Biotechnological conversions of bio-diesel-derived crude glycerol by Yarrowia lipolytica strains

In the present report, crude glycerol, waste discharged from bio-diesel production, was used as carbon substrate for three natural Yarrowia lipolytica strains (LFMB 19, LFMB 20 and ACA-YC 5033) during growth in nitrogen-limited submerged shake-flask experiments. In media with initial glycerol concentration of 30 g/L, all strains presented satisfactory microbial growth and complete glycerol uptake. Although culture conditions favored the secretion of citric acid (and potentially the accumulation of storage lipid), for the strains LFMB 19 and LFMB 20, polyol mannitol was the principal metabolic product synthesized (maximum quantity 6.0 g/L, yield 0.20-0.26 g per g of glycerol consumed). The above strains produced small quantities of lipids and citric acid. In contrast, Y lipolytica ACA-YC 5033 produced simultaneously higher quantities of lipid and citric acid and was further grown on crude glycerol in nitrogen-limited experiments, with constant nitrogen and increasing glycerol concentrations (70-120 g/L). Citric acid and lipid concentrations increased with increment of glycerol; maximum total citric acid 50.1 g/L was produced (yield 0.44 g per g of glycerol) while simultaneously 2.0 g/L of fat were accumulated inside the cells (0.31 g of lipid per g of dry weight). Cellular lipids were mainly composed of neutral fraction, the concentration of which substantially increased with time. Moreover, in any case, the phospholipid fraction was more unsaturated compared with total and neutral lipids, while at the early growth step, microbial lipid was more rich in saturated fatty acids (e.g. C16:0 and C18:0) compared with the stationary phase.