New insights into the effect of medium-chain-length lactones on yeast membranes. Importance of the culture medium.

In hydrophobic compounds biotechnology, medium-chain-length metabolites often perturb cell activity. Their effect is usually studied in model conditions of growth in glucose media. Here, we study whether culture on lipids has an impact on the resistance of Yarrowia lipolytica to such compounds: Cells were cultured on glucose or oleate and submitted to gamma-dodecalactone. After a 60-min exposure to 3 g L(-1), about 80% of the glucose-grown cells (yeast extract peptone dextrose (YPD) cells) had lost their cultivability, 38% their membrane integrity, and 31% their reducing capacity as shown with propidium iodide and methylene blue, respectively. For oleate-grown cells, treatment at 6 g L(-1) did not alter cultivability despite some transient loss of membrane integrity from 3 g L(-1). It was shown with diphenylhexatriene and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene that oleate-grown cells had membranes more fluid and less sensitive to the lactone-induced fluidization. Analyses revealed also higher contents of ergosterol but, for YPD- and minimum-oleate-grown cells (YNBO cells), the addition of lactone provoked a decrease in the concentration of ergosterol in a way similar to the depletion by methyl-beta-cyclodextrin and an important membrane fluidization. Ergosterol depletion or incorporation increased or decreased, respectively, cell sensitivity to lactone. This study shows that the embedment of oleate moieties into membranes as well as higher concentrations of sterol play a role in the higher resistance to lactone of oleate-grown cells (YPO cells). Similar oleate-induced increase in resistance was also observed for Rhodotorula and Candida strains able to grow on oleate as the sole carbon source whereas Saccharomyces and Sporidiobolus cells were more sensitive after induction.