Biotechnological valorization of biodiesel-derived glycerol: Trials with the non-conventional yeasts Yarrowia lipolytica and Rhodosporidium sp

Four non-conventional yeast strains belonging to the genera Yarrowia and Rhodosporidium were cultivated under nitrogen-limited conditions in shake flasks with biodiesel-derived glycerol employed as sole substrate.The strains R.toruloides DSM 4444 and Y.lipolytica ACA-DC 5033 displayed better performances and were further studied.At initial glycerol(Gly0)≈50 g/L,the strain ACA-DC 5033 produced dry cell weight(DCW)≈7.0 g/L,and also secondary extra-cellular metabolites as citric acid(CA)at≈16 g/L and polyols(Pol)(mannitol,erythritol and arabitol)at≈21 g/L.In double-media(besides nitrogen also Mg was limiting)for Gly0≈50 g/L,a shift towards CA production occurred(CAmax≈33 g/L).The strain DSM 4444 at Gly0≈50 g/L produced DCW=18.1 g/L containing lipids=30.3%in DCW.In single nitrogen-limited media with Gly0≈90 g/L,the strain ACA-DC 5033 produced Pol≈48 g/L and CA≈20 g/L,while the strain DSM 4444 produced DCW=27.3 g/L containing lipid=54.5%w/w.At the late growth phases,metabolites were re-consumed.Balanced growth phase(trophophase)and phase of secondary metabolite synthesis(idiophase)were successfully simulated with the aid of a modified Velhlust-Aggelis model.Lipid extraction process was studied for these two strains by using two different extraction methods.Yeast lipids contained mostly oleic acid,constituting suitable precursors for the synthesis of 2nd generation biodiesel.