Impact of morphogenetic effectors on the growth pattern and the lipid composition of the mycelium and the yeastlike cells of the fungus Mucor hiemalis

Abstract

We investigated the growth and the cell lipid composition of the mycelium and of the yeast-like form of Mucor hiemalis VKMF-1431 obtained under aerobic conditions by treatment with the morphogenetic agents itraconazole, exogenous triacylglycerols (TAGs), and trehalose. The sporangiospores of a 20-day culture were inoculated on the medium with glucose. Under these conditions, the fungus produced both mycelium and yeast-like cells. It was established that, upon the germination of old (20-day) sporangiospores, the fungus predominantly used the mycelium development strategy in the presence of trehalose and TAGs. It was characterized by a low ratio between the two bulk membrane lipids (PEA/PC) and increased levels of PC and polyunsaturated fatty acids (FA). Compared to the mycelium, the yeast cell morphotype obtained on the medium with glucose was distinguished by an elevated PEA/PC ratio, lowered TAG, free sterol (FS) and esterified sterol (ES) levels, a decreased ES/FS ratio that correlated with the reserve sterol pool size, and a lowered content of unsaturated fatty acids (the linoleic and the γ-linolenic acid). These peculiarities of the lipid composition of yeastlike cells correlated with the intensity of yeastlike growth. Light and electron microscopy revealed differences between the above cell morphotypes. With itraconazole, yeast-like cells were characterized by the destruction of the endoplasmic reticulum membranes and formation of a large number of vacuoles. The suggestion was confirmed that the state/age of inoculum sporangiospores exerts an influence on the capacity for dimorphism in mucorous fungi such as M. hiemalis. The data obtained testify to an involvement of lipids in the process of adaptation to environmental factors and to their regulatory role in morphogenetic processes associated with the formation of alternative morphotypes of the mucorous fungus.