Investigating the Bioconversion Potential of Volatile Fatty Acids: Use of Oleaginous Yeasts Rhodosporidium toruloides and Cryptococcus curvatus towards the Sustainable Production of Biodiesel and Odd-Chain Fatty Acids

Oleaginous yeasts have attracted increasing scientific interest as single cell oil (SCO) producers. SCO can be used as a fossil-free fuel substitute, but also as a source of rarely found odd-chain fatty acids (OCFAs), such as C15, C17, and C25 fatty acids which have a wide range of nutritional and biological applications. Volatile fatty acids (VFAs) have gained interest as sustainable carbon source for yeasts. This study aims to improve current knowledge on yeast species that yield high amounts of SCO using VFAs as a carbon source. Specifically, the growth of the promising yeasts Cryptococcus curvatus and Rhodotorula toruloides was evaluated on individual VFAs, such as acetic, propionic, and butyric acid. C. curvatus proved to be more tolerant in higher concentrations of VFAs (up to 60 g/L), while butyric acid favored biomass and lipid conversion (0.65 and 0.23 g/g(substrate), respectively). For R. toruloides, butyric acid favored biomass conversion (0.48 g/g(substrate)), but lipid conversion was favored using acetic acid, instead (0.14 g/g(substrate)). Propionic acid induced the formation of OCFAs, which yielded higher amounts for C. curvatus (up to 2.17 g/L). VFAs derived from the anaerobic digestion of brewer's spent grain were tested as a cost-competitive carbon source and illustrated the significance of the combination of different VFAs in the quality of the produced SCO, by improving the biodiesel properties and OCFAs production.

Automated summary

Oleaginous yeasts have gained scientific interest as producers of single cell oil (SCO), which serves as a fossil-free fuel substitute and a source of rarely found odd-chain fatty acids (OCFAs). This study evaluated the growth of Cryptococcus curvatus and Rhodotorula toruloides yeasts on volatile fatty acids (VFAs) as a carbon source. The results showed that different VFAs had varying effects on biomass and lipid conversion, and VFAs derived from anaerobic digestion of brewer's spent grain improved the quality and production of SCO.