Cellulose-coated double-shell microparticle integrated with yeasts for consolidated bioprocesses*

Efficient utilization of lignocellulosic biomass as a sustainable alternative resource for biofuels and chemicals is of great importance in view of global warming and depleting fossil fuel reserves. High-pressure homogenization of hydrophobic liquids with cellulose solution or aqueous dispersion of cellulose hydrogel particles yields emulsion of double-shelled micro-particles (dsMP) composed of a hydrophobic core with two concentric shells: an inner shell of aqueous cellulose hydrogel covered by an external coating of continuous amorphous cellulose. Enzymes introduced into the aqueous emulsion medium can be incorporated with the dsMPs: lipases penetrate the shells to the inner core-shell interface, so as to effectively catalyze trans-esterification reactions. Addition of yeasts (S. cerevisiae) to the emulsification process results in integrated hybrids in which the micro-particles are attached to the yeasts' surface. Cellulytic enzymes can be attached to the cellulose surface coatings and the integrated structures exhibited effective simultaneous cellulose saccharification and fermentation to ethanol. Lipase introduced to the aqueous medium are incorporated within the microparticles at the inner core-hydrogel interface, and function effectively in trans-esterification of long-chain molecules dissolved in the core. These results are promising steps towards "one-pot" processes for cellulose valorization by a cascade of biochemical reactions.