Occurrence of nickel and cobalt utilization traits in bacteria. The tree is based on a highly resolved phylogenetic tree of life (see Methods). We simplified the complete tree and only show bacterial branches. Phyla in which none of the organisms use Ni or Co are shown in blue (if containing at least 3 organisms, shown in bold). Phyla in which all organisms use both Ni and Co are shown in red (if containing at least 3 organisms, shown in bold).