The Physiology of Mould-Yeast Dimorphism in the Genus Mycotypha (Mucorales)

Abstract

SUMMARYMycotypha africana and four strains of Mycotypha microspora were studied. The former displayed total conversion from mycelium (M) to yeast (Y) when grown under N2 or in the presence of some electron-transport inhibitors with either glucose, fructose or mannose as carbon source. In air, mixed filamentous and yeast-like forms were frequently observed. Acid pH, high temperature, dense inoculum and high hexose level increased the proportion of the Y-form. Yeast and mycelial phases were interconvertible. All but one strains of M. microspora tested displayed similar dimorphism, but strain to strain variations were observed. I N T R O D U C T I O NMould-yeast (MY) dimorphism has been investigated in a number of pathogenic and non-pathogenic fungi from a wide range of taxonomic groups (see reviews of Romano, 1966, and Bartnicki-Garcia, I 968 a). Physiological control of this phenomenon varies between organisms ; temperature, medium composition and nature of the gas-phase have all been implicated.In the Mucorales, only the genus Mucor has been reported to display MY dimorphism (Bartnicki-Garcia & Nickerson, I 962 a). The major determining factors were the gas-phase and hexose sugar concentration (Bartnicki-Garcia, 1968 b). Yeast-like growth occurred under C 0 2 and a mycelium under N2 or air. These growth patterns were constant for Mucor rouxii over a wide range of physical and nutritional conditions but induction of the Y-phase by C 0 2 could be reversed by EDTA or other N-acetic acid type chelating agents (Bartnicki-Garcia & Nickerson, 19626). Mucor subtilissimus grew as a yeast under both N2 and C 0 2 . Hence, the existence of an EDTA-sensitive inducer of the Y-phase was postulated, the synthesis of which required C 0 2 in M. rouxii but not in M. subtilissimus, and which was thought to act on the wall polymers responsible for maintaining cell shape. A'greatly increased mannose content in the Y-phase wall (probably present as a mannose-polysaccharide) supported this suggestion (Bartnicki-Garcia & Nickerson, I 962 c).More recently Terenzi & Storck (1968) showed that 0.2 yo (v/v) of P-phenylethyl alcohol (PEA) also induced the Y-phase, inhibited the expression of cytochrome oxidase activity and stimulated alcoholic fermentation in Mucor rouxii, provided that 2% or more of a hexose was provided in the medium.In the present communication the factors controlling dimorphism in another genus of the Mucorales, namely Mycotypha, which was recently placed in the family Thamnidiaceae (Young, 1969), are described.

Observations on Thamnidiaceae (Mucorales). II. Chaetocladium, Cokeromyces, Mycotypha, and Phascolomyces.

“…These yeastlike cells regularly develop along the filamentous hyphae on the agar surface but usually are formed in greater abundance within the substrate. Physiological and ecological factors influencing yeast/ mold dimorphism in species of Mi1cotypha have been the subject of several recent investigations ( Price, Storck, and Gleason, 1973;Hall and Kolankaya, 1974;Schulz et al, 1974 ). ALISO [VoL.…”

Studies on Mucoralean Mycoparasites

“…The observation that high temperatures (35-45°C) favour Y-phase development in axenic culture (Hall and Kolankaya, 1974;Schulz et al, 1974) is in contrast to the conditions responsible for dimorphism induced by the mycoparasite where, above 15°C, persistent Y-phase cells do not develop. At 20°C, hyphal aberration is still evident but, at higher temperatures, the fast growth of Mycotypha microspora permits 'escape' from parasitism.…”

Studies ON MUCORALEAN MYCOPARASITES

“…Selective advantages accrue to hosts if they either lack growth-directing factors, as does C. mucoroides, or can prevent their release. Y-phase development in Mycotypha microspora is favoured by enhanced concentrations of CO2 (Hall and Kolankaya, 1974). However, there seems to be little possibility that there is such a response to respiratory CO2 from the mycoparasite and diffusible, non-volatile factors from germinating P. fimbriata spores appear to be responsible for this effect (Evans, unpublished).…”