Dynemicin A, a novel antibiotic containing the bicyclo[7.3.1]-1,5-diyn-3-ene and 1,4,6-trihydroxyanthraquinone functionalities, was isolated from the culture broth of Micromonospora chersina sp. nov. M956-1. The antibiotic exhibited potent in vitro antibacterial and cytotoxic activity, and in in vivo, it cured mice from lethal Staphylococcus aureus infection and prolonged survival time of mice inoculated with murine tumors. Three satellite components, dynemicins L, M and N, were also isolated from the culture broth and chemically characterized.