Wastewater treatment protects ecosystems from pollution, including dangerous heavy metal contaminants. Nitrogen and phosphorus can be removed from wastewater by denitrifying phosphorus removal sludge (DPRS). This artificial ecosystem contains many different microbes active in anaerobic, anoxic, and aerobic processes. However, heavy metal pollution can stop DPRS from reaching its full potential. So researchers examined DPRS microbiomes in response to Cr(VI), Ni(II), and Cd(II) contamination. Using metaproteomics, they found that different microbial groups adopted different resistance mechanisms. Nitrospira improved its oxygen utilization, and Nitrosomonas produced more enzymes under heavy metal stress. Phosphorus-accumulating bacteria also produced polyphosphate, which could support community-wide detoxification, and showed a variety of other resistance responses, illuminating different microbial responses to pollutants and how diversity within a community keeps it healthy. Future studies of heavy metal resistance in sludge-based ecosystems using genome-centric metaproteomics will help improve wastewater treatment.