Single Cell Oil Production by Oleaginous Yeasts Grown in Synthetic and Waste-Derived Volatile Fatty Acids

Abstract

Four yeast isolates from the species-Apiotrichum brassicae, Candida tropicalis, Metschnikowia pulcherrima, and Pichia kudriavzevii-previously selected by their oleaginous character and growth flexibility in different carbon sources, were tested for their capacity to convert volatile fatty acids into lipids, in the form of single cell oils. Growth, lipid yields, volatile fatty acids consumption, and long-chain fatty acid profiles were evaluated in media supplemented with seven different volatile fatty acids (acetic, butyric, propionic, isobutyric, valeric, isovaleric, and caproic), and also in a dark fermentation effluent filtrate. Yeasts A. brassicae and P. kudriavzevii attained lipid productivities of more than 40% (w/w), mainly composed of oleic (>40%), palmitic (20%), and stearic (20%) acids, both in synthetic media and in the waste-derived effluent filtrate. These isolates may be potential candidates for single cell oil production in larger scale applications by using alternative carbon sources, combining economic and environmental benefits.

Keywords: dark fermentation effluent; lipids; oleaginous yeasts; single cell oils; volatile fatty acids.

Figure 1

Time-course growth in YP:HAc 15 g L⁻¹ medium, during 168 h, using the four tested yeast species: (A) Apiotrichum brassicae V134; (B) Candida tropicalis V139; (C) Metschnikowia pulcherrima V213; (D) Pichia kudriavzevii V194. Colors indicate measurements (mean ± standard deviations) of the following characteristics: orange—relative fluorescent units (RFUs); green—optical density (OD_640 nm); blue—pH; red—acetic acid concentration (g L⁻¹).

Figure 2

Effect of volatile fatty acids (pure or in mixture) on single cell oil production (relative fluorescent units, RFUs) and yeast growth (dry cell weight, DCW) using the four tested yeast species: white—Apiotrichum brassicae V134; light grey—Candida tropicalis V139; dark grey—Metschnikowia pulcherrima V213; black—Pichia kudriavzevii V194. Letters indicate the medium in which yeasts were grown, during 120 h: (A) YP:HAc (5.1 g L⁻¹); (B) YP:HPr (2.7 g L⁻¹); (C) YP:HBut (3.5 g L⁻¹); (D) YP:HAc:HPr; (E) YP:HAc:HBut; (F) YP:HAc:HPr:HBut; (G) YP:HAc:HPr:HBut:isoHbut (0.2 g L⁻¹):HVal (0.9 g L⁻¹). Values represent mean of triplicates ± standard deviations.

Figure 3

Volatile fatty acid (VFA) consumption (%) after 120 h of incubation in effluent filtrate obtained from anaerobic digestion of organic wastes for: (A) Candida tropicalis V139 and (B) Metschnikowia pulcherrima V213. Values represent mean of triplicates ± standard deviations.