanogenic biodegradation. We measured the headspace concentrations and 13C isotope compositions of CH4 and CO2 and analyzed the porewater for pH, acetate, dissolved organic and inorganic carbon, and toluene. The numerical model represents solute diffusion, volatilization, sorption, as well as a reaction network of 13 biogeochemical processes. The model successfully simulates the soil porewater and headspace concentration time series data by representing the temperature dependencies of microbial reaction and gas diffusion rates during FTCs. According to the model results, the observed increases in the headspace concentrations of CH4 and CO2 by 87% and 136%, respectively, following toluene addition are explained by toluene fermentation and subsequent methanogenesis reactions. The experiment and the numerical simulation show that methanogenic degradation is the primary toluene attenuation mechanism under the electron acceptor-limited conditions experienced by the soil samples, representing 74% of the attenuation, with sorption contributing to 11%, and evaporation contributing to 15%. Also, the model-predicted contribution of acetate-based methanogenesis to total produced CH4 agrees with that derived from the 13C isotope data. The freezing-induced soil matrix organic carbon release is considered as an important process causing DOC increase following each freezing period according to the calculations of carbon balance and SUVA index. The simulation results of a no FTC scenario indicate that, in the absence of FTCs, CO2 and CH4 generation would decrease by 29% and 26%, respectively, and that toluene would be biodegraded 23% faster than in the FTC scenario. Because our modeling approach represents the dominant processes controlling PHC biodegradation and the associated CH4 and CO2 fluxes, it can be used to analyze the sensitivity of these processes to FTC frequency and duration driven by temperature fluctuations.

Effects of combined addition of 3-nitrooxypropanol and vitamin B12 on methane and propionate production in dairy cows by in vitro-simulated fermentation.

The compound 3-nitrooxypropanol (3-NOP) is a promising methane inhibitor, which performs well in inhibiting methane emission and does not affect animal feed intake and digestibility. However, it causes a significant increase in hydrogen production while suppressing methane emission, resulting in a waste of feed energy. Vitamin B12 is a key factor in the propionate production pathway and thus plays an important role in regulating the hydrogen utilization pathway. In this study, the effects of 3-NOP combined with vitamin B12 supplementation on rumen fermentation and microbial compositional structure in dairy cattle were investigated by simulating rumen fermentation in vitro. Experiments were performed using a 2 × 2-factorial design: two 3-NOP levels (0 or 2 mg/g dry matter) and 2 vitamin B12 levels (0 or 2 mg/g dry matter). Three experiments were performed, each consisting of 4 treatments, 4 replicates, and 4 blanks containing only inoculum. The combined supplementation of 3-NOP and vitamin B12 reduced methane emission by 12% without affecting dry matter digestibility. The combined addition of 3-NOP and vitamin B12 significantly increased the concentration of propionate and reduced the concentration of acetate and the acetate to propionate ratio. At the bacterial level, 3-NOP increased the relative abundances of Christensenellaceae_R-7_group and Lachnospiraceae_NK3A20_group. Vitamin B12 increased the relative abundances of unclassified_f__Prevotellaceae and Prevotellaceae_UCG-003 and decreased the relative abundance of Lachnospiraceae_NK3A20_group. At the archaeal level, the combination of 3-NOP and vitamin B12 increased the relative abundances of Methanobrevibacter_ sp._ Abm4, OTU1125, and OTU95 and decreased the relative abundances of uncultured_methanogenic_archaeon_g__Methanobrevibacter, OTU1147, OTU1056, and OTU55. The results indicated that 3-NOP combined with vitamin B12 could alleviate rumen hydrogen emission and enhance the inhibition of methane emission compared with 3-NOP alone.

Ruminal fermentation and methane production in vitro, milk production, nutrient utilization, blood profile, and immune responses of lactating goats fed polyphenolic and saponin-rich plant extracts.

This study was conducted to evaluate the effect of a composite plant extract (CPE) rich in polyphenolics and saponins from seeds of Dolichos biflorus (horse gram), root of Asparagus racemosus (shatavari), bark of Amoora rohituka (rohitaka), and peel of Punica granatum (pomegranate) on ruminal fermentation and methanogenesis in vitro, milk production, nutrient digestibility, immune response, and blood profiles in lactating Beetal goats fed CPE at 20 g/kg diet. Dose effect of CPE was assessed using different doses (0, 10, 20, 30, and 40 g/kg substrate) to find out an optimum dose for the in vivo study. The in vivo experiment lasted 70 days including a 10-day adaptation period. In the in vitro study, dry matter (DM) and fiber degradability increased linearly (P < 0.05) and methane production and ammonia concentration decreased linearly (P < 0.05) with increasing doses of CPE. Concentrations of total VFA and proportion of propionate increased (P < 0.001) linearly, whereas proportion of acetate and acetate to propionate ratio decreased with a linear effect. Dietary CPE increased milk yield (P = 0.017) and concentrations of protein and lactose (P = 0.045) by CPE, but concentrations of fat and solid not fat in milk were not affected (P > 0.10). Somatic cell counts in milk reduced (P = 0.045) in the CPE-fed goats. Apparent digestibility of DM (P = 0.037) increased significantly and NDF (P = 0.066) tended to increase due to supplementation of CPE. Blood glucose (P = 0.028) and albumin (P = 0.007) concentrations increased, while other liver-marker metabolites and enzyme activities and superoxide dismutase activity were not altered in goats due to feeding of CPE. Concentrations of total amino acids (P = 0.010), total essential amino acids (P = 0.012), and total ketogenic amino acids (P < 0.001) were greater in the CPE-fed goats than the control goats. Cell-mediated immune response improved due to CPE feeding. This study suggests that the CPE rich in both phenolics and saponins could improve ruminal fermentation, milk production, and nutrient utilization in lactating goats with better health status while decreasing methane emission.

Bacterial species in the ruminal content of steers fed oilseeds in the diet.

The aim of this study was to evaluate bacterial species and diversity of methanogenic Archaea in the solid fraction of the ruminal content, through the gene sequences of the conserved 16S rDNA region, in response to the following diets: canola, cottonseed, sunflower, soybean, corn silage, and control diet. Six rumen-fistulated crossbred steers, with body weight (BW) of 416.33 ± 93.30 kg, were distributed in a 6 × 6 Latin square design. Regardless of the diet provided, amylolytic, proteolytic, and lactic bacteria were identified in the rumen fluid. Cellulolytic bacteria were predominant for all diets, reaching 47.75% of operational taxonomic units (OTUs) in animals fed with the cottonseed diet. Amylolytic bacteria reach 62.51% of OTU in animal fed sunflower diet, while proteolytic bacteria correspond to 65.96% of OTU in this same diet. Also, Megasphaera elsdenii bacterium was identified for all diets, with a greater percentage of OTU in steers fed the cottonseed diet. The diversity analysis of the species identified the methanogenic Archaea Methanobrevibacter ruminantium in all diets. We conclude that the control and corn silage diets have the most similar bacterial flora; diets with oilseeds had 47.5% similarity in rumen flora bacteria species. Animals fed with soybean showed a reduced number of methanogenic Archaea in the rumen content, which could be an alternative feed for cattle due to their low potential for energy losses with the production of methane.

Iron (oxyhydr)oxides shift the methanogenic community in deep sea methanic sediment - insights from long-term high-pressure incubations.

Intermittent increases of dissolved ferrous iron concentrations have been observed in deep marine methanic sediments which is different from the traditional diagenetic electron acceptor cascade, where iron reduction precedes methanogenesis. Here we aimed to gain insight into the mechanism of iron reduction and the associated microbial processes in deep sea methanic sediment by setting up long-term high-pressure incubation experiments supplemented with ferrihydrite and methane. Continuous iron reduction was observed during the entire incubation period. Intriguingly, ferrihydrite addition shifted the archaeal community from the dominance of hydrogenotrophic methanogens (Methanogenium) to methylotrophic methanogens (Methanococcoides). The enriched samples were then amended with 13C-labeled methane and different iron (oxyhydr)oxides in batch slurries to test the mechanism of iron reduction. Intensive iron reduction was observed, the highest rates with ferrihydrite, followed by hematite and then magnetite, however, no anaerobic oxidation of methane (AOM) was observed in any treatment. Further tests on the enriched slurry showed that the addition of molybdate decreased iron reduction, suggesting a link between iron reduction with sulfur cycling. This was accompanied by the enrichment of microbes capable of dissimilatory sulfate reduction and sulfur/thiosulfate oxidation, which indicates the presence of a cryptic sulfur cycle in the incubation system with the addition of iron (oxyhydr)oxides. Our work suggests that under low sulfate conditions, the presence of iron (oxyhydr)oxides would trigger a cascade of microbial reactions, and iron reduction could link with the microbial sulfur cycle, changing the kinetics of the methanogenesis process in methanic sediment.

Calcium ion can alleviate ammonia inhibition on anaerobic digestion via balanced-strengthening dehydrogenases and reinforcing protein-binding structure: Model evaluation and microbial characterization.

Experimental investigation and model simulation was combined to identify the effect of metal ions on mitigating ammonia inhibition during anaerobic digestion. Five metal ions (Ca, Mg, Cu, Zn, Fe) were tested in reactors with 1 g-glucose/L/d and 5 g-N/L under fed batch operation. Ca addition was considered the optimal approach with a 25% increment in methane production via balanced-strengthening dehydrogenases and reinforcing protein-binding structure. Gene-sequencing results suggested 50% and 15% increment in acetotrophic-related and hydrogenotrophic-related dehydrogenases, respectively, after Ca addition. The Anaerobic Digestion Model No.1 was modified by introducing lactate-related reactions, syntrophic acetate oxidation process, and kinetic equation of metal ions, with satisfactory predictions of methane and intermediates (R2 > 0.80). The lowest affinity constant KI_MI value was obtained with Ca supplement, indicating the highest conversion rate of substrates to methane. The model evaluation revealed the balanced ratio on the enzyme contribution of acetotrophic to hydrogenotrophic methanogenesis.

Effects of medium-chain fatty acid supplementation on performance and rumen fermentation of lactating Holstein dairy cows.

Medium-chain fatty acids (MCFAs) have antimicrobial properties and cause negative or positive effects on animal performance depending on its dosage. We hypothesized that MCFA supplementation at a lower dose (i.e., 0.05-0.2% of dietary DM) would increase rumen pH and milk production without decreasing nutrient digestibility which is typically observed with the higher inclusion rates (i.e., >1% of dietary DM). The objective of this study was to evaluate the effects of MCFA supplementation at a lower dose on productivity, plasma energy metabolite concentrations, apparent total tract nutrient digestibility, rumen fermentation, and rumen microbial profile of lactating dairy cows. Thirty (n = 8 primiparous, n = 22 multiparous) Holstein cows in mid-lactation (637 ± 68.5 kg of initial BW, 98.5 ± 27.4 d in milk; mean ± standard deviation) were used in a crossover design with two 28-d periods. The MCFA supplement, consisted of 25% MCFA (containing 32% C8:0, 21% C10:0, 47% C12:0 on DM basis) and 75% carrier ingredients, was fed at 0.25% of dietary DM replacing dry ground corn in control (CON). Total inclusion of MCFA was 0.063% of dietary DM. No differences were observed in DM intake, apparent total tract nutrient digestibility and BW change between MCFA and CON. Milk and milk component yields did not differ between treatment groups. The MCFA supplementation tended to have higher minimum rumen pH (5.66 vs. 5.54), and decreased daily fluctuation range of rumen pH (1.17 vs. 1.40) compared to CON. However, the duration of acidosis (pH < 5.8, min/d) did not differ between treatment groups and ruminal total volatile fatty acid concentration and its profile did not differ between treatment groups. For rumen microbiota, the Chao1 index of bacterial community tended to be lower (10.9 vs. 11.6) whereas the Shannon index did not differ (0.91 vs. 0.93) in MCFA compared to CON, and both indices did not differ for archaeal and protozoan communities between treatment groups. The relative abundance of Methanobrevibacter gottschalkii increased when supplemented with MCFA (5.14 vs. 4.92%). These results suggest that supplementation of MCFA at 0.063% dietary DM may not affect overall animal performance or total tract nutrient digestibility, but decrease the daily range of pH and the bacterial richness in the rumen.

Anti-Methanogenic Traits of Safflower Oil Compounds Against Methyl-Coenzyme M Reductase Receptor in Equines: An In Silico Docking Analysis.

Greenhouse gases emission from livestock is the major concern for the ecosystem. Despite the lower contribution of non-ruminants towards greenhouse gas emission as compared to the ruminants, the emission of methane (CH4) gas from equines is expected to be increased in future due to its increasing population. Thus, it is essential to find or screen potential anti-methanogenic agent in a cost-effective and quicker manner. Considering this, the present investigation was aimed to analyze anti-methanogenic characteristic of bioactive compounds of safflower oil by targeting methanogenesis catalyzing enzyme (Methyl-coenzyme M reductase; MCR) via in silico tool. Initially, a total of 25 compounds associated with safflower oil were selected and their drug-likeness traits were predicted through Lipinski's rule of 5. Of 25 compounds, 9 compounds passed all the parameters of Lipinski's rule of five. These 9 ligands were further submitted for ADME traits analysis using Swiss ADME tool. Results revealed the absence of Lipinski's violation and approval of drug-likeness attributes of methyl tetradecanoate, 3-isopropyl-6-methylenecyclohex-1-ene, trans-2,4-decadienal, cis-6-nonenal, limonene, syringic acids, matairesinol, acacetin, and 2,5-octanedione. Molecular docking analysis was performed for analyzing the affinity between the selected 9 ligands and MCR receptor using FRED v3.2.0 from OpenEye Scientific Software and Discovery Studio client v16.1.0. Results showed maximum binding interaction of acacetin with MCR with the chemguass4 score of -13.35. Other ligands showed comparatively lower binding affinity in the order of matairesinol (-12.43) > methyl tetradecanoate (-9.25) > cis-6-nonenal (-7.88) > syringic acids (-7.73) > limonene (-7.18) > trans-2,4-decadienal (-7.07) > 3-isopropyl-6-methylenecyclohex-1-ene (-7.01) > 2,5-octanedione (-7.0.). In a nutshell, these identified compounds were observed as potential agents to reduce CH4 production from equines by targeting MCR. This in silico study emphasized the role of safflower-associated compounds in developing anti-methanogenic drug for equines in future.

Exploration of the biotransformation of phenanthrene degradation coupled with methanogensis by metabolites and enzyme analyses.

The ubiquitous environmental contaminants, polycyclic aromatic hydrocarbons (PAHs), can be aerobically biodegraded. Strategies for biodegradation of PAHs are needed for the persisted character of it in anoxic environments. In current study, we obtained a highly enriched anaerobic, PAHs-degrading co-culture DYM1, from petroleum-polluted soil. DYM1 significantly degrades a range of PAHs in 4 days without supplementary terminal electron acceptors. Co-culture DYM1 is consists of two microorganisms (a degrading bacterium Paracoccus sp. strain PheM1 and an aceticlastic methanogen Methanosaeta concilii.) that utilize different carbon sources in a syntrophic metabolic process of phenanthrene. About 93% of phenanthrene (104.5 µM) has been removed under methanogenic conditions after incubation with co-culture DYM1 for 4 d, and produced 33.68 µmol CH4. Carboxylation, which is catalyzed by UbiD-like carboxylase, was proposed as the initial steps of methanogenic phenanthrene-degrading pathway based upon the detection of 2-phenanthroic acid and 4-phenanthrene acid. Reduction and hydration of the benzene rings were followed by the initial reaction. Hydrated phenanthroic acid metabolites were newly detected and characterized under anaerobic conditions. Anaerobic degradation of phenanthrene without terminal electron acceptor addition not only sheds light on a poorly understood and environmentally relevant biological process, but also supply a novel approach to recover the energy of toxic pollutant in forms of methane.

Sediment Remediation with New Composite Sorbent Amendments to Sequester Phosphorus, Organic Contaminants, and Metals.

This study tested two sediment amendments with active sorbents: injection of aluminum (Al) into sediments and thin-layer capping with Polonite (calcium-silicate), with and without the addition of activated carbon (AC), for their simultaneous sequestration of sediment phosphorus (P), hydrophobic organic contaminants (HOCs), and metals. Sediment cores were collected from a eutrophic and polluted brackish water bay in Sweden and incubated in the laboratory to measure sediment-to-water contaminant release and effects on biogeochemical processes. We used diffusive gradients in thin-film passive samplers for metals and semi-permeable membrane devices for the HOC polychlorinated biphenyls and polycyclic aromatic hydrocarbons. Al injection into anoxic sediments completely stopped the release of P and reduced the release of cadmium (Cd, -97%) and zinc (Zn, -95%) but increased the sediment fluxes of PAH (+49%), compared to the untreated sediment. Polonite mixed with AC reduced the release of P (-70%), Cd (-67%), and Zn (-89%) but increased methane (CH4) release. Adding AC to the Al or Polonite reduced the release of HOCs by 40% in both treatments. These results not only demonstrate the potential of innovative remediation techniques using composite sorbent amendments but also highlight the need to assess possible ecological side effects on, for example, sedimentary microbial processes.

Methanogenesis at High Temperature, High Ionic Strength and Low pH in the Volcanic Area of Dallol, Ethiopia.

The Dallol geothermal area originated as a result of seismic activity and the presence of a shallow underground volcano, both due to the divergence of two tectonic plates. In its ascent, hot water dissolves and drags away the subsurface salts. The temperature of the water that comes out of the chimneys is higher than 100 °C, with a pH close to zero and high mineral concentration. These factors make Dallol a polyextreme environment. So far, nanohaloarchaeas, present in the salts that form the walls of the chimneys, have been the only living beings reported in this extreme environment. Through the use of complementary techniques: culture in microcosms, methane stable isotope signature and hybridization with specific probes, the methanogenic activity in the Dallol area has been assessed. Methane production in microcosms, positive hybridization with the Methanosarcinales probe and the δ13CCH4-values measured, show the existence of extensive methanogenic activity in the hydrogeothermic Dallol system. A methylotrophic pathway, carried out by Methanohalobium and Methanosarcina-like genera, could be the dominant pathway for methane production in this environment.

Calcium hypochlorite enhances the digestibility of and the phosphorus recovery from waste activated sludge.

Waste activated sludge (WAS) can be treated using anaerobic digestion (AD) for biogas recovery and volume reduction. However, the poor digestibility and hydrolysis of WAS limit AD applications. The current study investigated the feasibility of applying calcium hypochlorite as a WAS pretreatment strategy to improve AD treatment efficiency using laboratory reactors. The results showed that pretreatment with 5 - 20% Ca(ClO)2 (total suspended solids basis) significantly enhanced WAS anaerobic digestibility, and led to significantly enhanced methane production rate and biomethane yield comparing to the AD of raw WAS (P < 0.05). Low Ca(ClO)2 pretreatment (5 - 10%) significantly enhanced digestion efficiency, which can be attributed to the development of fermentative and syntrophic bacteria. However, high Ca(ClO)2 doses (>20%) reduced microbial activities, leading to slow release of dissolved organic compounds and prolonged methane production lag phase. In addition, high Ca(ClO)2 removed 82.7% of the initial phosphate by calcium-phosphate binding, reducing the phosphorus in liquid digestate.