NITRIFIERS AND METHANE-OXIDIZING ARCHAEA COEXISTING WITH METHANE AS SOLE CARBON SOURCE

Methane oxidation was thought to be a marginal and rare metabolism, but recently it was found to play a key role on carbon and nutrient cycling under various conditions. To shed light on the dynamics of methanotrophic community under microoxic and anoxic conditions, we operated two sequencing batch reactors (SBR), under microoxic (MO2-SBR) and anoxic (Anox-SBR) conditions. Methane oxidation rate was higher under microoxic conditions (5.3 ±0.9 mmol. batch cycle-1 for MO2-SBR and 3.1 ± 0.8 mmol batch cycle-1 for Anox-SBR). 16S rRNA sequencing presented reads affiliated with Nitrosospira genera (26.6% for Anox-SBR and 28.3% for MO2-SBR), which is a nitrifying organism, and reads related to Anaerobic Methane-Oxidizing Archaea (ANME) (3.5% for MO2-SBR and 4.0% for Anox-SBR). These results suggest that non-methanotrophic organisms can carry out methanotrophic oxidation and couple with other metabolisms, such as denitrification. It also hints at the possibility of different methanotrophic pathways coexisting in the same community, which implies that methane oxidation is a highly versatile metabolism.