An Atomic Force Microscopy Study of the Mechanism of Cellulose Biodegradation

Cellulose, a biopolymer consisting of long chains of β (1→4) linked glucose sugars, is used as structural material by plants, bacteria, and some animals, and is the most abundant polymer on earth. Degradation of cellulose to glucose, a sugar easily fermented to ethanol, occurs by the enzymatic hydrolysis of cellulose by cellulase enzymes. The enzymes have a complex structure including carbohydrate binding modules responsible for binding the enzyme to the cellulose and catalytic domains responsible for the biodegradation of cellulose. Atomic force microscopy (AFM) was used to study native cellulose films prepared from a bacterial cellulose source, Acetobacter xylinum, using a novel application of the Langmuir-Blodgett technique. These films allowed high resolution AFM images of single fibers and their microfibril structure to be obtained. Further in situ AFM imaging studies of single cellulose fibers were performed in solution using cellulolytic enzymes. By using genetically modified enzymes with either active or inactive catalytic domains, the catalytic and binding properties of the enzyme-cellulose system can be independently investigated. Studying the modular enzyme action separately will provide insight into the mechanism of cellulose binding and contribute to our understanding of the biodegradation process.