Aluminum (Al) is the major factor which affects crop productivity in acid soils that comprise about 40 percent of the world's arable land. Yeast has proven to be an excellent system for isolating and characterizing genes responsive to environmental signals including salt, oxidative and various metal stresses. Addition of 0.5 mM AlK(SO₄)₂ to culture medium adjusted to pH 4.5 resulted in 37% inhibition of the growth of the fission yeast Schizosaccharomyces pombe. This inhibition was already detectable after 3 hr of treatment and was accompanied by changes in cell morphology and increase of calcium influx in yeast cells. Organic acid excretion has been correlated with aluminum tolerance in higher plants. Consistent with this idea, 0.1 mM citrate antagonized the toxic effects of Al on fission yeast. Next, we analyzed the effect of Al on the dimorphic fungus Yarrowia lipolytica. This ascomycetous yeast can be isolated from diverse sources including agricultural soils. Surprisingly, Al concentration which was toxic to S. pombe did not affected Y. lipolytica growth neither induced drastic changes in morphology, as revealed by SEM, although higher Al concentrations reduced cell growth, indicating the resistance of this microorganism to Al. Such resistance can be attributed to citrate secretion by Y. lipolytica as revealed by using inhibitors of H⁺-ATPase and citrate transporters. These data are discussed in relation of the possibility of using Y. lipolytica as a model to understand the role of citrate metabolism in mediating Al tolerance and as a potential bioamendment to improve the crop productivity in acid soils.