Abstract
BackgroundMicrobial lipid is a potential raw material for large-scale biodiesel production and lignocellulosic hydrolysate has been considered as promising low-cost substrate for lipid fermentation. Lignocellulosic biomass needs to be pretreated before enzymatic hydrolysis, and biocompatible cholinium ionic liquids (ILs) have been demonstrated to be highly efficient for pretreatment. However, the impact of these ILs residues in hydrolysates on downstream biotransformation remains unknown. Therefore, the influence of three typical cholinium ILs on the lipid production by Trichosporon fermentans was first investigated.ResultsThe cell growth of T. fermentans was stimulated in the presence of cholinium lysine ([Ch][Lys]) and cholinium serine ([Ch][Ser]), while the lipid accumulation was inhibited by [Ch][Lys]) and [Ch][Ser]. Both cell growth and lipid accumulation of T. fermentans were inhibited in the presence of cholinium acetate ([Ch][OAc]). Despite the reduction in lipid content, the lipid production by T. fermentans was improved in the presence of low concentrations of [Ch][Lys] (≤30 mM) and [Ch][Ser] (≤20 mM) due to the remarkable increase of biomass. It was found that cholinium cation had minor influence on lipid production. However, the anions of [Ch][Lys] and [Ch][Ser] could be assimilated as nitrogen source by T. fermentans and the reduced C/N ratio accounts for the inhibition of lipid accumulation, which could be alleviated by improving C/N ratio of medium. In addition, the anion of [Ch][OAc] could be metabolized by T. fermentans, leading to a rapid alkaline-pH shift and strong inhibition of lipid production. And this inhibitory effect on lipid production could be significantly reduced by controlling culture pH.ConclusionsThe anions of [Ch][Lys], [Ch][Ser] and [Ch][OAc] play an important role in affecting the cell growth and lipid accumulation of T. fermentans, and the inhibition of these three ILs on lipid production can be alleviated by careful fermentation condition control. Hence, T. fermentans is a promising strain for microbial lipid production from cholinium ILs-pretreated lignocellulosic hydrolysates.
Highlights
Microbial lipid is a potential raw material for large-scale biodiesel production and lignocellulosic hydro‐ lysate has been considered as promising low-cost substrate for lipid fermentation
T. fermentans is a promising strain for microbial lipid production from cholinium ionic liquid (IL)-pretreated lignocellulosic hydrolysates
Three cholinium ILs were investigated for their influences on lipid production by T. fermentans
Summary
Microbial lipid is a potential raw material for large-scale biodiesel production and lignocellulosic hydro‐ lysate has been considered as promising low-cost substrate for lipid fermentation. Lignocellulosic biomass needs to be pretreated before enzymatic hydrolysis, and biocompatible cholinium ionic liquids (ILs) have been demonstrated to be highly efficient for pretreatment. Lignocellulosic biomass needs to be pretreated in order to enhance its accessibility to enzymatic hydrolysis [5]. Imidazolium ILs have been proved to be the most effective ILs used in biomass pretreatment This type of ILs can greatly increase the enzymatic hydrolysis rate of pretreated biomass, they are recently demonstrated to be harmful to microbes. It was found that the presence of [Emim][OAc] could induce morphological changes of S. cerevisiae, which exhibited wrinkled, softened, and holed shapes [14] Irrespective of their cytotoxicity, the nonbiodegradable characteristics of imidazolium ILs would be another hamper to their wide application [15]. It is of urgent need to find new solvents with more biocompatible and biodegradable properties for biomass pretreatment
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