Part II: Degradation During Growth of Cellulolytic Microorganisms

Electron microscopical studies were made of changes in cotton fiber microstructure on samples from cultures of the bacterium Cellvibrio fulvus and the fungus Myrothecium verrucaria. Bacterial colonies, growing in the folds of the primary wall, caused diagonal or longitudinal splitting of the fiber surface. Degradation by the fungus was charac terized by transverse cracks in the fiber wall. Other changes in fiber microstructure during microbial growth were similar for both organisms. In areas of intense attack, surface replicas showed single fibrils detached from the underlying structure; on mer cerized fibers, hydrocellulose-like particles on the surface at times obscured the surface structure. Fragmentation patterns indicated a continued breaking down of the fibrillar structure into small fragments and particles. The final degradation products, seen in electron micrographs, resembled particles produced by a limited, heterogeneous acid hydrolysis, but positive identification with hydrocellulose particles has not been made. Cottons modified to produce a more expanded microstructure with higher amorphous cellulose content showed large decreases in resistance to microbial attack. Attack by growing microorganisms was more intense and rapid than degradation by growth filtrates obtained from cultures of cellulolytic fungi, but the mode of degradation was similar.