Whole-cell biotransformation for simultaneous synthesis of allitol and d-gluconic acid in recombinant Escherichia coli

Allitol and gluconic acid (GA) are important industrial compounds that are preferably produced via bio-production processes. In this research, d-psicose-3-epimerase (DPEase), glucose dehydrogenase (GDH), and ribitol dehydrogenase (RDH) were heterologously expressed in Escherichia coli, realizing the co-production of allitol and GA. Compared to the loss of carbon flux from formate dehydrogenase (FDH), glucose dehydrogenase can produce GA while generating NAD(H). The recombinant strain Ec/pAd-pRrg boosted NADH production to 2.4 μmol/gDCW, 118% higher than with the control strain. Under the optimized conditions, 12.0 g/L allitol and 14.8 g/L GA were produced from 25 g/L d-fructose and 20 g/L d-glucose; i.e., 66.7% and 66.3% higher yields compared to the case of fermentation without optimization, respectively. Furthermore, 42.7 g/L allitol and 56.2 g/L GA can be obtained from pretreated molasses (containing 139.2 g/L d-fructose and 149.1 g/L d-glucose). This work provides a practicable strategy for industrial and efficient co-production of allitol and GA from a cheap raw substrate.