In vitro synthesis and self-assembly of cellulose II nanofibrils catalyzed by the reverse reaction of Clostridium thermocellum cellodextrin phosphorylase.

In nature, various organisms produce cellulose as microfibrils, which are processed into their nano- and microfibrillar and/or -crystalline components by humans in order to obtain desired material properties. Interestingly, the natural synthesis machinery can be circumvented by enzymatically synthesizing cellulose from precursor molecules in vitro. This approach is appealing for producing tailor-made cellulosic particles and materials because it enables optimization of the reaction conditions for cellulose synthesis in order to generate particles with desired morphology in pure form. Here we present enzymatic cellulose synthesis catalyzed by the reverse reaction of Clostridium thermocellum cellodextrin phosphorylase in vitro. We were able to produce cellulose II nanofibril networks in all conditions tested, using varying concentrations of the glycosyl acceptors ᴅ-glucose or ᴅ-cellobiose (0.5, 5, and 50 mM). We show that shorter cellulose chains assemble into flat ribbon-like fibrils with greater diameter, while longer chains assemble into cylindrical fibrils with smaller diameter.