A Fast and Simple Qualitative Method for Screening Oleaginous Yeasts on Agar

Finding new oleaginous yeasts is of great interest due to their many important applications. Currently available screening procedures are time-consuming, and most of these require liquid cultures. In this work, a new, fast, economical, and simple qualitative method for screening oleaginous yeasts was developed. The fluorescent dye, Rhodamine B, was selected because its fluorescence is directly correlated to lipid content, and no additional steps or special equipment are needed. This method only requires growing the yeasts on dyed agar plates. Under visible light, it is easy to observe that nonpigmented oleaginous yeasts become colored, whereas non-oleaginous yeasts remain uncolored. The developed method is also useful for improving medium composition in specific applications. Moreover, it was also adapted to use alternative carbon sources, such as lignocellulosic materials and glycerol. The developed method was applied to screen 124 recently isolated nonpigmented yeasts on three different carbon sources, namely, glucose, glycerol, and agave bagasse hydrolysate. Five strains were selected as good lipid producers on all tested carbon sources and accumulated over 48% lipids. Furthermore, the assay was adapted to screen reddish-pigmented yeasts. Considering all the above, the developed method has a wide range of applications in the field of microbial oils.