Sunday, May 4, 2008
2-15

Engineering Actinobacillus succinogenes for succinate production

Claire Vieille, James "Jake" McKinlay, and Bryan Schindler. Biochemistry & Molecular Biology, Michigan State University, 110 Biochemistry, East Lansing, MI 48824

Succinate is produced petrochemically from butane through maleic anhydride to satisfy a specialty chemical market, for uses as surfactant, ion chelator, food additive, and pharmaceutical ingredient. While this specialty chemical market is relatively small at 15,000 t/yr in the US, the development of bio-based succinate production is targeting a much larger commodity chemical market (i.e., 270,000 t/yr) to produce bulk chemicals such as 1,4-butanediol, tetrahydrofuran, and γ-butyrolactone. Gram-negative Actinobacillus succinogenes produces among the highest succinate levels ever reported (up to 110 g/l for some mutants), making it a natural choice for industrial succinate production. We used metabolic flux analysis studies to identify the main sources of NADPH in the cell and the nodes for flux distribution between succinate and alternative fermentation products in glucose-grown cultures. Using the same approach, we identified the mechanisms by which A. succinogenes maintains a constant growth rate and biomass yield when redox demands are changed in the presence of different NaHCO3 and H2 concentrations. A. succinogenes grows on D-glucose, cellobiose, D-xylose, D-mannose, and L-arabinose, the most abundant sugars present in cellulose and hemicellulose, and it can ferment multiple carbon sources simultaneously. These features suggest that we can develop a lignocellulose-based succinate production process using A. succinogenes. We are evolving A. succinogenes to grow faster on individual lignocellulosic sugars. Growth parameters and fermentation balances are then compared on the different sugars in evolved and non-evolved strains. Follow-up studies will involve sugar mixtures and corn stover lignocellulosic hydrolysates.