Exploring Anaerobic Routes

A promising approach for anaerobic fermentation is the nonnaturally occurring four pathways that process via 2,3-dihydroxyisovalerate (DHIV), a precursor for L-valin biosynthesis which has the correct carbon skeleton of isoprene and requires only two steps from Pyr, with high theoretical yield (0.324 g isoprene/g glucose) [102]. All the proposed pathways are redox-balanced and require the same number of steps as the original routes. In addition, one of them is 

ATP-neutral and the others are ATP-positive [102]. This work offers an exciting potential approach for anaerobic isoprene production, but still remains theoretical. 

In conclusion, to allow the cells to gain ATP under anaerobic condition is the challenge for isoprene fermentation. Constructing a module from an anaerobic microorganism, such as acetogenic bacteria [75, 95, 100], to produce or even to conserve energy may increase the yield via the MVA/MEP pathways. 

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