Effect of K+, Na+ and uracil on sporangiospore-yeast transformation of Mucor circinelloides Tieghe

Abstract

Potassium is a key constituent element that functions in intracellular metabolism of eukaryotes. This study demonstrates potassium is absolutely necessary for the formation of Mucor circinelloides protoplasts, the cross over transient form in the sequential transformation of sporangiospores to yeast cells. We also show that Na+ contributes significantly to the induction of yeast form from protoplast in
synthetic broth and this is time related. Two distinct anamorphic patterns were induced, initialized by thallic growth and growth sphere wall lyses. Thallic growth was determinate with subtype’s production of conidia after growth cessation as in vesicular head group conidial form or enterothallic conidia and catenulate formation of conidia on same plane with short germ tube represented by holothallic conidia, as well as holoblastic conidia. The second growth pattern was proliferate, with yeast cell giving rise to
daughter buds. Biomass profile exhibited 2-phases common in Na+ supplemented broths with determinate thallic growth contributing  proportionally to the first peak. On thallic cell wall rupture,
released cytosolic units progressively convert to protoplasts and subsequently to yeast cells. Uracil supplementation eliminated determinate thallic anamorphs with morphological expression occurring as
ovoid to long ovoidal, ellipsoidal and cylindrical yeast cells, which were polar, bipolar or multilateral
budding. Thin tree-like branched yeasts were scanty at 100 mM uracil supplementation. The results
offer new insights into the phenomenon of fungal morphogenesis. It attributed specific effects to K+,
Na+ and uracil as key factors to which Mucor circinelloides respond, phenotypically