Chance and necessity in the evolution of minimal metabolic networks

The cart before the horse? It is common enough to read a paper that uses genome-sequence data to make conclusions about how an organism lives. Less common is the approach used by Pál et al. who have generated gene networks for a group of related organisms with similar lifestyles, and used those to infer gene content of another member of the group. With the genome of E. coli as starting point, they predicted the metabolism of Buchnera, an intracellular symbiont with a heavily reduced genome, that was derived from an ancestor of E. coli. This work has implications for the search for a ‘minimal genome’, and already indicates that the concept of a ‘non-essential gene’ can be spurious, as a gene can easily become essential in changing genomic contexts.