Factors Affecting Dimorphism in Mycotypha (Mucorales): a Correlation with the Fermentation/Respiration Equilibrium

SUMMARY The yeast/mould (Y/M) dimorphism of three strains of the genus Mycotypha (Zygomycetes, Mucorales) was investigated. The Y-form is most readily induced in M. africana (CBSI22.64), whereas M. microspora (CBS230.32) has a strong tendency to grow as M-form. The Y-form is promoted by anaerobiosis, increased Pco 2, increased temperatures, pH values between 5-8 and 6-5, and 10% (w/v) glucose in the culture medium, as well as by the addition of certain inhibitors of the respiratory chain or mitochondrial protein synthesis. In contrast, M-form is stimulated by aerobic conditions, by temperatures below approximately 20 °C and at pH values below 4-5 and above 7-4. Ultraviolet-induced mutants with a defective respiratory system invariably grow as pure Y-form. Suppression of aerobic metabolism leads to a simultaneous suppression of mycelial growth. This correlation was confirmed by studies of fine structure with the electron microscope.