Comparative study of changes in reaction profile and microbial community structure in two anaerobic repeated-batch reactors started up with different seed sludges

► Two anaerobic repeated-batch reactors differing in seed source performed similarly. ► H2-Utilizing pathway was likely the main route for methanogenesis in both reactors. ► The reactor methanogen communities were likely dominated by Methanospirillum hungatei strains. ► Bacterial community structure changed dynamically over cycles in both reactors. ► Bacterial community shifts caused little change in methanogen community structure.