Unique redox couplings enable microbial survival and methane mitigation in methanogenic sediments

A complex and active microbial population was observed to exhibit both aerobic and anaerobic microbial activity in methanogenic lake sediments. This study shows how communities manage to survive under such energy limited, highly reduced conditions, through redox cycles of Mn-Fe-N-CH₄ that control the emissions of the greenhouse gas methane to the atmosphere. The cycles were quantified using geochemical and microbial profiles and stable isotope probing (SIP) experiments close to natural conditions. Profiles surprisingly revealed an increase of nitrite concentrations together with elevated dissolved iron and manganese levels, decreased methane concentrations and a notable increase of NC10 bacteria activity. Controlled anaerobic incubation experiments with methanogenic sediment labeled with ¹⁵N-ammonium indicated anaerobic production by ammonium oxidation, most likely coupled to manganese oxide reduction. A sink for nitrite was observed by a series of on-top-core experiments, and it was shown to be coupled to ferrous oxidation, which is partly originated from anaerobic oxidation of methane (AOM). Nevertheless, NC10 activity in this setting is responsible for dark production of oxygen through N-methane coupling, which enables aerobic methane oxidation. The complex microbial couplings demonstrated here are significant in mitigating methane emissions and provide insight for survival mechanisms of microbes under limited energy conditions.  

Presentation Preference: Oral

Primary Presenter: Orit Sivan, Ben Gurion University of the Negev (oritsivan@gmail.com)

Authors:

Amit Waisman, Ben Gurion University of the Negev  (amitwa@post.bgu.ac.il)

Werner Eckert, Israel Oceanographical and limnological institute  (werner@ocean.org.il)

Oded Bergman, Ben Gurion University of the Negev  (odedbergman@ocean.org.il)