Effect of inoculum sources on the enrichment of nitrite-dependent anaerobic methane-oxidizing bacteria

Nitrite-dependent anaerobic methane oxidation (n-damo) is a newly discovered biological process that couples anaerobic oxidation of methane (AOM) to nitrite reduction. In this study, three different inocula, methanogenic sludge, paddy soil, and freshwater sediment were used to enrich n-damo bacteria in three sequencing batch reactors (SBRs), and three n-damo enrichment cultures, C1, C2 and C3, were obtained, respectively. After 500 days of incubation, Methylomirabilis oxyfera-like bacteria and n-damo activities were observed in cultures C1, C2, and C3, and the specific activities were 0.8 ± 0.1, 1.4 ± 0.1, and 1.0 ± 0.1 μmol CH4 h−1 g−1 VSS, respectively. The copy numbers of 16S rRNA genes from cultures C1, C2, and C3 were 5.0 ± 0.4 × 108, 6.1 ± 0.1 × 109, and 1.0 ± 0.2 × 109 copies g−1 dry weight, respectively. The results indicated that paddy soil is an excellent inoculum for n-damo bacterial enrichment. This work expanded the alternative source of n-damo inoculum and benefited the further research of n-damo process.