Proteomic tree of species with similar metabolic capacities. There are 67 photosynthetic microbes recorded in the GOLD database . These microbes belong to six different phyla. In this probe-set classification tree, each organism is represented by its taxonomic ID. These microbes are clustered into six groups, each of which precisely corresponds to a phylum, as indicated by the labels at the outer tracks. This example illustrates that the probe-set method can well reveal the phylogenetic relationships among species with highly similar metabolic capabilities.