Distinct and diverse anaerobic respiration of methanogenic community in response to MnO 2 nanoparticles in anaerobic digester sludge.

Recently, the influence of metal oxide nanoparticles (NPs) on methanogenesis in anaerobic digestion has drawn much attention, however, the changes in NPs and functioning consortia within the methanogenic community are usually not investigated. Therefore, the methanogenesis performance, NPs transformation and methanogenic community development in anaerobic digester sludge under MnO2 NP supplementation were demonstrated in this study. MnO2 NPs (400 mg/gVSS) stimulated the methane (CH4 ) yield by 42% for a final CH4 proportion of 81.8% of the total gas production. Meanwhile, the coenzyme F420 and INT-electron transport system activities showed positive correlation with MnO2 concentration. Microbial Mn reduction and oxidation occurred in conjunction with methanogenesis, resulting in transformation of the shape of the MnO2 NPs from wire-like to globular particles. Microbial community analysis indicated that the relative abundances of genera Methanobacterium, Methanosaeta, and Methanosarcina were higher in the presence of MnO2 NPs. Moreover, a new and different crucial synergy within the methanogenic community was formed with low-abundance consortia driving Mn respiration coupled to methanogenesis in anaerobic digestion. To our knowledge, this is the first report on transformation of metal oxides NPs combined with syntrophic community development in studies focusing on methanogenesis in response to NPs.