ABSTRACT
121Anaerobic oxidation of methane (AOM) coupled to sulphate reduction (SR) is mediated by a consortium of anaerobic methanotrophic archaea (ANME) and sulphate reducing bacteria (SRB). Although this has been studied for many years, the metabolic interactions and pathways involved are still unclear. In this work ANME-2 (ANME group 2)/SRB enriched biomass was incubated under high methane-pressure with several labelled and non-labelled substrates and several labelled and non-labelled substrates and the AOM and SR activities were compared individually for each group based on the production of CO2 and sulphide. Acetate was the tested compound with the highest positive effect on the SR activity (reducing the lag phase) without a visible effect on the AOM. To understand which pathway is taking place for the acetate oxidation, isotopically labelled carbon compounds were added, i.e. (1) non-labelled acetate (together with 13CH4), (2) 2-13C labelled together with 12CH4 and (3)13C2 labelled together with 13CH4. Group 2 presented the lowest lag phase, possibly due to the preference of the ANME to 12CH4 over 13CH4. Given the higher amount of 13CO2 produced in group 3, it is likely that most 13CO2 comes from the oxidation of the non-methyl carbon of the acetate. This paper shows that the ANME-2 enriched community present in the inoculum has diverse pathways, being able to use sulphate, thiosulphate, sulphur as electron acceptor, and methane, acetate as electron donor. In addition, it gave an indication that ANME-2 may oxidize methane anaerobically via an undefined mechanism where SRB is not required as partner.
