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. 2021 May 29;14(1):124.
doi: 10.1186/s13068-021-01974-2.

Oleaginous yeasts respond differently to carbon sources present in lignocellulose hydrolysate

Jule Brandenburg  1 , Johanna Blomqvist  1 , Volha Shapaval  2 , Achim Kohler  2 , Sabine Sampels  1 , Mats Sandgren  1 , Volkmar Passoth  3
Affiliations

Oleaginous yeasts respond differently to carbon sources present in lignocellulose hydrolysate

Jule Brandenburg et al. Biotechnol Biofuels. .

Abstract

Background: Microbial oils, generated from lignocellulosic material, have great potential as renewable and sustainable alternatives to fossil-based fuels and chemicals. By unravelling the diversity of lipid accumulation physiology in different oleaginous yeasts grown on the various carbon sources present in lignocellulose hydrolysate (LH), new targets for optimisation of lipid accumulation can be identified. Monitoring lipid formation over time is essential for understanding lipid accumulation physiology. This study investigated lipid accumulation in a variety of oleaginous ascomycetous and basidiomycetous strains grown in glucose and xylose and followed lipid formation kinetics of selected strains in wheat straw hydrolysate (WSH).

Results: Twenty-nine oleaginous yeast strains were tested for their ability to utilise glucose and xylose, the main sugars present in WSH. Evaluation of sugar consumption and lipid accumulation revealed marked differences in xylose utilisation capacity between the yeast strains, even between those belonging to the same species. Five different promising strains, belonging to the species Lipomyces starkeyi, Rhodotorula glutinis, Rhodotorula babjevae and Rhodotorula toruloides, were grown on undiluted wheat straw hydrolysate and lipid accumulation was followed over time, using Fourier transform-infrared (FTIR) spectroscopy. All five strains were able to grow on undiluted WSH and to accumulate lipids, but to different extents and with different productivities. R. babjevae DVBPG 8058 was the best-performing strain, accumulating 64.8% of cell dry weight (CDW) as lipids. It reached a culture density of 28 g/L CDW in batch cultivation, resulting in a lipid content of 18.1 g/L and yield of 0.24 g lipids per g carbon source. This strain formed lipids from the major carbon sources in hydrolysate, glucose, acetate and xylose. R. glutinis CBS 2367 also consumed these carbon sources, but when assimilating xylose it consumed intracellular lipids simultaneously. Rhodotorula strains contained a higher proportion of polyunsaturated fatty acids than the two tested Lipomyces starkeyi strains.

Conclusions: There is considerable metabolic diversity among oleaginous yeasts, even between closely related species and strains, especially when converting xylose to biomass and lipids. Monitoring the kinetics of lipid accumulation and identifying the molecular basis of this diversity are keys to selecting suitable strains for high lipid production from lignocellulose.

Keywords: Ascomycetes; Basidiomycetes; Biofuels; FTIR; Lignocellulose; Lipids; Oleaginous yeasts; Xylose.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Growth and lipid content of Rhodotorula and Lipomyces strains grown in medium containing glucose (G), xylose (X) or a glucose/xylose mixture (M). The cultivations were done in shake flasks at 25 ºC, 130 rpm and performed in duplicates. Dark green represents strong growth and high lipid content, light green/white little or no growth and low lipid content. (nd) = not determined due to no or very poor growth. Exact values are given in Additional file 2
Fig. 2
Fig. 2
Lipid production, growth, sugar and acetic acid consumption of a Rhodotorula babjevae DVBPG 8058, b Rhodotorula glutinis CBS 2367, c Rhodotorula toruloides CBS 14, d Lipomyces starkeyi CBS 1807 and e Lipomyces starkeyi CBS 7544 grown in bioreactors containing wheat straw hydrolysate. All cultivations were performed in triplicates. Lipid production over time was determined by Fourier transform-infrared (FTIR) spectroscopy (calculated from biological triplicates, for R. babjevae DVBPG from duplicates). For R. babjevae DVBPG 8058 and R. glutinis CBS 2367 the end point values of lipid concentration were determined gravimetrically
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