Mucor circinelloides aerobically exhibits coenocytic thallic growth habit with straight and circinate sporangiophores which culminate in globose or pyriform columellae enclosed within sporangial walls. It undergoes dimorphic switch with its conversion to multipolar budding yeast-like cells or thallic conidia. This paper confirms the induction of plurality of reproductive structures of the pleomorphic microorganism in minimal medium. Furthermore, construction of pH differentials at inflection points in the biphasic profiles during sporangiospore-yeast transformation indicated the intensity of H+ release from intracellular medium of the growing microorganism in a study conducted with K+ levels (0.0, 0.5, 0.7, 0.9, 1.0,1.10？g/L)-mediated broths. Optimum proton release was at 0.00 and 1.0？g/L？K+-supplemented broths, but specific growth rate was least in the latter. It also coincided with a preponderance of neoplastic units, protoplasts, and terminal budding yeast cells. On either side of this K+ level, variation in morphologies, including neoplasts, protoplasts, septate hyphae, thallic, holothallic, and holoblastic conidia, was greater, although olive-green septate hyphae with vesicular conidiogenous apparatus occurred at all K+ levels tested. This study suggested that following the establishment of transmembrane pH gradient across protoplast membrane, operation of Mitchellian proton pump was further promoted, thus leading to active transport mechanism, a prelude to yeast morphology induction. 1. Introduction Fungi produce spores so as to reproduce the species. Zygomycetes are well known for zygospore formation in sexual reproduction but sporangiospores in asexual reproduction. Mucor circinelloides has large multispored sporangia, which contain well-defined columellae. Although monotypic with coenocytic thallic growth, it speciates by the possession of two types of columellae, which are spherical and pyriform (ending with a truncate base), and two types of sporangiophores, upright and circinate—from which it derives its name [1]. Sporangiophores are abundant and this gives the colony a compact appearance. This is the common expression in aerobic environment. M. circinelloides (syn: M. racemosus) exhibits dimorphism as it converts to multipolar budding yeast-like cells in CO2 atmosphere [2]. An additional growth form, thallic conidia formation, like the arthric conidia of the nature of Geotrichum candidum [3], was shown by McIntyre et al. [4] when this fungus was grown in minimal Vogels medium. The formation of thallic conidia by M. circinelloides was
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