Synthesis of cellulose by Acetobacter xylinum. 3. Substrates and inhibitors

Abstract

Hexoses (glucose, fructose), 3 C compounds (glycerol, dihydroxyacetone) and hexonates (gluconate, 2- and 5-oxogluconate) were converted into cellulose by the action of washed cells of A. xylinum. The substrate range of the cells was a function of their history and the conditions in which they were assayed. Acetate, pyruvate and citrate-cycle intermediates were oxidized without attendant conversion into cellulose. Phosphate esters (including glucose 6-phosphate, [alpha]-glucose-1-phosphate, [beta]-glucose-1-phosphate and uridine diphosphoglucose) presumably failed to penetrate into the cells (fresh and freeze-dried). Such esters, added exogenously, did not form cellulose. The sole product of assimilation formed in substantial amount from glucose was cellulose. Glucose was converted via gluconate into 2- and 5-oxogluconate. It was assimilated into cellulose and oxidized to CO2 facultatively via these gluconates. The highest encountered valve of the molar ratio, cellulose monomer: glucose oxidized to carbon dioxide, was 1.7, i.e. significantly greater than unity. In all instances, only a small portion of the total energy liberated by concurrent oxidation of hexose was utilized for cellulose porduction (cellulose monomer: oxygen atom = 0.1). Exogenously provided adenosine triphosphate failed to sustain an anaerobic synthesis of cellulose. Electron acceptors other than O2 permitted restricted oxidation of glucose and gluconate, presumably to oxogluconates, but such oxidation did not enable formation either of cellulose or of CO2. Synthesis of cellulose from glucose was blocked by appropriate respiration inhibitors, sulfhydryl reagents, "narcotics" and even by the oxidizable metabolites acetate and acetate-forming pyruvate. Synthesis was retarded by arsentate; this effect was alleviated by added orthophosphate. Whereas 10 m[image]-fluoroacetate blocked acetate oxidation and caused that of pyruvate to cease at the level of acetate, it permitted both cellulose and carbon dioxide to be formed from glucose. Fluoride (10 m[image]) blocked the synthesis of cellulose but not the formation of CO2. 2,4-Dinitrophenol (4 m[image]) permitted oxogluconate production but blocked the formation of cellulose and retarded that of CO2 from glucose. The findings are in agreement with the suggestion that alternate metabolic pathways are available to the washed A. xylinum cell for the conversion of exogenous substrates into CO2 and cellulose and with the hypothesis than an intracellular hexose phosphate is an intermediate in cellulose production.