Production of added-value metabolites during growth of wild-type yeast strains on media composed of biodiesel-derived crude glycerol

Wild-type yeast strains of Metschnikowia sp., Rhodotorula sp. and Rhodosporidium sp. were grown under nitrogen-limited conditions with crude glycerol employed as sole substrate in shake flasks, under nitrogen-limited conditions, with initial glycerol concentration (Glol0) ≈45 g/L. Yeasts presented interesting DCW production. Metschnikowia sp. strains produced significant quantities of intra-cellular polysaccharides (i.e. the strain V.V.-D4 produced 11.0 g/L of endopolysaccharides, with polysaccharides in DCW ≈63% w/w). The only yeast strain presenting typical oleaginous characteristics was the strain Rhodosporidium toruloides DSM 4444, that presented lipid in DCW values >20% w/w, and increased its lipid concentration (in g/L) over the whole period of the fermentation performed. On media with higher Glol0, interesting lipid-accumulating capacities (maximum lipid =12.5 g/L, maximum lipid in DCW =43.0-46.0% w/w, conversion yield of lipid on glycerol consumed =0.16 g/g) were seen. Cellular lipids of most yeasts contained mainly oleic and palmitic acid. Finally, “crude” lipids (chloroform/methanol 2/1 v/v extract) produced by R. toruloides DSM 4444 during growth on glycerol, were mainly composed of triacylglycerols.