Section: New Results

Core and periphery of metabolic networks

The core metabolism can be defined as the reactions present in every organism, however it is not robust considering that adding or removing one organism in the study will modify the resulting set. An alternative way is to include in the core the reaction that is present in a large enough proportion of species. For that, we proposed a method where the threshold to decide what is large enough is not set by the user (thus relying on a subjective choice), but rather automatically selected by the method, relying on the information contained in the data. Two approaches are being proposed, one is EM (Expectation Maximization) which relies only on the information of presence / absence of a reaction in a species while the second (NEM - Neighboring Expectation Maximization) relies on a neighbouring relation between reactions. The latter tends to classify in a same group (core or periphery) a reaction for which a majority of neighbours belong to a same group. The work is being done with Ana Tereza Vasconcelos in a collaboration with Catherine Matias, Christophe Ambroise, Yolande Diaz (Genopole, CNRS).