Elementary mode analysis of Ralstonia Eutropha H16 metabolism for the production of useful metabolites

Abstract

Ralstonia eutropha H16 is a Gram-negative, facultative chemolithoautotrophic bacterium with the capability to synthesize many useful metabolites. One of the keys to the organism's lifestyle is its ability to use--alternatively or concomitantly--both organic compounds and molecular H2 as sources of energy. It can fix CO2 via the Calvin-Benson-Bassham (CBB) cycle and produces several useful metabolites like Poly(3-hydroxybutyric acid), isobutanol, 2,3-butanediol and ethanol. To quantitatively evaluate the capabilities of the metabolism we have set up models of the central metabolism that is based on known pathways of the organism. The lithoautotrophic metabolic model consists of 29 reversible reactions, 33 irreversible reactions, 59 internal metabolites and 11 external metabolites exchanged through the cell membrane. The heterotrophic model with fructose as a substrate has 31 reversible reactions, 47 irreversible reactions, 66 internal metabolites and 13 external metabolites. Elementary Mode Analysis identified 759 modes during lithoautotrophic growth and 135074 modes during heterotrophic growth. We have used the results from this analysis to predict key genetic alterations in the metabolism that would direct the metabolic flux towards the production of ethanol, isobutanol or polyhydroxybutanoate.