5-17: Survey of yeasts for identification of oleaginous species

Several oleaginous yeast species such as Yarrowia lipolytica, Lipomyces lipofer, and Rhodotorula glutinis are being studied for use in production of oleochemicals such as biodiesel. However, most of the known yeast species have not been analyzed to determine their lipid content and growth profiles. Expanding the known panel of oleaginous yeast species will allow selection of the yeast strain with appropriate growth characteristics such as nutrient utilization and toxin tolerance. A set of 66 yeast species was selected from the Phaff Yeast Culture Collection at UC Davis based on similarity to known oleaginous species, and on buoyancy observations. Yeasts were grown in a carbon-rich defined medium for 72 hr. Part of the culture was then stored at -80°C, while the remainder was washed, divided, and resuspended either in the same medium or medium lacking a nitrogen source. After an additional 48 hr growth, cells were centrifuged, washed, and freeze-dried for further analysis of biomass yield and lipid quantification for all three conditions.  Total lipid content was determined gravimetrically. Four yeasts species, Lipomyces lipofer UCDFST 78-19, Rhodotorula graminis UCDFST 81-485.4, R. glutinis UCDFST 05-775 and Prototheca zopfii var. zopfii UCDFST 60-48 exhibited total lipid content higher than 60% w/w.  Selected strains were then analyzed for their fatty acid composition by GC/FID analysis. The most prevalent fatty acids for all yeasts examined were oleic (C 18:1n9), palmitic (C 16:0) and stearic (C 18:0) acids. This study is the first survey of lipid accumulation by a large number of potentially oleaginous yeast species.