Synthesis of cellulose by Acetobacter xylinum. V. Ultrastructure of polymer.

Appearance of cellulose microfibrils in the medium of a suspension of cells of Acetobacter xylinum in buffered glucose solution was preceded by a stage during which the cellulose in the medium was amorphous within the available resolution. The size of the vertical axis of the microfibrils of the bacterial cellulose was found on the basis of measurement of shadow length to be only about 16 A. In good agreement with findings of earlier workers, the size of the lateral axis ("width") of the image of the metal-shadowed cellulose microfibrils was found to be 11 mmicro. After correcting for a large part probably contributed by deposited metal in the observed width of the microfibrils, the real width is estimated roughly to be in the neighborhood of 3 mmicro. To account for the occurrence of diverse morphological elements in the fields and for the fact that the cellulose fibrils are free entities rather than physical appendages of the cell, it is suggested that individual cellulose molecules are released at the cell surface and diffuse into the medium, wherein they finally enter into crystal-line patterns.