title: Environmental variability and modularity of bacterial metabolic networks.
abstract: BACKGROUND
  Biological systems are often modular: they can be decomposed into nearly-independent structural units that perform specific functions. The evolutionary origin of modularity is a subject of much current interest. Recent theory suggests that modularity can be enhanced when the environment changes over time. However, this theory has not yet been tested using biological data.
  
  
  RESULTS
  To address this, we studied the relation between environmental variability and modularity in a natural and well-studied system, the metabolic networks of bacteria. We classified 117 bacterial species according to the degree of variability in their natural habitat. We find that metabolic networks of organisms in variable environments are significantly more modular than networks of organisms that evolved under more constant conditions.
  
  
  CONCLUSIONS
  This study supports the view that variability in the natural habitat of an organism promotes modularity in its metabolic network and perhaps in other biological systems.
authors: Molecular Cell Biology Department, Weizmann Institute of Science, Rehovot 76100, Israel. merav.parter@weizmann.ac.il
authors: Merav
authors: M
authors: Parter
authors: Nadav
authors: N
authors: Kashtan
authors: Uri
authors: U
authors: Alon