Isolation, identification and screening of yeasts towards their ability to assimilate biodiesel-derived crude glycerol: microbial production of polyols, endopolysaccharides and lipid.

Abstract

To assess the ability of various newly isolated or belonging in official collections yeast strains to convert biodiesel-derived glycerol (Gly) into added-value compounds. Ten newly isolated yeast strains belonging to Debaryomyces sp., Naganishia uzbekistanensis, Rhodotorula sp. and Yarrowia lipolytica, isolated from fishes, metabolized Gly under nitrogen limitation. The aim of the study was to identify potential newly isolated microbial candidates that could produce single-cell oil (SCO), endopolysaccharides and polyols when these micro-organisms were grown on biodiesel-derived Gly. As controls producing SCO and endopolysaccharides were the strains Rhodotorula glutinis NRRL YB-252 and Cryptococcus curvatus NRRL Y-1511. At initial Gly (Gly0 ) ≈40gl-1 , most strains presented remarkable dry cell weight (DCW) production, whereas Y. lipolytica and Debaryomyces sp. produced non-negligible quantities of mannitol and arabitol (Ara). Five strains were further cultivated at increasing Gly0 concentrations. Rhodotorula glutinis NRRL YB-252 produced 7·2gl-1 of lipid (lipid in DCW value ≈38% w/w), whereas Debaryomyces sp. FMCC Y69 in batch-bioreactor experiment with Gly0 ≈80gl-1 , produced 30-33gl-1 of DCW and ~30gl-1 of Ara. At shake-flasks with Gly0 ≈125gl-1 , Ara of ~48gl-1 (conversion yield of polyol on Gly consumed ≈0·62gg-1 ) was achieved. Cellular lipids of all yeasts contained in variable concentrations oleic, palmitic, stearic and linoleic acids. Newly isolated, food-derived and non-previously studied yeast isolates converted biodiesel-derived Gly into several added-value metabolites. Alternative ways of crude Gly valorization through yeast fermentations were provided and added-value compounds were synthesized.