Dynamic Control Strategy to Produce Riboflavin with Lignocellulose Hydrolysate in the Thermophile Geobacillus thermoglucosidasius

Efficient
utilization of both glucose and xylose, the two most
abundant sugars in biomass hydrolysates, is one of the main objectives
of biofermentation with lignocellulosic materials. The utilization
of xylose is commonly inhibited by glucose, which is known as glucose
catabolite repression (GCR). Here, we report a GCR-based dynamic control
(GCR-DC) strategy aiming at better co-utilization of glucose and xylose,
by decoupling the cell growth and biosynthesis of riboflavin as a
product. Using the thermophilic strain Geobacillus
thermoglucosidasius DSM 2542 as a host, we constructed
additional riboflavin biosynthetic pathways that were activated by
xylose but not glucose. The engineered strains showed a two-stage
fermentation process. In the first stage, glucose was preferentially
used for cell growth and no production of riboflavin was observed,
while in the second stage where glucose was nearly depleted, xylose
was effectively utilized for riboflavin biosynthesis. Using corn cob
hydrolysate as a carbon source, the optimized riboflavin yields of
strains DSM2542-DCall-MSS (full pathway dynamic control strategy)
and DSM2542-DCrib (single-module dynamic control strategy) were 5.3-
and 2.3-fold higher than that of the control strain DSM 2542 Rib-Gtg
constitutively producing riboflavin, respectively. This GCR-DC strategy
should also be applicable to the construction of cell factories that
can efficiently use natural carbon sources with multiple sugar components
for the production of high-value chemicals in future.