Production of Single Cell Oils by the Cold-Adapted Oleaginous Yeast Rhodotorula glacialis AS 4.7: Effects of the Growth Temperature and the C:N Ratio.

Rhodotorula glacialis AS 4.7 is an oleaginous psychrophilic yeast which was isolated from glacial environments. Despite its origin, the strain abundantly grew and accumulated lipids up to 20°C. The growth temperature did not influence the yield coefficients of both biomass and lipids production, but had significant effects on the growth rate and thus on volumetric productivity of lipid. 15°C were identified as the optimum temperature for lipid production. As the growth temperature decreased, the abundance of C18 fatty acids (FA) increased at the expenses of C16 FA and the unsaturation degree increased as well. In particular, remarkable amounts of linolenic acid (C18:3 ω-3) were produced at -3°C, accounting for 29% of FA. Lipid production by R. glacialis AS 4.7 especially occurred in carbon rich media, through a two-stages process. The first stage resulted in multiplication of cells and finished with the exhaustion of a nutrient other than the carbon source. During the second stage, the excess glucose was converted into intracellular storage lipids. The extent of the carbon excess had major positive effects on lipid production. The lipid content of biomass, glucose conversion into lipids, lipid concentration, and lipids productivity were all maximum with 120 g L-1 glucose (68%, 16%, 19 g L-1, and 0.054 g L-1 h-1, respectively). The results herein reported suggest that R. glacialis AS 4.7 could be considered as an interesting microorganism for the production of single cell oils and represent the first proposed biotechnological application for this yeast species.