Cytoplasmic membrane of a sensitive yeast is a primary target for Cryptococcus humicola mycocidal compound (microcin)

A basidiomycetous yeast strain, Clyptococcus humicola 9-6, secretes a mycoc idal compound (microcin) which is lethal for many yeasts. In this study a n ew protocol for microcin purification has been developed, and TLC-purity pr oduct was obtained. Using fluorescein as a pi-I-sensitive probe it was foun d that microcin treatment of Cryptococcus terreus, a model microcin-sensiti ve yeast, immediately caused transient alkalization followed by acidificati on of the cells' cytoplasm. Upon completion of this process, endogenous res piration as well as activity of unspecific esterases were inhibited, and al terations in cell wall and/or capsule started. Microcin was shown to make t he cells leaky for intracellular ATP. The mycocidal effect of microcin did not depend on the cell cycle phase of C. terreus. Based on these observatio ns and on electrical measurements on planar phospholipid bilayers, which in dicated a microcin-induced membrane permeabilization, it is suggested that the cytoplasmic membrane of the sensitive yeast is a primary target of micr ocin action. The conjectured mode of microcin action involves gradual incre ase of the cytoplasmic membrane's unspecific permeability. Intracellular io n homeostasis changes induced by microcin are considered to be the main cau se of enzyme inhibition, alterations in the outer layers of the cell envelo pe and, finally, division arrest. (C) 2001 Elsevier Science B.V. All rights reserved.