Verrucomicrobia is a phylum of bacteria. This phylum contains only a few described species (Verrucomicrobium spinosum, is an example, the phylum is named after this). The species identified have been isolated from fresh water and soil environments and human faeces. A number of as-yet uncultivated species have been identified in association with eukaryotic hosts including extrusive explosive ectosymbionts of protists and endosymbionts of nematodes residing in their gametes. While verrucae is another name for the warts often found on hands and feet, this phylum is so called not because it is a causative agent thereof, but because of its wart-like morphology.
Evidence suggests that verrucomicrobia are abundant within the environment, and important (especially to soil cultures). This phylum is considered to have two sister phyla: Chlamydiae and Lentisphaerae within the PVC group. The Verrucomicrobia phylum can be distinguished from neighbouring phyla within the PVC group by the presence of several conserved signature indels (CSIs). These CSIs represent unique, synapomorphic characteristics that suggest common ancestry within Verrucomicrobia and an independent lineage amidst other bacteria. CSIs have also been found that are shared by Verrucomicrobia and Chlamydiae exclusively of all other bacteria. These CSIs provide evidence that Chlamydiae is the closest relative to Verrucomicrobia, and that they are more closely related to one another than to the Planctomycetales.
Cavalier-Smith has postulated that the Verrucomicrobia belong in the clade Planctobacteria in the larger clade Gracilicutes. 16S rRNA data corroborate that view. In 2008, the whole genome of Methylacidiphilum infernorum (2.3 Mbp) was published. On the single circular chromosome, 2473 predicted proteins were found, 731 of which had no detectable homologs. These analyses also revealed many possible homologies with Proteobacteria.