Abstract

BackgroundMicrobial 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).ResultsTwenty-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.ConclusionsThere 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.

Highlights

  • Microbial oils, generated from lignocellulosic material, have great potential as renewable and sustainable alternatives to fossil-based fuels and chemicals

  • We found considerable differences between different oleaginous yeast species, with Rhodotorula babjevae having almost twice as high lipid productivity from wheat straw hydrolysate compared with Lipomyces starkeyi [25]

  • This study investigated the physiological diversity of 29 oleaginous yeast strains regarding their ability to produce lipids in model media containing the two major present in lignocellulosic hydrolysate sugars

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Summary

Introduction

Microbial oils, generated from lignocellulosic material, have great potential as renewable and sustainable alternatives to fossil-based fuels and chemicals. As a first-generation biofuel, it is produced mainly from oil-producing crops like rapeseed, soy or oil palm This leads to direct competition between biofuels and food or feed production, or competition for agricultural land. Lignocellulose is the most abundant biomass on earth [6] and has great potential as a raw material for microbial lipid production, decreasing the risk of competing with food production or land usage compared with first-generation substrates. When residues such as sawdust, straw, hemicellulose residues from the pulp and paper industry or crude glycerol are used, microbial lipid production can add value to forestry and agriculture and improve the sustainability of these industries. Microbial oils can be used for feed, food or other chemical applications [7,8,9,10]

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