Customizing lipids from oleaginous microbes: leveraging exogenous and endogenous approaches.

To meet the growing demands of the oleochemical industry, tailored lipid sources are expanding to oleaginous microbes. To control the fatty acid composition of microbial lipids, ground-breaking exogenous and endogenous approaches are being developed. Exogenous approaches employ extracellular tools such as product-specific feedstocks, process optimization, elicitors, and magnetic and mechanical energy, whereas endogenous approaches leverage biology through the use of product-specific microbes, adaptive laboratory evolution (ALE), and the creation of custom strains via random and targeted cellular engineering. We consolidate recent advances from both fields into a review that will serve as a resource for those striving to fulfill the vision of microbial cell factories for tailored lipid production.

Compositional Shift in Fatty Acid Profiles of Lipids Obtained from Oleaginous Yeasts upon the Addition of Essential Oil from Citrus sinensis L.

Tailoring lipids from oleaginous yeasts to contain specific types of fatty acid is of considerable interest to food, fuel, and pharmaceutical industries. In this study, the essential oil obtained from Citrus sinesus L. has been used to alter the fatty acid composition of two common oleaginous yeasts, Rhodosporidium toruloides and Cryptococcus curvatus. With increasing levels of essential oil in the medium, the metabolic flux of the fatty acid biosynthesis pathway shifted towards saturated fatty acid production. Essential oil reduced the activities of elongase and ∆9 desaturase. This made the lipid obtained from both these yeasts rich in saturated fatty acids. At certain specific concentrations of the essential oil in the medium, the lipid obtained from R. toruloides and C. curvatus cultures was similar to mahuwa butter and palm oil, respectively. Limonene is the major constituents of orange essential oil. Its effect on one of the oleaginous yeasts, R. toruloides, was also studied separately. Effects similar to orange essential oil were obtained with limonene. Thus, we can conclude that limonene in orange essential oil brings about compositional change of microbial lipid produced in this organism.

Utilization of microbial oil obtained from crude glycerol for the production of polyol and its subsequent conversion to polyurethane foams.

We have demonstrated possible use of microbial oil in biopolymer industries. Microbial oil was produced from biodiesel based crude glycerol and subsequently converted into polyol. Fermentation of crude glycerol in a batch bioreactor using Rhodosporidium toruloides ATCC 10788 produced 18.69g/L of lipid at the end of 7days. The microbial oil was then chemically converted to polyol and characterized using FT-IR and 1H NMR. For comparison, canola oil and palm oil were also converted into their respective polyols. The hydroxyl numbers of polyols from canola, palm and microbial oil were found to be 266.86, 222.32 and 230.30 (mgKOH/g of sample) respectively. All the polyols were further converted into rigid and semi-rigid polyurethanes (maintaining the molar -NCO/-OH ratio of 1.1) to examine their suitability in polymer applications. Conversion of microbial lipid to polyurethane foam also provides a new route for the production of polymers using biodiesel based crude glycerol.

Enhanced Production of Xylitol from Poplar Wood Hydrolysates Through a Sustainable Process Using Immobilized New Strain Candida tropicalis UFMG BX 12-a.

A new strain, Candida tropicalis UFMG BX 12-a, was found to produce higher yields of xylitol on poplar wood hemicellulose hydrolysate. The hemicellulose hydrolysate liquor was detoxified using a novel method we developed, involving vacuum evaporation and solvent separation of inhibitors which made the hydrolysate free of toxins while retaining high concentrations of fermentable sugars. The effect of the detoxification method on the fermentation was also reported and compared to well-known methods reported in literature. In this study, the new strain C. tropicalis UFMG BX 12-a was used on the detoxified hydrolysate to produce xylitol. It was also compared to Candida guilliermondii FTI 20037, which has been reported to be one of the best strains for fermentative production of xylitol. To further improve the efficiency of the fermentation process, these strains were immobilized in calcium alginate beads. The yield (0.92 g g-1) and productivity (0.88 g L-1 h-1) obtained by fermenting the wood hydrolysate detoxified by our new detoxification technique using an immobilized new Candida strain were found to be higher than the values reported in literature.