ELKs in the prokaryotes as a function of the genome size. All of the complete genomes of prokaryotes deposited at the database of the NCBI have been included, except for the myxobacteria. Genomes encoding <15 ELKs are represented in dark gray. Those containing >15 ELKs are color-coded according to the phylum to which they belong: green, Actinobacteria; blue, Cyanobacteria; yellow, Acidobacteria; pink, Planctomycetes; orange, Chloroflexi. Strains with multicellular behavior are represented by circles.