Prodigiosin is a natural red bacterial pigment that has antibiotic, antitumor, and immunosuppressant properties. It blocks T cell proliferation at a concentration of 30 ng/ml, by interfering with IL-2 receptor expression. Prodigiosin induces apoptosis in cancer cells by diverse mechanisms and rescues deficient p53 signaling. Prodigiosin derivatives can uncouple vacuolar H+-ATPase and inhibit osteoclast function. Prodigiosin is cytolytic against the red tide dinoflagellate Cochlodinium at very low concentrations (1 ppb), suggesting an application in controlling algal blooms.