Characterization of newly isolated oleaginous yeasts - Cryptococcus podzolicus, Trichosporon porosum and Pichia segobiensis

Abstract

The yeast strains Cryptococcus podzolicus, Trichosporon porosum and Pichia segobiensis were isolated from soil samples and identified as oleaginous yeast strains beneficial for the establishment of microbial production processes for sustainable lipid production suitable for several industrial applications. When cultured in bioreactors with glucose as the sole carbon source C. podzolicus yielded 31.8% lipid per dry biomass at 20°C, while T. porosum yielded 34.1% at 25°C and P. segobiensis 24.6% at 25°C. These amounts correspond to lipid concentrations of 17.97 g/L, 17.02 g/L and 12.7 g/L and volumetric productivities of 0.09 g/Lh, 0.1 g/Lh and 0.07 g/Lh, respectively. During the culture of C. podzolicus 30 g/l gluconic acid was detected as by-product in the culture broth and 12 g/L gluconic acid in T. porosum culture. The production of gluconic acid was eliminated for both strains when glucose was substituted by xylose as the carbon source. Using xylose lipid yields were 11.1 g/L and 13.9 g/L, corresponding to 26.8% and 33.4% lipid per dry biomass and a volumetric productivity of 0.07 g/Lh and 0.09 g/Lh, for C. podzolicus and T. porosum respectively. The fatty acid profile analysis showed that oleic acid was the main component (39.6 to 59.4%) in all three strains and could be applicable for biodiesel production. Palmitic acid (18.4 to 21.1%) and linolenic acid (7.5 to 18.7%) are valuable for cosmetic applications. P. segobiensis had a considerable amount of palmitoleic acid (16% content) and may be suitable for medical applications.

Keywords: Cryptococcus podzolicus; Microbial lipid production; Oleaginous yeasts; Pichia segobiensis; Screening; Trichosporon porosum.

Figure 1

Lipid content in shake flask cultivation at 25°C in YM medium after 120 h of all four isolates TPST6, CSOH1, SSOH12 and CPOH4 as well as oleaginous yeast Cryptococcus curvatus ( C.c. ) and non oleaginous yeast Saccharomyces cerevisiae ( S.c. ).

Figure 2

CPOH4 cultivated on glucose in 2.5 L-bioreactor in mineral salt medium at pH 5 and 20°C; glucose was fed daily; NH ₄ ⁺ consumption, production of biomass, lipid and gluconic acid are presented.

Figure 3

CPOH4 cultivated on xylose in 2.5 L-bioreactor in mineral salt medium at pH 5 and 20°C; xylose was fed daily. NH₄⁺ consumption, production of biomass and lipid are presented.

Figure 4

TPST6 cultivated on glucose in 2.5 L-bioreactor in mineral salt medium at pH 5 and 25°C; glucose was fed daily. NH₄⁺ consumption, production of biomass, lipid and gluconic acid are presented.

Figure 5

TPST6 cultivated on xylose in 2.5 L-bioreactor in mineral salt medium at pH 5 and 25°C; xylose was fed daily. NH₄⁺ consumption, production of biomass and lipid are presented.

Figure 6

SSOH12 cultivated on glucose in 2.5 L-bioreactor in mineral salt medium at pH 5 and 25°C; glucose was fed daily. NH₄⁺ consumption, production of biomass, lipid and ethanol are presented.