Abstract
Triacylglycerols (TAGs) are in the spotlight as a feasible source of hydrocarbon-based biofuels. Rhodococcus opacus PD630 produces large amounts of intracellular TAGs in cultivations containing high concentrations of glucose, but it does not utilize xylose present in all hydrolysates of lignocellulosic biomass. We constructed a highpotency xylose-fermenting R. opacus strain MITXM-61 that exhibited robust growth and TAG biosynthesis on high concentrations of xylose by activating potential xylose-metabolism genes. MITXM-61 had the uncommon capacity to grow in defined media supplemented with xylose at concentrations of greater than 200 gl-1. MITXM-61 grown in corn stover hydrolysates containing 118 gl-1 of initial total sugars was capable of completely and simultaneously utilizing both xylose and glucose in the genuine lignocellulosic feedstock, and yielded 15.9 gl-1 of TAGs, corresponding to 54% of the cell dry weight. The oleaginous bacterium R. opacus strain proved useful for developing a new manufacturing paradigm to generate advanced lignocellulosic biofuels.
Highlights
Advanced biofuels from renewable sources have been recognized as a potential solution for the interrelated issues of energy sustainability and environmental protection [1,2]
We have recently enabled xylose metabolism in R. opacus PD630 by expressing heterologous xylA and xylB genes derived from Streptomyces padanus [24]
MITXM-61 started growing in media containing up to 120 gl-1 of xylose after 1 day of cultivation and was able to grow on media containing greater than 200 gl-1 xylose within 3 days post-inoculation
Summary
Advanced biofuels from renewable sources have been recognized as a potential solution for the interrelated issues of energy sustainability and environmental protection [1,2]. Hydrocarbon-based biofuels are converted from triacylglycerols (TAGs), esters in which three fatty acid molecules are linked to glycerol [5]. Technology for producing hydrocarbon-based biofuels that are identical in virtually every respect to commercially available petroleum-derived fuels has been developed [6,7]. Renewable fuels are significantly more expensive than conventional petroleum-derived fuel, and should be produced from sustainable lignocellulosic biomass resources to preclude “food versus fuel” concerns [2,7]. Algae have been explored as a renewable source for lipid-based fuels owing to the ability to produce substantial amounts of TAGs, it is considered that commercial-scale production of biofuels from algae is incompatible with existing technologies [12,13]. One of the vital challenges is efficient fermentations of the sugar mixtures, which contain glucose and xylose as major components, present in all hydrolysates of lignocellulosic biomass [17,18,19,20,21]
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