新しい系統樹では細菌が圧倒的に優勢

A dramatically expanded tree of life, created with new genomic data from over 1,000 little-known organisms and genomes from public databases, is published online this week in Nature Microbiology. The study reveals the vast diversity of Bacteria compared with the other two domains of life - Archaea and Eukarya - and highlights both the major branches of the tree that are currently under-represented and the branches that are probably important for future evolutionary analyses.

The tree of life is one of the most important organizing principles in biology, but an approximation of its full scale, with its enormous number of branches, has remained elusive. Although depictions of the tree of life traditionally focus on the known, well-classified diversity of life within eukaryotes - the domain of life that includes all animals, including humans - genomic sampling of previously unexamined environments and new methods for generating genome sequences are dramatically changing our understanding of life’s diversity.

Jill Banfield and colleagues constructed their new tree of life from genomes from public databases and 1,011 newly reconstructed genomes from a variety of environments, using a genomic approach that does not rely on the ability to grow or cultivate organisms in the lab. Taking more than 6,000 computer hours to construct, the updated tree of life provides a snapshot of diversity within each branch. The authors find the most diverse branch is the ‘Candidate Phyla Radiation’, a group of bacteria that have never been cultivated but make up the majority of life’s current diversity, and suggest their diversity could be due to their early emergence and/or rapid evolution.