In this paper, a method based on laser tweezers Raman spectroscopy (LTRS) was developed to directly detect carotenoids, as well as other important biological molecules in single live R. glutinis cells.

The data showed that the accumulation of carotenoids and lipids occurred mainly in the late exponential and stationary phases when the cell growth was inhibited Transmembrane Transporters inhibitor by nutrient limitation. Meanwhile, the carotenoid concentration changed together with the concentration of nucleic acids, which increased in the first phase and decreased in the last phase of the culture. These data demonstrate that LTRS is a rapid, convenient, and reliable method to study the carotenogenesis process in vivo. Carotenoids represent a group of important natural pigments widely used in the pharmaceutical, cosmetic, food, and feed industries. The biological sources of carotenoids have received more attention because they have lower toxicity and higher bioavailability than their chemically synthesized counterparts. Several microorganisms, including bacteria, algae, molds, and check details yeasts, are able to produce carotenoids. Among these microorganisms,

yeasts such as Phaffa rhodozyma and Rhodotorula glutinis are of commercial interest due to their unicellular nature and high growth rate. Rhodotorula glutinis can produce carotenoids when the cell is under stress, such as nutrient limitation Aldol condensation (Simpson et al., 1964). Carotenoid content in wild strains of R. glutinis is relatively low for industrial purposes, and efforts have been made to increase the carotenoid content through strain improvement (Bhosale & Gadre, 2001a) and optimization of the culture condition (Wang et al., 2007). Recently, Frengova & Beshkova (2009) reviewed the factors affecting

carotenogenesis in the yeast Rhodotorula. However, the molecular mechanism of carotenogenesis regulation is still not well understood. The conventional methods for quantifying the total carotenoid level in microorganisms involve UV (Tereshina et al., 2003) or HPLC (Kaiser et al., 2007) measurement after organic solvent extraction. However, the extraction step may cause degradation or isomerization of carotenoids, affecting the measurements. In addition, the in vitro methods based on solvent extraction can only obtain information regarding the averaging effect of a population of cells. To better understand the regulation of carotenogenesis, it requires the development of rapid, convenient, and reliable methods, which could quantify the carotenoid content in live cells. In recent years, Raman spectroscopy has been widely applied in biological fields like disease diagnosis (Kanter et al., 2009), tissue engineering (Notingher et al., 2003), microorganism identification (Buijtels et al., 2008), and protein conformation determination (Rousseau et al., 2004).