Biological systems often maintain phenotypic stability when exposed to diverse perturbations arising from environmental changes, intracellular stochastic events (or noise), and genetic variation. This robustness is an inherent property of all biological systems and is strongly favoured by evolution. This is well demonstrated through systematic genetic perturbations. Functional robustness arises from the many redundancies, interlocking pathways and feedback mechanisms inherent to the complexity of biological networks that allow the system to dynamically adapt or compensate for losses or environmental changes. It is one of the main limitations in the design and use of bacterial strains in biotechnology.

The systematic reconstruction and analysis of the global metabolic network and of its regulation in the model bacterium B. subtilis has uncovered its general organization. The metabolic network is composed of a set of simple modules strongly coordinated at the global level. This systemic feature of modules forms the basis of a first mathematical explanation of the robustness of such a complex system. Consequently, this modular organization and the knowledge of the main players open the way for a rational modification of the metabolic network regulation.