Utilization of xylose by engineered strains of Ashbya gossypii for the production of microbial oils.

BACKGROUND: Ashbya gossypii is a filamentous fungus that is currently exploited for the industrial production of riboflavin. The utilization of A. gossypii as a microbial biocatalyst is further supported by its ability to grow in low-cost feedstocks, inexpensive downstream processing and the availability of an ease to use molecular toolbox for genetic and genomic modifications. Consequently, A. gossypii has been also introduced as an ideal biotechnological chassis for the production of inosine, folic acid, and microbial oils. However, A. gossypii cannot use xylose, the most common pentose in hydrolysates of plant biomass.

RESULTS: In this work, we aimed at designing A. gossypii strains able to utilize xylose as the carbon source for the production of biolipids. An endogenous xylose utilization pathway was identified and overexpressed, resulting in an A. gossypii xylose-metabolizing strain showing prominent conversion rates of xylose to xylitol (up to 97% after 48 h). In addition, metabolic flux channeling from xylulose-5-phosphate to acetyl-CoA, using aheterologous phosphoketolase pathway, increased the lipid content in the xylose-metabolizing strain a 54% over the parental strain growing in glucose-based media. This increase raised to 69% when lipid accumulation was further boosted by blocking the beta-oxidation pathway.

CONCLUSIONS: Ashbya gossypii has been engineered for the utilization of xylose. We present here a proof-of-concept study for the production of microbial oils from xylose in A. gossypii, thus introducing a novel biocatalyst with very promising properties in developing consolidated bioprocessing to produce fine chemicals and biofuels from xylose-rich hydrolysates of plant biomass.