Use of batch and fed-batch fermentation for studies on the variation of glutathione content and its influence on the genotoxicity of methyl-nitro-nitrosoguanidine in yeast.
We have applied fermenter techniques to analyse the variations of glutathione (GSH) content in cultures of the diploid strain D7 of Saccharomyces cerevisiae. Choosing various experimental conditions of controlled batch and fed-batch fermentation we give evidence that the GSH levels of the yeast cultures depend on growth phase, the carbon source supply and the carbon source metabolism in an unexpectedly complex manner. Additionally, we analysed yeast cells with low GSH levels which were obtained either by depleting GSH with chloroacetophenone (CN) chemically or by using a GSH-deficient diploid strain (gsh1/gsh1). In order to study the relevance of the factors influencing the GSH concentration for genotoxicity testing in yeast we have used N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) which is activated by GSH. We show that in cells which are GSH proficient the extent of genotoxicity of MNNG correlates well with the GSH levels in the cells. Conditions of high GSH content (stationary phase of growth) corresponds with high genotoxic activity of MNNG, whereas conditions of low GSH content as logarithmic growth, glucose repression, GSH deficiency caused by the gsh1 mutation and GSH depletion by CN treatment correspond with a very moderate genotoxic effect of MNNG. These findings emphasize the necessity to use metabolically highly standardized cells for genotoxicity testing, since the carbon source catabolism, the concentration of glucose, growth rate and possibly other parameters influence the metabolization of xenobiotic agents in yeast.
Berthe-Corti
L
L
Universität Oldenburg, Fachbereich Biologie, FRG.
Hulsch
R
R
Nevries
U
U
Eckardt-Schupp
F
F
D005285:Fermentation / Q000502:physiology*; D005947:Glucose / Q000378:metabolism; D005978:Glutathione / Q000032:analysis*; D008769:Methylnitronitrosoguanidine / Q000633:toxicity*; D009152:Mutagenicity Tests; D009154:Mutation / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*
D008769:Methylnitronitrosoguanidine; D005978:Glutathione; D005947:Glucose