Enhancement of riboflavin production in Bacillus subtilis via in vitro and in vivo metabolic engineering of pentose phosphate pathway.

Objectives: The production of riboflavin with Bacillus subtilis, is an established process, however it is yet to be fully optimized. The aim of this study was to explore how riboflavin yields can be improved via in vitro and in vivo metabolic engineering modification of the pentose phosphate pathway (PPP).

Results: In vitro, glucose was replaced with sodium gluconate to enhance PPP. Flask tests showed that the riboflavin titer increased from 0.64 to 0.87 g/L. The results revealed that the direct use of sodium gluconate could benefit riboflavin production. In vivo, gntP (encoding gluconate permease) was overexpressed to improve sodium gluconate uptake. The riboflavin titer reached 1.00 g/L with the mutant B. subtilis RF01. Ultimately, the fermentation verification of the engineered strain was carried out in a 7-L fermenter, with the increased riboflavin titer validating this approach.

Conclusions: The combination of metabolic engineering modifications in vitro and in vivo was confirmed to promote riboflavin production efficiently by increasing PPP and has great potential for industrial application. This work is aimed to explore how to improve the riboflavin yield by the rational renovation of the pentose phosphate pathway (PPP). In vitro, metabolic engineering mainly uses sodium gluconate as a carbon source instead of glucose, and in vivo, metabolic engineering mainly includes the overexpression of sodium gluconate utility-related genes. The effect of sodium gluconate on cell growth, riboflavin production was investigated in the flasks and fermenter scale.