Efficient conversion of acetate into lipids by the oleaginous yeast Cryptococcus curvatus

Abstract

Background: Acetic acid is routinely generated during lignocelluloses degradation, syngas fermentation, dark hydrogen fermentation and other anaerobic bioprocesses. Acetate stream is commonly regarded as a by-product and detrimental to microbial cell growth. Conversion of acetate into lipids by oleaginous yeasts may be a good choice to turn the by-product into treasure.

Results: Ten well-known oleaginous yeasts were evaluated for lipid production on acetate under flask culture conditions. It was found that all of those yeasts could use acetate for microbial lipid production. In particular, Cryptococcus curvatus accumulated lipids up to 73.4 % of its dry cell mass weight. When the culture was held in a 3-L stirred-tank bioreactor, cell mass, lipid content, lipid yield and acetate consumption rate were 8.1 g/L, 49.9 %, 0.15 g/g and 0.64 g/L/h, respectively. The fatty acid compositional profiles of the acetate-derived lipids were similar to those of vegetable oil, suggesting their potential for biodiesel production. Continuous cultivation of C. curvatus was conducted under nitrogen-rich condition at a dilution rate of 0.04 h(-1), the maximal lipid content and lipid yield were 56.7 % and 0.18 g/g, respectively. The specific lipid formation rate, lipid content and lipid yield were all higher under nitrogen-rich conditions than those obtained under nitrogen-limited conditions at the same dilution rates. Effective lipid production by C. curvatus was observed on corn stover hydrolysates containing 15.9 g/L acetate.

Conclusions: Acetate is an effective carbon source for microbial lipid production by oleaginous yeasts. Continuous cultivation of C. curvatus on acetate was promising for lipid production under both nitrogen-rich and nitrogen-limited conditions. These results provide valuable information for developing and designing more efficient acetate-into-lipids bioprocess.

Keywords: Acetic acid; Biodiesel; Biomass hydrolysates; Continuous culture; Cryptococcus curvatus; Microbial lipids; Oleaginous yeast.

Fig. 1

Results of lipid production by C. curvatus on acetate. a Profiles of acetate consumption, cell growth and lipid accumulation. b The evolution of lipid and non-lipid cell mass

Fig. 2

Steady-state lipid yields and non-lipid cell mass yields of C. curvatus at different dilution rates under nitrogen-rich and nitrogen-limited conditions. Error bars mean ± standard deviation of four samples

Fig. 3

Steady-state specific lipid formation rates of C. curvatus at different dilution rates under nitrogen-rich conditions. Error bars mean ± standard deviation of four samples

Fig. 4

Steady-state specific acetic acid consumption rates of C. curvatus at different dilution rates under nitrogen-limited conditions. Error bars mean ± standard deviation of four samples

Fig. 5

Steady-state specific lipid formation rates of C. curvatus at different dilution rates under nitrogen-limited conditions. Error bars mean ± standard deviation of four samples

Fig. 6

Results of lipid production by C. curvatus on corn stover hydrolysates containing acetate. a Profiles of substrates consumption. b Profiles of cell growth and lipid accumulation. Error bars mean ± standard deviation of three samples