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

Municipal solid waste (MSW) landfills are the third largest anthropogenic source ofmethane (CH4) emissions in the United States. The majority of CH4 generated inlandfills is converted to carbon dioxide (CO2) by CH4-oxidizing bacteria (MOB) presentin the landfill cover soil, whose activity is controlled by various environmental factorsincluding temperature. As landfill temperature can fluctuate substantially seasonally,rates of CH4 oxidation can also vary, and this could lead to incomplete oxidation. Thisstudy aims at analyzing the effect of temperature on CH4 oxidation potential andmicrobial community structure of methanotrophs in laboratory-based studies of landfillcover soil and cultivated consortia. As landfill covers can experience a wide range oftemperatures, soil and enrichments were incubated at temperatures ranging from 6C to70C, and rates of CH4 oxidation were measured, and microbial community structurewas analyzed using 16S rRNA gene amplicon sequencing and shotgun metagenomesequencing. CH4 oxidation occurred at temperatures from 6° to 50C in soil microcosmtests, and 6° to 40C in enrichment batch tests; maximum rates of oxidation wereobtained at 30°C. A corresponding shift in the soil microbiota was observed, with atransition from putative psychrophilic to thermophilic methanotrophs with increasingincubation temperature. A strong shift in methanotrophic community structure wasobserved above 30°C. At temperature up to 30°C, methanotrophs from the genusMethylobacter were dominant in soils and enrichments; at temperatures of 40°C,putative thermophilic methanotrophs from the genus Methylocaldum becomedominant. Maximum rate measurements of nearly 195 μg CH4 g-1 d-1 were observedin soil incubations, while observed maximum rates in enrichments were significantlylower, likely as a result of diffusion limitations. We demonstrate that temperature is acritical factor affecting rates of landfill soil CH4 oxidation in vitro, and that changingrates of CH4 oxidation are in part driven by changes in dominant methylotrophcommunity structure.