## 2 Results
### Membrane Lipids Profile of E. magnusii Mitochondria during Long-Lasting Cultivation  
The amount and composition of the mitochondrial membrane lipids also changed significantly during growth and ageing of the culture. The membrane lipid amount reached its peak of 118.120 mg/g mitochondrial protein in the early growth stationary stage (48 h of cultivation) (Figure 4B), whereas the minimum content of 59.086 mg/g mitochondrial protein was in the deep stationary phase (96 h). The dynamics of the mitochondria membrane lipids showed a gradual increase by 48 h of cultivation with a nearly twofold drop in the deep stationary phase. The main fractions were sterols St (10-40%), PE (10-15%), PC (13-22%), CL (47%), and lysophosphatidylethanolamine + PI (up to 13%) (Figure 4A).  
The PE fraction remained constant at the level of about 10% throughout the experiment with a concurrent increase up to 15% in the late stationary phase (168 h of cultivation). The PC fraction gradually increased up to 22% in the 48-h growth stage and nearly halved in the 168-h growth stage while the CL content reached its peak in the logarithmic growth stage (47%), decreased by more than two times in the 24-h stage (up to 18%) with a slight increase in the 48-h growth phase (up to 29.4%), and stabilized in the late stationary phase at 18%.  
The LPE + PI fraction decreased during the cultivation from 13% to 4%. The St level changed in waves in different growth phases, reaching its maximum of 36-39% in the 24-h, 96-h, and 168-h growth phases (Figure 4A). The minor components of the lipid spectrum with the share of less than 10%, comprised lysophosphatidylcholines (LPC) and  
Figure 4: Membrane lipid composition of the mitochondria from _E. magnusii_ cells raised in the different growth phases upon ageing during the seven-day cultivation. (**A**)—the share of each membrane lipid fraction; PE—phosphatidylethanolamines; PC—phosphatidylcholines; CL—cardiolipins; PS—phosphatidylserine; LPE + PI—lysophosphatidylethanolamine + phosphatidylinositol; LPC—lysophosphatidylcholines; SL—sphingolipids; St—sterols; X1, X2—unknown; (**B**)—the total membrane lipid content. \({}^{\text{a--m}}\) Means with the same letter did not differ significantly.  
Figure 3: The storage lipid composition in _E. magnusii_ yeast in the different growth phases during long-lasting cultivation. (**A**)—the share of each storage lipid fraction,%; TAGs—triacylglycerlevels; DAGs—diacylglycerols; FFAs—free fatty acids; Est—sterol esters; Y1—unknown fraction (**B**)—the share of each storage lipid fraction (mg/g). \({}^{\text{a--h}}\) Means with the same letter did not differ significantly. Values are mean \(\pm\) S.E.M from three independent experiments and three analytical replicates.  
sphingolipids (SL). It is noteworthy that two unidentified lipid components were revealed: X1 was in the 24- and 48-h growth phases, and X2 was in 96- and 168-h growth stages.  
The overall degree of acyl residue unsaturation, Index of Hydrogen Deficiency (IHD) in phospholipids determines the fluidity of the membrane lipid bilayer, which in turn may affect the adaptation and survival of the yeast under stress conditions, including ageing. Thus, we next assayed the FFAs composition and amount of the membrane lipids.