Delineating the Drivers and Functionality of Methanogenic Niches within an Arid Landfill.

Microbial communities mediate the transformation of organic matter within landfills into methane (CH). Yet their ecological role in CH production is rarely evaluated. To characterize the microbiome associated with this biotransformation, the overall community and methanogenic were surveyed in an arid landfill using leachate collected from distinctly aged landfill cells (i.e., younger, intermediate, and older). We hypothesized that distinct methanogenic niches exist within an arid landfill, driven by geochemical gradients that developed under extended and age-dependent waste biodegradation stages. Using 16S rRNA and gene amplicon sequencing, we identified putative methanogenic niches as follows. The order was the most abundant order in leachate from younger cells, where leachate temperature and propionate concentrations were measured at 41.8°C ± 1.7°C and 57.1 ± 10.7 mg L. In intermediate-aged cells, the family was identified as a putative specialist family under intermediate-temperature and -total dissolved solid (TDS) conditions, wherein samples had a higher alpha diversity index and near CH concentrations. In older-aged cells, accumulating metals and TDS supported , " Bathyarchaeota," and " Verstraetearchaeota" operational taxonomic units (OTUs). Consistent with the data, we assayed methanogenic activity across the age gradient through stable isotopic measurements of δC of CH and δC of CO. The majority (80%) of the samples' carbon fractionation was consistent with hydrogenotrophic methanogenesis. Together, we report age-dependent geochemical gradients detected through leachate in an arid landfill seemingly influencing CH production, niche partitioning, and methanogenic activity. Microbiome analysis is becoming common in select municipal and service ecosystems, including wastewater treatment and anaerobic digestion, but its potential as a microbial-status-informative tool to promote or mitigate CH production has not yet been evaluated in landfills. Methanogenesis mediated by is highly active in solid-waste microbiomes but is commonly neglected in studies employing next-generation sequencing techniques. Identifying methanogenic niches within a landfill offers detail into operations that positively or negatively impact the commercial production of methane known as biomethanation. We provide evidence that the geochemistry of leachate and its microbiome can be a variable accounting for ecosystem-level (coarse) variation of CH production, where we demonstrate through independent assessments of leachate and gas collection that the functional variability of an arid landfill is linked to the composition of methanogenic .