Biotechnological conversions of crude glycerol, residue deriving from biodiesel production facilities, by strains of the yeast Yarrowia lipolytica

Aim of the present study was to assess the ability of four Yarrowia lipolytica strains (ACA-DC 50109, LFMB Y-20, ATCC 20460 and LMBF Y-45) to grow on biodiesel-derived crude glycerol, the principal residue-stream deriving from biodiesel manufacture. Initial trials were carried out in shake-flasks under nitrogen limitation (initial glycerol Glol0~40 g/L, initial nitrogen ~0.35 g/L), that favor the production of cellular lipids and/or extra-cellular secondary metabolites like citric acid (CA). All strains produced appreciable dry cell weight (DCW) quantities (up to 13.0 g/L). The strain ACA-DC 50109 produced CA in concentrations up to 16.0 g/L, while lipid in DCW values of ~15% w/w were recorded. In the next stage, this strain was cultured on media with higher nitrogen limitation (Glol0~50 g/L, initial nitrogen ~0.15 g/L) in batch-bioreactor and shake-flask experiments, and comparable DCW (up to 8.0 g/L) and CA (25-28 g/L) quantities were reported for these trials. Lipid production was higher in the batch-bioreactor experiment. In fed-batch bioreactor trials performed thereafter, a maximum CA quantity of 66.1 g/L (conversion yield 0.66 g per g of glycerol) was obtained. Cellular lipids of all tested strains were mainly composed of the fatty acids Δ9C18:1, Δ9,12C18:2 and C16:0.