Respiratory-deficient,yeastlike mutant of Mucor

Stable mutants of Mucor bacilliformis having lost the ability to grow filamentously and to sporulate occur spontaneously with a frequency of about one in every 3000 colonies. On solid and in liquid medium these mutants have a typical yeastlike morphology and reproduce by budding. The detailed study of one of these mutants shows that the inability to form filaments and spores is accompanied by the loss of cytochrome oxidase activity. This mutant is unable to take up oxygen but has a high level of alcoholic fermentation, which appears to be the major if not the sole source of energy.This investigation was supported by Public Health Service Grant AI 07804 05.