Cellulose biosynthesis in Acetobacter xylinum: visualization of the site of synthesis and direct measurement of the in vivo process.

Abstract

In vivo synthesis of cellulose by Acetobacter xylinum was monitored by darkfield light microscopy. Cellulose is synthesized in the form of a ribbon projecting from the pole of the bacterial rod. The Cellulose biosynthesis by Acetobacter xylinum has been widely investigated (1)(2)(3)(4)(5)(6). It is generally believed that the synthesis of microfibrils occurs by an extracellular process involving the sequential addition of glucose residues to the growing tips at a distance from the cell (5-7). The biochemical reactions of cellulose synthesis have been extensively documented, the intermediate products being hexose phosphates (8), sugar nucleotides (9), and perhaps glycolipids (6). However, recent findings from kinetic data (1) and biochemical incorporation studies using defined cell wall extracts (2-4) indicate a closer relationship than previously expected between the bacterial envelope and the cellulose polymer.The purpose of this investigation is to clarify and lay groundwork on the cytology of cellulose formation in Acetobacter xylinum. In order to achieve this, we have carefully observed the dynamics of the in vWo process, using darkfield and Nomarski interference microscopy. We (Fig. 1)

Chitin-chitosan nanocomposite gels: reinforcement of chitosan hydrogels with rod-like chitin nanowhiskers

“…12,13 The microfibril cross-sections for bacterial cellulose are 10 Â 50 nm. 14 It is estimated that the lengths of all these microfibrils are at least several micrometers.…”

Visualization of pores (export sites) correlated with cellulose production in the envelope of the gram-negative bacterium Acetobacter xylinum.

“…Until recently, it was generally believed that the synthesis of crystalline microfibrils by Acetobacter is an extracellular process. The work of Brown and co-workers (2) and Zaar (18) has now shown that cellulose is produced in close contact with the bacterial envelope. Each bacterium assembles on its surface one flat ribbon consisting of cellulose.…”

“…The microfibrils lie side by side in a horizontal axis, thus giving rise to the fiat ribbon-like structures. Most ribbons are twisted in a very regular manner (2,18). Ribbons reaching more than 10 ~m in length project over one pole of the rod-like bacteria and taper to a point at the end distant from the cells.…”

“…Ribbons reaching more than 10 ~m in length project over one pole of the rod-like bacteria and taper to a point at the end distant from the cells. The assembly of the cellulose ribbons seems to be restricted to only a very small area in the longitudinal axis of the bacterial envelope (2,18). Furthermore, each microfibril of a ribbon is suggested to have an independent terminus in the bacterial envelope (2,18).…”

“…The assembly of the cellulose ribbons seems to be restricted to only a very small area in the longitudinal axis of the bacterial envelope (2,18). Furthermore, each microfibril of a ribbon is suggested to have an independent terminus in the bacterial envelope (2,18). This is a report concerning the ultrastructure of the particular area of ribbon assembly in the bacterial envelope as revealed by freeze-etch preparations.…”