## 1 Introduction  
Carotenoids are one of the most common classes of pigments that occur in nature. The carotenoids market has grown significantly in the past few years due to increasing end-use applications in animal feed, dietary supplements, pharmaceuticals, food, beverages, and cosme industries. The global market for carotenoids reached $1.5 billion in 2017 and should reach $2.0 billion by 2022 at a compound annual growth rate (CAGR) of 5.7% for the period of 2017-2022 [1]. To satisfy the increasing demand for carotenoids, they can be produced easily via chemical synthesis. However, due to general consumer concern against synthetic pigments, the biotechnological production of carotenoids (via de novo microbial synthesis) is becoming an appealing alternative to the synthetic route [2]. Microbial fermentation is a promising alternative source of natural carotenoids. High yields of carotenoids can be produced by coloured microorganisms using economic substrates during a short period when the process parameters were efficiently controlled. Among the carotenoid producingmicroorganisms are algae, bacteria, filamentous fungi, and yeasts, such as _Streptomyces chrestomyceticus_, _Blakesela trispora_, _Phycomyces blakesleeanus_, _Flavourbacterium_ sp., _Phaffia_ sp., and _Rhodotorula_ sp., have been described as highly carotenoid-producing microorganisms [3; 4]. _Rhodotorula glutinis_ (_R. glutinis_) is capable of synthesizing numerous valuable compounds with a wide industrial usage. This yeast is a red oleaginous yeast that produces a significant amount of both lipids and carotenoids. _R. glutinis_, as a potential alternative candidate for lipid production, can accumulate a significant amount of lipids in cells (especially in lipid droplets) up to 70% of dry cell weight [5; 6; 7; 8]. The lipid profile produced by _R. glutinis_ has confirmed the dominance of oleic acid, which was considered an excellent substitute for vegetable oil for biodiesel production [9; 10]. Meanwhile, the carotenoid profile produced by _R. glutinis_ mainly consists of \(\beta\)-carotene, \(\gamma\)-carotene, torulene, and torularhodin, but the proportion of different carotenoid fractions varies significantly among different strains [11], culture conditions, C/N ratio [12], salt stress [13], metal stress [14], and nitrogen deficiency [15]. Carotenoid torulene has 13 double bonds, one \(\beta\)-ionone, and a longer polyene chain than \(\beta\)-carotene. Torulene exhibits properties of provitamin A and anti-prostate cancer activity, and is a safe food additive [16; 17]. Despite the benefits of torulene, its production does not upgrade to industrial scale due to its low production rate and the shortage of knowledge regarding the regulation of its biosynthesis and the optimized culture condition, in comparison with another yeast carotenoid like astaxanthin and \(\beta\)-carotene [13]. Although several studies have been conducted to optimize the production of lipids and carotenoids by _R. glutinis_[18; 19], only a few studies were tried to co-produce both products together [20; 21; 22; 23]. It has been known that nutrient-limitation, especially nitrogen and sulfur with high glucose concentration, can induce lipid accumulation from _R. glutinis_[24; 25; 26]. While the production of carotenoids is usually carried out in _R. glutinis_ under a low C/N ratio, in constrast to normal lipid production, even though it shares acetyl-CoA as a precursor for lipogenesis and carotenogenesis pathway, which was suggested the reverse relationship [10; 23]. Our initial results indicated that \(\gamma\)-carotene was detected as the dominant carotenoid with a 59% ratio produced by _R. glutinis_ under a low C/N ratio, but the carotenogenesis pathway was shifted significantly toward torulene and the total carotenoid production was decreased when increasing the C/N ratio for lipid production (data not shown). As a result, optimizing torulene production by _R. glutinis_ under a lipogenesis condition needs to be upgraded to industrial scale.