It is a disturbing reality that we have only fragmentary understanding of the enormous microbial diversity that exists on our planet. This applies not merely to microbes living in extreme environments, which would be expected to possess unusual and perhaps not yet fully characterized properties, but also to those microbes in more mundane habitats, like a gram of soil. One bacterial phylum that has few cultivated representatives, but is found routinely in clone libraries of amplified 16S rRNA genes, is Verrucomicrobia. More than 200 unique verrucomicrobial 16S rRNA genes have been identified from terrestrial and aquatic environments and associated with a variety of eukaryotic hosts. The Verrucomicrobia, most of whose sequences are more than 75% identical to one another, form a monophyletic group within the bacteria.
Novel culture methods have recently been integrated with molecular monitoring techniques to isolate previously uncultured strains of Verrucomicrobria from agricultural and pristine soils and from the termite hindgut. Preliminary analysis of one of the isolated strains has revealed the capacity for nitrogen fixation, a metabolism not previously identified in this bacterial phylum. Sequencing one member of this group, a Group 4 soil isolate, will increase our understanding of the physiological and ecological potential of the Verrucomicrobia role in local and global cycles of carbon, nitrogen, and sulfur, including carbon sequestration. We also expect to gain insights necessary for the cultivation of other members of the phylum, which are widespread in soils, lakes, and bioreactors and associated with eukaryotic hosts. The results will clarify the evolutionary relationship between the Verrucomicrobia and Planctomycetes and probe the potential for a deep positioning of these sister taxa in the bacterial domain of the tree of life, examining the unusual occurrence of eukaryotic gene homologs.
CSP project participants: Thomas M. Schmidt (proposer) and Jorge L.M. Rodrigues (Michigan State Univ.).