Increasingly, technologies that use sulfide as an electron donor are being considered for nitrogen removal; however, our understanding of how sulfide affects microbial communities in nitrifying treatment processes is limited. In this study, we used batch experiments to quantify sulfide inhibition of both ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) using activated sludge from two full-scale treatment plants with distinct treatment processes. The batch experiments showed that NOB were more vulnerable to sulfide inhibition than AOB, and that inhibition constants (K_I) for NOB were distinct between the two treatment plants, which also had distinct nitrite oxidizing microbial communities. A Nitrospira-rich, less diverse NOB community was inhibited more by sulfide than a more diverse community rich in Nitrotoga and Nitrobacter. Therefore, sulfide-induced nitritation may be more successful in less diverse, Nitrospira-rich communities. Additionally, sulfide significantly influenced the activity of non-nitrifying microbial community members, as measured by 16S rRNA cDNA sequencing. Overall, these results indicate that sulfide has a strong impact on both nitrification and the activity of the underlying microbial communities, and that the response is community-specific.