Utilization of glucose and xylose simultaneously by Clostridium tyrobutyricum : Effect of glucose and xylose consumption rate on butyric acid production

Lignocellulosic biomass, mainly composed of glucose and xylose, is an attractive resource for bio-based chemical production. Clostridium tyrobutyricum ATCC 25755 is one of the most popular butyric acid producers and is capable of utilizing glucose or xylose separately as a sole carbon source. However, due to carbon catabolite repression, this strain sequentially utilized glucose and xylose with a diauxic production of butyric acid. In this study, we developed a strain (AD 25755) capable of consuming glucose and xylose simultaneously by adapting ATCC 25755 on a mixture of xylose and 2-deoxy-glucose, a non-metabolizable analogue of glucose. The strain AD 25755 consumed glucose slower than ATCC 25755, but glucose and xylose were consumed simultaneously at the same rate (i.e., glucose consumption rate = xylose consumption rate). When AD 25755 was serially transferred to the medium with glucose only, the regenerated strain (RE 25755) was obtained exhibiting high glucose consumption rate of ATCC 25755 and xylose utilization rate of AD 25755 (i.e., glucose consumption rate > xylose consumption rate). Comparing butyric acid productivity of ATCC 25755 with AD 25755 and RE 25755, butyric acid productivity was 1.3-fold and 1.8-fold higher than ATCC 25755 with AD 25755 and RE 25755, respectively. Specifically, RE 25755 completely consumed glucose and xylose without a diauxic butyric acid production, resulting in the most efficient butyric acid production among three strains. This study would provide a practical insight for the strategy developing C. tyrobutyricum ATCC 25755 to efficiently utilize glucose and xylose simultaneously for butyric acid production.