Synergistic effects of vegetation and microorganisms on enhancing of biodegradation of landfill gas

The uncontrolled release of landfill gas represents a significant hazard to both human health and ecological well-being. However, the synergistic interactions of vegetation and microorganisms can effectively mitigate this threat by removing pollutants. This study provides a comprehensive review of the current status of controlling landfill gas pollution through the process of revegetation in landfill cover. Our survey has identified several common indicator plants such as Setaria faberi, Sarcandra glabra, and Fraxinus chinensis that grow in covered landfill soil. Local herbaceous plants possess stronger tolerance, making them ideal for the establishment of closed landfills. Moreover, numerous studies have demonstrated that cover plants significantly promote methane oxidation, with an average oxidation capacity twice that of bare soil. Furthermore, we have conducted an analysis of the interrelationships among vegetation, landfill gas, landfill cover soil, and microorganisms, thereby providing a detailed understanding of the potential for vegetation restoration in landfill cover. Additionally, we have summarized studies on the rhizosphere effect and have deduced the mechanisms through which plants biodegrade methane and typical non-methane pollutants. Finally, we have suggested future research directions to better control landfill gas using vegetation and microorganisms.

Microbial Processes and Microbial Communities in the Water Column of the Polar Meromictic Lake Bol'shie Khruslomeny at the White Sea Coast

Microbiological, molecular ecological, biogeochemical, and isotope geochemical research was carried out at the polar Lake Bol'shie Khruslomeny at the coast of the Kandalaksha Bay, White Sea in March and September 2017. The uppermost mixolimnion was oxic, with low salinity (3-5%). The lower chemocline layer was brown-green colored, with very high content of particulate organic matter (up to 11.8 mg C L-1). The lowermost monimolimnion had marine salinity (22-24%) and very high concentrations of sulfide (up to 18 mmol L-1) and CH4 (up to 1.8 mmol L-1). In the chemocline, total microbial abundance and the rate of anoxygenic photosynthesis were 8.8 × 106 cells mL-1 and 34.4 μmol C L-1 day-1, respectively. Both in March and September, sulfate reduction rate increased with depth, peaking (up to 0.6-1.1 μmol S L-1 day-1) in the lower chemocline. Methane oxidation rates in the chemocline were up to 85 and 180 nmol CH4 L-1 day-1 in March and September, respectively; stimulation of this process by light was observed in September. The percentages of cyanobacteria and methanotrophs in the layer where light-induced methane oxidation occurred were similar, ∼2.5% of the microbial community. Light did not stimulate methane oxidation in deeper layers. The carbon isotope composition of particulate organic matter (δ13C-Corg), dissolved carbonates (δ13C-DIC), and methane (δ13C- CH4) indicated high microbial activity in the chemocline. Analysis of the 16S rRNA gene sequences revealed predominance of Cyanobium cyanobacteria (order Synechococcales) in the mixolimnion. Green sulfur bacteria Chlorobium phaeovibrioides capable of anoxygenic photosynthesis constituted ∼20% of the chemocline community both in March and in September. Methyloprofundus gammaptoteobacteria (family Methylomonaceae) were present in the upper chemocline, where active methane oxidation occurred. During winter, cyanobacteria were less abundant in the chemocline, while methanotrophs occurred in higher horizons, including the under-ice layer. Chemolithotrophic gammaproteobacteria of the genus Thiomicrorhabdus, oxidizing reduced sulfur compounds at low oxygen concentrations, were revealed in the chemocline in March. Both in March and September archaea constituted up to 50% of all microorganisms in the hypolimnion. The percentage of putative methanogens in the archaeal community was low, and they occurred mainly in near-bottom horizons.

Effect of temperature on methane oxidation and community composition in landfill cover soil

Municipal solid waste (MSW) landfills are the third largest anthropogenic source of methane (CH₄) emissions in the United States. The majority of CH₄ generated in landfills is converted to carbon dioxide (CO₂) by CH₄-oxidizing bacteria (MOB) present in the landfill cover soil, whose activity is controlled by various environmental factors including temperature. As landfill temperature can fluctuate substantially seasonally, rates of CH₄ oxidation can also vary, and this could lead to incomplete oxidation. This study aims at analyzing the effect of temperature on CH₄ oxidation potential and microbial community structure of methanotrophs in laboratory-based studies of landfill cover soil and cultivated consortia. Soil and enrichment cultures were incubated at temperatures ranging from 6 to 70 °C, and rates of CH₄ oxidation were measured, and the microbial community structure was analyzed using 16S rRNA gene amplicon sequencing and shotgun metagenome sequencing. CH₄ oxidation occurred at temperatures from 6 to 50 °C in soil microcosm tests, and 6-40 °C in enrichment culture batch tests; maximum rates of oxidation were obtained at 30 °C. A corresponding shift in the soil microbiota was observed, with a transition from putative psychrophilic to thermophilic methanotrophs with increasing incubation temperature. A strong shift in methanotrophic community structure was observed above 30 °C. At temperatures up to 30 °C, methanotrophs from the genus Methylobacter were dominant in soils and enrichment cultures; at a temperature of 40 °C, putative thermophilic methanotrophs from the genus Methylocaldum become dominant. Maximum rate measurements of nearly 195 μg CH₄ g^-1 day^-1 were observed in soil incubations, while observed maximum rates in enrichments were significantly lower, likely as a result of diffusion limitations. This study demonstrates that temperature is a critical factor affecting rates of landfill soil CH₄ oxidation in vitro and that changing rates of CH₄ oxidation are in part driven by changes in methylotroph community structure.

Effect of temperature on methane oxidation and community composition in landfill cover soil

Municipal solid waste (MSW) landfills are the third largest anthropogenic source of methane (CH₄) emissions in the United States. The majority of CH₄ generated in landfills is converted to carbon dioxide (CO₂) by CH₄-oxidizing bacteria (MOB) present in the landfill cover soil, whose activity is controlled by various environmental factors including temperature. As landfill temperature can fluctuate substantially seasonally, rates of CH₄ oxidation can also vary, and this could lead to incomplete oxidation. This study aims at analyzing the effect of temperature on CH₄ oxidation potential and microbial community structure of methanotrophs in laboratory-based studies of landfill cover soil and cultivated consortia. Soil and enrichment cultures were incubated at temperatures ranging from 6 to 70 °C, and rates of CH₄ oxidation were measured, and the microbial community structure was analyzed using 16S rRNA gene amplicon sequencing and shotgun metagenome sequencing. CH₄ oxidation occurred at temperatures from 6 to 50 °C in soil microcosm tests, and 6-40 °C in enrichment culture batch tests; maximum rates of oxidation were obtained at 30 °C. A corresponding shift in the soil microbiota was observed, with a transition from putative psychrophilic to thermophilic methanotrophs with increasing incubation temperature. A strong shift in methanotrophic community structure was observed above 30 °C. At temperatures up to 30 °C, methanotrophs from the genus Methylobacter were dominant in soils and enrichment cultures; at a temperature of 40 °C, putative thermophilic methanotrophs from the genus Methylocaldum become dominant. Maximum rate measurements of nearly 195 μg CH₄ g^-1 day^-1 were observed in soil incubations, while observed maximum rates in enrichments were significantly lower, likely as a result of diffusion limitations. This study demonstrates that temperature is a critical factor affecting rates of landfill soil CH₄ oxidation in vitro and that changing rates of CH₄ oxidation are in part driven by changes in methylotroph community structure.

Members of the Genus Methylobacter Are Inferred To Account for the Majority of Aerobic Methane Oxidation in Oxic Soils from a Freshwater Wetland

Microbial carbon degradation and methanogenesis in wetland soils generate a large proportion of atmospheric methane, a highly potent greenhouse gas. Despite their potential to mitigate greenhouse gas emissions, knowledge about methane-consuming methanotrophs is often limited to lower-resolution single-gene surveys that fail to capture the taxonomic and metabolic diversity of these microorganisms in soils. Here our objective was to use genome-enabled approaches to investigate methanotroph membership, distribution, and in situ activity across spatial and seasonal gradients in a freshwater wetland near Lake Erie. 16S rRNA gene analyses demonstrated that members of the methanotrophic Methylococcales were dominant, with the dominance largely driven by the relative abundance of four taxa, and enriched in oxic surface soils. Three methanotroph genomes from assembled soil metagenomes were assigned to the genus Methylobacter and represented the most abundant methanotrophs across the wetland. Paired metatranscriptomes confirmed that these Old Woman Creek (OWC) Methylobacter members accounted for nearly all the aerobic methanotrophic activity across two seasons. In addition to having the capacity to couple methane oxidation to aerobic respiration, these new genomes encoded denitrification potential that may sustain energy generation in soils with lower dissolved oxygen concentrations. We further show that Methylobacter members that were closely related to the OWC members were present in many other high-methane-emitting freshwater and soil sites, suggesting that this lineage could participate in methane consumption in analogous ecosystems. This work contributes to the growing body of research suggesting that Methylobacter may represent critical mediators of methane fluxes in freshwater saturated sediments and soils worldwide.IMPORTANCE Here we used soil metagenomics and metatranscriptomics to uncover novel members within the genus Methylobacter We denote these closely related genomes as members of the lineage OWC Methylobacter Despite the incredibly high microbial diversity in soils, here we present findings that unexpectedly showed that methane cycling was primarily mediated by a single genus for both methane production ("Candidatus Methanothrix paradoxum") and methane consumption (OWC Methylobacter). Metatranscriptomic analyses revealed that decreased methanotrophic activity rather than increased methanogenic activity possibly contributed to the greater methane emissions that we had previously observed in summer months, findings important for biogeochemical methane models. Although members of this Methylococcales order have been cultivated for decades, multi-omic approaches continue to illuminate the methanotroph phylogenetic and metabolic diversity harbored in terrestrial and marine ecosystems.

Evaluation of the influence of methane and copper concentration and methane mass transport on the community structure and biodegradation kinetics of methanotrophic cultures

The environmental conditions during culture enrichment, which ultimately determine its maximum specific biodegradation rate (qmax) and affinity for the target pollutant (Ks), play a key role in the performance of bioreactors devoted to the treatment of methane emissions. This study assessed the influence of Cu(2+) and CH4 concentration and the effective CH4 supply rate during culture enrichment on the structure and biodegradation kinetics of methanotrophic communities. The results obtained demonstrated that an increase in Cu(2+) concentration from 0.05 to 25 μM increased the qmax and Ks of the communities enriched by a factor of ≈ 3, even if the Cu(2+) concentration did not seem to have an effect on the enzymatic "copper switch" and only pMMO was detected. In addition, high Cu(2+) concentrations supported lower diversity coefficients (Hs ≈ 1.5× lower) and apparently promoted the growth of more adapted methanotrophs such as Methylomonas. Despite no clear effect of CH4 concentration on the population structure or on the biodegradation kinetics of the communities enriched was recorded at the two low CH4 concentrations studied (1 and 8%), a higher agitation rate increased the qmax by a factor of ≈ 2.3 and Ks by a factor of ≈ 3.1.