(529e) De Novo Biosynthesis of Vitamin B Complex from Second-Generation Carbon Feedstocks

Lignocellulosic biomass is complex and recalcitrant. It contains mixed sugars such as C6 sugars (e.g., glucose) and C5 sugars (e.g., xylose). Most microorganisms do not efficiently consume these mixed sugars due to the well-known carbon catabolite repression (CCR) effect. In this study, we attempted to develop the fermentation process to evaluate the conversion of non-edible sugars into vitamins for food and feed by an oleaginous yeast, Yarrowia lipolytica.

Y. lipolytica is a nonconventional yeast due to its distinctive genome structure and its relatively large phylogenetic distance to other yeasts. This yeast was originally isolated from lipid-rich or protein-rich environments such as fermented dairy products, meat, poultry, and from wastes such as lipid-rich sewage or oil-polluted environments. The wild isolates of Y. lipolytica have been used to produce lipids, organic acids, and polyols. Y. lipolytica is capable of assimilating complex substrates (e.g., organic acids, alcohols, triglycerides, and hydrocarbons). It can grow in a wide pH range (pH 2 to 11) and in the presence of inhibitory acid-pretreated biomass hydrolysates or high salt concentrations or even high concentrations of ionic liquids. Y. lipolytica can use xylose as a carbon source, but xylose dehydrogenase (XYL2) is the key bottleneck of xylose assimilation and is transcriptionally repressed by glucose. To be more specific, glucose-6-P can be competitively bound to XYL2; therefore, inhibits the conversion of xylitol to xylulose. However, some strain of Y. lipolytica did not show strong glucose repression.

Y. lipolytica TISTR5212 was previously tested in our lab for the ability to consume biosludge mainly contained the aromatic hydrocarbons and calcium residues for cell biomass production. This isolate grew well on both GYP (glucose-yeast extract-peptone) and XYP (xylose-yeast extract-peptone) media. The accumulation of vitamin B (B1, B6, B7) was also observed from the HPLC chromatograms during the cultivation in GYP medium. However, its capability of assimilating other sugars such as xylose and cellobiose and their mixtures with glucose was still unclear. Therefore, we aimed to determine the CCR effect in Y. lipolytica TISTR5212 when cultivated in cellulosic sugars comparing with the cultivation in the yeast nitrogen base medium supplemented with sole glucose. The production of single cell protein and vitamin B was also investigated. Vitamin B accumulation via de novo biosynthesis in Y. lipolytica cultivated in different media were observed. The concentrations of B vitamers varied with different carbon and nitrogen substrates. The experimental results suggested that Y. lipolytica assimilated B vitamers contained in the fermentation media and used the de novo pathway in synthesis of B1, B3, B6, B9, and B12 vitamers. B1 and B3 vitamers were found in all experimental runs while B6, B9, and B12 vitamers were observed under different environmental conditions.