Stable-isotopic and metagenomic analyses reveal metabolic and microbial link of aerobic methane oxidation coupled to denitrification at different O2 levels

Using RNA-Stable isotope probing to investigate methane oxidation metabolites and active microbial communities in methane oxidation coupled to denitrification

The active denitrifying communities performing methane oxidation coupled to denitrification (MOD) were investigated using samples from an aerobic reactor (∼20% O2 and 2% CH4) and a microaerobic reactor (2% O2, 2% CH4) undertaking denitrification. The methane oxidation metabolites excreted in the reactors were acetate, methanol, formate and acetaldehyde. Using anaerobic batch experiments supplemented with exogenously supplied 13C-labelled metabolites, the active denitrifying bacteria were identified using 16S rRNA amplicon sequencing and RNA-stable isotope probing (RNA-SIP). With the aerobic reactor (AR) samples, the maximum NO3- removal rates were 0.43 mmol g-1 d-1, 0.40 mmol g-1 d-1, 0.33 mmol g-1 d-1 and 0.10 mmol g-1 d-1 for exogenously supplied acetate, formate, acetaldehyde and methanol batch treatments respectively, while with the microaerobic reactor (MR) samples, the maximum NO3- removal rates were 0.41 mmol g-1 d-1, 0.33 mmol g-1 d-1, 0.38 mmol g-1 d-1 and 0.14 mmol g-1 d-1 for exogenously supplied acetate, formate, acetaldehyde and methanol batch treatments respectively. The RNA-SIP experiments with 13C-labelled acetate, formate, and methanol identified Methyloversatilis, and Hyphomicrobium as the active methane-driven denitrifying bacteria in the AR samples, while Pseudoxanthomonas, Hydrogenophaga and Hyphomicrobium were the active MOD bacteria in the MR samples. Collectively, all the data indicate that formate is a key cross-feeding metabolite excreted by methanotrophs and consumed by denitrifiers performing MOD.

Different oxygen affinities of methanotrophs and Comammox Nitrospira inform an electrically induced symbiosis for nitrogen loss

Aerobic methanotrophs establish a symbiotic association with denitrifiers to facilitate the process of aerobic methane oxidation coupled with denitrification (AME-D). However, the symbiosis has been frequently observed in hypoxic conditions continuing to pose an enigma. The present study has firstly characterized an electrically induced symbiosis primarily governed by Methylosarcina and Hyphomicrobium for the AME-D process in a hypoxic niche caused by Comammox Nitrospira. The kinetic analysis revealed that Comammox Nitrospira exhibited a higher apparent oxygen affinity compared to Methylosarcina. While the coexistence of comammox and AME-D resulted in an increase in methane oxidation and nitrogen loss rates, from 0.82 ± 0.10 to 1.72 ± 0.09 mmol CH4 d-1 and from 0.59 ± 0.04 to 1.30 ± 0.15 mmol N2 d-1, respectively. Furthermore, the constructed microbial fuel cells demonstrated a pronounced dependence of the biocurrents on AME-D due to oxygen competition, suggesting the involvement of direct interspecies electron transfer in the AME-D process under hypoxic conditions. Metagenomic and metatranscriptomic analysis revealed that Methylosarcina efficiently oxidized methane to formaldehyde, subsequently generating abundant NAD(P)H for nitrate reduction by Hyphomicrobium through the dissimilatory RuMP pathway, leading to CO2 production. This study challenges the conventional understanding of survival mechanism employed by AME-D symbionts, thereby contributing to the characterization responsible for limiting methane emissions and promoting nitrogen removal in hypoxic regions.

Management of biofilm by an innovative layer-structured membrane for membrane biofilm reactor (MBfR) to efficient methane oxidation coupled to denitrification (AME-D)

Aerobic methane oxidation coupled with denitrification (AME-D) has garnered significant attention as a promising technology for nitrogen removal from water. Effective biofilm management on the membrane surface is essential to enhance the efficiency of nitrate removal in AME-D systems. In this study, we introduce a novel and scalable layer-structured membrane (LSM) developed using a meticulously designed polyurethane sponge. The application of the LSM in advanced biofilm management for AME-D resulted in a substantial enhancement of denitrification performance. Our experimental results demonstrated remarkable improvements in nitrate-removal flux (92.8 mmol-N m-2 d-1) and methane-oxidation rate (325.6 mmol m-2 d-1) when using an LSM in a membrane biofilm reactor (L-MBfR) compared with a conventional membrane reactor (C-MBfR). The l-MBfR exhibited 12.4-, 6.8- and 3.4-fold increases in nitrate-removal rate, biomass-retention capacity, and methane-oxidation rate, respectively, relative to the control C-MBfR. Notably, the l-MBfR demonstrated a 3.5-fold higher abundance of denitrifying bacteria, including Xanthomonadaceae, Rhodocyclaceae, and Methylophilaceae. In addition, the denitrification-related enzyme activity was twice as high in the l-MBfR than in the C-MBfR. These findings underscore the LSM's ability to create anoxic/anaerobic microenvironments conducive to biofilm formation and denitrification. Furthermore, the LSM exhibited a unique advantage in shaping microbial community structures and facilitating cross-feeding interactions between denitrifying bacteria and aerobic methanotrophs. The results of this study hold great promise for advancing the application of MBfRs in achieving efficient and reliable nitrate removal through the AME-D pathway, facilitated by effective biofilm management.

Metagenomics coupled with thermodynamic analysis revealed a potential way to improve the nitrogen removal efficiency of the aerobic methane oxidation coupled to denitrification process under the hypoxic condition

Aerobic methane (CH4) oxidation coupled to denitrification (AME-D) is a promising wastewater treatment process for CH4 utilization and nitrogen removal. However, it is unclear which CH4-derived carbons are suitable for the AME-D process and how these organics are metabolized. In this study, metagenomics coupled with a thermodynamic model were used to explore the microorganisms and their metabolic mechanisms in an AME-D membrane biofilm reactor (MBfR) with high nitrogen removal efficiency. Results revealed that the aerobic methanotrophs of Methylomonas with the CH4-based fermentation potential were highly enriched and played an important role in CH4 conversion in the MBfR. Bacteria of Xanthomonadaceae, Methylophilaceae, Bacteroidetes, Rhodocyclaceae, Hyphomicrobium were the main denitrifiers. C1 compounds (methanol, formaldehyde and formate) and CH4-based fermentation products are promising cross-feeding intermediates of the AME-D. Specially, by means of integrating the CH4-based fermentation with denitrification, the minimum amount of CH4 required to remove per mole of nitrate can be further reduced to 1.25 mol-CH4 mol-1-NO3-, even lower than that of methanol. Compared to the choice to secrete methanol, type I aerobic methanotrophs require a 15 % reduction in the amount of oxygen required to secrete fermentation metabolites, but a 72 % increase in the amount of CH4-C released. Based on this trade-off, optimizing oxygen supply strategies will help to construct engineered microbiomes focused on aerobic methanotrophs with CH4-based fermentation potential. This study gives an insight into C and N conversions in the AME-D process and highlights the role of CH4-based fermentation in improving the nitrogen removal efficiency of the AME-D process.

Responses of greenhouse gas emissions to aeration coupled with functional membrane during industrial-scale composting of dairy manure: Insights into bacterial community composition and function

Greenhouse gas (GHG) emissions from manure management processes deserve more attention. Using three industrial-scale experiments, this study comprehensively evaluated the effects of different aeration coupled with semi-permeable membrane-covered strategies on the structure and function of bacterial communities and their impact on GHG emissions during dairy manure aerobic composting. The succession of the bacterial communities tended to be consistent for similar aeration strategies. Ruminiclostridium and norank_f__MBA03 were significantly positively correlated with the methane emission rate, and forced aeration coupled with semi-permeable membrane-covered decreased GHG emissions by inhibiting these taxa. Metabolism was the most active function of the bacterial communities, and its relative abundance accounted for 75.69%-80.23%. The combined process also enhanced carbohydrate metabolism and amino acid metabolism. Therefore, forced aeration coupled with semi-permeable membrane-covered represented a novel strategy for reducing global warming potential by regulating the structure and function of the bacterial communities during aerobic composting of dairy manure.

Microaerobic methane-driven denitrification in a biotrickle bed - Investigating the active microbial biofilm community composition using RNA-stable isotope probing

A microaerobic (2% O2 v/v) biotrickle bed reactor supplied continuously with 2% methane to drive nitrate removal (MAME-D) was investigated using 16S rDNA and rRNA amplicon sequencing in combination with RNA-stable isotope probing (RNA-SIP) to identify the active microorganisms. Methane removal rates varied from 500 to 1000 mmol m-3h-1 and nitrate removal rates from 25 to 58 mmol m-3h-1 over 55 days of operation. Biofilm samples from the column were incubated in serum bottles supplemented with 13CH4. 16S rDNA analysis indicated a simple community structure in which four taxa accounted for 45% of the total relative abundance (RA). Dominant genera included the methanotroph Methylosinus and known denitrifiers Nubsella and Pseudoxanthomonas; along with a probable denitrifier assigned to the order Obscuribacterales. The 16S rRNA results revealed the methanotrophs Methylocystis (15% RA) and Methylosinus (10% RA) and the denitrifiers Arenimonas (10% RA) and Pseudoxanthomonas (7% RA) were the most active genera. Obscuribacterales was the most active taxa in the community at 22% RA. Activity was confirmed by the Δ buoyant density changes with time for the taxa, indicating most of the community activity was associated with methane oxidation and subsequent consumption of methanotrophic metabolic intermediates by the denitrifiers. This is the first report of RNA stable isotope probing within a microaerobic methane driven denitrification system and the active community was markedly different from the full community identified via 16S-rDNA analysis.

Diversity and functional annotation of microorganisms in anaerobic chamber treating nitrate-rich wastewater

The vertical flow constructed wetlands (VFCW) for the treatment of domestic wastewater has become a conventional and cost effective treatment system with one of the major disadvantage of elevated nitrate concentrations. The present study makes an effort in providing a new design of anaerobic denitrification unit termed as anaerobic chamber (AC) which was introduced after two-stage VFCW to remove nitrates from the treated wastewater (WW). The AC provided all the essential conditions of effective denitrification such as anaerobic environment with enough carbon and nitrogen source. To understand the pollutant removal mechanism in AC, microbial diversity and functional annotation was studied by metagenomic analysis of sequences obtained from biofilm formed in AC. The efficiency of AC was measured with respect to physicochemical wastewater quality parameters. The removal efficiencies were 88, 65, 43 and 27% for total nitrogen, nitrate (NO3), ammoniacal-nitrogen (NH4) and ortho-phosphate respectively. The microbial flora was much more diverse and unique pertaining to anaerobic microbes in AC compared to WW with total of 954 and 1191 genuses respectively with minimum abundance of 10 hits. The metagenomes exhibited 188% more Archaea in the AC than WW where Crenarchaeota, Euryarchaeota, Korarchaeota, Nanoarchaeota and Thaumarchaeota were major phyla with 60 genuses. The nitrogen metabolism was reported in terms of assimilatory nitrate reductase. As the class, Proteobacteria, Actinobacteria were prominent in WW, whereas Proteobacteria, Chloroflexi in AC were abundant. From functional annotation of sequences, the microbial flora in AC has the potential of removal of pollutants present in the form of carbon, nitrogen, and phosphorus.

A municipal wastewater treatment plant "drinking beer" for reduction of cost and carbon emission

In wastewater treatment plants (WWTPs), external carbon sources are often required due to low C/N influent. However, the use of external carbon sources can increase treatment costs and cause large carbon emissions. Beer wastewater, which contains a substantial amount of carbon, is often treated separately in China, consuming significant energy and cost. However, most studies using beer wastewater as an external carbon source are still on a laboratory scale. To address this issue, this study proposes using beer wastewater as an external carbon source in an actual WWTP to reduce operating costs and carbon emissions while achieving a win-win situation. The denitrification rate of beer wastewater was found to be higher than that of sodium acetate , resulting in improved treatment efficiency of the WWTP. Specifically, COD, BOD₅, TN, NH₄⁺-N and TP increased by 3.4%, 1.6%, 10.8%, 1.1%, and 1.7%, respectively. Additionally, the treatment cost and carbon emission per 10 000 tons of wastewater treated were reduced by 537.31 yuan and 2.27 t CO₂, respectively. These results indicate that beer wastewater has significant utilization potential and provide a reference for using different types of production wastewater in WWTPs. This study's findings demonstrate the feasibility of implementing this approach in an actual WWTP setting.

Eichhornia crassipes-rhizospheric biofilms contribute to nutrients removal and methane oxidization in wastewater stabilization ponds receiving simulative sewage treatment plants effluents

Wastewater stabilization ponds (WSPs) have been used in treating sewage treatment plants (STPs) effluents. However, little is known about the role of rhizospheric biofilms on methane release in WSPs with floating plants. In the present study, the nutrient removal, CH₄ fluxes, CH₄ oxidization potential and rhizospheric bacterial community were investigated in WSPs with Eichhornia crassipes under simulate STPs effluents for 31 days. At the end of the experiment, E. crassipes biomass was 5.60-8.81 times of initial weight and increased with increasing nutrients concentration. E. crassipes effectively reduced methane release and nutrients. Compared to control, E. crassipes reduced 52.30%-83.21% of CH₄ fluxes at water-atmosphere interface and had better inhibition effect on CH₄ fluxes in treatments with high nutrients. However, methane oxidization rates of E. crassipes roots were higher in low nutrients (0.83 ± 0.046 mg CH₄ (kg fresh plant)^-1 day^-1) than high nutrients (0.12 ± 0.04 mg CH₄ (kg fresh plant)^-1 day^-1). Structural equation modeling revealed that biomass of E. crassipes has negative effect on CH₄ fluxes (-0.453, p = 0.000). Proteobacteria, Bacteroidetes, Planctomycetes, Chloroflexi and Actinobacteria were the predominant phyla in the rhizospheric biofilm of E. crassipes and contributed to nutrients removal. Aerobic methanotrophs and pomA abundances were higher in rhizospheric biofilm exposed to high nutrients than low nutrients and aerobic methanotrophs had close interactions with other microorganisms and participated in the carbon and nitrogen cycle, demonstrating that many bacteria harboring pmoA gene did not fully involve in methane oxidization. These data highlight plants E. crassipes have an important role in both reducing methane release and nutrients removal.

Characterization of methanotrophic community and activity in landfill cover soils under dimethyl sulfide stress

Landfill cover soil is the environmental interface between landfills and the atmosphere and plays an important role in mitigating CH₄ emission from landfills. Here, stable isotope probing microcosms with CH₄ or CH₄ and dimethyl sulfide (DMS) were carried out to characterize activity and community structure of methanotrophs in landfill cover soils under DMS stress. The CH₄ oxidation activity in the landfill cover soils was not obviously influenced at the DMS concentration of 0.05%, while it was inhibited at the DMS concentrations of 0.1% and 0.2%. DMS-S was mainly oxidized to sulfate (SO₄^2-) in the landfill cover soils. In the landfill cover soils, DMS could inhibit the expression of bacteria and decrease the abundances of pmoA and mmoX genes, while it could prompt the expression of pmoA and mmoX genes. γ-Proteobacteria methanotrophs including Methylocaldum, Methylobacter, Crenothrix and unclassified Methylococcaceae and α-Proteobacteria methanotrophs Methylocystis dominated in assimilating CH₄ in the landfill cover soils. Of them, Methylobacter and Crenothrix had strong tolerance to DMS or DMS could promote the growth and activity of Methylobacter and Crenothrix, while Methylocaldum had weak tolerance to DMS and showed an inhibitory effect. Metagenomic analyses showed that methanotrophs had the genes of methanethiol oxidation and could metabolize CH₄ and methanethiol simultaneously in the landfill cover soils. These findings suggested that methanotrophs might metabolize sulfur compounds in the landfill cover soils, which may provide the potential application in engineering for co-removal of CH₄ and sulfur compounds.

Synergy effects of Methylomonas koyamae and Hyphomicrobium methylovorum under methanethiol stress

Methanotrophs are able to metabolize volatile organic sulfur compounds (VOSCs), excrete organic carbon during CH₄ oxidation, and influence microbial community structure and function of the ecosystem. In return, microbial community structure and environmental factors can affect the growth metabolism of methanotrophs. In this study, Methylomonas koyamae and Hyphomicrobium methylovorum were used for model organisms, and methanethiol (MT) was chosen for a typical VOSC to investigate the synergy effects under VOSC stress. The results showed that when Hyphomicrobium methylovorum was co-cultured with Methylomonas koyamae in the medium with CH₄ used as the carbon source, the co-culture had better MT tolerance relative to Methylomonas koyamae and oxidized all CH₄ within 120 h, even at the initial MT concentration of 2000 mg m^-3. The optimal co-culture ratios of Methylomonas koyamae to Hyphomicrobium methylovorum were 4:1-12:1. Although MT could be converted spontaneously to dimethyl disulfide (DMDS), H₂S, and CS₂ in air, faster losses of MT, DMDS, H₂S, and CS₂ were observed in each strain mono-culture and the co-culture. Compared with Hyphomicrobium methylovorum, MT was degraded more quickly in the Methylomonas koyamae culture. During the co-culture, the CH₄ oxidation process of Methylomonas koyamae could provide carbon and energy sources for the growth of Hyphomicrobium methylovorum, while Hyphomicrobium methylovorum oxidized MT to help Methylomonas koyamae detoxify. These findings are helpful to understand the synergy effects of Methylomonas koyamae and Hyphomicrobium methylovorum under MT stress and enrich the role of methanotrophs in the sulfur biogeochemical cycle. KEY POINTS: • The co-culture of Methylomonas and Hyphomicrobium has better tolerance to CH₃SH. • Methylomonas can provide carbon sources for the growth of Hyphomicrobium. • The co-culture of Methylomonas and Hyphomicrobium enhances the removal of CH₄ and CH₃SH.

Characterization of anaerobic oxidation of methane and microbial community in landfills with aeration

Landfills are the third largest source of anthropogenic CH₄ emissions. Anaerobic oxidation of methane (AOM) activity and communities of methane-oxidizing bacteria were investigated in three informal landfills in this study, namely, BJ, CH and SZ landfills, among which BJ and CH represent traditional anaerobic landfills, while the SZ landfill was subjected to aeration to accelerate waste stabilization. The AOM rates of the investigated landfilled wastes ranged from 3.66 to 23.91 nmol g^-1 h^-1. Among the three landfills, the AOM rate was highest in the SZ-1-Top sample, which was closest to the aeration pipe. Among the possible electron acceptors for AOM, including NO₃^-, NO₂^-, SO₄^2- and Fe³⁺, the NO₂^--N content was the only variable that was positively correlated with the AOM rate. Compared with α-Proteobacteria methanotrophs, γ-Proteobacteria methanotrophs were more abundant in the landfilled waste, especially Methylobacter, which was detected in nearly all samples. Members of the family Methylomirabilaceae, including Candidatus Methylomirabilis, were also detected in the SZ-1 and SZ-2-Bot samples. The relative abundance of the main methanotrophs in the families Methylomonadaceae, Methylococcaceae, Rokubacteriales and Methylomirabilaceae, the genus Methylocystis and the phylum NC10 were all positive correlations with the contents of NO₂^--N in the landfilled waste samples. Additionally, significantly positive correlations were observed between the AOM rates and the relative abundance of the main methanotrophs except for the family Methylococcaceae. This indicated that aeration could enhance the conversion of nitrogen compounds in the landfilled waste, in which the high contents of NO₂^--N could stimulate the growth of methanotrophs and increase AOM rate. These findings are helpful for understanding the mechanisms of CH₄ oxidation in landfills and for taking effective measures to mitigate CH₄ emissions from landfills.

Impact of Petroleum Contamination on the Structure of Saline Soil Bacterial Communities

Petroleum contamination may lead to variations in soil microbial community structure and activities. The bioremediation of petroleum-contaminated soil typically depends on the characteristics and activities of oil-degrading microorganisms, which can be introduced or be part of the native soil microbiota. Thus, analyzing the structure of the microbial community and internal relationships in the bioremediation process is critical. Our study characterized the physical and chemical properties, microbial community structure, and microbial diversity of surface soil collected near an oilfield. The total carbon (TC), total organic carbon (TOC), and microbial diversity in oil-contaminated soil was found higher than in uncontaminated samples. Proteobacteria abundance was inhibited with oil pollution, while Actinomycetes abundance was enhanced. Some indigenous hydrocarbon-degrading bactera were enriched by oil pollution, such as Bacillus, Actinomarinales norank, Balneolaceae uncultured, Marinobacter, and Pseudomonas. Furthermore, Rokubacteria, Nitrospirae, and Entotheonellaeota were significant differences in the contaminated group. There were 16 genera with significant differences in the polluted group, such as Woeseia, Pelagibius, Pontibacillus, IS_44, Aliifodinibius, while Halothiobacillus, Algoriphagus, Novosphingobium, etc. had significant differences in the uncontaminated group. Redundancy analysis demonstrated that the responses of the microorganisms to the evaluated environmental factors were different, and TC was the most important driver of microbial community variation. Moreover, TOC was the largest contributor to operational taxonomic unit (OTU) and Chao index variations. Our results provide a theoretical basis for the enhancement of microbial activity in oil-contaminated soil, which might improve bioremediation efficacy.

Nitrate/nitrite-dependent anaerobic oxidation of methane (N-AOM) as a technology platform for greenhouse gas abatement in wastewater treatment plants: State-of-the-art and challenges

Nitrate/nitrite-dependent anaerobic oxidation of methane (N-AOM) is a metabolic process recently discovered and partially characterized in terms of the microorganisms and pathways involved. The N-AOM process can be a powerful tool for mitigating the impacts of greenhouse gas emissions from wastewater treatment plants by coupling the reduction of nitrate or nitrite with the oxidation of residual dissolved methane. Besides specific anaerobic methanotrophs such as bacteria members of the phylum NC10 and archaea belonging to the lineage ANME-2d, recent reports suggested that other methane-oxidizing bacteria in syntrophy with denitrifiers can also perform the N-AOM process, which facilitates the application of this metabolic process for the oxidation of residual methane under realistic scenarios. This work constitutes a state-of-art review that includes the fundamentals of the N-AOM process, new information on process microbiology, bioreactor configurations, and operating conditions for process implementation in WWTP. Potential advantages of the N-AOM process over aerobic methanotrophic biotechnologies are presented, including the potential interrelation of the N-AOM with other nitrogen removal processes within the WWTP, such as the anaerobic ammonium oxidation. This work also addressed the challenges of this biotechnology towards its application at full scale, identifying and discussing critical research niches.

Heterogeneity of CH4-derived carbon induced by O2:CH4 mediates the bacterial community assembly processes

The mechanism by which O₂:CH₄ controls microbial community assembly in the process of aerobic methane oxidation coupled to denitrification (AMED) remains largely uncharacterized, which hinders the design of engineering microbiomes for the AMED. In this study, the changes in the bacterial community in fed-batch serum bottle reactors under different O₂:CH₄ ratios were systematically characterized. The ratios of CH₄ consumption to the amount of nitrate removal in the treatment with O₂:CH₄ = 1.5:1, O₂:CH₄ = 0.5:1, and O₂:CH₄ = 0.25:1 were 13.1 ± 3.4, 4.7 ± 1.1, and 5.9 ± 3.0 mol-CH₄ mol^-1-NO₃^-, respectively. The α-diversity of the bacterial community increased as O₂:CH₄ decreased. Significantly different selection patterns were found for the high and low O₂:CH₄ ratios. The coherence process dominated the selection at high O₂:CH₄ ratios, while the diversification process played a role when O₂:CH₄ was low. Differences were also observed in the composition of CH₄-derived carbon between treatments with O₂:CH₄ = 1.5:1 and O₂:CH₄ = 0.5:1. Compared with the treatments with O₂:CH₄ = 1.5:1, the concentrations of methanol, formaldehyde, acetate, and ethanol in the treatment with O₂:CH₄ = 0.5:1 were significantly higher, while the concentration of formate was significantly lower. The heterogeneity of CH₄-derived carbon induced by O₂:CH₄ was likely to be responsible for the differences in the selection patterns. Our findings bridge the gaps between the observations of bacterial community perturbations and ecological community assembly theories, highlighting the potential of the bottom-up design approach to improve the nitrate removal rate of the AME-D.

Identifying spatiotemporal patterns of COVID-19 transmissions and the drivers of the patterns in Toronto: a Bayesian hierarchical spatiotemporal modelling

Spatiotemporal patterns and trends of COVID-19 at a local spatial scale using Bayesian approaches are hardly observed in literature. Also, studies rarely use satellite-derived long time-series data on the environment to predict COVID-19 risk at a spatial scale. In this study, we modelled the COVID-19 pandemic risk using a Bayesian hierarchical spatiotemporal model that incorporates satellite-derived remote sensing data on land surface temperature (LST) from January 2020 to October 2021 (89 weeks) and several socioeconomic covariates of the 140 neighbourhoods in Toronto. The spatial patterns of risk were heterogeneous in space with multiple high-risk neighbourhoods in Western and Southern Toronto. Higher risk was observed during Spring 2021. The spatiotemporal risk patterns identified 60% of neighbourhoods had a stable, 37% had an increasing, and 2% had a decreasing trend over the study period. LST was positively, and higher education was negatively associated with the COVID-19 incidence. We believe the use of Bayesian spatial modelling and the remote sensing technologies in this study provided a strong versatility and strengthened our analysis in identifying the spatial risk of COVID-19. The findings would help in prevention planning, and the framework of this study may be replicated in other highly transmissible infectious diseases.

CS2 increasing CH4-derived carbon emissions and active microbial diversity in lake sediments

Lakes are important methane (CH₄) sources to the atmosphere, especially eutrophic lakes with cyanobacterial blooms accompanied by volatile sulfur compound (VSC) emissions. CH₄ oxidation is a key strategy to mitigate CH₄ emission from lakes. In this study, we characterized the fate of CH₄-derived carbon and active microbial communities in lake sediments with CS₂ used as a typical VSC, based on the investigation of CH₄ and VSC fluxes from Meiliang Bay in Lake Taihu. Stable isotope probing microcosm incubation showed that the efficiency of CH₄-derived carbon incorporated into organic matter was 21.1% in the sediment with CS₂ existence, which was lower than that without CS₂ (27.3%). SO₄^2--S was the main product of CS₂ oxidation under aerobic condition, accounting for 59.3-62.7% of the input CS₂-S. CS₂ and CH₄ coexistence led to a decrease of methanotroph and methylotroph abundances and stimulated the production of extracellular polymeric substances. CS₂ and its metabolites including total sulfur, SO₄^2- and acid volatile sulfur acted as the main drivers influencing the active microbial community structure in the sediments. Compared with α-proteobacteria methanotrophs, γ-proteobacteria methanotrophs Methylomicrobium, Methylomonas, Crenothrix and Methylosarcina were more dominant in the sediments. CH₄-derived carbon mainly flowed into methylotrophs in the first stage. With CH₄ consumption, more CH₄-derived carbon flowed into non-methylotrophs. CS₂ could prompt more CH₄-derived carbon flowing into non-methanotrophs and non-methylotrophs, such as sulfur-metabolizing bacteria. These findings can help elucidate the influence of VSCs on microorganisms and provide insights to carbon fluxes from eutrophic lake systems.

Application of external carbon source in heterotrophic denitrification of domestic sewage: A review

The carbon source is essential as an electron donor in the heterotrophic denitrification process. When there is a lack of organic carbon sources in the system, an external carbon source is needed to improve denitrification efficiency. This review compiles the effects of liquid, solid and gaseous carbon sources on denitrification. Sodium acetate has better denitrification efficiency and is usually the first choice for external carbon sources. Fermentation by-products have been demonstrated to have the same denitrification efficiency as sodium acetate. Compared with cellulose-rich materials, biodegradable polymers have better and more stable denitrification performance in solid-phase nitrification, but their price is higher than the former. Methane as a gaseous carbon source is studied mainly by aerobic methane oxidation coupled with denitrification, which is feasible using methane as a carbon source. Liquid carbon sources are better controlled and utilized than solid carbon sources and gaseous carbon sources. In addition, high carbon to nitrogen ratio and hydraulic retention time can promote denitrification, while high dissolved oxygen (DO>2.0 mg L^-1) will inhibit the denitrification process. At the same time, high temperature is conducive to the decomposition of carbon sources by microorganisms. This review also considers the advantages and disadvantages of different carbon sources and cost analysis to provide a reference for looking for more economical and effective external carbon sources in the future.

Iron-Activated Carbon Systems to Enhance Aboriginal Aerobic Denitrifying Bacterial Consortium for Improved Treatment of Micro-Polluted Reservoir Water: Performances, Mechanisms, and Implications

Although many source waterbodies face nitrogen pollution problems, the lack of organic electron donors causes difficulties when aerobic denitrifying bacteria are used to treat micro-polluted water. Different forms of iron with granular activated carbon (AC) as carriers were used to stimulate aboriginal microorganisms for the purification of micro-polluted source water. Compared with the iron-absent AC system, targeted pollutants were significantly removed (75.76% for nitrate nitrogen, 95.90% for total phosphorus, and 80.59% for chemical oxygen demand) in the sponge-iron-modified AC system, which indicated that iron promoted the physical and chemical removal of pollutants. In addition, high-throughput sequencing showed that bacterial distribution and interaction were changed by ion dosage, which was beneficial for pollutant transformation and reduction. Microbial functions, such as pollutant removal and expression of functional enzymes that were responsible for the transformation of nitrate nitrogen to ammonia, were highly efficient in iron-applied systems. This study provides an innovative strategy to strengthen in situ remediation of micro-pollution in waterbodies.

Novel intertidal wetland sediment-inoculated moving bed biofilm reactor treating high-salinity wastewater: Metagenomic sequencing revealing key functional microorganisms

In this study, two lab-scale moving bed biofilm reactors (MBBR), seeded with intertidal wetland sediment (IWS) and activated sludge (AS), were constructed to compare their performances in treating high-salinity (3%) wastewater. Under a wide range of influent TOC (178-620 mg/L) and NH₄⁺-N (25-100 mg/L), both the MBBRs (R_iws and R_as) exhibited excellent TOC removal efficiencies of >95%. Regarding nitrogen reduction, R_iws exhibited a significantly superior TN removal efficiency of 90.2 ± 1.8% than that of R_as (76.8 ± 2.9%). A correlation analysis was innovatively conducted comparing the results between metagenomic sequencing and DNA pyrosequencing, and positive linear relationships were found with R² values of 0.763-0.945. Meanwhile, for illustration of different TN removal performance, nitrogen metabolic pathways were also assessed. Moreover, a list of functional oxidases (EC: 1.13.11.1, EC: 1.13.11.2, EC: 1.13.11.24, EC: 1.13.12.16, EC: 1.4.3.4, EC: 1.16.3.3, EC: 1.14.14.28) was found in IWS, revealing its potential in degradation of recalcitrant organics.

Metabolic flexibility of aerobic methanotrophs under anoxic conditions in Arctic lake sediments

Methane (CH₄) emissions from Arctic lakes are a large and growing source of greenhouse gas to the atmosphere with critical implications for global climate. Because Arctic lakes are ice covered for much of the year, understanding the metabolic flexibility of methanotrophs under anoxic conditions would aid in characterizing the mechanisms responsible for limiting CH₄ emissions from high-latitude regions. Using sediments from an active CH₄ seep in Lake Qalluuraq, Alaska, we conducted DNA-based stable isotope probing (SIP) in anoxic mesocosms and found that aerobic Gammaproteobacterial methanotrophs dominated in assimilating CH₄. Aerobic methanotrophs were also detected down to 70 cm deep in sediments at the seep site, where anoxic conditions persist. Metagenomic analyses of the heavy DNA from ¹³CH₄-SIP incubations showed that these aerobic methanotrophs had the capacity to generate intermediates such as methanol, formaldehyde, and formate from CH₄ oxidation and to oxidize formaldehyde in the tetrahydromethanopterin (H₄MPT)-dependent pathway under anoxic conditions. The high levels of Fe present in sediments, combined with Fe and CH₄ profiles in the persistent CH₄ seep site, suggested that oxidation of CH₄, or, more specifically, its intermediates such as methanol and formaldehyde might be coupled to iron reduction. Aerobic methanotrophs also possessed genes associated with nitrogen and hydrogen metabolism, which might provide potentially alternative energy conservation options under anoxic conditions. These results expand the known metabolic spectrum of aerobic methanotrophs under anoxic conditions and necessitate the re-assessment of the mechanisms underlying CH₄ oxidation in the Arctic, especially under lakes that experience extended O₂ limitations during ice cover.