Effects of pH and dissolved oxygen on cellulose production by Acetobacter xylinum BRC5 in agitated culture

Acetobacter xylinum BRC5 was cultivated in a jar fermenter using glucose as the sole carbon source. Strain BRC5 oxidized almost all of the glucose to gluconic acid; thereafter, it biosynthesized cellulose by utilizing gluconic acid accumulated in the broth. The optimal: pH for metabolizing glucose to gluconic acid was 4.0, while a pH of 5.5 was preferred for cell growth and cellulose production from the accumulated gluconic acid in the medium. Shifting the pH from 4.0 to 5.5 during the cellulose production phase in batch cultures improved cellulose production and reduced the total fermentation time, compared to batch cultures at constant pH. In constant fed-batch culture, 10 g/l of cellulose was obtained from 40 g/l of glucose, a yield which was approximately 2-fold higher than in batch culture with the same initial glucose concentration, even without control of the level of dissolved oxygen. The highest cellulose yield was obtained in fed-batch cultures in which the dissolved oxygen concentration was controlled at 10% saturation. Control of pH and dissolved oxygen to optimal levels was effective for improving the production rate and yield of cellulose, to achieve a high cellulose productivity of 0.3 g cellulose/l.h. Approximately 15 g/l of cellulose was considered to be the highest yield obtainable using conventional fermenters because the culture broth then became too viscous to allow satisfactory aeration.