Influence of a subinhibitory dose of antifungal atty acids fromSporothrix flocculosa on cellular lipid composition in fungi

Antifungal fatty acids produced by the biocontrol fungusSporothrix flocculosa were studied on the basis of their effect on growth and cellular lipid composition of three fungi,Cladosporium cucumerinum, Fusarium oxysporum, andS. flocculosa, whose growth was decreased by 51, 33, and 5% respectively, when exposed to 0.4 mg fatty acid per ml. The sensitivity to fatty acid antibiotics fromS. flocculosa was related to a high degree of unsaturation of phospholipid fatty acids and a low proportion of sterols. The major responses of sensitive fungi to sublethal doses of antifungal fatty acids from liquid culture ofS. flocculosa were: (i) a decrease in total lipid; (ii) an increase in the degree of fatty acid unsaturation (18∶1>18∶2 > 18∶3); (iii) an increase in free fatty acids and phosphatidic acid and a decrease in total phospholipids; and (iv) an increase in sterol/phospholipid ratio. These modifications in lipid composition led to an increase in membrane fluidity in sensitive fungi, as demonstrated by assessment of fluorescence anisotropy using liposomes and 1,6-diphenyl-1,3,5-hexatriene probe. This alteration in the physical state of lipids appears to be responsible for the previously demonstrated alteration of membrane structure and function in fungi confronted toS. flocculosa.