The aerobic granular sludge process and the membrane bioreactor process are promising, novel environmental bioprocesses for the reclamation of industrial and municipal wastewaters. They are practical and have attracted much research interest. The combination of these two processes in the aerobic granular membrane bioreactor (AGMBR), yields reclaimed water of high quality in a compact reactor. Information on the microbial community in an AGMBR operated at a high organic loading rate is lacking. This study elucidates the microbial dynamics in acetate-fed AGMBR operated in sequencing batch reactor mode. The structure of the microbial community revealed by denaturing gradient gel electrophoresis, demonstrates the dominance of the denitrifying microbial community, which is affiliated with members of the families Comamonadaceae and Alcaligenaceae, of the class Betaproteobacteria. The role of the predominant strains in the AGMBR is discussed.