Lipid production by Rhodosporidium toruloides during growth on biodiesel-derived crude glycerol

Rhodosporidium toruloides DSM 4444 when grown on biodiesel-derived glycerol under nitrogen-limited conditions was revealed as an efficient microbial lipid produced. This strain when cultivated on glycerol at initial concentration (Gly0) ~50 g/L produced dry cell weight (DCW) =18.1 g/L containing lipids =30.3% in DCW. This strain produced DCW=27.3 g/L containing lipid =54.5% w/w when Gly0 concentration was adjusted to ~90 g/L, with all other fermentation parameters (including nitrogen concentration) remaining constant. At the late growth phases, cellular lipids were re-consumed. Balanced growth phase (trophophase) and idiophase (phase of synthesis of the secondary metabolite) at the trial with Gly0~90 g/L were successfully simulated with the aid of a modified Velhlust-Aggelis model that fitted very well on the experimental data, while optimized parameter values were found to be close to the experimental ones. Lipid extraction process was studied by using two different methods [extraction of DCW with a mixture of chloroform/methanol 2/1 (v/v) or acidification of DCW, boiling and subsequent extraction with a mixture of chloroform/methanol 2/1 (v/v)] and no differences were observed for the studied strain. Cellular lipids of this yeast contained mostly oleic acid, constituting suitable precursors for the synthesis of 2nd generation biodiesel.