Effect of ethanol on bacterial cellulose production from fructose in continuous culture

Effect of ethanol on bacterial cellulose (BC) production from fructose by Acetobacter xylinum subsp. sucrofermentans BPR3001A was investigated in continuous culture. Supplementation of 10 g·l⁻¹ ethanol to the feed medium containing 30 g·l⁻¹ fructose as the main carbon source enhanced the ATP content of viable cells, cell concentration, and fructose consumption rate, establishing a 72-h steady state with 0.95 g·l⁻¹·h⁻¹ of BC production rate and 46% of BC yield in continuous culture with a dilution rate of 0.07 h⁻¹. However, an increase in concentration of ethanol to more than 15 g·l⁻¹ decreased BC production rate due to the inhibition of cell growth by the generated acetate. Results from batch culture experiment using ethanol as the main carbon source suggested that ethanol functioned as an energy source for ATP generation, and not as a substrate for BC biosynthesis. On the other hand, fructose hexokinase (FHK) activity was increased and activities of glucose 6-phosphate dehydrogenases (G6PDs) were inhibited by ATP, suggesting that the improved BC production from fructose by ethanol supplementation was a result of increased fructose dissimilation and abundant flow of glucose 6-phosphate (G6P), a precursor of BC, into the BC biosynthetic pathway due to the inhibition of G6PDs by increased levels of ATP.