COMPARATIVE-STUDIES ON THE ENZYMOLOGICAL BASIS FOR GROWTH-INHIBITION BY GLYPHOSATE IN SOME YEAST SPECIES

We examined the mode of the action of the herbicide glyphosate (N-[phosphonomethyl]-glycine) on 19 strains of ascomycetous and basidiomycetous yeasts [Brettanomyces, Candida, Cryptococcus, Hansenula, Kluyveromyces, Lodderomyces, Pichia, Rhodosporidium, Rhodotorula, Saccharomycopsis, Schizosaccharomyces, Sporobolomyces, Yarrowia]. In all yeast species we observed the following physiolgical and enzymological effects: (i) aromatic amino acids reverse the glyphosate-induced growth inhibition, (ii) yeast cells excrete shikimic acid in the presence of glyphosate, (iii) the tyrosine-sensitive enzyme was the only one of the 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase isoenzymes which was inhibited by glyphosate at concentrations in the millimolar range, (iv) 5-enolpyruvylshikimate 3-phosphate (EPSP) synthase activity was inhibited by micromolar concentrations of glyphosate. Yarrowia lipolytica was extremely sensitive, whereas a similar growth inhibition of Candida albicans, C. utilis and Hansenula polymorpha was only achieved by about 400-fold concentration of the herbicide. Our in vivo results show that the presumable primary site of the glyphosate action in all yeast strains is the effective inhibition of the EPSP synthase activity.