Photosynthetic bacteria (PSB) are widely used in the purification of aquaculture waters due to their ability to utilize ammonia, nitrite, hydrogen sulfide, etc. However, PSB are usually considered to be ineffective in removing biologically inert pharmaceutical residues in aquaculture waters. Herein, we found that PSB were capable of degrading pharmaceuticals in aquaculture waters, such as cimetidine and sulfamethazine, by generating extracellular singlet oxygen (