Abstract
Conversion of lignocellulosic biomass into lipids and related chemicals has attracted much attention in the past two decades, and the oleaginous yeast Rhodosporidium toruloides has been widely used in this area. While R. toruloides species naturally have physiological advantages in terms of substrate utilization, lipid accumulation, and inhibitor resistance, reduced lipid production and cell growth are noticed when biomass hydrolysates are used as feedstocks. To improve the robustness of R. toruloides, here, we devised engineered strains by overexpressing genes responsible for phenolic compound degradation. Specifically, gene expression cassettes of the manganese peroxidase gene (MNP) and versatile peroxidase gene (VP) were constructed and integrated into the genome of R. toruloides NP11. A series of engineered strains were evaluated for lipid production in the presence of typical phenolic inhibitors. The results showed that R. toruloides strains with proper expression of MNP or VP indeed grew faster in the presence of vanillin and 5-hydroxymethylfurfural than the parental strain. When cultivated in concentrated mode biomass hydrolysates, the strain VP18 had improved performance as the cell mass and lipid content increased by 30% and 25%, respectively. This study provides more robust oleaginous yeast strains for microbial lipid production from lignocellulosic biomass, and similar efforts may be used to devise more advanced lipid producers.
Highlights
The bioconversion of lignocellulose into biofuels and other high value-added chemicals is of significant potential for its environmental protection and energy sustainability (Jin et al, 2015)
The results clearly indicated the presence of manganese peroxidase gene (MNP) and versatile peroxidase gene (VP) genes for most transformants
The results showed that 2.5 g/L of PHB, vanillin, and syringaldehyde, except HMF, inhibited the cell growth of all strains (Supplementary Figures S1, S2)
Summary
The bioconversion of lignocellulose into biofuels and other high value-added chemicals is of significant potential for its environmental protection and energy sustainability (Jin et al, 2015). Lignocellulose contains roughly 40% of cellulose, 25% of hemicellulose, and 20% of lignin (Kim et al, 2021). During chemical or biological pretreatment, lignin is degraded into monomeric compounds, mainly as p-hydroxybenzaldehyde (PHB), vanillin, syringaldehyde, and Engineering of Oleaginous Yeast their corresponding reduced or oxidized products (Zhu et al, 2017; Osorio–González et al, 2019). These lignin-derived phenols, associated with organic acids and furnaldehydes, usually have inhibitive and toxic effects on microorganisms, playing negative roles in biological processes (Ragauskas et al, 2014)
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