Under anaerobic conditions, E. coli performs a mixed acid fermentation as illustrated in the Figure A. Glycolysis (EMP) converts 1 glucose into 2 pyruvates and generates 2 net ATPs and 2 NADHs. For wild-type E. coli, pyruvate dehydrogenase complex (PDH) is not active while pyruvate formate lyase (PFL) is active under anaerobic conditions. Both of them catalyze the decarboxylation of pyruvate into acetyl-CoA but with different cofactors involved and products generated as shown in Figure B. There is no NADH produced if using pyruvate formate lyase (Figure B). E. coli has its native pathway converting acetyl-CoA to ethanol as shown in Figure C. Scientists deleted all the fermentation competing pathways such as lactate, formate and succinate pathways and left only ethanol producing pathway (glycolysis, PFL and alcohol dehydrogenase) intact. However, this genetically modified E. coli cannot successfully perform ethanol fermentation under anaerobic conditions. Please give an explanation