Anaerobic Methane-Oxidizing Microbiomes in Agriculturally Influenced Riparian Zones and Their Linkage to Reactive Nitrogen Removal
Authors
Anthony Bertagnolli1* (anthony.bertagnolli@montana.edu), Frank Stewart1, Stephanie A. Ewing2, Emma Tate2, Robert Payn2
Institutions
1Microbiology and Cell Biology, Montana State University, Bozeman, MT; 2Land Resources and Environmental Sciences, Montana State University, Bozeman, MT
Abstract
Anaerobic methane oxidation (AMO) is a microbe-mediated process active in anoxic aquatic habitats. Riparian zones (RZs) along streams in agricultural regions may be hot spots for anaerobic cycling of methane and inorganic nitrogen from leaching of excess fertilizer. However, AMO in RZs, and its potential linkage to nitrogen cycling, remains largely uncharacterized. Agricultural lowlands in the Judith River Watershed (JRW) of central Montana harbor aquifers with elevated reactive nitrogen loading and riparian aquifers that consistently display biogeochemical signatures associated with denitrification. Microbiome exploration of these riparian aquifers has suggested relatively high abundances of 16S rRNA genes related to Candidatus methylomirabilis, a bacterium known to link methane to nitrogen cycling through nitrite-dependent anaerobic methane oxidation (N-DAMO). Metabolic activity from this species would suggest a role for N-DAMO in both methane and nitrogen removal from the JRW with implications on models of greenhouse gas emissions. Goals of the project include: (1) characterize methane and other redox-sensitive compounds in JRW-RZ porewater under contrasting hydrological conditions; (2) identify genes and transcripts associated with N-DAMO and other relevant biogeochemical processes; (3) quantify AMO activity over relevant oxygen concentrations; and (4) adapt thermodynamically constrained biogeochemical models of microbial metabolisms to predict the scale of N-DAMO (and other AMO processes) in RZs.
Metagenomic analyses have extended the evidence for N-DAMO as the dominant AMO process based on the recovery of particulate methane monooxygenase (pmoA) genes matching Ca. methylomirabilis. Genes diagnostic for canonical denitrification were also recovered at high frequency, while genes of anaerobic ammonium oxidation (anammox) were present but less common. These results indicate a complex anaerobic community with diverse pathways of both AMO and nitrogen loss. Incubation experiments will quantify rates of these processes over environmental gradients, informing development of RZ biogeochemical models that properly account for the influence of AMO.