Lipid composition and amino acid transport in a nystatin-resistant mutant of Aspergillus niger

Abstract

A nystatin-resistant mutant of Aspergillus niger has been isolated and used as a model system to study the effect of altered sterol levels on lipid composition, transport behavior and physical properties of membrane lipids. There is a decrease in the sterol to phospholipid ratio in the mutant compared to the wild type. Although there is no qualitative change in phospholipid composition, the mutant contains a higher amount of phosphatidylcholine and a lower amount of phosphatidylethanolamine compared to the wild type. The most significant change is the elevated level of linoleic acid in the mutant, concomitant with a decreased level of oleic acid. These adaptive changes to nystatin resistance are manifested in the altered thermotropic behavior of membrane lipids as studied by the steady-state fluorescence polarization technique. These changes are also associated with altered membrane permeability as evidenced by the change in V_max values for uptake of some amino acids in the mutant compared to the wild type.