Nitrosomonas europaea (ATCC19718) participates in the biological removal of nitrogen from wastewater by oxidizing ammonia to nitrite, the first step in nitrification. This bacterium is sensitive to heavy metals (Zn²⁺, Cd²⁺, Cu²⁺, and Hg²⁺) and cyanide, compounds commonly encountered in wastewater treatment plants. Therefore, we characterized physiological and transcriptional responses...