Abstract
Methane can be converted to triose dihydroxyacetone (DHA) by chemical processes with formaldehyde as an intermediate. Carbon dioxide, a by-product of various industries including ethanol/butanol biorefineries, can also be converted to formaldehyde and then to DHA. DHA, upon entry into a cell and phosphorylation to DHA-3-phosphate, enters the glycolytic pathway and can be fermented to any one of several products. However, DHA is inhibitory to microbes due to its chemical interaction with cellular components. Fermentation of DHA to d-lactate by Escherichia coli strain TG113 was inefficient, and growth was inhibited by 30 g⋅L-1 DHA. An ATP-dependent DHA kinase from Klebsiella oxytoca (pDC117d) permitted growth of strain TG113 in a medium with 30 g⋅L-1 DHA, and in a fed-batch fermentation the d-lactate titer of TG113(pDC117d) was 580 ± 21 mM at a yield of 0.92 g⋅g-1 DHA fermented. Klebsiella variicola strain LW225, with a higher glucose flux than E. coli, produced 811 ± 26 mM d-lactic acid at an average volumetric productivity of 2.0 g-1⋅L-1⋅h-1 Fermentation of DHA required a balance between transport of the triose and utilization by the microorganism. Using other engineered E. coli strains, we also fermented DHA to succinic acid and ethanol, demonstrating the potential of converting CH4 and CO2 to value-added chemicals and fuels by a combination of chemical/biological processes.