Antagonism correlates with metabolic similarity in diverse bacteria

In the Origin of Species, Charles R. Darwin [Darwin C (1859) On the Origin of Species] proposed that the struggle for existence must be most intense among closely related species by means of their functional similarity. It has been hypothesized that this similarity, which results in resource competition, is the driver of the evolution of antagonism among bacteria. Consequently, antagonism should mostly be prevalent among phylogenetically and metabolically similar species. We tested the hypothesis by screening for antagonism among all possible pairwise interactions between 67 bacterial species from 8 different environments: 2,211 pairs of species and 4,422 interactions. We found a clear association between antagonism and phylogenetic distance, antagonism being most likely among closely related species. We determined two metabolic distances between our strains: one by scoring their growth on various natural carbon sources and the other by creating metabolic networks of predicted genomes. For both metabolic distances, we found that the probability of antagonism increased the more metabolically similar the strains were. Moreover, our results were not compounded by whether the antagonism was between sympatric or allopatric strains. Intriguingly, for each interaction the antagonizing strain was more likely to have a wider metabolic niche than the antagonized strain: that is, larger metabolic networks and growth on more carbon sources. This indicates an association between an antagonistic and a generalist strategy.