Fig. 9

Metabolic Flux vs Gene Expression. Ratio of metabolic fluxes compared to ratio of gene expression for growth in different media. Each point represents a mapping between one reaction and one gene; therefore each reaction or gene may be represented by multiple points. If the same biomass requirements are used for the different growth substrates few of the reactions show any difference in flux (green diamonds) and there is weak correlation between expression and flux. The differences in fluxes that are observed are primarily due to genes encoding proteins that act in methanogenesis. By relaxing the assumption that biomass coefficient are constants across all growth substrates the model can be fit to improve the correlation between regulation and metabolism (red circles). After fitting, many additional pathways are predicted to carry different flux, as demonstrated by more points moving off the horizontal towards y=x (dashed line)