Bio-lipid production from crude glycerol and lignocellulosic hydrolysate with oleaginous yeasts

Abstract

Background: Crude glycerol (CG) and hemicellulose hydrolysate (HH) are low- value side-products of biodiesel transesterification and pulp- and paper industry, respectively, which can be converted to microbial lipids by oleaginous yeasts. This study aimed to test the ability of oleaginous yeasts to utilise CG and HH and mixtures of them as carbon source. Results: Eleven out of 27 tested strains of oleaginous yeast species were able to grow in plate tests on CG as sole carbon source. Among them, only one ascomycetous strain, belonging to Lipomyces starkeyi , was identified, the other 10 strains were Rhodotorula spec. When yeasts were cultivated in mixed CG/ HH medium, we observed an activation of glycerol conversion in the Rhodotorula strains, but not in L. starkeyi . Two strains - Rhodotorula toruloides CBS 14 and Rhodotorula glutinis CBS 3044 were further tested in controlled fermentations in bioreactors in different mixtures of CG and HH. The highest measured average biomass and lipid concentration were achieved with R. toruloides in 40% HH medium mixed with 60 g/L CG - 19.4 g/L and 10.6 g/L, respectively, with a lipid yield of 0.22 g lipids per consumed g of carbon source. Fatty acid composition was similar to other R. toruloides strains and comparable to that of vegetable oils. Conclusions: There were big strain differences in the ability to convert CG to lipids, as only few of the tested strains were able to grow. Lipid production rates and yields showed that mixing GC and HH have a stimulating effect on lipid accumulation resulting in shortened fermentation time to reach maximum lipid concentration, which provides a new perspective on converting these low- value compounds to biolipids.

Oleaginous yeasts for biochemicals, biofuels and food from lignocellulose‐hydrolysate and crude glycerol

“…Acetyl‐CoA is the precursor of fatty acid (FA)‐synthesis, which is finally converted to triacylglycerol (TAG) and stored in lipid droplets. Pentoses like xylose are converted to lipids via the pentose‐phosphate pathway or a phosphoketolase reaction (see text, modified from Chmielarz [2021]).…”

“…However, at least for R. toruloides CBS 14 an increased specific glycerol uptake rate has been demonstrated (Chmielarz et al, 2021). This indicates that there are probably also other mechanisms responsible for the metabolic activation, for example, the availability of additional nitrogen sources in the hydrolysate or the activation of some stress response, which then might result in a higher substrate uptake (Chmielarz, 2021).…”