Cellulose biogenesis: Polymerization and crystallization are coupled processes in Acetobacter xylinum

Abstract

Calcofluor White ST, a stilbene derivative used commercially as an optical brightener for cellulose, increased the rate of glucose polymerization into cellulose by resting cells of the gram-negative bacterium A. xylinum. This bacterium normally produces a ribbon of cellulose that is a composite of crystalline microfibrils. In concentrations above 0.1 mM, Calcofluor disrupts the assembly of crystalline cellulose I microfibrils and their integration into a composite ribbon by stoichiometric binding to glucose residues of newly polymerized glucan chains. Under these conditions, the rate of glucose polymerization increases up to 4 times the control rate, whereas O2 uptake increases only 10-15%. These observed effects are readily reversible. If free Calcofluor is washed away or depleted below the threshold value by binding to cellulose as polymerization continues, ribbon production and the normal rate of polymerization resume. Polymerization and crystallization are cell-directed, coupled processes; the rate of crystallization determines the rate of polymerization. Coupling must be maintained for biogenesis of crystalline cellulose I.