Tuesday, May 3, 2011
Synthesis gas (Syngas) can be produced from renewable organic material making it an attractive yet challenging feedstock for the production of fuels and chemicals. Carbon monoxide (CO) is a major component of syngas along with hydrogen and carbon dioxide. The goal of this proof-of-concept study was to develop a platform microorganism that is readily amenable to genetic manipulation and is also capable of oxidizing CO. To accomplish this we utilized Rhodospirillum rubrum as a host organism to express known pathways for ethanol and n-butanol production. The n-butanol pathway consisted of genes from Clostridium acetobutylicum for crotonase (crt), butyrl-CoA dehydrogenase (bcd), electron transfer flavoproteins A/B (etfAB), and alcohol dehydrogenase (adhe). Attempts at ethanol production were made by chromosomal integration of Zymomonas mobilis pyruvate decarboxylase and alcohol dehydrogenase genes using a transposon-based strategy. A CO sensitive promoter allowed heterologous expression of codon-optimized constructs in a broad-host-range shuttle vector. In addition, a metabolic model was used to predict gene knockouts that may increase n-butanol and ethanol production. As hypothesized, elimination of poly-beta-hydroxybutyrate (PHB) synthesis was predicted to increase yield; therefore, both PHB synthases were targeted for deletion.