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

Bacterial cellulose (BC) was produced from fructose by Acetobacter xylinum subsp. sucrofermentans BPR3001A was performed in continuous culture and the effect of lactate on the production was investigated. In continuous culture with feeding of CSL-Fru medium containing 30 g·l⁻¹ fructose at a dilution rate of 0.07 h⁻¹, a higher production rate (0.62 g·l⁻¹·h⁻¹) was obtained than that (0.40 g·l⁻¹·h⁻¹) in a batch culture using CSL-Fru medium with 70 g·l⁻¹ initial fructose. However, when the dilution rate or fructose concentration in the feed medium were increased, the total yield of BC declined because the residual fructose concentration in the drawn broth increased. Supplementing 12.5 g·l⁻¹ lactate to the feed medium increased the cell concentration and fructose consumption at a steady state, resulting in a production rate of 0.90 g·l⁻¹·h⁻¹ and a BC yield of 36% at a dilution rate of 0.1 h⁻¹. The ATP content of viable cells was maintained at a higher level by feeding a lactate-supplemented medium rather than the unsupplemented CSL-Fru medium. In a batch culture using lactate as the main carbon source, 77% of the lactate consumed was oxidized to CO₂ and only 6.9% was converted to BC. These findings indicated that lactate functioned as an energy source, not as a substrate for BC biosynthesis. Increased intracellular ATP resulting from lactate oxidation may have improved the fructose consumption and BC production in the continuous culture.