## Results and Discussion
### Cellular Lipids of Yarrowia lipolytica LMBF Y-46  
Total cellular lipids were extracted and quantified for both the shake-flask and the bioreactor experiments, and the kinetics of the evolution of lipids in DCW are depicted in Figure 7a,b. In all cases, and as it had previously been demonstrated (Figure 1b), the microorganism under investigation did not produce remarkable quantities of total lipids in yeast biomass, irrespective of the culture configuration (flask or bioreactor experiments). In fact, as it has been demonstrated in several previous studies dealing with wild-type and genetically engineered _Y. lipolytica_ strains cultured in batch experiments in both shake-flask and bioreactor trials, the oleaginous character of this species is strain dependent;  
Figure 5: Experimental data and fitted values showing the evolution of biomass (_X_), glycerol (_Gly_) and total polyols (_Po_) concentration during growth of _Yarrowia lipolytica_ on glycerol at: \(\approx\)100 g/L (**a**); \(\approx\)120 g/L (**b**); \(\approx\)150 g/L (**c**), initial substrate concentrations in shake-flask experiments under nitrogen-limited conditions. Culture conditions as in Table 3. Each experimental point is the mean value of two independent determinations (SE \(\leq\) 18%). in fact, in culture conditions of nitrogen starvation, in which carbon is found in the form of glucose, glycerol or similarly metabolized compounds (that favors the so-called \"de novo\" cellular lipid accumulation process; [5; 83]), excess carbon is directed either towards the synthesis and secretion of low-molecular weight compounds (i.e., citric acid, polyols) or it is channeled towards the accumulation of storage lipids [5; 9; 83]. In _Y. lipolytica_, the above-indicated regulation is difficult, and it has been demonstrated that it depends on the availability of extra-cellular nitrogen (for example, [PERSON] and [PERSON] [84] have demonstrated that a C/N ratio of 11.7 yields lipid accumulation, while a ratio of 47.6 favors _CA_ production using D-stat continuous cultivation techniques), the utilization of double- or multiple-limited media (for example in multiple-limited media and during growth on glucose or glycerol batch-wise, significant lipid quantities have been produced by _Y. lipolytica_ yeasts that in simple nitrogen-limited ones produced mostly _CA_[8; 23; 85]), etc. Adaptive laboratory evolution strategies or genetic engineering approaches have resulted in the formation of _Y. lipolytica_ strains that are capable of producing high amounts of cellular lipids and limited amounts of citric acid [43; 86; 87; 88]. In a number of cases, _Y. lipolytica_ strains cultured in nitrogen-limited glucose- or glycerol-based media, produced sequentially lipid and extra-cellular low molecular-weight metabolites (citric acid and polyols); in the first steps of the culture, lipid accumulation was somehow induced, and then lipid in DCW values were depleted with time, even though significant substrate quantities remained unconsumed into the medium. At that period, secretion of citric acid or polyols, in high quantities, was carried out [18; 22; 38; 39; 40; 85]. Exactly the same feature as regards lipid production and secretion of polyols was observed for the strain LMBF Y-46 in shake-flask experiments; somehow elevated lipid DCW values (i.e., 13-15% _u/v_) were recorded at the earlier growth phases of the strain cultured on glycerol in flasks, irrespective of the _Gly\({}_{0}\)_ concentration set into the medium, and these values were significantly reduced when the culture proceeded (Figure 7a). The onset of secretion of polyols into the medium was carried out at _c. t_ = 50 \(\pm\) 3 h, occurring simultaneously with lipid DCW value depletion. In contrast, different kinetic profiles were recorded for the bioreactor experiment (Figure 7b).