Bacterial community structure of full-scale anammox bioreactor is still mainly unknown. It has never been analyzed whether different anammox bioreactor configurations might result in the development of different bacterial community structures among these systems. In this work, the bacterial community structure of six full-scale autotrophic nitrogen removal bioreactors located in The Netherlands and China operating under three different technologies and with different influent wastewater characteristics was studied by the means of pyrotag sequencing evaluation of the bacterial assemblage yielded a great diversity in all systems. The most represented phyla were the Bacteroidetes and the Proteobacteria, followed by the Planctomycetes. 14 OTUs were shared by all bioreactors, but none of them belonged to the Brocadiales order. Statistical analysis at OTU level showed that differences in the microbial communities were high, and that the main driver of the bacterial assemblage composition was different for the distinct phyla identified in the six bioreactors, depending on bioreactor technology or influent wastewater characteristics. (C) 2015 American Institute of Chemical Engineers