## 3 Results
### Changes in Lipid Content and Neutral Lipid Composition  
Nile red fluorescent staining proved the increasing appearance of neutral lipid droplets in nitrogen depleted cultures in both reactor types (Figure S1). Besides the greater extent of a cluster formation of cells in the hybrid reactor, other morphological differences between the cells from the two reactor types were not observed. Regarding the changes in the total lipid content of the cultures, it can be stated that the lipid content of the cells in both the hybrid reactor and the tank reactor increased as the amount of nitrate decreased (Figure 7). The lipid contents were significantly higher in 50%-N and 25%-N cultures than in the control and 75%-N cultures in both reactor types on a dry mass basis (\(p<0.05\); Figure 7a), but the total lipid contents of the same treatments did not differ significantly in the two reactor types (Figure 7a). There was significantly higher lipid content in the 50%-N and 25%-N cultures than in the control and 75%-N cultures in the hybrid reactor (\(p<0.05\); Figure 7b). However, under the applied conditions, a significantly higher amount of lipid can be produced in the tank reactor in a given volume than in the hybrid reactor (\(p<0.001\); Figure 7b). During preliminary TLC analysis of the lipid composition, altogether, eight bands, i.e., eight different types of lipids, were separated (Figures S2 and S3). As it is described in the Materials and Methods section, the run was performed on silica gel impregnated with 2% AgNO\({}_{3}\), the role of which in the reaction is to form stronger bonds with the lipids containing more double bonds, so they are retained better in the layer so that they can be separated from the more saturated ones. The results showed that the most unsaturated peak, 1, and the most saturated peaks, 7 and 8, dominate all treatments in both reactor types (complemented with peak 2 in control cultures from the tank reactor). The results also show that the lower the nitrate content in the culturing medium, the higher the number of bands (identifiable peaks), i.e., the number of different types of lipids (Figures S2 and S3; Figure 8). Although the method applied in the present form was not suitable for identifying the  
Figure 7: Total lipid contents (**a**) per unit of dry mass and (**b**) per unit of culture volume on the last (7 th) day of the experiment in the control (C) and nitrogen depleted (75, 50, and 25%-N) _Monorabiulum pusillum_ cultures in the hybrid reactor (HR) and in the tank reactor (TR). Different lowercase letters represent significant differences. Means (n = 3) and standard deviations are plotted. different lipids, it clearly showed that new forms in different amounts appeared in nitrate-depleted cultures. The differences were more pronounced in the case of the hybrid reactor: there were no detectable lipids in the control, four peaks appeared in the 75 and 50%-N cultures, and seven peaks were detectable in the 25%-N culture (Figure S2). Peak areas of peaks 1 and 6 were significantly higher, while the peak area of peak 7 was significantly lower in the 75 and 50%-N cultures than in the 25%-N culture (\(p<0.001\); Figure 8a). There were six identifiable peaks in the control culture from the tank reactor, and two new peaks (peak 3 and 4) appeared in the nitrate-depleted cultures (Figure S3). Peak areas of peaks 1, 6 (except control vs. 75%-N), and 7 were significantly higher; 2 and 5 (except control vs. 25%-N) were significantly lower (\(p<0.001\)) in nitrate-depleted cultures than in the control (\(p<0.001\); Figure S3 and Figure 8b).