Thu, May 2, 2019, 12:30 pm to 1:30 pm
Anaerobic oxidation of methane (AOM) is a significant but poorly constrained biological sink in the global carbon cycle. While several studies estimate AOM is responsible for consuming ~80-90% produced in marine sediments, its role in curbing the CH4 atmospheric flux in terrestrial freshwater systems, particularly the deep continental biosphere, is only just beginning to be explored. Recent breakthroughs have vastly improved our understanding of AOM, identifying a wide range of oxidants utilizable via diverse metabolic strategies in the anaerobic methane-oxidizing archaea (ANMEs) and the bacterium “Candidatus Methylomirabilis oxyfera”. However, the details of AOM’s contribution to the global methane (CH4) budget remains poorly constrained and includes systematic discrepancies such as the documentation of AOM in environments where known microbial mediators appear absent, as well as a global stoichiometric imbalance in observed fluxes of CH4 and oxidants into regimes where AOM is known to occur. The recent identification of a “cryptic” CH4 cycle – in which AOM and methanogenesis proceed concurrently along small and geochemically nearindiscernible temporospatial scales – may play a key role in filling these gaps in our understanding.
The uncultured “Ca. Bathyarchaeota” is a deeply branching phylum whose members are among the most widespread and abundant archaea inhabiting the deep biosphere. Though a pure culture isolate remains elusive, recent studies have attributed diverse metabolic capabilities to the “Ca. Bathyarchaeota”, including acetogenesis, fermentation, methanogenesis, and denitrification. We recently identified Candidatus Bathyarchaeota BE326-BA-RLH, the first member of the phylum “Ca. Bathyarchaeota” whose genome encodes proteins that appear to couple AOM to dissimilatory nitrate and nitrite reduction. While initially discovered in continental subsurface fracture fluid from a South African gold mine, Ca. Bathyarchaeota BE326-BA-RLH and closely related sister lineages have also been identified in AOM enrichment incubations of sub-seafloor sediments from the Nankai Trough as well as coastal peatlands from Brunei. Here we will address preliminary evidence from high throughput sequencing coupled to radio-, stable-, and clumped isotope geochemistry data to consider a role that Ca. Bathyarchaeota may play in cryptic, nitrogen-driven AOM and to identify novel geochemical isotopic markers for these cryptic processes of the subsurface CH4 cycle.