Evolution under fluctuating environments explains observed robustness in metabolic networks.

Area of Science:

• Biochemistry and Evolutionary Biology
• Systems Biology and Metabolic Networks

Background:

• Organisms exhibit significant robustness to gene deletion, but the underlying biochemical features and evolutionary origins remain unclear.
• A key hypothesis suggests metabolic network robustness arises as a byproduct of selection for biomass production across diverse environments.

Purpose of the Study:

• To investigate whether evolutionary simulations under fluctuating environments can explain observed metabolic network robustness.
• To identify the biochemical features contributing to robustness and assess its environmental specificity.

Main Methods:

• Performed evolutionary simulations of metabolic networks under both stable and fluctuating environmental conditions.
• Assessed the impact of single gene deletions on network function across different environments.
• Analyzed the structural and functional properties of evolved metabolic networks, including enzyme multifunctionality and flux independence.

Main Results:

• Networks evolved in fluctuating environments demonstrated greater tolerance to gene deletions in specific environments compared to those evolved in stable conditions.
• This enhanced robustness was associated with an increased number of independent metabolic fluxes and enzymes with multiple functions.
• The observed robustness was 'apparent,' significantly decreasing when gene deletion effects were evaluated across all experienced environments.
• Continued evolution in a stable environment led to a complete loss of acquired robustness.

Conclusions:

• Evolution under fluctuating environments can indeed account for the observed robustness in metabolic networks.
• Organisms in stable environments are predicted to have lower metabolic robustness.
• A shift towards more stable environments may lead to a decrease in metabolic robustness.