Tolerance of Aceticlastic Methanogenesis Enhanced by Magnetite under the Condition of Ammonia Stress

Magnetite-mediated direct interspecies electron transfer (DIET) has been considered as an effective mechanism to proceed the syntrophic methanogenic metabolism. However, the enhancement effect of magnetite on the methanogenesis via DIET is occasionally insignificant. Several clues have shown that the dominant aceticlastic methanogenesis could be a restrictive factor for the DIET enhancement of magnetite. To prove this, ammonia was used to inhibit the aceticlastic methanogenesis, and response of microorganisms to the ammonia stress in the presence of magnetite (2 g Fe/L, group M) and silica (2 g Si/L, group S) was investigated. Results showed that under the low ammonium concentration condition (147.3 mg-NH4+-N/L), aceticlastic methanogenesis was dominant in both groups, and the effect of magnetite addition was insignificant. With increasing ammonium concentration to above 1600 mg-NH4+-N/L, the methanization of acetate in both groups was inhibited. However, the methane production rate of group M was 50% higher than that of group S, and the candidate DIET partner Methanosarcina became more competitive in the presence of magnetite. The increase of key enzyme activities and expression of functional genes involved in the acetoclastic methanogenesis in group M indicated that the tolerance of aceticlastic methanogenesis could be enhanced by the magnetite addition under ammonia stress.