Whole genome-based phylogenetic analysis of free-living microorganisms

A phylogenetic 'tree of life' has been constructed based on the observed pr esence and absence of families of protein-encoding genes observed in 11 com plete genomes of free-living microorganisms, Past attempts to reconstruct t he evolutionary relationships of microorganisms have been limited to sets o f genes rather than complete genomes, Despite apparent rampant lateral gene transfer among microorganisms, these results indicate a single robust unde rlying evolutionary history for these organisms. Broadly, the tree produced is very similar to the small subunit rRNA tree although several additional phylogenetic relationships appear to be resolved, including the relationsh ip of Archaeoglobus to the methanogens studied. This result is in contrast to notions that a robust phylogenetic reconstruction of microorganisms is i mpossible due to their genomes being composed of an incomprehensible amalga m of genes with complicated histories and suggests that this style of genom e-wide phylogenetic analysis could become an important method for studying the ancient diversification of life on Earth, Analyses using informational and operational subsets of the genes showed that this 'tree of life' is not dependent on the phylogenetically more consistent informational genes.