## 3 Results  
Effect of Different Nitrogen Sources and Different C/N Ratios on Cell Biomass, and Lipid and Carotenoid Production by R. glutinis  
The effect of different nitrogen sources PEP, YE, and Amm with different concentrations (C/N ratios 146, 94, and 70) was studied. Those ratios were selected in accordance with our previous work, which showed the best range for the highest lipid and carotenoid production using a mixture of Amm and YE as a nitrogen source (data not shown). At the end of incubation, the cells were collected and examined under a fluorescence microscope after staining with Nile red fluorescence dye. The differences in the cells size and golden fluorescence lipid bodies were shown in Figure 1. The largest cells with highly accumulated lipid bodies were observed with PEP at a C/N ratio of 146 and a C/N ratio of 94 (Figure 1a,b with PEP). The number of lipid bodies inside the cells was reduced when the C/N ratio decreased. This qualitative result indicated that when using peptone with a high C/N as a nitrogen source for yeast cultivation, lipid production was dramatically increased compared with other nitrogen sources. As shown in Table 3, the lower C/N ratios with an organic nitrogen source were more favourable for biomass production; the highest biomass was 12.2 g/L after six days, which was achieved with YE. The enhancement of biomass production with YE may be related to the high vitamin content in the yeast extract compared with PEP as organic nitrogen sources. In contrast, increasing the C/N ratio from 70 to 146 was accompanied by the increase of lipid accumulation in yeast cells whatever nitrogen source was used. Similarly, the rapid stimulation of lipogenesis in _R. glacialis_ and _Rhodotorula kratochvilovae_ was achieved when the yeast was cultivated on a medium with high C/N ratios of 160 and 120, respectively [45; 46]. On the other hand, an increase of C/N ratio in medium from 20 to 70 was accompanied by a lipid accumulation increase in _R. glutinis_[10; 12], but had a negative effect on lipid accumulation was found [10], and also no effect on lipid accumulation [12], when the C/N ratio was further increased to 100. The reasons for the lipid accumulation increase with a high C/N ratio,even at 146 (Table 3) and 160 [45], could be related to the ability of the yeast strain to resist a high sugar concentration, where the _R. glutinis_ used in this study is able to grow at a high 30% glucose concentration (data not shown). PEP was considered the best nitrogen source for lipid accumulation from _R. glutinis_, and L-RP was highest at the C/N ratios of 146, 96, and 70 with 54.2%, 51.5%, and 46.9%, respectively, after 6 days of cultivation. This is consistent with reported data from _Trichosporon fermentans_[47]. Comparing with other nitrogen sources, the highest L-SR was recorded with YE because of the high biomass production (Table 3). For carotenoid production in _R. glutinis_, the total volumetric pigment increased with decreasing C/N ratio, recording 0.53, 0.852, and 0.881 mg/L with PEP, YE, and Amm after six days, respectively, which was mainly due to the high biomass production. Whatever the nitrogen sources, cellular carotenoid accumulation was enhanced significantly in a high C/N ratio compared to a low C/N ratio, as an approximately 1-fold increase was observed when Amm-C/N 146 was compared with Amm-C/N 70; this result is similar to [PERSON] et al [12]. On the other hand, there was no effect of C/N ratio change on carotenogenesis in _R. mucilaginous_ and cellular pigment accumulation in _R. glutinis_[19; 48]. It was also reported that pigment accumulation was reduced dramaticly under a high C/N ratio due to lipid production [10; 23]. We believe that the enhancement of carotenoid production in _R.