Effects of Oxygen and Glucose on Energy Metabolism and Dimorphism of Mucor genevensis Grown in Continuous Culture: Reversibility of Yeast-Mycelium Conversion

Abstract

Mucor genevensis was grown in both glucose-limited and glucose-excess continuous cultures over a range of dissolved oxygen concentrations (<0.1 to 25 ,uM) to determine the effects of glucose and the influence of metabolic mode (fermentative versus oxidative) on dimorphic transformations in this organism. The extent of differentiation between yeast and mycelial phases has been correlated with physiological and biochemical parameters of the cultures. Under glucose limitation, oxidative metabolism increased as the dissolved oxygen concentration increased, and this paralleled the increase in the proportion of the mycelial phase in the cultures. Filamentous growth and oxidative metabolism were both inhibited by glucose even though mitochondrial development was only slightly repressed. However, the presence of chloramphenicol in glucose-limited aerobic cultures inhibited mitochondrial respiratory development but did not induce yeast-like growth, indicating that oxidative metabolism is not essential for mycelial development. Once mycelial cultures had been established under aerobic, glucose-limited conditions, subsequent reversal to anaerobic conditions or treatment with chloramphenicol caused only a limited reversal ( <35%) to the yeast-like form. Glucose, however, induced a complete reversion to yeast-like form. It is concluded that glucose is the most important single culture factor determining the morphological status of M. genevensis; mitochondrial development and the functional oxidative capacities of the cell appear to be less important factors in the differentiation process.Fungi which exist in two morphological forms provide a useful system in which to study the biochemical basis of vegetative differentiation; the nature of the dimorphic change and its regulation have been the subject of much experimentation and speculation (for reviews, 1-3, 19, 23). Among species of fungi which are dimorphic, the genus Mucor has attracted considerable attention. It is known that for some species of this genus culture conditions which favor fermentation also promote yeast-like morphology, whereas oxidative conditions promote mycelial development (5,9,14,23,24).To gain a better insight into the molecular processes underlying the transformation from yeast-like to mycelial forms, a more precise understanding of the transition from fermentative to oxidative metabolism is required. Furthermore, a knowledge of the extent to which

Glucose metabolism and dimorphism in Mucor

“…We conclude from these observations that in Mucor the morphological conversion of yeast to mycelia can occur without a radical change in catabolic carbon metabolism. This observation is consistent with the earlier observations of Paznokas and Sypherd (12) and Rogers et al (13). The study reported here also shows that the yeast form is consistently correlated with a high flux of glucose carbon through the EMP and PP pathways, whereas the mycelial form does not show a consistent pattern in catabolic carbon metabolism.…”

“…Indeed, these aerobic yeast cells continued to produce ethanol and carbon dioxide at a rate indicative of a fermentative metabolism. These workers (13) concluded that respiratory capacity was not correlated with morphology. In addition, Paznokas and Sypherd (12) measured the respiratory capacity of aerobic mycelia and aerobic dbcAMP-treated yeast and concluded that morphology was independent of respiratory capacity.…”

“…Mooney and Sypherd (10) reported, however, that effects of glucose concentration on morphology were not observed with M. racemosus if one carefully regulated the flow rate of nitrogen through the culture. When M. genevensis yeast cells were grown in continuous culture with excess glucose, mycelial cells were not formed even at high oxygen concentrations (13). Indeed, these aerobic yeast cells continued to produce ethanol and carbon dioxide at a rate indicative of a fermentative metabolism.…”

Effect of oxygen on morphogenesis and polypeptide expression by Mucor racemosus

“…The numbered proteins are discussed in the text. laboratories (5,10,12). Other metabolic events requiring molecular oxygen might be important to mycelial development.…”

Induction of yeast cells from sporangiospores of Rhizopus stolonifer was inhibited by sodium fluoride

“…The Mucorales contains a number of species that are known to undergo this dual morphogenetic change. They include the much-researched Mucor rouxii (Bartnicki-Garcia, 1968;Bartnicki-Garcia and Nickerson, 1962a, b, c, d;Schulz et al, 1974), Mucor circinelloides (Lubberhusen et al, 2003;McIntyre et al, 2002), Mucor genevensis (Rogers et al, 1974), Mucor racemosus (Mooney and Sypherd, 1976), Mucor pusillus (Fisher, 1977), Mucor hiemalis (Mysyakina and Funtikova, 2000), Cokeromyces poitrasii (Price et al, 1973), Mycotypha spp. (Hall and Kolankaya, 1974).…”