UC Davis

Engineered microorganisms capable of producing commodity chemicals have gained traction as viable alternative to traditional petrochemical approaches. Expanded feedstock pools, engineering regulatory elements of metabolism, and fermentation optimization are all methods employed to increase productivity in these microbial hosts. Plant biomass refined into pure sugars are commonly used as a substrate for these fermentations. Heterotrophic hosts can convert these pure sugars into various chemical compounds, however, using sugars for fermentation directly competes with global food supply. One alternative carbon source to these sugars is using atmospheric CO2 to power biochemical production in these organisms. However, native biological CO2 fixation is slow, limiting growth and production rates. This dissertation seeks to address the challenges intrinsic to using CO2 as a chemical production feedstock. First, by engineering photomixotrophy into the naturally photosynthetic microorganism cyanobacteria to supplement chemical production and growth by directing the excess carbon from sugars towards the substrate for the dominant CO2 fixing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase. Second, by engineering a non-canonical CO2 fixing pathway known as the reductive glycine pathway into the heterotroph, Escherichia coli, in conjunction with using formate produced in a novel electrocatalytic setting and optimizing biochemical production in E. coli from this electrocatalytic reaction mixture. Both strategies demonstrate methods where chemical production can be made more renewable with the aid of engineered microorganisms capable of utilizing CO2 from the atmosphere to make industrially relevant chemicals such as isobutanol and succinate.