André Michel Lwoff (1902 – 1994) received one-third of the 1965 Nobel Prize in Physiology or Medicine for his discoveries about the genetic control of enzymes and virus synthesis. Lwoff contributed to the understanding of lysogeny, in which a virus called bacteriophage infects bacteria and is transmitted to subsequent bacterial generations by cell division. Lwoff showed that, after infection, the virus is passed on to the succeeding generations of bacteria in a noninfective form called a prophage. But he also demonstrated that, under certain conditions, this prophage can become infective and cause bacterial cells to disintegrate, releasing the viruses, which can then infect other bacteria. Lwoff also discovered that vitamins serve both as growth factors for microbes and as coenzymes.