Abstract
BackgroundRhodotorula toruloides is a promising platform organism for production of lipids from lignocellulosic substrates. Little is known about the metabolic aspects of lipid production from the lignocellolosic sugar xylose by oleaginous yeasts in general and R. toruloides in particular. This study presents the first proteome analysis of the metabolism of R. toruloides during conversion of xylose to lipids.ResultsRhodotorula toruloides cultivated on either glucose or xylose was subjected to comparative analysis of its growth dynamics, lipid composition, fatty acid profiles and proteome. The maximum growth and sugar uptake rate of glucose-grown R. toruloides cells were almost twice that of xylose-grown cells. Cultivation on xylose medium resulted in a lower final biomass yield although final cellular lipid content was similar between glucose- and xylose-grown cells. Analysis of lipid classes revealed the presence of monoacylglycerol in the early exponential growth phase as well as a high proportion of free fatty acids. Carbon source-specific changes in lipid profiles were only observed at early exponential growth phase, where C18 fatty acids were more saturated in xylose-grown cells. Proteins involved in sugar transport, initial steps of xylose assimilation and NADPH regeneration were among the proteins whose levels increased the most in xylose-grown cells across all time points. The levels of enzymes involved in the mevalonate pathway, phospholipid biosynthesis and amino acids biosynthesis differed in response to carbon source. In addition, xylose-grown cells contained higher levels of enzymes involved in peroxisomal beta-oxidation and oxidative stress response compared to cells cultivated on glucose.ConclusionsThe results obtained in the present study suggest that sugar import is the limiting step during xylose conversion by R. toruloides into lipids. NADPH appeared to be regenerated primarily through pentose phosphate pathway although it may also involve malic enzyme as well as alcohol and aldehyde dehydrogenases. Increases in enzyme levels of both fatty acid biosynthesis and beta-oxidation in xylose-grown cells was predicted to result in a futile cycle. The results presented here are valuable for the development of lipid production processes employing R. toruloides on xylose-containing substrates.
Highlights
Rhodotorula toruloides is a promising platform organism for production of lipids from lignocellulosic substrates
Cultivation on xylose in combination with glucose was investigated using Lipomyces starkeyi with 61% lipids of dry cell weight (DCW) produced [12], while engineering of Yarrowia lipolytica strain enabled it to assimilate xylose [13, 14]
Batch cultivation of Rhodotorula toruloides Growth, sugar consumption and lipid production of R. toruloides in medium containing either glucose or xylose as a carbon source were monitored in batch cultivations (Fig. 1)
Summary
Rhodotorula toruloides is a promising platform organism for production of lipids from lignocellulosic substrates. Little is known about the metabolic aspects of lipid production from the lignocellolosic sugar xylose by oleaginous yeasts in general and R. toruloides in particular. Some oleaginous yeasts can convert xylose to lipids up to more than 20% of its dry cell weight: 22% Rhodotorula glutinis [5], 58% Trichosporon fermentans [6], 37% Cryptococcus curvatus [7], 33% Cryptococcus albidus [8], 42% Rhodotorula toruloides [9,10,11]. Cultivation on xylose in combination with glucose was investigated using Lipomyces starkeyi with 61% lipids of dry cell weight (DCW) produced [12], while engineering of Yarrowia lipolytica strain enabled it to assimilate xylose [13, 14]. Microbial production of lipids from xylose was investigated in filamentous fungi: Cunninghamella echinulata (lipids constituted 58% DCW), Mortierella isabellina (lipids constituted 66% DCW) [15]
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