Methanogenesis Process Research Articles

Magnetite-mediating direct interspecies electron transfer is not pivotal role in directing electrons toward methane production from sulfate containing wastewater

Sulfate reduction can compete for electrons with methane production, thereby reducing methane production. Several factors, such as magnetite addition, carbon sources, and the chemical oxygen demand (COD)/SO42− ratio, can influence the direction of electron flow toward methanogenesis. However, their contributions to methane production remain unclear. In this study, the addition of magnetite significantly enhanced the maximum methane production rate (Rmax). The enrichment of Methanothrix and Methanobacterium in the conductive material groups indicated the establishment of a methanogenesis process through direct interspecies electron transfer (DIET). Although the DIET pathway enhanced Rmax in the conductive material groups, this increase did not translate into a higher methane yield in this study. The contribution of DIET pathway to methane yield was negligible compared with the effect of COD/SO42− ratio and carbon sources. The relative contribution of COD/SO42− ratio exceeded 40 % in directing electron flow.

The origin of methyl group in methanogen-mediated mercury methylation: From the Wolfe cycle

Methylmercury (MeHg) is a bioaccumulating neurotoxin mainly produced by anaerobic microorganisms, with methanogen being one of the important methylators. A critical aspect for understanding the mechanism for microbial mercury (Hg) methylation is the origin of the methyl group. However, the origin of methyl group in methanogen-mediated Hg methylation remains unclear. This study aims to identify the source of methyl group for MeHg synthesis in methanogens. Our study revealed that Hg methylation in Methanospirillum hungatei JF-1 is closely related to methanogenesis process, according to the results of proteomic study and substrate limitation study. Next, we proved that nearly all methyl group in MeHg derives from the Wolfe cycle in this species, rather than the previously demonstrated acetyl-coenzyme A pathway, based on the results of 13C labeling study. We then proposed the Wolfe cycle-dependent Hg methylation mechanism in this species. Further genome analyses and 13C labeling experiments indicated that the involvement of the Wolfe cycle in Hg methylation is probably a universal feature among Hg-methylating methanogens. These findings reveal a unique Hg methylation mechanism in methanogens. Our study broadens the carbon substrates and controlling factors for MeHg synthesis in the environment, which can inform the prediction of MeHg production potential and remediation strategies for MeHg contamination.

Insights into links between redox cycling of dissolved organic matter ranked by molecular weight and methanogen-bacteria symbiosis-driven methane production

Molecular weight (MW) of dissolved organic matter (DOM) governs its redox capacity, playing pivotal roles in methanogen-bacteria symbiosis-driven CH4 production. However, the effect of redox capacity of DOM ranked by MW on these symbiotic associations during anaerobic digestion have never been investigated. The electron–donating (EDC) and –accepting capacity (EAC) of DOM with different MW were quantified, elucidating their impacts on bacteria-methanogen symbiosis-driven CH4 production. By contrast, DOM with 7000 > MW > 14,000 Da constituted the primary contribution to EAC, with an average contribution of 44.63 %. DOM with MW > 14,000 Da emerged as the predominant contributor to EDC, with an average contribution of 49.10 %. Random forest showed that EAC/EDC of DOM ranked by MW was the important factors for methanogenesis by driving shifts in microbial symbiotic relationships. 46 genera (relative abundance of 69.55 %) of microorganisms exhibited robust associations with EAC/EDC. EDC of DOM with 3500 < MW < 7000 Da exerted positive effect on CH4 by modulating the corporation of Caldicoprobacter, norank_o__TSCOR001-H18, norank_o__MBA03 and Methanobrevibacter. EDC of DOM (7000 < MW < 14,000 Da) promotes CH4 production by regulating cooperation of Corynebacterium, Pseudomonas and Methanosarcina, Methanothermus. EDC of DOM (MW > 14,000 Da) enhances CH4 production by modulating cooperation of Ureibacillus, Treponema and methanomassiliicoccus, methanogenium. EAC of DOMs were negatively correlated with CH4. This study broadens our knowledge on the intricate process of methanogenesis and holds significant importance in developing a microbial symbiosis regulation strategy based on electron transfer system.

Lacustrine groundwater discharge-derived carbon and nitrogen to regulate biogeochemical processes as revealed by stable isotope signals in a large shallow eutrophic lake

Eutrophic shallow lakes are hotspots of carbon (C) and nitrogen (N) accumulation and transformation, and are increasingly recognized as important sources of greenhouse gases (GHGs: CO2, CH4 and N2O). Lacustrine groundwater discharge (LGD) is a crucial component of the water budget and terrestrial material delivery for lakes, but its interplays with intrinsic CN biogeochemical processes remain less tackled. In this study, C and N ingredients and multiple stable isotopes (δ2H, δ18O, δ13C, and δ15N) were measured seasonally in groundwater, river water and lake water of a large eutrophic shallow lake in eastern China. The results revealed that groundwater is enriched with various forms of C and N that have similar sources and pathways as surface water in the lake and rivers. The isotope balance model also indicated that LGD derived C and N contribute significantly to lake inventories in addition to river runoff. These allochthonous C and N provide extra substrates for related biogeochemical processes, such as algae proliferation, organic matter degradation, methanogenesis and denitrification. Simultaneously, the excess oxygen consumption leads to depletion and hypoxia in the lake, further facilitating the processes of methanogenesis and denitrification. LGD functions not only as an external source of C and N that directly increases GHG saturations, but also as a mediator of internal CN pathways, which significantly affect hypoxia formation, GHG productions and emissions in the eutrophic lake. This study highlights the unrevealed potential regulation of LGD on biogeochemical processes in the eutrophic lake, and underscores the need for its consideration in environmental and ecological studies of lakes both regionally and globally.

Biokinetic and microbial insights into regulatory mechanisms of long-chain fatty acid degradation during food waste-lipid co-digestion within anaerobic membrane bioreactor

This study investigated the effects of varying lipid ratios on the anaerobic co-digestion of high-lipid food waste (FW) in a mesophilic anaerobic membrane bioreactor (AnMBR). At a lipid concentration of 5 %, optimal biogas production (3.84 L/L/d) and lipid removal efficiency (78 %) were achieved; however, increasing lipid concentrations resulted in significant accumulations of long-chain fatty acids (LCFAs) and volatile fatty acids (VFAs). Batch tests further demonstrated the impact of various types of LCFAs, with stearic acid showing the slowest microbial growth rate (0.033d-1), confirming its role in the accumulation of acetate-dominated VFAs, potentially limiting the methanogenesis process at elevated lipid levels. Furthermore, at 8 % lipid content, the downregulation of key LCFA degradation enzymes and dominance of hydrogenotrophic methanogens indicated adverse conditions. The importance of the intricate interplay between LCFA degradation kinetics and microbial community for the system efficiency was evidenced, offering insights for optimizing and managing high-lipidic wastes.

Effect of Stepwise Exposure to High-Level Erythromycin on Anaerobic Digestion.

High-level erythromycin (ERY) fermentation wastewater will pose serious threats to lake environments. Anaerobic digestion (AD) has advantages in treating high-level antibiotic wastewater. However, the fate of antibiotic resistance genes (ARGs) and microbial communities in AD after stepwise exposure to high-level ERY remains unclear. In this study, an AD reactor was first exposed to 0, 5, 10, 50, 100 and 200 mg/L ERY and then re-exposed to 0, 50, 200 and 500 mg/L ERY to investigate the effect of ERY on AD. The results show that AD could adapt to the presence of high-level ERY (500 mg/L) and could maintain efficient CH4 production after domestication with low-level ERY (50 mg/L). The AD process could achieve higher removal of ERY (>94%), regardless of the initial ERY concentration. ErmB and mefA, conferring resistance through target alteration and efflux pumps, respectively, were dominant in the AD process. The first exposure to ERY stimulated an increase in the total ARG abundance, while the AD process seemed to discourage ARG maintenance following re-exposure to ERY. ERY inhibited the process of acetoclastic methanogenesis, but strengthened the process of hydrogenotrophic methanogenesis. This work provides useful information for treating high-level ERY fermentation wastewater by the AD process.

Insights into mechanisms of red mud promoting biogas production from waste activated sludge anaerobic digestion

Anaerobic digestion of waste activated sludge is usually limited by the low overall methane yield. The addition of exogenous materials is considered to be a potential method to improve anaerobic methane production. In this study, red mud was added into waste activated sludge anaerobic digester and its effects on anaerobic digestion were investigated. Results showed that methane production was improved with the addition of red mud, and almost reached maximum in 10 g/L red mud added reactor (124.4 mL/g VSS), which was about 24.0 % higher than control. Further investigation indicated that the key genes related to methane metabolism, the activity of the corresponding coenzymes and the rate of extracellular electron transfer were also increased in red mud added reactor. Batch experiments on the effects of red mud in each stage of waste activated sludge anaerobic digestion showed that red mud could improve solubilization, hydrolysis, and acidification processes, but inhibit the methanogenesis process. The potential mechanism behind the enhancement of methane production during whole waste activated sludge anaerobic digestion is that the addition of red mud can intensify the hydrolysis and acidification processes, thereby providing more substrates for methanogens and subsequently enhancing the activity of coenzymes related to methane production.

The resistance of hydrogenotrophic methanogenic microorganisms to ofloxacin in sludge anaerobic digestion process

Ofloxacin (OFL) is a commonly used antibiotic that can enter wastewater treatment plants and be adsorbed by the sludge, resulting in a high OFL concentration in sludge and affecting the subsequent sludge anaerobic digestion process. However, the micro mechanisms involved in this process have not been thoroughly studied. Therefore, this study focuses on the effect of OFL on the sludge anaerobic digestion of sludge to provide such support. The experimental results showed that the maximal methane yield decreased from 277.7 to 164.7 mL/g VSS with the OFL concentration increased from 0 to 300 mg/L. Additionally, OFL hindered the intermediate biochemical processes of hydrolysis, acidogenesis, acetogenesis, and acetoclastic methanogenesis. However, it promoted hydrogenotrophic methanogenesis process, using H2 as substrate, with the concentration of 300 mg/L OFL was 5.54 fold methane production of that in the control. Further investigation revealed that the negative effect of OFL was likely due to the induction of reactive oxygen species, which led to a decrease in cell activity and interference with the activity of key enzymes. Microbiological analysis revealed that OFL reduced the relative abundance of hydrolysis and acidogenesis bacteria, and Methanosaeta archaea, while increasing the relative abundance of hydrogenotrophic methanogenesis microorganism from 36.54% to 51.48% as the OFL concentration increase from 0 to 300 mg/L.

Optimization of sulfate reduction and methanogenesis via phase separation in a two-phase internal circulation reactor for the treatment of high-sulfate organic wastewater

To enhance the performance of the internal circulation (IC) reactor when treating high-sulfate organic wastewater, a laboratory-scale two-phase IC reactor with distinct phase separation capabilities was designed, and the sulfate reduction and methanogenesis processes were optimized by segregating the reactor into two specialized reaction zones. The results demonstrated that the first and second reaction areas of the two-phase IC reactor could be maintained at 4.5–6.0 and 7.5–8.5, respectively, turning them into the specialized phase for sulfate reduction and methanogenesis. Through phase separation, the two-phase IC reactor achieved a COD degradation and sulfate reduction efficiency of more than 80% when the influent sulfate concentration exceeded 5,000 mg/L, which were 32.32% and 16.04% higher than that before phase separation. Functional analyses indicated a greater activity of both the dissimilatory and assimilatory sulfate reduction pathways in the acidogenic phase, largely due to a rise in the relative abundance of the genera Desulfovibrio, Bacteroides, and Lacticaseibacillus, the primary carriers of sulfate reduction functional genes. In contrast, all the acetoclastic, hydrogenotrophic, and methylotrophic methanogenesis pathways were inhibited in the acidogenic phase but thrived in the methanogenic phase, coinciding with shifts in the genus Methanothrix, which harbors the mcrA, mcrB, and mcrG genes essential for the final transformation step of all three methanogenesis pathways.

Integrated microalgae cultivation and sustainable biofuel production from pretreated food waste

Repurposing of food waste (FW) affords an alternate waste management strategy and sustainable product yield. Thus, this study proposed an integrated biorefinery approach, repurposing pretreated FW hydrolysate for microalgae cultivation and utilizing residual solids for biomethane recovery. FW biomass with different solubilization ranging from (10–15 to 60–65%) obtained during surfactant coupled disperser pretreatment was used as a substrate for microalgae (Chlorella vulgaris) cultivation. A higher microalgae biomass productivity of 0.87 ± 0.003 g/g substrate was obtained from the FW hydrolysate with 40–45% solubilization. The microalgae cultivated in FW hydrolysate with 40–45% solubilization yielded a higher protein, carbohydrate, and lipid accumulation of 380 ± 20 mg/g, 480 ± 30 mg/g and 360 ± 15 mg/g. Besides, the methanogenesis process showed a higher methane yield of 0.294 ± 0.003 L/g COD utilizing residual solids of pretreated food waste as substrate. This integrated biorefinery provides a sustainable platform for completely valorizing food waste biomass and recovery of multiple products.

A novel player of methylotrophic methanogensis pathway in boosting anaerobic digestion of corn stover with effluents recycling

Effluents recycling proves to be an effective method for enhancing the performance of anaerobic digestion system for lignocellulosic-like biomass. However, a limited understanding exists regarding the regulation mechanisms of methanogens. This study aims to systematically assess the dynamic interactions between process parameters, microbial communities, and methanogenic activity throughout the AD process of corn stover with effluents recycling. The results show a significant increase in the specific biogas yields of corn stover to 369 ± 115 mL/g VS with effluents recycling, an 87 % improvement compared to the control system. Effluents recycling can recover nitrogen and selectively enrich the abundances of microorganisms such as Herbinix hemicellulosilytica, Bacteroides paurosaccharolyticus and Methanosarcina mazei, etc. Correspondingly, the strategy improves the abundance of CAZymes, enhancing the efficient depolymerization of cellulose, glucuronoarabinoxylan, xyloglucan and pectin. Methanol and methylamines originating from enhanced pectin hydrolyzation and the biogenic amine pathway boost methylotrophic methanogenesis. This study addresses knowledge gaps in producing-pathways of precursors for methylotrophic methanogenesis and elucidates the mechanism to boost methanogenesis process of lignocellulosic-like biomass with effluents recycling.

Unraveling roles of dissolved organic matter in the co-occurrence of arsenic and ammonium in Quaternary alluvial-lacustrine aquifers

Geogenic arsenic (As) and ammonium (NH4+)-contaminated groundwaters are global public concerns, posing threats to human health and ecological security. However, when considering the enrichment of either As or NH4+ in groundwater, the concurrent occurrence of both contaminants warrants further discussion. Herein, we conducted a hydrogeochemical study in the shallow confined aquifer of the central Yangtze River basin to elucidate the key mechanism of coexistence of As and NH4+ through a thorough analysis of groundwater chemistry, inorganic carbon isotope (δ13C-DIC), and dissolved organic matter (DOM). High As and NH4+ groundwater mainly occurs in meanders of the middle reaches of Yangtze River, with maximum concentrations up to 936 μg/L and 45.3 mg/L, respectively. Our findings indicate that the degradation levels and characteristics of DOM play a significant role in the co-occurrence of As and NH4+ with varying concentrations in groundwater. δ13C-DIC signatures show that there was a simultaneous increase in the concentrations of As and NH4+ in groundwater, with the highest concentration of As during fermentative conditions. In contrast, during the progression of OM degradation towards methanogenesis, the NH4+ concentration reached its peak, while the As concentration was lower compared to the fermentation stage. Optical properties of DOM demonstrate that elevated levels of NH4+ result from the mineralization of N-containing organic compounds particularly as the degradation proceeds to methanogenesis stage, while both fermentation and methanogenesis processes significantly contribute to the microbially reductive dissolution of As-bearing iron oxides in groundwater systems. This study presents isotopic and fluorescent evidence to clarify the co-existence of As and NH4+ in Quaternary alluvial-lacustrine aquifers.

Mitigation of Triclocarban Inhibition in Microbial Electrolysis Cell-Assisted Anaerobic Digestion.

Triclocarban (TCC), as a widely used antimicrobial agent, is accumulated in waste activated sludge at a high level and inhibits the subsequent anaerobic digestion of sludge. This study, for the first time, investigated the effectiveness of microbial electrolysis cell-assisted anaerobic digestion (MEC-AD) in mitigating the inhibition of TCC to methane production. Experimental results showed that 20 mg/L TCC inhibited sludge disintegration, hydrolysis, acidogenesis, and methanogenesis processes and finally reduced methane production from traditional sludge anaerobic digestion by 19.1%. Molecular docking revealed the potential inactivation of binding of TCC to key enzymes in these processes. However, MEC-AD with 0.6 and 0.8 V external voltages achieved much higher methane production and controlled the TCC inhibition to less than 5.8%. TCC in the MEC-AD systems was adsorbed by humic substances and degraded to dichlorocarbanilide, leading to a certain detoxification effect. Methanogenic activities were increased in MEC-AD systems, accompanied by complete VFA consumption. Moreover, the applied voltage promoted cell apoptosis and sludge disintegration to release biodegradable organics. Metagenomic analysis revealed that the applied voltage increased the resistance of electrode biofilms to TCC by enriching functional microorganisms (syntrophic VFA-oxidizing and electroactive bacteria and hydrogenotrophic methanogens), acidification and methanogenesis pathways, multidrug efflux pumps, and SOS response.

Non-targeted facilitation of primary sludge anaerobic fermentation by micro-aeration and the simultaneous nutrients transformations

Anaerobic fermentation is a widely used technology for resource recovery from municipal sludge (e.g., primary sludge). Micro-aeration is an emerging strategy which can be incorporated into this technology. However, the effect of micro-aeration on the anaerobic fermentation performance and the nutrients transformations are not well known. This study investigated the impact of micro-aeration on the production of volatile fatty acids (VFAs) from primary sludge as well as the simultaneous nitrogen (N) and phosphorus (P) transformations in the system. The obtained results indicated that application of micro-aeration improved the microbial activities and facilitated all the hydrolysis, acetogenesis and methanogenesis processes. Hydrogenotrophic methanogen was enriched by micro-aeration while the acetoclastic methanogenesis was still the dominant CH4 production pathway at gene level. The concentration of VFAs was lower with micro-aeration than in the control system, which could be attributed to the enhanced consumption of VFAs. The simultaneous transformations of N and P were observed with different patterns. Micro-aeration led to removal of up to 131.6 mg/L of N, with occurrence of nitrification and denitrification found to be responsible for the N removal. In contrast, the total P content remained unchanged in the reactor. However, micro-aeration was found to inhibit both extracellular organic-P mineralization and intracellular poly-P degradation, resulting in lower soluble PO43−-P and more P distributed in the organic-P fraction in solid phase. This study provides novel insights into the microscopic mechanisms of the micro-aeration on anaerobic fermentation and the simultaneous regulation of N and P release.

Unraveling the Coupled Dynamics between DOM Transformation and Arsenic Mobilization in Aquifer Systems during Microbial Sulfate Reduction: Evidence from Sediment Incubation Experiment

Geogenic arsenic (As)-rich groundwater poses a significant environmental challenge worldwide, yet our understanding of the interplay between dissolved organic matter (DOM) transformation and arsenic mobilization during microbial sulfate reduction remains limited. This study involved microcosm experiments using As-rich aquifer sediments from the Singe Tsangpo River basin (STR) and Jianghan Plain (JHP), respectively. The findings revealed that microbial sulfate reduction remarkably increased arsenic mobilization in both STR and JHP sediments compared to that in unamended sediments. Moreover, the mobilization of As during microbial sulfate reduction coincided with increases in the fluorescence intensity of two humic-like substances, C2 and C3 (R = 0.87/0.87 and R = 0.73/0.66 in the STR and JHP sediments, respectively; p &lt; 0.05), suggesting competitive desorption between DOM and As during incubation. Moreover, the transformations in the DOM molecular characteristics showed significant increases in CHOS molecular and low-O/C-value molecular intensities corresponding to the enhancement of microbial sulfate reduction and the possible occurrence of methanogenesis processes, which suggests a substantial bioproduction contribution to DOM components that is conducive to As mobilization during the microbial sulfate reduction. The present results thus provide new insights into the co-evolution between As mobilization and DOM transformations in alluvial aquifer systems under strong microbial sulfate reduction conditions.

Mechanisms of metabolic regulation and enhanced methane production by hydrolytic nanozyme in sludge anaerobic digestion

Artificial nanozymes have demonstrated potential as natural enzyme substitutes due to their efficient biomacromolecule hydrolysis. However, the metabolic and catalytic mechanisms of nanozyme during the biodegradation of complex organics remain inadequately understood. This study evaluated the effect of the hydrolytic mechanism of cerium-based metal–organic frameworks (Ce-MOFs) hydrolytic nanozyme on shaping microbiome and metabolic functions. Biochemical methane potential test revealed that Ce-MOF-based hydrolytic nanozyme increased methane production by 7.8 − 22.2% as the hydrolytic nanozyme dosage increased from 50 to 150 mg/g VS. The highest methane production observed in 150 mg/g VS dosage of Ce-MOF (Ce-MOF-150) could be attributed to the enhanced sludge hydrolysis, acidogenesis, and methanogenesis processes, proven by the increased relative abundance of dominant acidogens and methanogens. Furthermore, 150 mg/g VS hydrolytic nanozyme bolstered the relative abundance of genes encoding acetyl-CoA carboxylase (accABCD) and involving in glycolysis (hxk and pfkA). These quantities were higher (8.31 − 34.14%) than that without nanozyme addition. The enhanced relative abundance of ackA, pta, cdhCDE, mvhAD, fpoABCDHIJKLMNO, vhoC, rnfABCDEG, mtrABCDEFGH, and hdrABC in the Ce-MOF-150 test indicated that the high proton conductivity of nanozyme facilitated acetoclastic methanogenesis and membrane-bound electron transport system, thereby enhancing methane production. These findings contribute to the expanding understanding of the application of artificial nanozymes as biocatalysts for solid waste resource recovery, providing a promising approach for methane production from sewage sludge.

Microbial Community Structure in Anaerobic Digestion for Green Energy Production: A Mini Review

Anaerobic digestion (AD) is a process driven by microbes that supports renewable energy production, together with waste utilization. The role of microorganisms is undisputable as they are involved in the subsequent processes of hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Microbial communities vary in wide ranges, depending on the type of substrates used and the conditions provided. Anaerobic systems are addressed, operating under mesophilic and thermophilic conditions for the biodegradation of agricultural wastes for biogas/biomethane production. AD comprises successive degradation pathways and syntrophic microbial consortia activities. Identifying the microbial content in digesters could help attaining new information on the digester performance. Archaeal and bacterial associations have to be determined as their important role to be elucidated. Molecular-biological methods of metagenomics are applied to identify the residing mixed cultures therein. Methanogens have been attained to the domain Archaea. Bacterial and archaeal populations, specific for each stage are differentiated in thermophilic or mesophilic conditions as temperature plays a crucial role in AD process, especially for hydrolysis and methanogenesis and determines microorganisms’ variety

Evaporation-driven interfacial restructuring induces highly efficient methanogenesis of waste biomass

Methanogenesis of waste biomass (WB) is a promising method for global sustainable development, reduction of pollution and carbon emission levels, and recovering bioenergy. Unlike in the methanogenesis of organic wastewater, in which microbial cells come into direct contact with the dissolved substrate, the ‘solid–liquid–solid’ modes in WB and between WB and microbial cells, which involve numerous solid–liquid interfaces, greatly hinder the methanogenesis efficiency of WB. Amongst all WB, waste activated sludge is the most complex, poorly biodegradable and representative. Herein, we highlight the role of water evaporation-driven solid-liquid interfacial restructuring of sludge in determining its methanogenesis efficiency. Non-free water evaporation increased surface roughness and adhesion, and compressed pore structure with numerous capillaries in sludge, resulting in a new solid-liquid interface of sludge with great capillary force and highly ordered interfacial water molecules, which provides an extremely favourable condition for high mass transfer and proton-coupled electron transfer (PCET) in sludge. This restructuring was confirmed to induce the enhancement of solid–liquid interfacial noncovalent interactions and electron transfer efficiency in the subsequent methanogenesis process (P < 0.05), promoting the effective contact between the sludge substrate and microbial cells, thereby enriching the methanogenic consortia (i.e., Clostridia and Methanosarcina were increased by 290.0 % and 239.7 %, respectively) and improving the activities of key enzymes. Stable isotope tracing and metagenomic analysis further reveal that this restructuring promoted the participation of water molecules in the methane formation by PCET-driven release of protons from water, and enhanced main methanogenesis metabolic pathways, especially the metabolic pathway of CO2-reduction methanogenesis (+65.2 %), thereby resulting in a great advance in methane generation (+147 %, P < 0.001). The findings can provide a reference for regulating directional anaerobic biotransformation of water-rich multiphase complex substrates by interfacial restructuring inducement.

Microbial Assemblages and Metabolic Activity in Organic‐Rich Subterranean Estuaries: Impact of Climate and Land Use Changes

AbstractMicrobial communities in subterranean estuaries mediate biogeochemical reactions of coastal groundwater discharging into the oceans; however, studies on their response to abrupt environmental changes caused by climate and land use alterations are still limited. In this study, we conducted a controlled laboratory study using combined geochemical and metagenomic approaches to investigate microbial structures and their metabolic pathways under a wide range of nitrate () inputs, saline solutions, and incubation times. These factors served as proxies for land use, salinization of the shallow aquifer, and climate changes. We found a highly reducing habitat and an amplification of genes related to denitrification, sulfate reduction, and methanogenesis processes. Core communities consisting of Clostridia, Bacilli, Alphaproteobacteria, Gammaproteobacteria, and Desulfobaccia were observed across all treatments. The metabolic prediction of plant‐derived organic matter (i.e., tannin and lignin) degradation was not affected by inputs or salinity because of it being implemented by core communities and the abundance of electron donors and acceptors. Quantification of denitrification genes shows that they are susceptible to inputs and seawater ions. Long‐term incubation allowed sufficient time for microbes to degrade less labile DOM, promoting the re‐release of buried solid phase organic matter into the active carbon cycle and increasing the relative abundance of biofilm or spore‐forming taxa while decreasing that of rare taxa. Our results illustrate the sensitivity of microbial assemblages to environmental changes and their capacity to altering the C and N cycles in coastal areas, further affecting coastal water quality and ecosystem‐scale biogeochemistry.

Methane Biofiltration Processes: A Summary of Biotic and Abiotic Factors

The ongoing yearly rise in worldwide methane (CH4) emissions is mostly due to human activities. Nevertheless, since over half of these emissions are scattered and have a concentration of less than 3% (v/v), traditional physical–chemical methods are not very effective in reducing them. In this context, biotechnologies like biofiltration using methane-consuming bacteria, also known as methanotrophs, offer a cost-efficient and practical approach to addressing diffuse CH4 emissions. The present review describes recent findings in biofiltration processes as one of the earliest biotechnologies for treating polluted air. Specifically, impacts of biotic (such as cooperation between methanotrophs and non-methanotrophic bacteria and fungi) and abiotic factors (such as temperature, salinity, and moisture) that influence CH4 biofiltration were compiled. Understanding the processes of methanogenesis and methanotrophy holds significant importance in the development of innovative agricultural practices and industrial procedures that contribute to a more favourable equilibrium of greenhouse gases. The integration of advanced genetic analyses can enable holistic approaches for unravelling the potential of biological systems for methane mitigation. This study pioneers a holistic approach to unravelling the biopotential of methanotrophs, offering unprecedented avenues for biotechnological applications.