Environmental versatility promotes modularity in genome-scale metabolic networks

Areejit Samal 1, 2, Andreas Wagner 3, 4, 5, Olivier C. Martin 2, 6

BMC Systems Biology 5 (2011) 135

The ubiquity of modules in biological networks may result from an evolutionary benefit of a modular organization. For instance, modularity may increase the rate of adaptive evolution, because modules can be easily combined into new arrangements that may benefit their carrier. Conversely, modularity may emerge as a by-product of some trait. We here ask whether this last scenario may play a role in genome-scale metabolic networks that need to sustain life in one or more chemical environments. For such networks, we define a network module as a maximal set of reactions that are fully coupled, i.e., whose fluxes can only vary in fixed proportions. This definition overcomes limitations of purely graph based analyses of metabolism by exploiting the functional links between reactions. We call a metabolic network viable in a given chemical environment if it can synthesize all of an organism’s biomass compounds from nutrients in this environment. An organism’s metabolism is highly versatile if it can sustain life in many different chemical environments. We here ask whether versatility affects the modularity of metabolic networks.

  • 1. Max Planck Institute for Mathematics in the Sciences (MPI-MIS),
  • 2. Laboratoire de Physique Théorique et Modèles Statistiques (LPTMS),
    CNRS : UMR8626 – Université Paris XI – Paris Sud
  • 3. Department of Biochemistry,
    University of Zurich
  • 4. Swiss Institute of Bioinformatics (SIB),
    Swiss Institute of Bioinformatics
  • 5. Santa Fe Institute,
    Santa Fe Institute
  • 6. Laboratoire de Génétique Végétale du Moulon,
    Université Paris XI – Paris Sud
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