## 3 Results
### Impact of Aluminium Sulfate on Lipogenesis and Caroenoid Production
All the reports that have studied the effect of metal on carotenoid production confirmed its stimulatory role on carotenoid production, explaining this by hypothesising a possible activation or inhibition mechanism of selected metal ions on specific carotenoid enzymes, in particular,  
Figure 4: Influence of different Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\) concentrations on growth, and lipid and carotenoid production by _Riodotornia glutinis_. Yeast cells were grown in the shaken flask using the optimised medium as a control with C/N equal to 146 (using ammonium sulfate as a sole nitrogen source) and C/S equal to 120, and incubated at180 rpm and 28 \({}^{\circ}\)C for six days: (a) dry cell weight (DCW) (g/L), (b) total lipid (TL (g/L)) and lipid relative productivity (LRP = (g\({}_{\text{lipid}}\)/g\({}_{\text{DCW}}\)) \(\times\) 100), and (c) total pigment (TP mg/L) and carotenoid relative productivity (Car-RP mg\({}_{\text{pig pigment}}\)/100 g\({}_{\text{DCW}}\)). The data are the mean of three repeated tests, and the standard deviation was calculated and represented as an error bar. Asterisks ** represent a statistically significant difference between the single-Al-treated group and the control at \(p\leq 0.01\), and asterisk * represents a statistically significant difference between single-Al-treated group and control at \(0.01<p\leq 0.05\). on a specific desaturase involved in carotenoid biosynthesis [14]. Elsewhere, it was noted that the determination of physiological and biochemical changes of _Rhodotorula mucilaginous_ AN5 after progressive copper treatment stated a significant increase in the antioxidative reagents content and enzymes activity, which quenched the active oxygen species to maintain the intercellular balance of the redox state and ensure the cellular fission and growth [55]. Another recent study implemented multi-omics metabolism analysis to investigate the mechanisms involved in irradiation-induced stress resistance in _R. glutritis_. The results confirmed the significant upregulation of the carotenoid biosynthetic pathway, which revealed that increased carotenoid content is a cellular defence mechanism against oxidative stress generated by irradiation [56]. Focusing mainly on aluminium, there is a study that reported that most divalent cation salts increase cellular carotenoid accumulation, and observed an around 1.6-fold increase in both volumetric and cellular carotenoids compared with the control, as well as an around 9% torulene increase when AlNO3 was tested as a stress factor [18]. The carotenoid fractions showed a 62% domination of torulene in the control treatment, which had around the same ratio compared with Amm-146 C/N (C/S 133). The torulene ratio was increased to 65% with 0.1 mM Al2(SO4)3, then increased to 98% with the further higher concentrations till 0.7 mM, followed by decreasing again to 73% with 1 mM (Figure 5). The retention times of \(\gamma\)-carotene and torulene with the control and 0.5 mM Al2(SO4)3 treatment is shown in Figure 6a,b. Memorably, after adding aluminium sulfate into the optimized medium, a characteristic intense red pigmentation of yeast pellets was observed, which indicated the effect of the new conditions on both the carotenoid composition and concentration (Figure 6c). Finally, comparing the production of carotenoid and torulene from this study with the previously reported studies that used glucose as carbon sources under flask fermentation conditions is shown in Table 6. Most of the previous literature used low C/N ratios for optimizing carotenoid production [19; 50; 57; 12], while other studies also conducted the experiments under a high C/N ratio, and a high yield of carotenoid was produced [10; 11; 12]. The differences in the yield of carotenoid production under different C/N ratios may be mainly related to different yeast strains, as each strain responds differently under different culture conditions. The highest carotenoid producing _Rhodotorula_ strain was _R.