As stated above, mannitol might be more favorable carbon source for ethanol production by Enterobacter sp. JMP3. Regarding to the anaerobic metabolism of mannitol and glucose in Enterobacter sp. JPM3, the driving force of redox potential, intracellular ratio of NADH/NAD+, offers a reasonable explanation. As referred to the
Appendix, it should be noted that there would be one additional mol of NADH generated by the oxidation of one mol of mannitol compared with glucose (Quain and Boulton, 1987). This leads to increase of the intracellular NADH/NAD+ ratio. Thus, in order to keep the redox balance inner cell environment, this redox potential would drive carbon flux into NADH-consuming pathways. Comparing to the metabolic pathway related to ethanol and acetic acid formation (see Fig. S4), it is noticed that with 1 mol of ethanol is generated, there would be 2 mol of NADH consumed; while acetic