Abstract
BackgroundMicrobial lipid production by using lignocellulosic biomass as the feedstock holds a great promise for biodiesel production and biorefinery. This usually involves hydrolysis of biomass into sugar-rich hydrolysates, which are then used by oleaginous microorganisms as the carbon and energy sources to produce lipids. However, the costs of microbial lipids remain prohibitively high for commercialization. More efficient and integrated processes are pivotal for better techno-economics of microbial lipid technology.ResultsHere we describe the simultaneous saccharification and enhanced lipid production (SSELP) process that is highly advantageous in terms of converting cellulosic materials into lipids, as it integrates cellulose biomass hydrolysis and lipid biosynthesis. Specifically, Cryptococcus curvatus cells prepared in a nutrient-rich medium were inoculated at high dosage for lipid production in biomass suspension in the presence of hydrolytic enzymes without auxiliary nutrients. When cellulose was loaded at 32.3 g/L, cellulose conversion, cell mass, lipid content and lipid coefficient reached 98.5%, 12.4 g/L, 59.9% and 204 mg/g, respectively. Lipid yields of the SSELP process were higher than those obtained by using the conventional process where cellulose was hydrolyzed separately. When ionic liquid pretreated corn stover was used, both cellulose and hemicellulose were consumed simultaneously. No xylose was accumulated over time, indicating that glucose effect was circumvented. The lipid yield reached 112 mg/g regenerated corn stover. This process could be performed without sterilization because of the absence of auxiliary nutrients for bacterial contamination.ConclusionsThe SSELP process facilitates direct conversion of both cellulose and hemicellulose of lignocellulosic materials into microbial lipids. It greatly reduces time and capital costs while improves lipid coefficient. Optimization of the SSELP process at different levels should further improve the efficiency of microbial lipid technology, which in turn, promote the biotechnological production of fatty acid-derived products from lignocellulosic biomass.
Highlights
Microbial lipid production by using lignocellulosic biomass as the feedstock holds a great promise for biodiesel production and biorefinery
In the first stage cells were cultivated in a nutrient-rich medium, while in the second stage cells were resuspended in a glucose solution without auxiliary nutrients
Since our results demonstrated that cellulose hydrolysis and lipid production proceeded concurrently and efficiently during the simultaneous saccharification and enhanced lipid production (SSELP) process, we further followed the process for 72 h under an optimal condition (Figure 3)
Summary
Microbial lipid production by using lignocellulosic biomass as the feedstock holds a great promise for biodiesel production and biorefinery This usually involves hydrolysis of biomass into sugar-rich hydrolysates, which are used by oleaginous microorganisms as the carbon and energy sources to produce lipids. In one recent example of integration of lipid production and enzymatic hydrolysis of corn stover, lipid titre reached 3.23 g/L when the yeast Trichosporon cutaneum was cultivated in 50-L stirredtank bioreactor [9]. In another example, lipid production by Microsphaeropsis sp. Because cell density was high and cell propagation was inhibited by nutrient deficiency, lipid productivity and yield were significantly enhanced
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