Effect of xylose concentration on byproduct
production Using xylose as a sole carbon source, we reported
on metabolic shift from homo-fermentation to hetero-fermentation
at high and low initial xylose concentration, respectively (12).
To study the relationship between xylose concentration and acetic
acid production, a mixtures of glucose and xylose in batch
fermentations with G10X10 (Fig. 1A) and G10X50 (Fig. 1B) were
investigated. Lactic acid levels of 10.7 g/L and 50.7 g/L were
attained with acetic acid production of 1.98 g/L and 0.260 g/L
from G10X10 and G10X50 g/L, respectively. With G10X10, acetic
acid was produced throughout the fermentation, while no acetic
acid production was observed with G10X50 until the xylose
concentration fell below 10 g/L. In addition, G10X50 fermentation
resulted in a higher yield of lactic acid (0.876 g/g) and lower yield
of acetic acid (0.005 g/g) than G10X10 fermentation (0.557 g/g
and 0.103 g/g, respectively). These results indicated that a higher
initial xylose concentration resulted in a higher concentration
and yield of lactic acid in the fermentation using a mixture of
glucose and xylose, and that we can restrict byproduct
production by maintaining the concentration of xylose in the
fermentation broth at higher than 10 g/L.