Comparative lipid production by oleaginous yeasts in hydrolyzates of lignocellulosic biomass and process strategy for high titers

Abstract

Oleaginous yeasts can convert sugars to lipids with fatty acid profiles similar to those of vegetable oils, making them attractive for production of biodiesel. Lignocellulosic biomass is an attractive source of sugars for yeast lipid production because it is abundant, potentially low cost, and renewable. However, lignocellulosic hydrolyzates are laden with byproducts which inhibit microbial growth and metabolism. With the goal of identifying oleaginous yeast strains able to convert plant biomass to lipids, we screened 32 strains from the ARS Culture Collection, Peoria, IL to identify four robust strains able to produce high lipid concentrations from both acid and base-pretreated biomass. The screening was arranged in two tiers using undetoxified enzyme hydrolyzates of ammonia fiber expansion (AFEX)-pretreated cornstover as the primary screening medium and acid-pretreated switch grass as the secondary screening medium applied to strains passing the primary screen. Hydrolyzates were prepared at $18-20% solids loading to provide $110 g/L sugars at $56:39:5 mass ratio glucose: xylose:arabinose. A two stage process boosting the molar C:N ratio from 60 to well above 400 in undetoxified switchgrass hydrolyzate was optimized with respect to nitrogen source, C:N, and carbon loading. Using this process three strains were able to consume acetic acid and nearly all available sugars to accumulate 50-65% of cell biomass as lipid (w/w), to produce 25-30 g/L lipid at 0.12-0.22 g/L/h and 0.13-0.15 g/g or 39-45% of the theoretical yield at pH 6 and 7, a performance unprecedented in lignocellulosic hydrolyzates. Three of the top strains have not previously been reported for the bioconversion of lignocellulose to lipids. The successful identification and development of top-performing lipidproducing yeast in lignocellulose hydrolyzates is expected to advance the economic feasibility of high quality biodiesel and jet fuels from renewable biomass, expanding the market potential for lignocellulose-derived fuels beyond ethanol for automobiles to the entire U.S. transportation market. Biotechnol. Bioeng. 2016; 9999: XX-XX.

Bioethanol and lipid production from the enzymatic hydrolysate of wheat straw after furfural extraction

“…We found considerable differences between the two tested yeast strains when grown on the tested substrate, with R. babjevae (lipid yield 0.17 and production rate 0.18 g/L h) being superior over L. starkeyi (0.09 and 0.08 g/L h). The physiological basis of this difference on the same substrate is not clear; however, it fits well to results on other lignocellulose hydrolysate, where L. starkeyi -strains produced rather low lipid amounts compared to other oleaginous yeasts (Slininger et al 2016). The order of magnitude of the lipid yield of L. starkeyi was similar to a recent study in our group, where we obtained the highest lipid yield from hemicellulose hydrolysate that has been reported so far (Brandenburg et al 2016).…”

“…Between the two tested species, R. babjevae seems to be the yeast of choice in terms of further research for biofuel production from lignocellulose. The obtained lipid yield- and -production rate were also relatively high compared to other oleaginous yeasts, cultivated on either lignocellulosic hydrolysate or a glucose-based model substrate (Slininger et al 2016, Shen et al 2013). In recent system analyses, we pointed out that rapid conversion of the substrate to lipids has great impact on the sustainability of the conversion, because aerobic cultivations, as required for lipid production, require much energy, implying that a faster fermentation will largely improve process efficiency (Karlsson et al 2016, Karlsson et al 2017).…”

Comprehending the influence of critical cultivation parameters on the oleaginous behaviour of potent rotten fruit yeast isolates

“…), while some require excessively high initial concentration with respect to starved nitrogen for displaying high oleaginicity (Slininger et al . ). Sometimes composition of microbial oils are also influenced by ratio of carbon and other essential nutrient/mineral mainly nitrogen and phosphorous (Wu et al .…”

Conversion of sugar beet residues into lipids by Lipomyces starkeyi for biodiesel production

“…Different studies demonstrated that the application of two stage cultures is advantageous compared with singlestage cultures for microbial lipid accumulation, thanks to the spatial and temporal separation of a rst phase in which cells reach high cell density in a nitrogen enriched medium, and a second phase where cells accumulate lipids in a nitrogen limited medium with excess of carbon [43,49,50]. In this work, the availability of molasses achieved by pulsed-fed fermentations in shake asks resembled the principles of two stage cultures and, accordingly, enabled a higher intracellular lipid accumulation compared with batch fermentations, leading to an average of 9.7 g/L and 0.178 g/g of lipid production and yield, respectively (Table 1).…”