Fungitoxic activity of saponins: practical use and fundamental principles

Saponins, as aescin or alfalfa saponins have fungistatic activity on Trichoderma viride G fungal strain. (Biacs and Gruiz, 1982) The principle of fungistatic activity is an interaction between saponin and membrane constituents, such as sterols, proteins and phospholipids. The interaction results in the destruction of the cell membrane and an increase of the ion permeability (Gruiz and Biacs, 1989). Some Trichoderma strains are sensitive, whereas others are resistant to saponins. Their lipid composition after treatment differs considerably (Biacs and Gruiz, 1984), although ergosterol content of the membrane increased in both sensitive and nonsensitive strains. The possible metabolic changes in fatty acid composition of membrane phospholipids influence sensitivity of fungi to saponins. An important role is attributed to linoleic acid (Gruiz and Biacs, 1989). Since the fungal membrane composition can be changed by exogenously added sterols and fatty acids or triglycerides (Gruiz and Biacs, 1990), experiments were made to decrease saponin sensitivity of Trichoderma viride by giving linoleic-acid-containing oil and ergosterol. In such a way the elimination of the inhibitory effect of saponins was successful. The ergosterol content after saponin treatment is almost equal value not depending on the sensitivity and the ergosterol content of control or modified cells. This equalizing behavior of saponins is remarkable; its regulatory effect affects not only the ergosterol content, but also the fatty acid composition of the fungal membrane.