Influence of carbon source on glutathione accumulation in methylotrophic yeasts

Glutathione (GSH) plays a pivotal role in protecting cells from by-products generated by oxidative! metabolism, and is strongly involved in metabolism and processes of formaldehyde detoxication in methylotrophs. This paper investigates GSH accumulation by methylotrophic yeasts, belonging to Candida (13 strains) and Pichia (11 strains) genera. To evaluate the influence of different carbon sources on GSH intracellular levels, fermentations were carried out in a medium supplemented with methanol, ethanol and glucose, comparatively. The highest cell growths were evidenced employing glucose (9.9 g l(-1) for Candida nemodendra) and ethanol (9.7 g l(-1) for Pichia pastoris), while the lowest with methanol (up to 4.0 g l(-1) for 80% of the Candida and 40% of the Pichia strains). The highest GSH contents (% dw) were always highlighted in samples from methanol (3.9 and 3.5% for Candida pini and Pichia philodendri respectively). Nevertheless, it must be noted that around 50% of the Candida and Pichia tested strains showed a decrease in GSH content when grown on methanol, compared to the data obtained on glucose. These results evidenced that methylotrophic yeasts possess different detoxification mechanisms, protecting themselves from the toxic metabolites generated during methanol assimilation.