Abstract
Background Through simulation studies and genomic data analysis, researchers have shown that modularity in metabolic networks is an important adaptive mechanism enabling survival in changing environments. Another global property of networks, flow hierarchy, is often used in optimizing information flow in designed networks. Hierarchy also arises in self-organized networks as an optimal way to aggregate flows while minimizing costs of connections.
Results Using a comparative approach on 2,935 bacterial metabolic networks, we show that hierarchy evolves with modularity and is conserved to a high degree. Hierarchy in bacterial metabolic networks reflects a fundamental tradeoff between growth rate and biomass production, and reflects a bacteria’s realized ecological strategy. Additionally, by inferring the ancestral metabolic networks, we find that hierarchy decreases with distance from the root of the tree, suggesting the important pressure of increased growth rate relative to efficiency in the face of competition.
Conclusions Just as hierarchical character is an important structural property in efficiently engineered systems, we see that it evolves in self-organized bacterial metabolic networks, is reflective of the life-history strategy of the bacteria, and plays an important role in network organization and efficiency.