Effect of exogenous lipids on morphogenesis of the fungus Mucor lusitanicus 12M

Abstract

The composition of spores and conditions of their formation significantly influence the development of the resulting cultures of mycelial fungi. The viability of spores of the fungus Trichoderma harzianum has been reported to depend on the duration of their maturation [1]. The germination of Aspergillus niger conidia is influenced by the intensity of the culture sporulation: the stimulation of sporulation with blue illumination led to lower germinability of the spores obtained [2]. Previously, we found that the sporangiospores formed by older cultures of the fungus Mucor lusitanicus 12 M grown on wheat bran or sunflower oil cake tend to produce yeast-like growth. With further ageing of the culture, the sporangiospores completely lost their viability [3, 4]. Microscopic examination demonstrated that the sporangiospores of the young and old cultures grown on bran differed in their volume and structure of their surfaces [5]. The spores of M . lusitanicus lost their germinability obviously due to autolysis of the mycelium and liberation of abundant biologically active organic substances and enzymes after the end of mycelium growth and spore formation. In the period of spore maturation in senescent cultures of the fungus, the lipase activity results in the degradation of lipids, phospholipids in particular. The composition of lipids of the spores from a 25-day-old culture, including phospholipids, significantly differed from that of young spores [3]. In light of recent publications on the multiple-factor influence of lipids on morphogenesis and differentiation of both micro- and macroorganisms, it may be assumed that fungal dimorphism is caused by lipid compounds and/or by changes in the properties of membranes of sporangiospores occurring due to change in the composition of phospholipids. It was reported previously that the products of phospholipid metabolism—diacylglycerols, phosphatidic acid, and lysophosphatidic acid—are messengers of morphological transitions [6‐8]. Phosphatidic acid also participates, directly or indirectly, in the reorganization of the cytoskeleton during changes in cell morphology [9], and diacylglycerols may be sensors in the Golgi apparatus, which regulates the secretory function of membranes in the process of formation and transportation of vesicles during yeast budding [10]. It was shown that exogenously added phospholipase D causes dimorphism in the yeast Candida albicans [11]. Discontinuation of phospholipid synthesis caused by the addition of cerulenin caused dimorphism in Mucor racemosus [12]. Along with the products of the activity of phospholipases, other lipid compounds influence fungal morphogenesis. A paper has been published on the effect of prostaglandins, products of fatty acid metabolism, on the morphological development of microscopic fungi [13]. It has been noted that sterols play an important role in the dimorphism of pathogenic fungi [14].