Large-scale in vivo flux analysis shows rigidity and suboptimal performance of Bacillus subtilis metabolism Ref: Eliane Fischer & Uwe Sauer, Nature Genetics 37:636 Presented by Shenghua Liang

Bow-tie 13 C technology For the first time, a large-scale experimental analysis of intracellular flux distributions.

Experiments 137 mutants in 9 groups covering all major functional categories –Central carbon metabolism –Biosynthetic reactions –Catabolic reactions and transport –Transcriptional regulators –Signal transduction –Inorganic ion transport and metabolism –Energy production and conversion –Other functions –Unknown or general function

Lethality, flexibility and optimality

Absolute and relative fluxes

Effect of knockouts on relative fluxes

Effect of knockouts on absolute fluxes and optimality

Conclusions - 1 In contrast to peripheral biosynthetic network, no kinetic effect modulates the distribution of central metabolic fluxes Neither flux into PPP nor that into TCA is driven by the biosynthetic demand for the cofactors of NADPH and ATP Maximal energy yield is not a relevant metabolic objective during exponential growth phase of B. subtilis

Conclusions - 2 Control architecture of central metabolism is designed to provide a rigid flux distribution that is independent of the rate and yield of biomass formation B. subtilis maintains a stable metabolic state under a given environmental condition The state is robust against random genetic perturbations because the exclusive flexible acetyl-CoA branch point provide sufficient flexibility At the expense of optimal biomass productivity, metabolic fluxes are fine-tuned by developmental regulators that control adaptive responses. B. subtilis maintains in a standby mode that allows rapid responses to variations in environmental conditions.