EFFECT OF N-ALKANOLS ON ACIDIFICATION CURVES OF AUREOBASIDIUM-PULLULANS SUSPENSIONS

n-Alkanols, from methanol to 1-hexanol, induce yeast-to-hyphae transit ion in the dimorphic fungus Aureobnsidium pullulans. In order to eluci date whether triggering of the morphogenetic event is membrane related , we have studied the effect of the morphogenetic n-alkanols on the pH of suspensions of A. pullulans, with no external carbon source. n-Alk anols, at their hyphal inducing concentration or higher, caused a decr ease in the initial acidification rate (C) of yeast-phase cell suspens ions of A. pullulans. From this effect on C, an inhibition coefficient (K) was deduced, specific for each alcohol. These coefficients were d irectly related to the lipid/buffer partition coefficients of the alka nols. On the other hand, germ tubes of A. pullulans, obtained in the p resence of n-propanol, showed a much slower acidification rate in wate r than yeast cells. Moreover, 1-propanol or 1-butanol did not signific antly affect the initial acidification rate of germ tubes. The latter observation was interpreted as an adaptation of cells grown in the pre sence of alcohol. The results of all these experiments support our hyp othesis that the plasma membrane is a target of the morphogenetic effe cts of n-alkanols. (C) 1994 Academic Press, Inc.