Microbial conversion of mixed volatile fatty acids into microbial lipids by sequencing batch culture strategy

- The highest lipid yield was achieved when acetic:propionic:butyric acid was 6:3:1.
- Utilization and conversion of VFAs were different during sequencing batch culture.
- Lipids produced from mixed VFAs were ideal raw materials for biodiesel.
- High content of propionate in VFAs lead to high yield of odd-numbered fatty acids.

Four mixed volatile fatty acids (VFAs) were used as sole carbon source to culture oleaginous yeast Cryptococcus curvatus by sequencing batch culture strategy. The highest lipid content (42.7%) and concentration (1.77 g/L) were achieved when the ratio of VFAs (acetic, propionic, and butyric acids) was 6:3:1. The oleaginous yeast favored to use VFAs for lipid biosynthesis rather than cell proliferation. With regard to the utilization ratio of VFAs, acetic acid reached over 99%, whereas propionic acid was barely 35%. The produced lipids contained nearly 45% of monounsaturated fatty acids, which can be the ideal raw materials for biodiesel production. Additionally, the produced odd-numbered fatty acid content reached 23.6% when the propionate acid content of VFAs was 50%. Further analysis showed that increasing the ratio of acetic acid was most beneficial to cell mass and lipid production, whereas propionic acid and butyric acid were more conducive to lipid and cell mass synthesis, respectively.

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