Horizontal subsurface flow constructed wetlands (HSSF CWs) with and without redox manipulation by front aeration were operated to treat mechanically pretreated wastewater from a nearby wastewater treatment plant. Polymerase chain reaction-denaturing gradient gel electrophoresis and 454-pyrosequencing were used to characterize the shifts in bacterial community diversity and composition in response to front aeration in the HSSF CWs. Both techniques revealed similar bacterial diversity between the HSSF CWs with (ACW) and without front aeration (NACW). Differences in microbial functional groups between the ACW and the NACW substrate samples were identified with 454-pyrosequencing. Nitrite-oxidizing bacteria (Nitrospira) and ammonia-oxidizing bacteria (Nitrosomonas) had much higher abundances in the ACW, whereas more sequences related to sulfate-reducing bacteria and anaerobic sulfur-oxidizing bacteria (genera Sulfuricella, Sulfuritalea, and Sulfuricurvum) were detected in the NACW. Removal efficiencies for NH₄(+)-N, PO₄(3-)-P and chemical oxygen demand in the ACW were 48.7 ± 15.5, 70.2 ± 13.5, and 82.0 ± 6.4%, respectively, whereas the removal efficiencies for these parameters in the NACW were 10.3 ± 14.0, 53.1 ± 18.9, and 68.8 ± 10.7%, respectively. In the ACW, the stimulation of nitrification via front aeration supplied more NO₂(-)-N and NO₃(-)-N to the subsequent denitrification process than in the NACW, resulting in higher total inorganic nitrogen removal efficiency. The differences in treatment efficiencies between the ACW and the NACW could be partially explained by the different bacterial community compositions in the two CWs.